Assessment and Evaluation of Noise Controls on Roof Bolting Equipment and A Method 

For Predicting Sound Pressure Levels in Underground Coal Mining 

Rudy J. Matetic 

Dissertation Submitted to the 

College of Engineering and Mineral Resources 

at West Virginia University 

in partial fulfillment of the requirements 

 for the degree of 

Doctor of Philosophy 

In 

Engineering 

Syd Peng, Ph.D., Chair 

Felicia Peng, Ph.D. 

Yi Luo, Ph.D. 

Keith Heasley, Ph.D. 

Gerald Finfinger, Ph.D. 

Department of Mining Engineering 

Morgantown, West Virginia 

2006 

Keywords: Roof Bolting, Drilling, Sound Power, Sound Pressure, Noise Controls, Drill 

Bits, Drill Steel 

Copyright 2006 Rudy J. Matetic 
ABSTRACT 

Assessment and Evaluation of Noise Controls on Roof Bolting Equipment and A Method 

For Predicting Sound Pressure Levels in Underground Coal Mining 

Rudy J. Matetic 

Over-exposure to noise remains a widespread and serious health hazard in the 

U.S. mining industries despite 25 years of regulation. Every day, 80% of the nation’s 

miners go to work in an environment where the time weighted average (TWA) noise 

level exceeds 85 dBA and more than 25% of the miners are exposed to a TWA noise 

level that exceeds 90 dBA, the permissible exposure limit (PEL). Additionally, MSHA 

coal noise sample data collected from 2000 to 2002 show that 65% of the equipment 

whose operators exceeded 100% noise dosage comprise only seven different types of 

machines; auger miners, bulldozers, continuous miners, front end loaders, roof bolters, 

shuttle cars (electric), and trucks. In addition, the MSHA data indicate that the roof 

bolter is third among all the equipment and second among equipment in underground 

coal whose operators exceed 100% dosage. 

A research program was implemented to: 1) determine, characterize and to 

measure sound power levels radiated by a roof bolting machine during differing drilling 

configurations (thrust, rotational speed, penetration rate, etc.) and utilizing differing types 

of drilling methods in high compressive strength rock media (>20,000 psi). The research 

approach characterized the sound power level results from laboratory testing and 

provided the mining industry with empirical data relative to utilizing differing noise 

control technologies (drilling configurations and types of drilling methods) in reducing 

sound power level emissions on a roof bolting machine; 2) distinguish and correlate the 

empirical data into one, statistically valid, equation, in which, provided the mining 

industry with a tool to predict overall sound power levels of a roof bolting machine given 

any type of drilling configuration and drilling method utilized in industry; 3) provided the 

mining industry with several approaches to predict or determine sound pressure levels in 

an underground coal mine utilizing laboratory test results from a roof bolting machine 

and 4) described a method for determining an operators’ noise dosage of a roof bolting 

machine utilizing predicted or determined sound pressure levels. 
iii

TABLE OF CONTENTS 

Title Page ..............................................................................................................................i

Abstract.................................................................................................................................ii

List of Figures.......................................................................................................................vi 

List of Tables........................................................................................................................xi 

Nomenclature .......................................................................................................................xiv 

Dedication.............................................................................................................................xvii 

Acknowledgement................................................................................................................xviii 

Chapter 1: INTRODUCTION...........................................................................................1 

Chapter 2: LITERATURE REVIEW...............................................................................6 

Chapter 3: OBJECTIVE OF RESEARCH......................................................................14 

Chapter 4: SCOPE AND METHODS OF RESEARCH.................................................16 

4.1. Standard Operating Procedure for Conducting Noise 

 Measurements (Sound Power) of Roof Bolting Machines 

In the Pittsburgh Research Laboratory’s Reverberation 

Room..............................................................................................................16 

4.1.1 Preface for Determining Sound Power Level ....................................17 

4.1.2 Introduction .......................................................................................17 

4.1.3 Scope..................................................................................................18 

4.1.4 Normative Reference .........................................................................22 

4.1.5 Definitions..........................................................................................22 

 4.1.6 Requirements for a Special Reverberation Test Room......................22 

 4.1.7 Installation and Operation of Source under Test ...............................24 

4.1.8 Measurements in Test Room .............................................................25 

4.1.9 Calculation of Sound Power Levels...................................................29 

4.1.10 Information Reported for Each Test Condition .................................30 

 4.2 Modification of Steel Test Fixture for Roof Bolter Testing in the 

Reverberation Room .....................................................................................33 

4.2.1 Objective............................................................................................33 

4.2.2 Tests Performed to Assess Sound Power Radiated from Test 

 Fixture................................................................................................34 

 4.2.3 Conclusions........................................................................................40 

 4.3 Sound Power Level Testing in Reverberation Room ....................................41 

 4.3.1 Setting of Thrust Configurations. ......................................................44 

 4.3.2 Setting Rotational Speed Configurations...........................................47 

 4.3.3 Determining Penetration Rate or Displacement during Testing........48 

 4.3.4 Pulse System and Excel Data Collection Common to Speed 

 And Displacement...............................................................................49 

4.4 Rock Media and Strength Property Testing of Drilling Media......................50 

 4.4.1 Type of Rock Media ..........................................................................50 

 4.4.2 Obtaining Rock Cores of Rock Media...............................................51 

 4.4.3 Unconfined Compressive Strength of Rock Media ...........................52 

 4.5 Testing of Differing Bits and Drill Steel........................................................53 

 4.5.1 Drill Bits..............................................................................................53 

 4.5.2 Drill Steel............................................................................................54 
iv

 4.6 Testing of Different Drilling Methods...........................................................55 

 4.6.1 Dry (Vacuum), Wet and “Mist” System............................................55 

 4.7 Summary of Tests Conducted in the Reverberation Room ...........................56 

Chapter 5: APPLICATIONS OF SOUND POWER LEVEL MEASUREMENTS 

CONDUCTED IN THE REVERBERATION ROOM................................58

5.1 Drilling Components and Parameters Utilized for Testing............................58 

5.2. Data Collected for Sound Power Level Tests................................................59 

 5.3. Experimental Test Results – Sound Power Levels ........................................72 

 5.3.1 Round Drill Steel Compared to Hexagonal Drill Steel......................73 

 5.3.2 One Inch Diameter Compared to One and Three-Eighths Inch 

Diameter Drill Bits.............................................................................80 

 5.3.3 General Conclusions Regarding Data Collection ...............................83 

 5.4. Development of a Statistical Model for Determining Sound Power Levels..85 

 5.4.1 Introduction........................................................................................85 

 5.4.2 Statistical Accuracy of the Model......................................................98 

 5.4.3 Development of Equation for Determining a Sound Power Level...111 

 Chapter 6: DEVELOPMENT AND UTILIZATION OF MODELS FOR 

PREDICTING SOUND PRESSURE LEVELS FROM LABORATORY 

TESTS..............................................................................................................114 

 6.1. Introduction....................................................................................................114 

 6.2. Model for Predicting Sound Pressure Levels Using Overall Sound 

 Power Levels..................................................................................................115 

 6.2.1 Introduction........................................................................................115 

6.2.2 Predicting Underground Sound Pressure Levels from 

Measurements Above Ground ...........................................................116 

6.2.2.1 Differences between the Room Acoustic Method and

Imaging Method ....................................................................116 

 6.2.2.2 Predicting Sound Levels at a Single Point.............................118 

 6.2.2.3 Predicting Sound Levels at Multiple Points...........................119 

 6.2.2.4 Predicting Sound Levels in the Near-Field............................124 

 6.2.3 Limitations of Model Utilizing Overall Sound Power Level.............126 

 6.3. Model for Predicting Sound Pressure Levels Using Full-Octave 

 Band Frequency Sound Power Level.............................................................127 

 6.3.1 Ray-tracing Technique.......................................................................127 

 6.3.2 Raynoise Computer Program.............................................................127 

 6.3.3 Absorption Coefficients......................................................................129 

6.3.4 Method for Determining Absorption Coefficients in an Underground 

Coal Mine...........................................................................................130 

 6.3.4.1 Underground Measurements and Testing Parameters ...........130 

 6.3.4.2 Utilizing the Excelparse Program for Calculating OctaveBand Information...................................................................137 

 6.3.4.3 Development of an Equivalent Model in Raynoise for 

Predicting Sound Pressure Levels..........................................141 

 6.3.5 Predicting Sound Pressure Levels Underground Due to Drilling 

Cycle of Roof Bolting Machine.......................................................158 
v

 6.3.5.1 Full-Octave Band Sound Power Levels from Laboratory

Testing....................................................................................158 

6.3.5.2 Specific Characteristics of the Roof Bolting Machine ..........159 

 6.3.5.3 Establishment of a Measurement Grid for the Underground 

Mine Section ..........................................................................161 

6.3.5.4 Development of a Command File for Input into Raynoise

Program..................................................................................164 

6.3.5.5 Sound Pressure Levels Determined from Raynoise 

Program..................................................................................166 

6.3.5.6 Comparing Sound Pressure Levels - Model Prediction 

vs.Underground Measurements .............................................169 

 6.3.6 Determining the Noise Dosage a of Roof Bolter Operator from 

Predicted Sound Pressure Levels.......................................................181 

Chapter 7: CONCLUSIONS..............................................................................................184 

Chapter 8: RECOMMENDATIONS FOR FUTURE RESEARCH..............................188 

REFERENCES.....................................................................................................................191 

 

 

 

 

 

 

 
vi

LIST OF FIGURES

Figure # Page

1.1 Analysis of Audiograms for Coal and Metal/Non-Metal 2 

 Miners 

1.2 MSHA Coal Noise Sample Data – Percentage of Equipment 4 

 Whose Operators Exceeded 100% Dose 

1.3 Noise Testing of Roof Bolter in Reverberation Room 5 

4.1 Sketch of the PRL Reverberation Chamber 20 

4.2 One-third Octave Sound Power Levels Determined for a 32 

 Specific Control Test 

4.3 Test Fixture in Reverberation Room 33 

4.4 Location of Test Fixture Support Tubes and Accelerometers 36 

4.5 Estimated Sound Power Level (dBA) and Reduction in 39 

 Sound Power Level Before and After Modifications 

4.6 Reverberation Room at PRL 41 

4.7 Bruel & Kjaer Pulse Data Acquisition System 41 

4.8 Joystick on Control Panel 44 

4.9 Drill Mast of Roof Bolting Machine Raised to Test Stand 45 

4.10 Location of Thrust Pressure Gauge 46 

4.11 Location of Relief Valve Control 46 

4.12 Pulser Disk and Electro-sensors Mounted on Drill Chuck 47 

4.13 Location of String Potentiometer for Determination of 48 

 Penetration Rate 

4.14 Example of a Test Report – Sound Power 50 

4.15 Barre Granite – Rock media used for testing in phase 1 51 
vii

LIST OF FIGURES

Figure # Page

4.16 Sample of Core Collected from Barre Granite Rock Media 52 

4.17 Types of Drill Bits Used During Roof Bolting Operations 53 

4.18 Types of Drill Steel Used During Roof Bolting Operations 54 

4.19 Photograph of “Mist” System Used During Noise Testing 55 

5.1 Drill Steels - Round and Hex (1-inch) – Thrust vs. 73 

 Penetration Rate 

5.2 Drill Steels - Round and Hex (1-inch) – Penetration Rate 75 

 vs. Sound Power Level 

5.3 Drill Steels - Round and Hex (1.375-inch) – Thrust vs. 77 

 Penetration Rate 

5.4 Drill Steels - Round and Hex (1.375-inch) – Penetration Rate 79 

 vs. Sound Power Level 

5.5 One-inch vs. 1.375-inch Drill Bit – 81 

 (Penetration Rate vs. Thrust) 

5.6 One-inch vs. 1.375-inch Drill Bit – 82 

 (Penetration Rate vs. Sound Power Level) 

5.7 One-inch Round Drill Steel - Vacuum and Wet – 84 

 Sound Power Levels - 4,949 lbs Thrust, 

 200 rpm Rotational Speed 

5.8 Histogram Representing the Fit Accuracy of Statistical 99 

 Run of Model 

6.1 Comparison of Imaging and Room Acoustics Method of 117 

 Predicting Sound Pressure Levels 

6.2 Correction Factors for Converting Above Ground 118 

 Measurements to Underground Sound Pressure 

 Levels (Tunnels) 
viii

LIST OF FIGURES

Figure # Page

6.3 Correction Factors for Converting Above Ground 119 

 Measurements to Underground Sound Pressure 

 Levels (Flat Rooms) 

6.4 Correction Factors for Determining Underground 122 

 Sound Pressure Levels from Sound Power Measurements 

 Above Ground (Tunnels) 

6.5 Correction Factors for Determining Underground Sound 123 

 Pressure Levels from Sound Power Measurements Above 

 Ground (Flat Rooms) 

6.6 Correction Factors for Determining Sound Pressure Levels 125 

 Underground in the Near Field 

 (Top-Tunnel and Bottom-Flat Room) 

6.7 Sound Pressure Level Contour Plot Using the Raynoise 128 

 Program 

6.8 Illustration of Ray Tracing Model for Analyzing the Acoustic 130 

 Environment 

6.9 Measurement Layout Used for Determining Absorption 131 

 Coefficients in an Underground Coal Mine 

6.10 Photograph of Calibrated Sound Source Used for 132 

 Underground Testing 

6.11 Photograph of a A Brüel and Kjaer 2260 Investigator 134 

6.12 Measurement Locations for Determining Acoustical 135 

 Properties Underground 

6.13 Screenshot of the Excelparse Program 138 

6.14 Test Layout for First Run in Raynoise Model 142 

6.15 Sound Pressure Levels at 1,000 Hz Full-Octave Band 144 

6.16 Comparing Calculated vs. Measured Sound Pressure Levels for 146 

 63-Hz Octave Band 
ix

LIST OF FIGURES

Figure # Page

6.17 Comparing Calculated vs. Measured Sound Pressure Levels for 147 

 125-Hz Octave Band 

6.18 Comparing Calculated vs. Measured Sound Pressure Levels for 147 

 250-Hz Octave Band 

6.19 Comparing Calculated vs. Measured Sound Pressure Levels for 148 

 500-Hz Octave Band 

6.20 Comparing Calculated vs. Measured Sound Pressure Levels for 148 

 1,000-Hz Octave Band 

6.21 Comparing Calculated vs. Measured Sound Pressure Levels for 149 

 2,000-Hz Octave Band 

6.22 Comparing Calculated vs. Measured Sound Pressure Levels for 149 

 4,000-Hz Octave Band 

6.23 Comparing Calculated vs. Measured Sound Pressure Levels for 150 

 8,000-Hz Octave Band 

6.24 Comparing Calculated vs. Measured Sound Pressure Levels for 151 

 63-Hz Octave Band (Model Run 5) 

6.25 Comparing Calculated vs. Measured Sound Pressure Levels for 151 

 125-Hz Octave Band (Model Run 5) 

6.26 Comparing Calculated vs. Measured Sound Pressure Levels for 152 

 250-Hz Octave Band (Model Run 5) 

6.27 Comparing Calculated vs. Measured Sound Pressure Levels for 152 

 500-Hz Octave Band (Model Run 5) 

6.28 Comparing Calculated vs. Measured Sound Pressure Levels for 153 

 1,000-Hz Octave Band (Model Run 5) 

6.29 Comparing Calculated vs. Measured Sound Pressure Levels for 153 

 2,000-Hz Octave Band (Model Run 5) 

6.30 Comparing Calculated vs. Measured Sound Pressure Levels for 154 

 4,000-Hz Octave Band (Model Run 5) 
x

LIST OF FIGURES

Figure # Page

6.31 Comparing Calculated vs. Measured Sound Pressure Levels for 154 

 8,000-Hz Octave Band (Model Run 5) 

6.32 AutoCAD drawing of a Roof Ranger II Roof Bolting Machine 160 

6.33 AutoCAD drawing of a HDDR Roof Bolting Machine 161 

6.34 Measurement Grid Developed for a Roof Bolting Machine 162 

 at the Mine Face 

 

6.35 Measurement Grid Developed for a Roof Bolting Machine at 163 

 a Crosscut 

6.36 Measurement Grid Developed for a Roof Bolting Machine at 163 

 an Intersection 

6.37 Screenshot of a Command File for Input into Raynoise Program 165 

6.38 Determined Sound Pressure Level Contours in an Underground 166 

 Coal Mine 

6.39 Determined Sound Pressure Levels (Numerical) in an 167 

 Underground Coal Mine 

6.40 Zoom-view of Determined Sound Pressure Levels Near a Roof 168 

 Bolting Machine 

6.41 Roof Bolting Plan at the Underground Coal Mine 169 

6.42 Model Simulation for Predicting Sound Pressure Levels 171 

6.43 Sound Pressure Level Contours for Model Run 173 

6.44 A-Weighted Sound Pressure Levels Near Operator Position 179 

 of Roof Bolting Machine 
xi

LIST OF TABLES

Table # Page

4.1 Reverberation Chamber-Surface Area and Volume 19 

4.2 Estimated Values of the Standard Deviation of 21 

Reproducibility of Sound Power Levels 

4.3 Normative References 22 

4.4 Evaluation Test for the Suitability of the Test Chamber 24 

4.5 Minimum Distances of Microphones 26 

4.6 Minimum Number of Source Locations 27 

4.7 Corrections for Background Sound Pressure Levels 28 

4.8 Typical Background Noise Sound Pressure Levels 29 

4.9 Example of Reported Information for Each Sound Power 31 

 Test 

4.10 One-third Octave Sound Power Levels Determined for a 32 

 Specific Test (numeric) 

4.11 Test Data Collected During Sound Power Level Testing 43 

4.12 Unconfined Compressive Strength Results of Barre Gray 52 

Granite 

5.1 Variables for Sound Power Level Testing 58 

5.2 Sound Power Level Testing - Vacuum Drilling Method, 60 

 1-inch bit, Round Drill Steel 

5.3 Sound Power Level Testing – Vacuum Drilling Method, 61 

 1-inch bit, Hex Drill Steel 

5.4 Sound Power Level Testing – Vacuum Drilling Method, 62 

 1-3/8-inch bit, Round Drill Steel 

5.5 Sound Power Level Testing – Vacuum Drilling Method, 63 

 1-3/8-inch bit, Hex Drill Steel 
xii

LIST OF TABLES

Table # Page

5.6 Sound Power Level Testing – Wet Drilling Method (3 gal/min), 64 

 1-inch bit, Round Drill Steel 

5.7 Sound Power Level Testing – Wet Drilling Method (3 gal/min), 65 

 1-inch bit, Hex Drill Steel 

5.8 Sound Power Level Testing – Wet Drilling Method (3 gal/min), 66 

 1-3/8-inch bit, Round Drill Steel 

5.9 Sound Power Level Testing – Wet Drilling Method (3 gal/min), 67 

 1-3/8-inch bit, Hex Drill Steel 

5.10 Sound Power Level Testing – Mist Drilling Method (3 qt/min), 68 

 1-inch bit, Round Drill Steel 

5.11 Sound Power Level Testing – Mist Drilling Method (3 qt/min), 69 

 1-inch bit, Hex Drill Steel 

5.12 Sound Power Level Testing – Mist Drilling Method (3 qt/min), 70 

 1-3/8-inch bit, Round Drill Steel 

5.13 Sound Power Level Testing – Mist Drilling Method (3 qt/min), 71 

 1-3/8-inch bit, Hex Drill Steel 

5.14 Sound Power Level Contributions of Two Frequency Bands 85 

5.15 Laboratory Data Utilized for Input into the Statistical Model 87 

5.16 Regression Coefficients Determined from the Statistical Model 98 

5.17 Comparing Laboratory Results to Model Results 100 

 (Sound Power Level) 

6.1 One-Third Octave-band Sound Power Levels for 133 

 Calibrated Noise Source 

6.2 Example of the One-Third Octave Data Collected Underground 136 
xiii

LIST OF TABLES

Table # Page

6.3 Measured Full-Octave Band Sound Pressure Levels 140 

 from Underground Testing 

6.4 Absorption Coefficients Utilized for First Run of 143 

 Raynoise Model 

6.5 Calculated Full-Octave Band Sound Pressure Levels – 145 

 First Run of Model 

6.6 Calculated Full-Octave Band Sound Pressure Levels – 155 

 Fifth Run of Model 

6.7 Differences Relative to the Measured and Calculated 156 

 Sound Pressure Levels 

6.8 Final Absorption Coefficients Determined from Model Runs 157 

6.9 Full-Octave Band Sound Power Levels from Laboratory Testing 159 

6.10 Sound Pressure Level Measurements at Operator Position 170 

 of Roof Bolting Machine 

6.11 Full-Octave Band Sound Power Levels – 172 

 Compressive strength-5,000 psi., hex drill steel, 1-inch bit, 

 rotational speed-500 rpm, Thrust setting-6,363 lbs. 

6.12 Sound Pressure Level Results (Numerically) of the Model Run 174 

6.13 Noise Dosage (MSHA and NIOSH) of Roof Bolting 183 

 Machine Operator 

 

 
xiv

NOMENCLATURE

Symbol Description Units

α Sabine or Absorption Coefficent 

σR Standard Deviation of Reproducibility 

θ Temperature degree Celsius 

λ Wavelength of Sound 

A Area of Rock Core in2

avthrust Average Thrust During Test lbs 

avspeed Average Rotational Speed During Test rpm 

C◦ Unconfined Compressive Strength (Corrected) psi 

C Unconfined Compressive Strength psi 

CL Criterion Level dBA 

D Diameter of Rock Core in 

dmin Minimum Distance Between Microphones m 

DUT Device Under Test 

ER Exchange Rate dBA 

FRF Frequency Response Function g/n 

Hz Hertz 

kHz Kilohertz 

L Length of Rock Core in 

Lpi Sound pressure level at the ith measurement dB 

 Position 

Lp Mean of Sound Pressure Levels dB 

Lw Sound Power Level dB of dBA 
xv

NOMENCLATURE

Symbol Description Units

Lv Surface Average Velocity Level dB or dBA 

LwA Average Sound Power Level dBA 

Lp (underground) (Patterson) A-weighted Sound Pressure Level dBA 

Lw (aboveground) (Patterson) A-weighted Sound power Level dBA 

MSHA Mine Safety and Health Administration 

MSHA-PEL MSHA-Permissible Exposure Limit % 

NIOSH National Institute for Occupational Safety 

 and Health 

NIOSH-REL NIOSH-Recommended Exposure Limit % 

N Newton lbs 

Ns Number of Source Positions 

P Load at Failure (rock core) lbs 

PRL Pittsburgh Research Laboratory 

PEL Permissible Exposure Limit 

pendepth Penetration Depth During Test in 

penrate Penetration Rate During Test in/sec 

R2

 Coefficient of Determination 

RTime Run Time sec 

S Surface Area m2 

S0 Reference Surface Area m2

setthrst Thrust Setting Prior to Drilling lbs 
xvi

NOMENCLATURE

Symbol Description Units

setspd Rotational Speed Setting Prior to Drilling rpm 

SPL Sound Pressure Level dB or dBA 

spdb Linear Sound Power For Test dB 

spdba A-weighted Sound Power for Test dBA 

TWA Time-Weighted Average dBA 

T60 Decay Time sec 

TC Criterion Time h or sec 

V Volume m3 
xvii

DEDICATION 

TO MY DECEASED FATHER AND MOTHER, MY DAUGHTER, MORGAN AND 

WIFE, DEB

For providing me with the motivation and determination to reach one’s full potential 
xviii

ACKNOWLEDGEMENTS

 The list of those deserving of mention is extensive and includes dedicated and 

extraordinary individuals from the National Institute for Occupational Safety and 

Health (NIOSH) and the West Virginia University (WVU). Each organization, 

contributed extensively to my ability to conduct the research and complete the 

dissertation. The individuals who provided substantial insight and direction include 

Professor Syd Peng, WVU (my Advisor and Committee Chair), Dr. Gerald 

Finfinger, NIOSH, Mr. Pete Kovalchik, NIOSH and Dr. Güner Gürtunca, NIOSH. 

Each played an integral role in the research endeavor and continued to provide me 

with a significant amount of devotion, intelligence and eagerness to mentor me thru 

this process. 
1

CHAPTER 1 

INTRODUCTION 

Over-exposure to noise remains a widespread and serious health hazard in the 

U.S. mining industries despite 25 years of regulation. Most other categories of illnesses 

and injuries associated with mining have improved dramatically, with the exception of 

hearing loss. The use of heavy equipment, the drilling and cutting of rock and coal, and 

the confined work environment are the major factors that contribute to high levels of 

noise exposure during mining operations. Every day, 80% of the nation’s miners go to 

work in an environment where the time weighted average (TWA) noise level exceeds 85 

dBA and more than 25% of the miners are exposed to a TWA noise level that exceeds 90 

dBA, the permissible exposure limit (PEL) (1). 

In January 1995, the Physical Agents Effects Branch, located in the National 

Institute for Occupational Safety and Health (NIOSH), Division of Biomedical and 

Behavioral Science, Cincinnati, Ohio, began collaboration on a project with the Mine 

Safety and Health Administration (MSHA) that was designed to determine the prevalence 

of hearing loss among miners. Two reports were forwarded to MSHA: one for coal 

miners, and one for metal/non-metal miners (2). After removing potentially invalid 

audiograms through a quality assurance process, the first report contained an analysis of 

17,260 audiograms for 2,871 coal miners, and the second report reviewed 22,488 

audiograms on 5,244 metal/non-metal miners. For comparison purposes, hearing 

thresholds were calculated for a similar-aged population of non-exposed individuals by 

using Annex A from ISO-1999 (ISO 1990) (3). The noise levels that would be predicted 
2

to cause the amount of hearing loss observed for the miners were also calculated from the 

ISO-1999. 

The results of these investigations showed that miners developed hearing loss 

much more quickly than those in the non-occupational noise-exposed database used by 

ISO-1999, and that the miners experienced a greater severity of hearing loss than would 

Figure 1.1 Analysis of Audiograms for Coal and Metal/Non-Metal Miners 

be expected for non-occupational noise-exposed persons of the same age and gender. 

Using hearing thresholds at 4000 Hz as an indicator, coal miners experienced hearing loss 

2 1⁄2 to 3 times greater than would be expected for persons not exposed to occupational 

noise. At age 55, 65% of the coal miners and metal/non-metal miners were found to have 

a hearing impairment. By comparison, only 10% of the non-occupationally exposed 

group had a hearing impairment at age 55 (Figure 1.1) (2). While Noise Induced Hearing 

Loss (NIHL) is the most common occupational illness in this country, this problem is 

especially acute among miners. NIOSH has recognized NIHL as one of the 10 leading 

0

20

40

60

80

100

20 25 30 35 40 45 50 55 60 65 Age

Percent with hearing impairment

Metal/Nonmetal

Coal

Non-noise exposed
3

work-related diseases and injuries in the Nation, and has emphasized its importance in the 

National Occupational Research Agenda (NORA). 

 Over the past decade, the Mine Safety and Health Administration (MSHA) has 

worked to develop a revised health standard for occupational noise exposure in coal, 

metal, and nonmetal mines. In December of 1996, the agency released its Proposed Rule 

in the Federal Register (30 CFR Parts 56, 57, 62, 70, and 71) (4). Unlike its predecessor, 

the proposed rule emphasizes the primacy of engineering controls as the strongest 

defense against excessive exposure to noise and the prevention of NIHL among miners 

and disallows reliance on personal hearing protection devices (PHPs) as a means of 

compliance with the standard. Despite the extensive work performed in the 1970’s and 

80’s, NIHL is still a pervasive problem in the mining industries. 

A new MSHA noise standard was published on September 13, 1999. This rule 

closely resembles the existing Occupational Safety and Health Administration (OSHA) 

Occupational Noise Exposure Standard and Hearing Conservation Amendment (29 CFR 

1910.95), and replaced the different standards for occupational noise exposure in coal 

mines and in metal/non metal mines with a single new standard applicable to all mines. 

MSHA concluded in a recent survey that if an OSHA-like hearing conservation program 

was adopted, hypothetically, 78% of the coal miners surveyed would be required to be in 

a hearing conservation program (5). Although the proposed noise exposure limits would 

not totally eliminate the risk of material impairment, it is expected to reduce by twothirds the number of miners currently projected to suffer a material impairment of their 

hearing. 
4

Additionally, MSHA coal noise sample data (6) collected from 2000 to 2002 show 

that 65% of the equipment whose operators exceeded 100% noise dosage comprise only 

seven different types of machines; auger miners, bulldozers, continuous miners, front end 

loaders, roof bolters, shuttle cars (electric), and trucks. In addition, the MSHA data 

indicates that the roof bolter is third among all the equipment and second among 

equipment in underground coal whose operators exceed 100% dosage (Figure 1.2). 

Figure 1.2 MSHA Coal Noise Sample Data – Percentage of Equipment Whose Operators 

Exceeded 100% Dose 

 Lesser elements in the hierarchy of controls for reduction of noise exposure, 

including administrative practices (e.g. job rotation), and the use of personal hearing 

protective devices (PHP’s) have been the main sources of noise control in the past, 

relying on workers to properly wear and maintain their hearing protection. A balanced 

approach to the prevention of NIHL that includes not only education, surveillance, and 
5

intervention, but a research emphasis on engineering controls for noise is absolutely 

necessary. The development and utilization of engineering noise controls represent a 

permanent solution while the use of PHP’s is seen as an interim solution. This research 

effort focuses on the development and assessment of engineering noise controls for 

mining equipment, specifically, roof bolters used in underground coal mining. The 

research will be conducted in a specialized laboratory using a standard roof bolter and a 

variety of operational conditions and settings representative of the underground coal 

mining industry as shown in figure 1.3 below. The data collected will provide 

information related to optimum drilling configurations, related to high compressive 

strength drilling media (>20,000 psi) for reducing sound power emissions from the 

machine. Additionally, the research will then persist, using a modeling approach, to 

predict the sound pressure level an operator is exposed to in an underground coal mine 

utilizing the sound power level data obtained from the laboratory. 

Figure 1.3 Noise Testing of Roof Bolter in Reverberation Room 
6

CHAPTER 2 

LITERATURE REVIEW 

 Recent research focusing on engineering noise controls, specifically, on 

underground coal mining roof bolters is considerably limited. In 1983, the former 

Bureau of Mines developed a handbook entitled, “Mining Machinery Noise Control 

Guidelines, 1983” (7) which documented available noise control information of 

numerous pieces of mining equipment for dissemination to the mining industry. Several 

noise treatments were proposed within the handbook related to roof bolting machines in 

underground coal settings, which included; modifying the dust collection blower or 

changing to a quieter model; cover or enclose the hydraulic pump and sealing the 

enclosure around motor and pump-blower drives using the existing cover panels. A 

major manufacturer of roof bolting equipment, J.H. Fletcher, Inc. has supported most of 

the recommended controls, however, when the drilling or bolting process occurs with the 

machine, noise levels experienced by the operator still exceed regulatory limits, therefore 

overexposing the operator to noise. 

 NIOSH has performed numerous noise exposure surveys related to roof bolting 

operators in underground coal mines. The data suggests that 81% of the samples 

collected (a total of 16 samples of roof bolter operators), exceeded the MSHA 

Permissible Exposure Level (8). Additionally, representatives from MSHA conducted a 

series of environmental noise surveys in 12 underground coal mines (9). Approximately, 

2,600 employees were included in the survey. The data suggested that 20% of all 

workers which are associated with face operations are exposed to noise levels which are 

in excess of the prescribed limits (MSHA Permissible Exposure Level). Specifically, 
7

while monitoring operators of roof bolting machines, the data suggested that noise levels 

exceeded 90 dBA during drilling and bolting activities, therefore contributing 

overexposure of noise to these operators. 

 Recent and prior research associated with noise controls for roof bolting machines 

utilized in underground coal (rotary) is significantly limited. Numerous attempts have 

been made to “quiet” percussive type drills (development of differing types of drill rod, 

utilization of water, etc.), mainly utilized in hard rock mining commodities that could 

possibly be applicable to rotary roof bolting machines. The noise radiated from 

percussive type drills can be classified into two different components: airflow noise due 

to the utilization of compressed air and mechanical noise, which generally is attributed by 

the impact and rattling of drill components; for example, drill rod noise. 

 Lesage, et. al (10) addressed an experimental approach to characterize the 

vibroacoustic behaviour of percussion drill steel rods under real operating conditions and 

laboratory controlled operating conditions. The contribution of longitudinal and flexural 

vibration related to noise generation was provided. The testing concluded that the 

bending waves within the drill steel were mainly responsible for the largest portion of 

noise radiation and the contribution of longitudinal waves to the noise radiation was 

found to be negligible. 

 Champoux, et. al. (11) addressed a method for determining the contribution of 

both longitudinal and flexural waves related to the radiation of noise associated with 

percussive type drill steel rods. The authors determined that in order to reduce the noise 

produced by the steel rod, one must understand significant aspects of the noise generation 

mechanism (12). A typical cylindrical steel rod was utilized as the test piece and hung 
8

vertically in a semi-anechoic room. A soft suspension was attached to a steel striking 

piece solidly attached at the top end of the rod. Being supported by the top, the steel rod 

was always aligned vertically. First, the vibration behavior of the structure was 

examined. The use of modal analysis was performed on the structure. Lateral impacts 

were administered using an impact hammer to exite predominantly the bending modes of 

the steel. Accelerometers were glued on the rod at several locations and transfer 

functions were recorded utilizing a two-channel frequency analyzer. The longitudinal 

modes and the corresponding frequencies were measured by impacting the striking end 

piece along the rod’s longitudinal axis and the response was measured with an 

accelerometer installed on the striking piece and oriented in the same axis. To determine 

noise radiation characteristics, a sinusoidal excitation was used initially, and to generate a 

longitudinal excitation, a 50-pound shaker was attached vertically to the upper part of the 

rod. However the noise generated by the rod when excited by the shaker was very low. 

An impact hammer was then used to control the amplitude and location of impact with 

respect to the rod. The end of the impact handle was attached to a hinge allowing a well 

controlled rotation along a horizontal axis. The blows of impact were then always 

applied on the striking end piece of the rod in a direction parallel to the longitudinal axis. 

The impacts were applied on the longitudinal center line of the rod (axial excitation) and 

near the edge of the tip of the rod (eccentric excitation). The force amplitude peaks were 

on the order of 1,000 N (225 lbF). To record the noise, a microphone, located 20 cm (7.9 

inches) from the rod was used. Results of the testing concluded that: 1) imperfection 

tends to create double peaks for the flexural modes; 2) flexural and longitudinal waves 

both contribute to the sound radiation; 3) for a given force amplitude, the longitudinal 
9

mode amplitude appears to be insensitive to impact force location and 4) flexural modes 

are very sensitive to imperfection of the rod and impact force location. 

 Stein and Aljoe (13) provided information on noise controls related to percussivetype drills. A concentric drill steel was designed for use as a drilling tool and noise 

control. The design differed from the typical drill steel because it was constructed of two 

members rather than the usual one member. The two members consisted of an inner 

pulse transmission rod and an outer torque transmission tube. The inner rod transmitted 

percussive energy to the bit just as the conventional steel would, however torque to the 

bit was eliminated. The other member, the torque tube, provided torque to the bit. The 

torque tube provided rotation to the bit and acted as a barrier to attenuate noise emitted 

for the inner rod. Testing of the concentric steel for noise output to the operator provided 

a 5 dBA reduction as compared to the standard steel. 

 Visnapu and Jensen (14) researched modifications on standard pneumatic rock 

drills to reduce the noise of the air exhaust, drill steel resonance noise and noise radiated 

by the drill body. The drill body was enclosed with a close-fitting case and muffler. The 

enclosure consisted of a metallic honeycomb skeleton filled with viscoelastic absorber on 

the inside and a durable outer shell, in which was designed to provide both exhaust and 

drill body noise muffling and absorption. Noise radiated by the drill steel was attempted 

to be reduced by utilization of a constrained-layer treatment consisting of a tubular metal 

cover bonded to the outside of the rod by a viscoelastic filler. The constrained-layer 

damped steels were prepared by slipping the metal tube over the drill steel, centering the 

steel in the tube, and then filling the space between the tube with liquid viscoelastic filler. 

Upon curing of the filler, part of the covering around the collar and shank was removed. 
10

Tubes with wall thicknesses from 0.049 to 0.065 inch and outside diameters of 1-1/4 to 1-

1/2 inches were bonded to 7/8-inch-diameter drill steels. Two viscoelastic fillers were 

selected, a two-part-mix urethane rubber, and a syntactic polyurethane foam. Noise 

testing related to the constrained-layer drill steels demonstrated to be an effective method 

for reducing drill steel noise. Results displayed a 3-6 dBA reduction when utilizing 

constrained-layer drill steels in comparison to standard steel. 

 Bartholomae (15) reported on an in-the-hole drill concept for noise control 

associated with percussive type drills. The concept eliminated the drill rod as a stress 

transfer mechanism so that the percussive motor is located just behind the drill bit. The 

motor is pushed into the borehole thru utilization of the drill pipe, which is used to rotate 

the percussion motor and drill bit to transmit the drill feed force. The noise reduction 

principle of the “in-the-hole” drill involved an operational effect. Once the borehole is 

started, the high energy noise from the percussive tool is contained entirely within the 

borehole, with the rock mass acting as an acoustic enclosure. This design was 

significantly different than standard percussive drills, in which the major noise producing 

components (drill hammer, drill steel, air exhaust) are located outside the borehole. 

Laboratory testing, for noise related to this concept, displayed that noise levels 

significantly decreased, 4 dBA (4 ft. into rock). However, mechanical difficulties 

associated with water leaks, percussion motor, etc. related to the drill eliminated any 

further testing. Future plans were to address the mechanical problems associated with the 

new design, since noise level reduction did show promise. 

 Paraszczak and Planeta (16) reported on the utilization of water-powered jackleg 

rock drills to be more efficient, faster and more comfortable (noise generation) than 
11

conventional pneumatic drills. The authors tested a water-powered hand-held drill in 

comparison to compressed-air jackleg drills in relation to: 1) penetration rate 2) energy 

consumption and 3) noise level to the operator. The tests concluded that the waterpowered jackleg drill achieved faster penetration rates (approximately 10-30% higher 

than the pneumatic drills), along with less energy consumption (12 times less) and lower 

drilling costs (40% less). Additionally, a reduced noise level (11 to 25 dBA) and a 

reduced vibration level was achieved thru utilization of the water-powered jackleg drill. 

 Additionally, high pressure water jets to assist rotary drilling operations were 

examined by Hurel and Cagnioncle (17). The idea associated with this research was to 

extend the application of rotary drilling to harder and more abrasive rocks, by assisting 

conventional mechanical bits with high pressure water jets, since, for hard and abrasive 

rocks, recourse is taken to percussive drilling which involves disadvantages concerning 

both the level of the cost of the installation and the nuisances it produces (noise, 

vibration, dust, etc.). Laboratory tests examined the following mining applications: 1) 

blast hole drilling for driving galleries by the use of explosives and 2) drilling holes for 

roof bolting. The latter, drilling holes for roof bolting will be addressed due to the 

relevance to the research proposed. A test bench was set up and coupled with a data 

acquisition system which enabled the recording of thrust, force, rotation speed, pressure, 

rate of water flow, drilling penetration rate and energy consumption. The diameter of the 

roof bolting bits utilized for testing was 22 mm (0.87 inch). The testing program was 

developed to determine the advantages resulting from water jet assistance related to key 

drilling parameters (thrust, rotation speed, water pressure, etc.). The drilling tests were 

performed on rocks whose uniaxial compressive strength reached 190 MPa 
12

(approximately 28,000 psi). Results displayed the following: 1) the increase in flow rate, 

water pressure, etc. provided an increase in penetration rate, along with a decrease in 

cutting energy; 2) the water jet assistance was more efficient when the jets come thru the 

tungsten carbide inserts of the drill bit, allowing the high-pressure jets to act precisely in 

the area of contact between the rock and the drill bit, consequently acting upon the 

cutting process initiated by the tungsten carbide insert and 3) the orientation of the jets 

should be such that one is directed towards the perimeter of the drill bit and the other 

towards the hole axis. Testing of the water-jet design was also performed in a uranium 

mine. Three separate sites were chosen underground to verify that the drilling of holes 

for roof bolting was possible in different roof material in the mine workings. Drilling 

was performed on rock whose uniaxial compressive strength ranged between 50 and 200 

MPa (7250 and 29,000 psi) and the water-pressure jet assistance was set to provide 

pressures between 220 and 240 MPa (32,000 and 35,000 psi). Results showed that in 

very hard rock strata, the penetration rate obtained was approximately 1.20 m/min 

(approximately 4 ft/min), whereas, in other bands, the penetration rate was measured to 

provide between 2 and 5 m/min (6.6 and 16.4 ft/min). Overall, the average penetration 

rate of drilled holes was approximately 1.80 m/min (approximately 6 ft/min). The 

penetration rates obtained for this study were comparable to those obtained with rotary 

percussion hammer drills utilized in the mine working. 

This research effort will focus on evaluating and assessing several noise controls 

to be utilized during drilling activities in high compressive strength media (> 20,000 psi) 

associated with the roof bolting machine and then, consequently utilizing a modeling 

approach, predict sound pressure levels to roof bolting machine operators in an 
13

underground coal mine to examine noise exposure. The ultimate objective of the 

research is to provide the mining industry with valuable information to minimize or 

eliminate noise overexposure to roof bolter operators during the drilling portion of the 

work cycle of the machine. 
14

CHAPTER 3 

OBJECTIVE OF RESEARCH 

The overall objective of the research is to determine, to characterize and to 

measure sound power levels radiated by a roof bolting machine during differing drilling 

configurations (thrust, rotational speed, penetration rate, etc.), along with utilizing a 

modeling approach for predicting sound pressure levels associated with roof bolter 

operators during the drilling cycle in high compressive strength rock media (>20,000 psi) 

utilizing the sound power level laboratory data measured. The determined sound power 

levels generated during the drilling cycle are of major interest because these levels 

represent the overall sound power being generated by the machine. These levels, 

determined from laboratory tests, can then be used to accurately assess the effectiveness 

of differing noise controls for reducing noise exposure to roof bolter operators. Utilizing 

sound power results obtained from the laboratory tests, a statistical model could then be 

developed for predicting sound power levels given differing drilling parameters (thrust, 

rotational speed, penetration rate, drill steel size and shape, drill bit size and drilling 

methods (vacuum, wet or mist). Additionally, utilizing the sound power levels related to 

differing drilling methods and parameters already determined and/or predicted, along 

with the utilization of knowledge related to the environmental noise characteristics 

associated with underground coal mining, sound pressure levels being experienced by 

roof bolter operators could then be determined and/or predicted to determine overall 

noise exposure using differing drilling configurations. The completion of the research 

will provide the mining industry with valuable information related to: 1) an 

understanding on how differing drilling configurations and drilling methods attribute to 
15

the sound power levels generated from a roof bolting machine while drilling into a high 

compressive rock media; 2) optimal drilling configurations and drilling methods in 

reducing sound power levels of the roof bolting machine; 3) a statistically valid equation 

for determining sound power levels of a roof bolting machine given differing drilling 

configurations and drilling methods; 4) a method for predicting sound pressure levels at 

the operator position and multiple locations in an underground mine related to the drilling 

cycle of a roof bolting machine and 5) a method for determining an operators’ noise 

dosage relative to a roof bolting machine given any type of drilling configuration or 

drilling method utilized. 
16

CHAPTER 4 

SCOPE AND METHODS OF RESEARCH 

 The first phase of the research study was conducted in the PRL’s reverberation room. 

The objective of the first phase was to conduct a myriad of sound power tests related to differing 

drilling parameters (thrust, rotational speed, penetration rate, drill steel size and shape, drill bit 

size) and drilling methods (vacuum, wet or mist) during the drilling cycle of a roof bolting 

machine in high compressive strength media (>20,000 psi). The laboratory results were then 

analyzed to provide the mining industry with valuable information related to optimum drilling 

configurations or parameters to be utilized when drilling into high compressive strength media 

(>20,000 psi) obtained from sound power levels collected in the laboratory. The second phase of 

the research was to use the data collected in the first phase of the research, and utilizing a 

modeling approach, predict the sound pressure levels the operator will experience in an 

underground coal mine in an effort in reducing noise exposure to the roof bolting operator. 

Procedures utilized for conducting the laboratory tests in the reverberation room are mentioned 

below. 

4.1 Standard Operating Procedure for Conducting Noise Measurements (Sound Power) 

 of Roof Bolting Machines in the Pittsburgh Research Laboratory’s Reverberation 

 Room 

 

The following information presented below relates to the method used (utilizing the ISO 

3740 series of acoustical standards) for determining sound power values (in 1/3 octave band 

frequencies) in the reverberation room at the Pittsburgh Research Laboratory (PRL) relative to 

the specific engineering noise control tests for the roof bolting machine. 
17

4.1.1 Preface for Determining Sound Power Levels

 The ISO 3740 series of acoustical standards specify various methods of determining the 

sound power levels of machines and equipment. The standards detail the acoustical requirements 

for the measurements appropriate for different test environments. Given the desired 

classification method for testing related to this research effort, the available test environment; a 

reverberation chamber, the expected characterization of the noise source; broad-band in 

frequency, and the desired output; A-weighted, octave and/or third octave sound power, the ISO 

3743-2 (18) standard served as the reference standard for the research. The information 

discussed below relates to each section of the ISO 3743-2 standard and explains the rational 

behind the decisions made to meet the standard for testing the roof bolting machine in the 

reverberation room at PRL (19). 

4.1.2 Introduction

 The introduction of the standard lists the general guidelines to assist in selecting the most 

appropriate ISO 3740 series standard, given the purpose of the test and the testing conditions. 

The ISO 3743 standard explains conducting engineering grade experiments where A-weighted 

(replicates the human response of the ear) and octave band sound pressure levels are measured at 

prescribed microphone locations or along prescribed paths. The measurements are then used to 

calculate sound power levels. The standard methods are applicable for “small” machines, 

devices, components, and sub-assemblies, particularly those considered portable. The standard 

suggests that the device-under-test (DUT) (e.g. roof bolting machine) preferably be less than one 

percent of the test room volume but the standard does not specifically disallow the testing of 

larger devices. The ISO 3743-2 specifically documents requirements for testing in a special 

reverberation chamber, a facility that is available at the NIOSH-PRL and thus the ISO 3743-2 
18

was considered the appropriate document to specify test procedures, analysis, and 

instrumentation specifications for this phase of the research study. 

4.1.3 Scope 

 This section (scope) of the standard documents the engineering method to determine the 

sound power of small, movable noise sources in a specifically designed room having a specified 

reverberation time over the frequency range of interest. There are two test methods available, 

the direct and comparison method. The comparison method was selected for testing. The 

methods of the ISO 3743-2 are suitable for the measurement of all types of noise within a 

specified frequency range. The maximum volume of the device-under-test (DUT) and the lower 

limit of the frequency range for the test methods depend upon the volume of the test chamber. 

While the standard states that measurements on sources emitting noise below 200 Hz may be 

difficult, this statement assumes reverberation chambers much smaller than the chamber at the 

PRL. Table 4.1 provides the surface area and volume associated with the reverberation room at 

PRL. Additionally, Figure 4.1 represents a sketch of the reverberation room at PRL used for 

testing of the roof bolting machine. 
19

Table 4.1 Reverberation Chamber-Surface Area and Volume 

Length (m) Width (m) Height (m) 

Major chamber dimensions 18.31 10.37 6.73 

Surface Area (m2) Volume (m3) 

Front wall 69.80

Rear wall 78.02

Right wall 123.22

Left wall 132.99

Floor 219.01

Ceiling 189.84

1,277.84 

Chamber door protrusion 4.25 6.26 

Trench 15.77 1.57 

Left wall window .43 0.07 

Left wall entry door 1.03 .32 

Right wall entry door 1.03 .32 

TOTAL 835.39 1,286.38 
20

Figure 4.1 Plan view of the Reverberation Room at the PRL

Reverberation Room

Building 154

A - WindowB - Small VentC - Large VentD - Fan

Dimensions in Meters

Left Wall of Reverb Room

End Wall of Reverb Room Floor of Reverb Room

Right Wall of Reverb Room
21

The ISO 3743-2 standard also addresses measurement uncertainty. These uncertainties arise 

from several different factors, including environmental conditions and experimental techniques. 

Given the standard deviations of A-weighted (replicates the human response of the ear) sound 

power levels calculated from test results generated in the reverberation room utilizing a known 

noise or sound source, the standard deviations should not exceed those shown in Table 4.2. The 

cumulative effects of the measurement uncertainty in applying the procedures of ISO 3743-2 are 

taken into account in the standard deviations of Table 4.2 but they do not include changes in the 

DUT operating or mounting conditions. The measurement uncertainty depends on the standard 

deviation of reproducibility (σR) listed in Table 4.2 and the degree of confidence required. Given 

a normally distributed sound power spectrum, there is 90% confidence that the true sound power 

of a source lies within the range of + 1.645 σR of the measured value and for a 95% confidence 

level, within + 1.96 σR of the measured value. 

Table 4.2 Estimated Values of the Standard Deviation of Reproducibility of Sound Power 

 Levels 

Octave Band Center 

Frequency (Hz) 

Standard Deviation 

of Reproducibility 

σR

125 5.0 

250 3.0 

500 to 4,000 2.0 

8,000 3.0 

A-weighted 2.0 
22

4.1.4 Normative References

Additional standards used in conjunction with the ISO 3743-2 standard are listed below. 

Table 4.3 Normative References. 

Number Title 

ISO 3741 Acoustics – Determination of sound power levels of noise sources 

Precision methods for broad-band sources in reverberation rooms. 

ISO 3743-1 Acoustics – Determination of sound power levels of noise sources – 

Engineering methods for small, movable sources in reverberant fields – 

Part 1: Comparison method for hard walled test rooms. 

ISO 3745 Acoustics – Determination of sound power levels of noise sources – 

Precision methods for anechoic and semi-anechoic rooms. 

ISO 6926 Acoustics – Determination of sound power levels of noise sources – 

Requirements for the performance and calibration of reference sound 

sources. 

ISO 7574-1 Acoustics – Statistical methods for determining and verifying stated 

noise emission values of machinery and equipment – Part 1: General 

considerations and definitions. 

ISO 7574-4 Acoustics – Statistical methods for determining and verifying stated 

noise emission values of machinery and equipment – Part 4: Methods for 

stated values for batches of machines. 

IEC 225 Octave, half octave and third-octave band filters intended for the analysis 

of sounds and vibrations. 

IEC 651 Sound level meters. 

IEC 804 Intergrating-averaging sound level meters. 

IEC 942 Sound calibrators. 

4.1.5 Definitions

 A single definition is listed for a special reverberation test room. It is defined as “A test 

room meeting the requirements of this part of the ISO 3743-2”. These are addressed in Section 

4.1.6. 

4.1.6 Requirements for a Special Reverberation Test Room

 Guidelines for the design of a suitable test room, the reverberation time, and surface 

treatment are discussed within this section. The reverberation chamber walls and floor were 

designed to have Sabine absorption coefficients (the ratio of the sound energy absorbed by a 
23

surface of a medium or material to the sound energy incident on the surface) less than 0.16, 

meeting the requirements of the standard. Another issue relates to background noise, this 

ensures that at each microphone the background sound pressure level noise shall be at least four 

decibels (dB), and preferably ten decibels less than the DUT sound pressure level. Background 

noise is measured as part of the test procedure and past test results show that it is unlikely a 

problem will occur. There are also additional criteria listed for temperature and relative 

humidity. As stated in the standard, with the relative humidity expressed as a % and the 

temperature in degrees C, the product 

 Relative Humidity x (θ + 5 degrees C) (1) 

shall not differ by more than + 10 % from the value of the product measured during the 

measurement of the reverberation time of the test room, where θ is the temperature in degrees 

Celsius. The temperature, relative humidity, and barometric pressure sensor data is fed into the 

data collection system to allow monitoring and recording of environmental data. Additionally, a 

four step process was utilized for testing the suitability of the test room. A small broad-band 

calibrated reference noise source was used following the procedures given in the standard ISO 

6926 (20). Calibration report data, test data and the allowable difference between the two is 

provided in Table 4.4 below. The reverberation chamber passed the suitability test. 
24

Table 4.4 Evaluation Test for the Suitability of the Test Chamber 

Octave Band 

Center Frequency 

(Hz) 

Calibration Report 

Sound Power Level 

(dB) 

NIOSH Chamber 

Test Sound Power 

Level (dB) 

Delta 

(dB) 

Allowable 

Difference 

(dB) 

125 83.1 83.1 0.0 + 5 

250 84.7 84.7 0.0 + 3 

500 85.4 85.4 0.0 + 3 

1,000 89.1 89.1 0.0 + 3 

2,000 90.1 90.1 0.0 + 3 

4,000 87.8 87.9 0.1 + 3 

8,000 84.3 83.6 0.7 + 4 

4.1.7 Installation and Operation of Source Under Test

 The acoustical properties of the reverberation chamber and the manner of source 

operation play a significant role in the sound power emitted by a device. The DUT shall be 

placed at one or more locations as if it were installed or used normally. If no such location may 

be found, then the DUT will be installed on the floor with at least one meter in distance between 

the DUT and the nearest wall. It may be necessary to test the DUT in multiple locations, if 

needed. Because roof bolter testing requires a rather large drill media, e.g. granite, as well as a 

large support stand, care must be taken to ensure that these do not radiate significant amounts of 

sound energy. To prevent this, the support stand, with the exception of its diagonal members and 

the short horizontal members along the minimum direction of the top of the structure, were filled 

with sand and two layers of urethane were bonded to the rock support members between the drill 

media due to a significant amount of vibration testing conducted (21). Finally, an additional 

layer of urethane was laid between the drill media and chain holding the media in place. All of 

this served to reduce vibration transmission and noise emission. See Section 4.2 - Modification 

of Steel Test Fixture for Roof Bolter Testing in the Reverberation Room. 
25

During the measurements, the device was operated under normal conditions. Test parameters, 

e.g. rotation speed, thrust, etc., were selected beforehand and held constant before and while 

acoustical measurements were being made. These conditions were then reported. 

4.1.8 Measurements in Test Room

 The calculation of the approximate sound power level of the DUT is based on measured 

mean-square values of the sound pressure averages in time over an appropriate number of 

microphone positions within the test room. Each test shall last approximately 30 seconds. 

No microphone position shall be closer to room boundaries than λ/4 where λ is the wavelength 

of the sound corresponding to the lowest third octave band frequency of interest (50 Hz). This 

value is dλ and at 50 Hz, equals 1.72 meters. The minimum distance between any microphone 

position and the surface of the DUT is then calculated by: 

 dmin = 0.3 * V 1/3 (2) 

Where V, is the volume of the reverberation room 

Or, for the NIOSH facility, dmin is 3.26 meters. The distance between any two microphone 

positions shall be at least λ/2, where λ is defined earlier. At 50 Hz, dmin equals 3.44 meters. 
26

In summary, 

Table 4.5 Minimum Distances of Microphones 

Condition Distance (meters) 

Microphone to room boundary 

(50 Hz) 

1.72 

Microphone and surface of DUT 3.26 

Microphone to microphone (50 Hz) 3.44 

The number of microphone positions and source locations necessary to obtain the specified 

precision of the sound power levels depend upon the room and noise source properties. For each 

source, the minimum number of positions required in obtaining the specified standard deviations 

which are equal to or less than those given in Table 4.2 will be determined by the following. 

Given a particular DUT location, the sound pressure will be measured at six microphone 

locations that are spread throughout the reverberation chamber. An estimate of the standard 

deviation, sM, in decibels, of the measured sound pressure levels will be established from the 

following equation. 

 sM = (n-1) –1/2 [ ∑=

n

i 1

(Lpi – Lp) 2 ] 1⁄2 (3) 

where 

Lpi is the sound pressure level at the ith measurement position (dB) (reference: 20 μPa) 

Lp is the mean value of Lp1, Lp2,...., Lp6 (dB) (reference : 20 μPa) 

n is the number of microphone positions, six. 

The mean value, Lp shall be calculated by 

 Lp = 10 log10[ (1/6) * ( 10 0.1Lp1 + 10 0.1Lp2 +...+ 10 0.1Lp6 ) ] dB (4) 

The calculated values for sM must be compared to the data listed in Table 4.6 to select a suitable 
27

combination of the minimum number of microphones, Nm, and source positions, Ns. Because the 

reverberation chamber is currently instrumented with fifteen microphones, 15 will serve as Nm, 

as this meets the requirements of the standard. Table 4.6 is used primarily to select, Ns, the 

minimum number of source positions for testing. 

Table 4.6 Minimum Number of Source Locations 

Number of Microphones, Nm

3 6 12 

sM (dB) 

Octave Band Frequency 

(Hz) 

Minimum Number of Source 

Locations, Ns

sM < 2.3 125 to 8,000 and Aweighting 1 1 1 

125 1 1 1 

2.3 < sM < 4 250, 500, and A-weighting 2 2 1 

1,000 to 8,000 2 1 1 

125 3 2 2 

250 and A-weighting 4 3 2 

500 4 2 2 sM > 4 

1,000 to 8,000 3 2 1 

The presence of irregularities in the frequency spectrum of an emitted sound can be determined 

from the values given above. Three ranges of the sM are selected to define the presence of 

discrete frequencies or narrow bands of noise: 

a) if sM > 4 dB, a discrete tone may be present in the frequency band in question; 

b) If 2.3 dB < sM < 4 dB, narrow-band noise components may be present in the 

frequency band in question; 

c) If sM < 2.3 dB, the frequency spectrum is probably broadband in nature. 

The suspected presence of any narrow-band or discrete frequencies in the spectrum of the 

emitted sound will then be reported. 
28

A third octave background noise level is measured at a minimum of twice per day, once in the 

morning and once in the afternoon. Additional measurements are taken if the background noise 

changes appreciably during the testing. The most recently collected background data will be 

included in each test report and will be used for a comparison with the DUT data and reference 

sound source data to determine the corrections for background noise. As per the 3743-2 

standard, if the third octave background noise is less than four decibels below the reference 

sound source or the DUT, no data shall be reported without clearly stating that that the 

background noise requirements of the standard have not been met. This is not expected to be an 

issue for the roof bolter testing as the third octave roof bolter sound pressure levels are expected 

to greatly exceed the typical background noise levels. The corrections for background sound 

pressure levels and typical third octave background noise levels are given below in table 4.7 and 

typical background sound pressure noise levels are shown in table 4.8. 

Table 4.7 Corrections for Background Sound Pressure Levels 

Difference between sound pressure 

level measured with sound source 

operating and background sound 

pressure alone. 

Correction to be subtracted from sound 

pressure level measured with noise 

source operating to obtain sound 

pressure level due to noise source alone. 

4 2 

5 2 

6 1 

7 1 

8 1 

9 0.5 

10 0.5 

> 10 0 
29

Table 4.8 Typical Background Noise Sound Pressure Levels 

Sound Pressure 

Level 

Third Octave Sound Pressure Level 

Band Frequency 

(Hz) (dB) (dBA) 

Third Octave 

band Frequency 

(Hz) (dB) (dBA) 

50 36.5 6.3 800 29.3 28.5 

63 38.9 12.7 1,000 33.8 33.8 

80 43.2 20.7 1,250 27.5 28.1 

100 35.1 16.0 1,600 23.8 24.8 

125 44.0 27.9 2,000 22.2 23.4 

160 32.3 18.9 2,500 21.3 22.6 

200 32.7 21.8 3,150 18.4 19.6 

250 35.8 27.2 4,000 15.2 16.2 

315 31.0 24.4 5,000 12.8 13.3 

400 33.9 29.1 6,300 11.0 10.9 

500 31.1 27.9 8,000 10.9 9.8 

630 27.8 25.9 10,000 10.0 7.5 

4.1.9 Calculation of Sound Power Levels

 From the measured one-third octave band sound pressure levels and the calculated third 

octave band sound pressure levels for frequency bands of interest, the mean overall value, in 

decibels, shall be calculated by; 

 Lp = 10 * Log[ (1/n) * (10 0.1Lp1 + 10 0.1Lp2 + ....+ 10 0.1Lpn) ] (5) 

where 

Lp1 is the third octave band level or A-weighted level for the first measurement (dB) 

Lpn is the third octave band level or A-weighted level for the nth measurement (dB) 

 n is the total number of measurements for a particular third octave band or with the A- 

 weighted network inserted. 

To conduct the comparison method for determining sound power, a Bruel & Kjaer 4204 

reference noise source will be placed on the floor of the test room at least 1.5 meters from any 

wall. The mean sound pressure level in each third octave band will then be determined and any 

background noise corrections will be performed if necessary, using the calculation procedure 
30

provided earlier. Then, the sound power level produced by the DUT will then be determined, 

Lwe, in decibels (reference: 1 pW) for each third octave band as follows. Subtract the band 

pressure level produced by the reference noise source, Lpr (after background noise corrections) 

from the know sound power level produced by the reference noise source and then add the 

difference to the band pressure level of the DUT, Lpe, (after corrections for background noise), 

i.e.; 

 Lwe = Lpe + (Lwr – Lpr) (6) 

Where 

Lpe is the mean band pressure level of the DUT (dB) (reference: 20 uPa) 

Lwr is the band power level of the reference noise source (dB) (reference: 1 pW) 

 Lpr is the mean band pressure level of the reference noise source (dB) (reference: 20 uPa) 

4.1.10 Information to be Reported for Each Test Condition

 The report for each test will state whether or not the reported sound power levels have 

been obtained in full conformity with the requirements of the ISO 3743-2 standard as mentioned 

in previous sections. The report for each test will provide the sound power levels in decibels 

referenced to one pW (picowatt). Sound level exposure of mining machine operators is 

determined both by the sound power radiated by the machine and by the acoustic characteristics 

of the mine environment. The sound power is the quantity of most interest, because this 

information provides the sound radiated by the machine. Once the sound power is known, the 

sound pressure level that the operator would experience can be predicted or determined based on 

the acoustic characteristics of the environment. Sound power gives a direct comparison of noise 
31

for any machine tested under the same conditions. An example of this data (report summary) for 

each test to be conducted (testing plan) in the reverberation room for the roof bolter testing is 

shown below: 

Table 4.9 Example of Reported Information for each Sound Power Test 

TEST SPECIFICATIONS REFERENCE SOURCE SPECIFICATIONS

SOURCE SPECIFICATIONS

X Y Z

9.0 6.0 1.0

12.0 4.0 0.0

LENGTH (M) WIDTH (M) HEIGHT (M)

9.0 4.0 1.5

LENGTH (M) WIDTH (M) HEIGHT (M) PRE-TEST POST-TEST

18.3 10.4 6.7 22.3 22.3

RIGHT 123.2 978.0 978.0

LEFT 133.0 66.4 66.9

FRONT 69.8

REAR 78.0

TOTAL 404.0

THRUST (lbs)

ROTATION SPEED (rpm)

WATER PRESSURE (psi)

WATER FLOW (gal / min)

MIST WATER FLOW (qt / min)

80

ROCK COMPRESSIVE 

STRENGTH (psi)

5,280

300

23,000

normal

DRILL STEEL SIZE (dia.)

ACOUSTICAL ENVIRONMENT

TYPE

SERIAL NUMBER

OPERATOR

COMMENTS

N/A

TECHNICAL COMMENTS

955307

2002

TECHNICAL COMMENTS

TEST PARTICULARS

INSTRUMENTATION

CALIBRATION : PLACE

SERIAL NUMBER

MANUFACTURER 8/9/02

TYPE

DRILL STEEL TYPE

93070/20000332

SOUND POWER MEASUREMENT REPORT

SOUND POWER MEASUREMENT AS PER THE ISO 3743-2 (comparison method)

DATE

LOCATION

DEVICE

BIT MANUFACTURER

BIT TYPE

CALIBRATION : DATE

CALIBRATION : METHOD

Bruel & Kjaer

Multi-channel Pulse

3560E

2361569

TEST TYPE

NAME

Last calibrated 12/20/02, certificate 

number P101784-1

Bruel & Kjaer

4204

MANUFACTURER

OPERATION CONDITIONS

MOUNTING CONDITIONS

SERIAL NUMBER

CHAMBER WALL 

SURFACES (METERS 

SQUARED)

LOCATION(S) OF 

SOURCE

AMBIENT PRESSURE (Pa)

CHAMBER DIMENSIONS AIR TEMPERATURE ©

RELATIVE HUMIDITY (%)

LOCATION(S) OF 

YEAR OF MANUFACTURE REFERENCE SOURCE

SOURCE DIMENSIONS

MANUFACTURER

Bruel & Kjaer

Calibration procedure 704823

3/20/03

PRL reverberation room, Bldg 154

J. Shawn Peterson

none

roof bolter

none

J. H. Fletcher

dry

Brady

carbide

hexagonal

1 inch

1

1
32

Table 4.10. One-third octave sound power levels determined for a specific test (numeric) 

100 125 160 200 250 315

103.7 106.1 108.2 109.9 109.0 106.9

400 500 630 800 1000 1250

109.0 110.7 110.2 110.9 109.6 109.8

1600 2000 2500 3150 4000 5000

108.3 107.8 105.1 104.6 101.6 98.5

6300 8000 10000 A L

98.5 92.9 89.2 118.9 120.7

Band (Hz)

Level (dB re 1 pW)

Band (Hz)

Level (dB re 1 pW)

OVERALL THIRD OCTAVE SOUND POWER LEVELS

Band (Hz)

Level (dB re 1 pW)

Band (Hz)

Level (dB re 1 pW)

0

20

40

60

80

100

120

140

100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

4000

5000

6300

8000

10000

A

L

Frequency (Hz)

Sound Power Level (dB re 1 pW)

Bkg OK Bkg CORR Bkg TOO HIGH

Figure 4.2 One-third Octave Sound Power Levels Determined for a Specific Control Test
33

4.2 Modification of Steel Test Fixture Used for Roof Bolter Testing in the Reverberation 

 Room 

4.2.1 Objective

 The sound power levels radiated by a roof bolting machine were evaluated by drilling 

into high compressive strength rock media (>20,000 psi) in the reverberation chamber. The rock 

media was supported on a steel structure that is comprised of rectangular tubes as shown in 

figure 4.3. 

Figure 4.3 Test Fixture in Reverberation Room. 

It was necessary to insure that the test fixture did not make a significant contribution to the sound 

power radiated during actual testing. Initially, the tubes were hollow and the rock was placed 

directly on the rock support tubes and held in place by a tensioned chain. The objective of the 

tests performed was to assess the potential sound power radiated by the rock support during 

drilling as discussed below. Then, modifications to the structure were performed to reduce the 

sound power radiated by the rock support. The tests performed are described below. 
34

4.2.2 Tests Performed to Assess Sound Power Radiated from Test Fixture

 Two types of tests were performed to assess the performance of the rock support structure 

before any modifications to the fixture were performed (21). First, Frequency Response 

Function (FRF) measurements were performed at several locations on the test fixture. The rock 

was placed directly on the rock support tubes and held in place with a tensioned chain. An 

instrumented impact hammer was used to apply an input force to the structure and 

accelerometers were used at several locations to measure the vibratory response of the structure. 

The input was then randomly moved to each accelerometer location to measure FRFs in g/N. 

The accelerometers were located and oriented as follows: 

1. Top Horizontal Tube at 34.5” from the end oriented to measure in the Y direction. 

2. Top Horizontal Tube at 34.5” from the end oriented to measure in the Z direction 

(vertical). 

3. Middle Horizontal Tube at 34.5” from the end oriented to measure in the Y 

direction. 

4. Middle Horizontal Tube at 34.5” from the end oriented to measure in the Z 

direction (vertical). 

5. Rock Support Tube #7 at 20.5” from the end oriented to measure in the X 

direction. 

6. Rock Support Tube #7 at 20.5” from the end oriented to measure in the Z 

direction (vertical). 

7. Vertical Support Tube at 20.5” from the top end oriented to measure in the X 

direction. 
35

8. Vertical Support Tube at 20.5” from the top end oriented to measure in the Y 

direction. 

Figure 4.4 below displays location of support tubes on the test fixture along with the specific 

accelerometer locations. 
36

Figure 4.4 Location of Test Fixture Support Tubes and Accelerometers

Bottom View

Front View

307.69

Accelerometers

88.46

92.31

Accelerometers

52.56

21.49

87.63

184.61

Accelerometers

Side View

Roofbolter Test Fixture

Units = Centimeters (inches)

212.82

82.05

52.56

(20.5)

(32.0)

(34.5)

(36.0)

(120.0)

(83.0)

(8.3)

(34.2)

(20.5)

(72.0)
 37

 The hollow tubes were then filled with sand, except for the diagonal tubes and the 

horizontal tubes along the short direction at the top of the structure. This was done for two 

reasons: convenience and to create an impedance mismatch in the structure to reduce vibration 

transmission. In addition to filling the tubes, two layers of a urethane material were bonded to 

the rock support tubes to break direct contact between the rock and the structure. Finally, a layer 

of urethane was placed between the rock and the chain. 

After measuring the FRFs in g/N, software was used to integrate the FRFs to provide the 

data into units of velocity per unit force: mm/s/N. Velocity-based (mobility) FRFs are better 

suited to judging noise radiation because the sound power radiated by an object is related to the 

surface averaged mean square velocity. After measuring the velocity-based (mobility) FRFs, a 

hole was drilled and the accelerations were measured at each of the accelerometer locations. An 

A-weighting filter was applied to the digital data in the time domain and the signals were 

integrated to obtain the A-weighted vibration velocity at each accelerometer location. 

 Software was then used to compute the 1/3-octave spectra with slow time weighting and 

RMS averaging for each time history. Finally, the A-weighted sound power radiated by the test 

fixture while drilling was calculated based on the data before and after the modifications using 

ISO/CD 7849 (22). The A-weighted sound power was used instead of the linear sound power 

because A-weighting is the frequency weighting that closely approximates the frequency 

response of the human ear. The influences of low and high frequencies are reduced in 

comparison to midrange frequencies because people are most sensitive to midrange sounds. 

Therefore, the sound power can be calculated from: 

 ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = +

0

10log S

S Lw Lv (7) 

where 
 38

Lv is the surface average velocity level with a reference of 50 nm/s 

 S is the surface area 

 S0 is the reference surface area of 1m2

. 

 The above equation was derived assuming a radiation efficiency of 1 and standard 

atmospheric conditions. It was unlikely that the radiation efficiency would be 1 at all 

frequencies, however, since the interest is the maximum sound power that can be radiated, this 

assumption would skew the estimate to the conservative side. Figure 4.5 shows the estimate of 

the sound power radiated by the test fixture before and after the modifications. The figure shows 

that the most significant sound power radiated by the fixture before the modifications is in the 

1600 and 2000 Hz 1/3-Octave bands. The figure also shows that with the modifications, the 

highest 1/3-Octave A-weighted sound power level would be in the 1600 and 2000 Hz 1/3-Octave 

bands. However, the modifications reduced the sound power level radiated to under 60 dBA (30 

dB) in all bands. Since it was likely that the drill will radiate much higher sound power levels, 

the fixture would not be a significant factor. 
39 

Figure 4.5 Estimated A-weighted Sound Power Level and Reduction in Estimated Sound Power Level Before an

Estimated Sound Power Level due to Test Fixture and Reduction in Sound Power 

38.9

38.9

46.2

59.8

72.0

54.8

53.0

54.5

55.3

66.0

69.7

58.0

60.3

63.9

63.9

74.9

74.7

78.4

87.9

91.4

83.3

82.0

83.0

30.4

37.3

42.3

48.7

52.2

53.3

48.4

48.5

51.8

53.6

48.5

46.4

45.2

44.8

46.9

50.0

43.6

47.9

58.5

56.8

53.0

53.8

50.6

0

102030405060708090

100

25

31.5

40

50

63

80

100

125

160

200

250

315

400

500

630

800

1000

1250

1600

2000

2500

3150

4000

1/3-Octave Band Center Frequency (Hz)

Sound Power Level (dBA re 1 x 10-12 watts)

BEFOREAFTERReduction in Lw
40 

4.2.3 Conclusions

 Velocity based FRFs indicated that filling the test fixture with sand significantly 

increased the damping of the structure. Subsequent recordings of accelerations at several 

locations showed that the vibration was significantly reduced for drilling conditions due to the 

added sand and isolating the rock from the test fixture. The procedure for estimating the sound 

power radiated from a structure using vibration data was followed to estimate the sound power 

level radiated by the fixture during drilling before and after the modifications. Before the 

modifications, the estimated sound power level radiated by the fixture exceeded 90 dBA in the 

2000 Hz 1/3-octave band. After the modifications, the estimated sound power level for all 1/3-

octave bands was below 60 dBA. Since the sound power level radiated by the roof bolting 

machine was expected to be much higher (more than 20 dBA) than 60 dBA, the test fixture was 

no longer a significant contributor to the sound power determined in the reverberation room, 

therefore sound power levels determined, will only be attributed to the activity of the roof bolting 

machine. 
41 

4.3 Sound Power Level Testing in Reverberation Room

 Sound power level testing was conducted in the reverberation room. Sound power level 

determination in a reverberant field is one of several methods available to calculate the noise 

emission of equipment and the reverberation room at the PRL has a unique facility which 

facilitates these measurements (figure 4.6). 

Figure 4.6 Reverberation Room at PRL 

Further, a state of the art data collection, analysis, and reporting system is in place and allows for 

high throughput, i.e., a significant amount of testing may be conducted, from data collection to a 

detailed test report, within a short period of time (figure 4.7). 

Figure 4.7. Bruel & Kjaer Pulse Data Acquisition System 
42 

As mentioned previously, the sound power level data collected, will be related to differing 

drilling parameters (thrust, rotational speed, penetration rate, drill steel size and shape, drill bit 

size) and drilling methods (vacuum, wet or mist) associated with the roof bolting machine during 

drilling operations in high-compressive strength (>20,000 psi) rock media. The reverberation 

room was used to determine the sound power generated by the roof bolting machine in relation to 

the type of drilling procedure utilized for drilling a bolt hole. Numerous tests were performed to 

determine the effectiveness of each possible noise control related to the overall sound power 

generated for each testing condition. Table number 4.11 below demonstrates the different tests 

conducted (rotational speeds and thrust configurations) for dry, wet and mist system drilling 

methods in high compressive strength rock media (>20,000 psi), along with the specific data 

collected for each test configuration. Additionally, the following sections illustrate how the 

selected drilling parameters (thrust, rotational speed and penetration rate) were set and 

determined for the differing testing conditions. 
43 

Vacuum, Wet or Mist

Kennametal 

Manual Carbide Granite 1 or 1.375 

SET POINTS AVERAGE SOUND POWER LEVEL PENETRATION 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 300 400 500 

2,121 

600 

200 300 400 500 

2,828 

600 

200 300 400 500 

3,535 

600 

200 300 400 500 

4,242 

600 

200 300 400 500 

4,949 

600 

200 300 400 500 

5,656 

600 

200 300 400 500 

6,363 

600 

Table 4.11 Test Data Collected During Sound Power Level Testing 
44 

4.3.1 Setting of Thrust Configurations

 The thrust setting on the bolting machine was set utilizing the following steps 

displayed below: 

1) Verify the required thrust pressure required for the specific test configuration. 

2) Determine the existing thrust setting. 

 a. Push the enable button on the operator joystick (figure 4.8), then push the 

joystick forward, causing the drill head to move up and contact the center 

beam of the test fixture. The mast should be located in a position which 

will allow the drill head to fully contact the center beam of the test fixture 

(figure 4.9). 

Figure 4.8 Joystick on Control Panel 
45 

Figure 4.9 Drill Mast of Roof Bolting Machine Raised to Test Stand 

 

b. While continuing to push forward on the operator joystick, examine the 

thrust pressure gauge located to the left of the hydraulic controls. Note the 

pressure. 
46 

Figure 4.10 Location of Thrust Pressure Gauge 

c. Determine direction to turn manual relief valve to reach desired thrust 

pressure (figure 4.11). 

.

Figure 4.11 Location of Relief Valve Control 

d. If desired thrust pressure is lower than existing pressure, reduce the 

pressure by turning the allen-wrench in a counter-clockwise direction. 
47 

e. If desired thrust pressure is higher than existing pressure, increase pressure 

by turning allen-wrench in a clockwise direction. 

 f. Follow steps a and b mentioned above to verify new pressure setting. 

g. If thrust setting does not match desired test pressure repeat steps above 

until desired setting is obtained. 

4.3.2 Setting Rotational Speed Configurations

The rotational speed was measured utilizing a pulser disk, electro-sensors and a 

signal conditioner (figure 4.12.). The pulser disk mounts on the roof bolting machine 

chuck, therefore the drill steel passes through a hole in the disk. Embedded in the disk 

are magnets that are sensed when the drill chuck rotates. The sensor signal is then 

transmitted to the signal conditioner unit, which displays the rotation speed in Hz, or 

magnetic pulses per second. The signal conditioner has a 0-10 Vdc output, scaled to Hz. 

This dc output is fed into the Bruel and Kjaer Pulse system and scaled into engineering 

units, represented by rpm. 

Figure 4.12 Pulser Disk and Electro-sensors Mounted on Drill Chuck 
48 

The scaling associated with the rotational speed system is shown below: 

0 – 240 Hz = 0 – 1,800 rpm = 0 – 10 Vdc out or; 

1 Hz = 7.5 rpm or; 

1 rpm = 5.556 mVdc out 

Thus, the Bruel and Kjaer Pulse system then scales 5.556 mVdc to 1 rpm. 

4.3.3 Determining Penetration Rate or Displacement During Testing

To determine penetration rate during testing a string potentiometer was installed 

on the roof bolting machine (figure 4.13). 

Figure 4.13 Location of String Potentiometer for Determination of Penetration Rate 

The unit output voltage varied linearly with the distance the cable was displaced and was 

usable from two to eighty inches. The unit was installed on the bottom of the roof bolting 

machine with the cable attached to the chuck. The output voltage was then fed into the 

Bruel and Kjaer Pulse system per the calibration reports provided for the instrument. 
49 

4.3.4 Pulse System and Excel Data Collection Common to Speed and Displacement

Data acquisition in the pulse system was started via a Visual Basic code launched 

in Excel. Speed and displacement data was fed into the pulse system and were displayed 

in windows in engineering units. Information in the pulse system was dynamically linked 

to the Excel spreadsheet and updated once per second. Once data collection was initiated 

in Excel, Visual Basic code reviewed the Excel cells containing the most recently 

collected speed, displacement, and time data and then copied the results to a table in the 

Excel worksheet, and then moved down into the next row. One second later, the 

dynamically linked data was updated, and the process repeated itself, adding rows of 

time, speed, and displacement data. This was plotted in essentially real time in Excel. 

Once the test was completed, an average of the speed data was calculated and used for 

the test report. The change in displacement and time were calculated and used to 

calculate the penetration rate, again for the test report. An example of a test report for 

one specific test is displayed below (figure 4.14). 
50 

Test Report

Test Type : wet 

Test Mode : manual

Material : granite

Compressive Strength (lbs) : 21,000 

Bit Manufacturer : A

Bit Type : carbide

Bit Size (in) : 1 

Drill Steel : round

Water Flow Rate (gal/min) : 3 g/m

Mist Flow Rate (qt/min) : N/A

Set Thrust (lbs) : 2,828

Average Thrust (lbs) : 3,113

Set Rotation Speed (rpm) : 500

Average Rotation Speed (rpm): 508

Penetration Rate (in/sec) : 0.434

Sound Power (dB) : 105.9

Sound Power (dBA) : 105.4

Time (sec) : 30.0

Figure 4.14 Example of a Test Report – Sound Power 

4.4 Rock Media and Strength Property Testing of Drilling Media 

4.4.1 Type of Rock Media

As mentioned earlier, for phase 1 of the research, differing drilling parameters 

were tested to determine sound power levels of the roof bolting machine during drilling 

into high compressive strength media (>20,000 psi). The type of material tested and 

utilized during phase 1 of the research study was Barre Gray Granite as shown in figure 

4.15 below. 
51 

Figure 4.15 Barre Gray Granite – Rock Media Used for Testing in Phase 1 

4.4.2 Obtaining Rock Cores of Drilling Media

 The rock media, Barre Gray Granite, was core drilled at the laboratory to obtain 

rock samples for rock strength testing. The individual rock samples were then tested in 

the rock mechanics lab to determine significant rock properties, such as unconfined 

compressive strength, used during noise testing in the reverberation room. Figure 16 

below displays several core samples obtained from the drilling of the Barre Gray Granite, 

rock media type used for phase 1 of the research study. 
52 

Figure 4.16 Sample of Core Collected from Barre Granite Rock Media 

4.4.3 Unconfined Compressive Strength Testing of Rock Media

 The rock cores obtained from the drilling procedure were then prepared and tested 

for rock strength properties (unconfined compressive strength). Dependent upon the size 

of samples available, the number of strength properties varied. The test procedures 

utilized adhered to the ASTM standards and were conducted on cores of 2-in in diameter. 

Results of the testing are shown in table 4.12 below. 

Table 4.12 Unconfined Compressive Strength Results of Barre Gray Granite 

Specimen 

Number 

Length (L), 

inches 

Diameter 

(D), inches L/D Ratio Area (A) in2 

Load at 

Failure (P), 

pounds 

Compressive 

Strength 

(C), psi 

Corrected 

Compressive 

Strength 

(C◦), psi 

D1 4.006 1.990 2.013 3.109 71,900 23,126 23,144 

D2 3.997 1.990 2.009 3.109 72,880 23,442 23,454 

D3 4.001 1.992 2.009 3.117 75,920 24,360 24,373 

 

AVERAGE 73,567 23,643 23,657 

 
53 

The average unconfined compressive strength of all cores tested was 23,657 psi, 

approximately 24,000 psi for the Barre Gray Granite rock media. 

4.5 Testing of Differing Bits and Drill Steel 

4.5.1 Drill Bits

A variety of types and sizes of drill bits are being utilized in the mining industry 

today during roof bolting operations (figure 4.17). 

1 3/8” Carbide 

Wet Bit

1” Ceramic 

Bit

1” 

Carbide 

Dry Bit 1” Carbide

Wet Bit 1 3/8 “ Carbide

Dry Bit

DRILL BITS

FOR

ROOF BOLTER TESTING

Figure 4.17 Types of Drill Bits Used During Roof Bolting Operations 

Critical information related to the type and/or size of bits in relation to noise output is 

very limited in the mining industry today. Noise testing was performed in the 

reverberation room on a variety of differing types and sizes of drill bits. The different 

types of drill bits tested included: 

 1-inch and 1 3/8-inch carbide bit used during dry drilling operations (new bit 

used for each test). 

 1-inch and 1 3/8-inch carbide bit used during wet drilling operations 

(including mist-system technology) (new bit used for each test) 
54 

4.5.2 Drill Steel

The mining industry utilizes different types of drill rod during roof bolting 

operations. Significant information related to the type and/or size of drill steel in relation 

to noise output is unidentified in the mining industry today. Noise testing was performed 

in the reverberation room on a variety of differing types and sizes of drill steel. The 

different types of drill steel tested (figure 4.18) for noise generation included: 

 1 inch and 1 3/8 inch round drill steel 

 1 inch and 1 3/8 inch hex drill steel 

1” & 1 3/8” ROUND 

DRILL STEEL

4 ft

1” & 1 3/8” HEX 

DRILL STEEL

4 ft

Figure 4.18 Types of Drill Steel Used During Roof Bolting Operations 
55 

4.6 Testing of Different Drilling Methods 

4.6.1 Dry (Vacuum), Wet and “Mist” Systems

During roof bolting operations, drilling of the immediate roof occurs by drilling the 

bolt hole dry (vacuum) or using water as a drilling fluid. Tests were conducted in the 

reverberation room to determine if the use of water during the drilling technique of a roof 

bolting operation minimizes noise output associated with the procedure. Noise testing 

was performed during dry and wet drilling operations. During wet drilling operations, 

differing flow rates of water was tested for noise characteristics. Additionally, the use of 

a “mist” system was also incorporated in the wet drilling tests to minimize the flow of 

water to the bit. The “mist” system is designed to provide minimal flow (e.g. 

quart/minute of water) to the bit, reducing the potential hazard of extreme amounts of 

water affecting the roof bolter operator. The “mist” system utilized a system of 

compressed air and water input for providing minimal flow rate to the bit. Figure 4.19 

displays a photograph of the “mist” system used during noise testing.

MIST SYSTEM

Figure 4.19 Photograph of “Mist” System Used During Noise Testing 
56 

4.7 Summary of Tests Conducted in the Reverberation Room

In summary, a total of approximately 500 noise tests (determination of sound 

power) were performed to characterize the differing noise controls associated with roof 

bolting operations in high compressive strength rock media (>20,000 psi). All tests were 

performed in the Pittsburgh Research Laboratory’s Reverberation Room to determine 

sound power levels, during drilling operations, associated with the following 

characteristics: 

• Vacuum (dry) Drilling 

• Wet Drilling (3 gallons of water per minute to drilling bit) 

• Mist System (3 quarts of water per minute to drilling bit) 

• Round Drill Steel 

• Hex Drill Steel 

• Drill Bit Size (1-inch and 1 3⁄8-inch) 

• Manual Drilling (differing thrust, rotational speed and penetration rate drilling 

parameters) 

Please note, sound levels experienced by a roof bolter operator are determined both by 

the sound power radiated by the drilling operation and by the acoustic characteristics of 

the mine environment. The sound power is the quantity of most interest, because this 

information provides the sound radiated by the drilling procedure related to any 

utilization of engineering noise controls. Because of all the variations both geometrically 

and acoustically in underground mines it would be difficult to achieve uniform test 

conditions in an underground mine setting. Additionally, it would be impossible to 

control the acoustic environment underground, which would make it difficult to evaluate 

the roof bolting machine and its components for noise levels. Therefore, testing was 

conducted in the Pittsburgh Research Lab (PRL) Reverberation Chamber for sound 

power levels generated from the roof bolting machine. Utilizing the reverberation 

chamber provided the determination of sound power radiating from the machine in a 
57 

controlled acoustic environment and would be independent of the many differing 

variables associated with the underground mining environment. The determination of 

sound power in the reverberation room provided a direct comparison of noise for any 

engineering noise controls tested during each individual test. The preceding chapter, 

Chapter 5, displays the data collected for all sound power tests conducted in the 

reverberation room, along with the methods and the applications used in determining 

constructive results related to the assessment of noise control technologies related to 

drilling operations associated with the roof bolting machine. 

As mentioned earlier, testing noise control technologies related to the roof bolting 

machine were conducted in the reverberation room due to the varying geometries and the 

acoustical characteristics associated with underground coal mines. Chapter 6 provides a 

methodology for characterizing the acoustical uniqueness of an underground coal mine 

and with the use of an acoustical model, provides the ability of the user to predict the 

sound pressure level the roof bolting machine operator would experience, given the 

measured sound power levels collected from the laboratory (reverberation room). The 

model provides the mining community with a state-of-the-art opportunity to examine and 

measure sound power in the laboratory (related to engineering noise controls) and then 

directly associate or correlate the measured value to a sound pressure level experienced 

by the operator of a specific mining machine, specifically, the roof bolting machine, in 

determining overexposure to noise. 
58

CHAPTER 5 

APPLICATIONS OF SOUND POWER LEVEL MEASUREMENTS CONDUCTED IN 

THE REVERBERATION ROOM 

 As mentioned in Chapter 4, a total of approximately 500 noise tests (determination of 

sound power) were performed to characterize the differing noise controls associated with roof 

bolting operations in high compressive strength rock media (>20,000 psi). All tests were 

performed in the Pittsburgh Research Laboratory’s Reverberation Room to determine sound 

power levels of roof bolting operations associated with the following characteristics: 

• Vacuum (dry) Drilling 

• Wet Drilling (3 gallons of water per minute to drilling bit) 

• Mist System (3 quarts of water per minute to drilling bit) 

• Round Drill Steel 

• Hex Drill Steel 

• Drill Bit Size (1-inch and 1 3⁄8-inch) 

• Manual Drilling (differing thrust, rotational speed and penetration rate drilling 

parameters) 

5.1 Drilling Components and Parameters Utilized for Testing 

In formulating a conservative test plan, it was decided to use drilling components and 

parameters that were representative of industry usage. These are listed below in Table 5.1. 

Table 5.1 Variables for Sound Power Level Testing 

Item Units Values 

Drilling type ----- vacuum, mist @ 3 qt/min, wet @ 3 gal/min 

Drill steel ----- round, hexagonal 

Drill bit size in one, one and three-eighths 

Rotation speed rpm 200, 300, 300, 400, 500, 600 

Thrust lbs 2,121, 2,828, 3,535, 4,242, 4,949, 5,656*, 6,363* 

• * One and three-eighths inch (1 3/8”) bit size only, due to safety limitations. 
59

Various combinations of these parameters are shown in table 5.1, in which, comprise the test 

configurations related to the testing of the high compressive strength rock media (>20,000 psi). 

Data was not obtained or collected for tests utilizing a 1-inch bit and 1-inch drill steel at thrust 

settings 5,656 and 6,363 lbs respectively due to safety concerns when drilling into the high 

compressive strength media and using a 1-inch drill steel. Additionally, several data points were 

not collected where thrust settings were low (2,121, 2,828 and 3535 lbs) and rotational speeds 

were high (500 and 600 rpm) due to ineffective performance of the drilling process. 

Additionally, the penetration depth (inches) was measured for each test and consequently the 

penetration rate (inches/second) for each test was determined or measured and displayed in the 

following tables listed below. 

5.2 Data Collected for Sound Power Level Tests 

Data collected for all sound power level tests conducted are shown in the following tables: 

• Table 5.2 – Vacuum drilling method, 1-inch bit, round drill steel 

• Table 5.3 – Vacuum drilling method, 1-inch bit, hex drill steel 

• Table 5.4 – Vacuum drilling method, 1-3/8-inch bit, round drill steel 

• Table 5.5 – Vacuum drilling method, 1-3/8-inch bit, hex drill steel 

• Table 5.6 – Wet drilling method (3 gal/min), 1-inch bit, round drill steel 

• Table 5.7 – Wet drilling method (3 gal/min), 1-inch bit, hex drill steel 

• Table 5.8 – Wet drilling method (3 gal/min), 1-3/8-inch bit, round drill steel 

• Table 5.9 – Wet drilling method (3 gal/min), 1-3/8-inch bit, hex drill steel 

• Table 5.10 – Mist drilling method (3 qt/min), 1-inch bit, round drill steel 

• Table 5.11 – Mist drilling method (3 qt/min), 1-inch bit, hex drill steel 

• Table 5.12 – Mist drilling method (3 qt/min), 1-3/8-inch bit, round drill steel 

• Table 5.13 – Mist drilling method (3 qt/min), 1-3/8-inch bit, hex drill steel 

Tables 5.2 thru 5.13 are shown respectively on the following pages. 
60

Table 5.2 Sound Power Level Testing – Vacuum Method, 1-inch bit, Round Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

2,239 209 106.8 106.6 3.42 0.125 200 

2,228 210 107.1 107.1 3.14 0.114 

2,282 306 108.2 108.3 3.49 0.128 300 

2,272 305 107.4 107.4 4.09 0.149 

2,324 400 108.3 108.4 3.85 0.141 400 

2,280 402 108.5 108.6 3.79 0.139 

500 2,220 514 109.3 109.5 4.38 0.168 

2,121 

600 2,241 609 108.7 108.8 3.53 0.134 

200 2,711 208 108.0 107.8 5.11 0.187 

2,696 305 109.8 109.9 5.21 0.190 300 

2,705 306 109.4 109.4 5.64 0.205 

400 2,701 402 109.8 109.9 4.82 0.177 

500 2,865 509 109.9 110.1 5.82 0.226 

2,828 

600 2,892 602 110.0 110.1 5.20 0.201 

200 3,435 215 110.1 110.2 7.12 0.260 

3,451 304 110.7 110.9 7.18 0.262 300 

3,620 311 109.5 109.6 9.97 0.390 

3,487 405 111.1 111.5 6.28 0.229 400 

3,483 404 111.4 111.6 6.28 0.229 

500 3,628 510 110.3 110.5 6.26 0.239 

3,535 

600 3,653 607 110.9 111.1 6.17 0.237 

200 4,085 208 111.0 111.2 9.67 0.353 

300 4,097 305 111.3 111.6 9.76 0.358 

4,111 404 111.5 111.5 8.39 0.305 400 

4,283 406 111.2 111.4 10.03 0.385 

500 4,291 509 110.7 110.9 8.09 0.311 

4,242 

600 4,314 604 110.7 110.9 7.24 0.279 

4,744 221 110.4 110.4 8.63 0.313 200 

4,778 223 110.4 110.6 10.41 0.394 

300 4,769 308 111.9 112.3 10.94 0.387 

4,800 404 112.3 112.6 11.90 0.432 400 

4,821 406 110.3 110.4 10.93 0.422 

500 4,870 507 111.1 111.4 8.22 0.311 

4,949 

600 4,822 607 110.4 110.7 5.78 0.222 
61

Table 5.3 Sound Power Level Testing – Vacuum Method, 1-inch bit, Hex Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 2,334 206 108.9 109.0 4.6 0.165 

300 2,333 303 110.0 110.2 3.9 0.141 

400 2,344 404 110.8 111.0 2.9 0.107 

500 2,226 508 109.9 110.2 3.9 0.150 

2,121 

600 2,241 602 112.4 112.8 4.2 0.163 

200 2,919 208 111.2 111.3 5.4 0.194 

300 2,933 305 112.5 112.7 7.6 0.219 

2,955 401 112.0 112.3 6.1 0.210 400 

2,849 406 110.2 110.5 4.8 0.187 

500 2,877 508 110.8 111.1 5.5 0.212 

2,828 

600 2,890 606 112.2 112.5 2.3 0.089 

3,587 207 112.5 112.7 8.0 0.287 200 

3,588 209 111.3 111.6 8.5 0.330 

3,622 307 112.5 112.8 8.7 0.334 300 

3,607 307 113.0 113.4 8.9 0.340 

3,642 400 112.9 113.2 8.1 0.288 400 

3,660 398 113.0 113.4 8.8 0.314 

500 3,622 508 113.1 113.6 4.4 0.212 

3,535 

600 3,651 606 112.5 112.9 4.5 0.173 

4,294 218 112.2 112.5 11.6 0.452 200 

4,238 208 110.9 110.8 7.0 0.249 

300 4,254 305 113.0 113.3 10.7 0.382 

400 4,258 402 112.4 112.7 10.1 0.361 

500 4,344 508 113.5 114.0 7.2 0.290 

4,242 

600 4,362 607 112.4 112.9 4.4 0.165 

4,818 209 111.9 112.3 11.2 0.395 200 

4,916 211 112.6 113.0 11.3 0.495 

300 4,869 306 112.8 113.2 13.8 0.475 

400 4,898 407 113.0 113.3 12.5 0.445 

500 4,979 510 113.9 114.3 13.0 0.509 

4,949 

600 4,995 607 112.6 113.0 4.6 0.172 
62

Table 5.4 Sound Power Level Testing – Vacuum Method, 1-3/8-inch bit, Round Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 2,268 203 105.7 105.5 2.12 0.087 

2,121 300 2,285 306 106.5 106.1 1.91 0.078 

400 2,293 402 108.8 108.6 1.84 0.076 

2,915 211 108.5 108.8 3.12 0.128 200 

2,908 215 108.2 108.5 2.96 0.121 

2,925 308 108.3 108.5 3.56 0.146 300 

2,923 311 108.1 108.3 2.94 0.120 

2,828 

400 2,952 404 109.2 109.6 3.42 0.139 

3,527 211 108.3 108.5 3.92 0.161 200 

3,522 213 108.1 108.3 4.30 0.176 

3,545 306 109.2 109.6 4.96 0.204 300 

3,545 305 108.6 108.9 4.40 0.181 

3,580 402 109.7 110.1 5.41 0.220 

3,535 

400 

3,567 402 109.8 110.2 4.43 0.182 

200 4,183 208 111.3 111.8 5.95 0.205 

4,181 306 112.4 113.0 5.72 0.197 300 

4,228 309 111.3 111.7 5.53 0.212 

4,239 403 112.5 113.0 4.51 0.173 400 

4,360 405 112.1 112.5 2.61 0.093 

500 4,303 511 111.1 111.3 1.66 0.059 

4,242 

600 4,405 606 109.9 110.0 1.32 0.047 

200 4,842 210 111.6 112.1 7.27 0.251 

4,865 307 111.7 112.3 6.32 0.218 300 

4,923 314 112.2 112.7 7.17 0.279 

400 4,886 405 113.6 114.2 6.85 0.237 

500 5,082 509 110.8 111.0 1.83 0.065 

4,949 

600 5,090 604 109.8 109.8 1.53 0.005 

200 5,415 215 113.1 113.6 8.33 0.287 

300 5,438 307 111.9 112.5 7.87 0.271 

400 5,446 403 112.5 113.1 7.25 0.250 

500 5,677 510 106.9 106.8 1.61 0.056 

5,656 

600 5,684 604 108.7 108.7 1.47 0.052 

6,195 207 112.9 113.4 9.48 0.339 200 

6,242 212 112.3 112.7 10.74 0.381 

6,234 312 113.7 114.3 9.92 0.354 300 

6,218 310 112.7 113.1 9.90 0.353 

6,167 402 114.1 114.8 8.35 0.288 400 

6,237 402 113.6 114.1 5.84 0.208 

500 6,261 505 109.5 109.8 2.29 0.081 

6,363 

600 6,283 602 106.5 106.1 1.40 0.049 
63

Table 5.5 Sound Power Level Testing – Vacuum Method, 1-3/8-inch bit, Hex Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 2,283 212 106.1 106.3 1.6 0.067 

2,121 300 2,302 309 109.0 109.5 1.9 0.078 

400 2,326 402 110.0 110.4 2.1 0.084 

200 2,892 209 109.3 109.7 2.8 0.115 

2,828 300 2,914 308 109.9 110.4 3.6 0.134 

400 2,943 405 112.2 113.0 3.5 0.145 

200 3,559 208 109.2 109.6 4.4 0.180 

3,575 304 111.3 111.9 5.0 0.205 300 

3,715 313 111.9 112.5 3.9 0.150 

3,591 402 112.2 112.8 4.9 0.200 

3,535 

400 

3741 405 112.7 113.3 4.3 0.167 

200 4,321 214 112.3 112.8 6.5 0.225 

4,316 309 113.4 114.1 5.7 0.195 300 

4,342 313 112.6 113.3 4.9 0.187 

4,330 402 113.9 114.6 5.9 0.202 400 

4,357 403 113.8 114.6 3.8 0.150 

500 4,407 505 113.9 114.7 3.1 0.115 

4,242 

600 4,420 604 113.4 114.1 1.6 0.059 

200 4,979 212 113.2 113.8 7.3 0.253 

5,001 310 113.1 113.8 8.3 0.285 300 

4,958 309 113.1 113.7 6.7 0.247 

5,047 405 114.8 115.5 5.8 0.200 400 

4,973 409 113.6 114.3 4.4 0.161 

500 4,982 511 114.0 114.7 2.8 0.104 

4,949 

600 4,992 604 113.2 113.9 1.2 0.044 

5,558 211 113.5 114.1 8.7 0.301 200 

5,485 218 112.7 113.3 8.7 0.324 

5,497 313 113.7 114.4 7.3 0.271 300 

5,502 310 113.7 114.3 8.4 0.312 

5,576 405 115.3 116.1 6.1 0.211 400 

5,510 408 114.5 115.2 4.6 0.167 

500 5,523 511 113.9 114.7 2.9 0.103 

5,656 

600 5,544 600 112.8 113.4 2.5 0.089 

6,342 212 113.5 114.1 9.8 0.337 200 

6,224 211 114.0 114.6 10.2 0.361 

6,360 311 114.5 115.2 10.5 0.361 300 

6,234 309 115.1 115.7 9.8 0.347 

6,382 404 115.5 116.2 6.6 0.227 400 

6,244 402 114.5 115.3 5.8 0.206 

500 6,256 506 113.7 114.3 2.8 0.099 

6,363 

600 6,205 603 112.6 113.2 1.8 0.065 
64

Table 5.6 Sound Power Level Testing – Wet Drilling Method (3 gal/min), 1-inch bit, Round 

Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

2,313 207 103.3 102.1 5.4 0.224 200 

2,306 211 102.9 102.0 5.2 0.213 

2,321 309 103.4 102.2 4.1 0.168 300 

2,318 308 104.8 104.0 5.8 0.237 

2,335 402 103.8 102.9 4.2 0.169 400 

2,329 405 106.2 105.5 6.4 0.262 

500 2,448 503 103.6 102.4 5.7 0.222 

2,121 

600 2,461 605 104.6 103.6 5.6 0.218 

200 2,909 205 104.0 103.5 4.2 0.340 

3,084 311 105.3 104.3 8.9 0.347 300 

3,005 312 105.0 104.4 4.5 0.367 

2,978 402 104.9 103.9 7.3 0.298 400 

3,098 403 104.4 103.2 7.8 0.301 

3,113 508 105.9 105.4 11.4 0.434 500 

3,012 507 103.7 102.5 9.3 0.357 

2,828 

600 3,129 605 106.4 105.7 9.8 0.377 

200 3,591 201 104.9 104.4 5.7 0.463 

3,605 308 106.5 106.3 6.6 0.540 300 

3,601 314 106.0 105.8 6.3 0.519 

400 3,617 401 107.1 106.8 7.5 0.681 

500 3,815 511 106.2 105.9 11.2 0.540 

3,535 

600 3,820 604 107.7 107.7 15.1 0.586 

4,275 210 106.4 105.8 6.2 0.616 200 

4,272 213 106.3 105.7 5.2 0.511 

4,285 309 107.4 107.0 6.7 0.654 300 

4,285 315 106.9 106.5 6.5 0.642 

4,288 411 107.6 107.3 7.0 0.680 400 

4,296 411 108.8 108.6 8.0 0.799 

500 4,411 508 106.3 105.8 15.6 0.594 

4,242 

600 4,434 595 106.9 106.7 15.4 0.598 

4,888 206 106.7 106.2 5.6 0.681 200 

4,899 205 106.8 106.3 5.1 0.626 

4,898 302 107.8 107.6 6.8 0.843 300 

4,916 307 108.3 108.2 6.3 0.770 

4,927 412 108.2 108.1 7.7 0.955 400 

4,912 412 109.0 108.9 7.5 0.928 

500 4,876 510 107.5 107.1 18.7 0.723 

4,949 

600 4,902 607 106.6 106.2 17.2 0.672 
65

Table 5.7 Sound Power Level Testing – Wet Drilling Method (3 gal/min), 1-inch bit, Hex Drill 

Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 2,314 207 102.1 100.6 1.8 0.196 

300 2,332 315 101.6 100.5 2.4 0.255 

400 2,347 404 104.0 103.8 2.3 0.249 

500 2,295 508 105.7 105.6 4.3 0.175 

2,121 

600 2,306 607 106.0 105.9 4.3 0.176 

2,924 214 103.1 101.5 2.9 0.320 200 

2,932 198 105.1 104.2 3.2 0.317 

300 2,939 306 103.9 102.8 3.6 0.386 

2,957 406 105.2 104.8 3.5 0.458 400 

3,121 403 105.8 105.7 7.8 0.309 

500 3,135 507 107.4 107.7 8.3 0.342 

2,828 

600 3,147 602 107.2 107.2 9.5 0.389 

3,670 215 104.4 103.8 3.8 0.416 200 

3,665 204 104.7 103.9 3.8 0.428 

3,715 316 106.0 105.3 8.5 0.344 300 

3,720 304 106.1 105.9 6.5 0.537 

3,578 409 108.0 108.2 4.6 0.457 400 

3,581 402 108.0 107.9 4.9 0.576 

3,741 517 107.6 107.5 11.2 0.451 500 

3,644 504 108.0 108.3 10.5 0.435 

3,755 606 108.2 108.3 11.1 0.443 

3,535 

600 

3,657 605 106.8 106.9 8.8 0.353 

4,273 202 103.0 101.7 6.3 0.680 200 

4,349 216 105.7 105.2 11.4 0.463 

300 4,272 310 104.6 103.8 6.6 0.719 

4,297 412 106.6 106.1 7.4 0.810 400 

4,296 398 105.2 104.8 7.5 0.805 

500 4,382 511 108.0 108.1 14.6 0.597 

4,242 

600 4,392 614 108.5 108.4 14.8 0.600 

4,793 215 105.8 105.1 12.9 0.529 200 

4,930 209 104.8 104.7 6.1 0.762 

4,940 306 105.8 105.6 9.4 1.025 300 

4,806 314 106.0 105.5 12.7 0.518 

400 4,944 414 106.4 105.7 8.9 0.965 

500 4,831 509 108.0 108.1 14.6 0.598 

4,949 

600 4,850 578 108.0 108.3 14.4 0.556 
66

Table 5.8 Sound Power Level Testing – Wet Drilling Method (3 gal/min), 1-3/8-inch bit, Round 

Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

2,335 210 105.8 104.9 1.0 0.094 200 

2,337 208 105.1 103.9 1.0 0.094 

2,340 310 105.1 104.3 2.6 0.107 300 

2,337 311 105.6 105.0 3.0 0.123 

2,351 406 106.9 106.6 2.7 0.113 

2,121 

400 

2,347 407 105.8 105.5 2.9 0.120 

2,916 211 104.3 103.5 3.0 0.122 200 

2,915 209 104.3 103.6 3.4 0.141 

2,937 305 105.2 104.9 4.5 0.188 300 

2,935 305 105.0 104.5 4.4 0.181 

2,959 411 106.3 106.1 4.6 0.189 

2,828 

400 

2,955 411 106.8 106.7 4.5 0.185 

3,611 218 106.2 105.9 5.0 0.203 200 

3,609 214 105.6 105.3 6.0 0.246 

3,623 313 105.5 105.1 6.5 0.266 300 

3,621 311 106.3 106.0 6.3 0.261 

3,709 408 108.4 108.0 5.9 0.366 

3,535 

400 

3,701 411 108.7 108.5 6.4 0.394 

4,187 217 107.2 106.8 5.1 0.320 200 

4,188 215 106.6 106.0 4.6 0.285 

4,210 313 108.3 108.1 6.0 0.368 300 

4,202 307 107.9 107.6 5.4 0.335 

4,233 408 109.0 108.8 8.1 0.429 400 

4,230 407 109.1 108.9 6.9 0.424 

500 4,456 510 108.7 108.9 8.4 0.321 

4,242 

600 4,485 603 109.0 109.2 9.5 0.365 

4,833 211 107.0 106.5 6.4 0.393 200 

4,808 217 106.9 106.3 7.0 0.428 

4,816 309 108.7 108.5 7.5 0.464 

300 4,826 310 107.8 107.4 7.7 0.466 

4,840 403 108.5 108.3 8.0 0.489 

500 5,110 506 109.6 109.8 11.0 0.409 

4,949 

600 5,136 604 110.6 110.8 10.2 0.386 

5,649 210 108.2 108.0 5.5 0.447 200 

5,644 212 107.5 107.3 5.1 0.411 

5,662 311 109.3 109.2 6.8 0.558 300 

5,512 310 108.5 108.6 7.3 0.604 

5,669 411 110.3 110.2 7.9 0.650 400 

5,666 401 109.0 108.7 7.0 0.573 

500 5,740 507 110.1 110.3 12.1 0.436 

5,656 

600 5,755 604 110.1 110.4 11.6 0.429 

200 6,298 206 108.3 108.0 6.2 0.511 

300 6,307 308 109.8 109.7 6.8 0.560 

6,320 407 109.7 109.6 7.6 0.628 400 

6,148 402 109.2 109.3 15.4 0.594 

500 6,161 504 108.4 108.4 11.9 0.452 

6,363 

600 6,369 601 109.6 109.4 18.2 0.688 
67

Table 5.9 Sound Power Level Testing – Wet Drilling Method (3 gal/min), 1-3/8-inch bit, Hex 

Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 2,338 209 104.5 104.2 1.3 0.055 

2,121 300 2,360 311 105.0 105.0 2.1 0.086 

400 2,378 403 106.3 106.1 2.4 0.099 

200 2,915 213 104.5 104.2 2.3 0.094 

2,828 300 2,937 309 106.2 106.3 3.3 0.134 

400 2,961 402 107.0 107.0 3.9 0.160 

200 3,593 209 105.0 104.9 4.7 0.190 

3,535 300 3,606 312 105.1 105.0 5.7 0.234 

400 3,622 400 106.1 106.1 5.9 0.246 

4,402 212 105.7 104.9 5.9 0.223 200 

4,207 208 105.8 105.7 2.6 0.285 

4,227 302 106.7 106.8 3.3 0.358 300 

4,277 309 106.4 106.4 6.8 0.278 

4,258 411 107.4 107.5 4.5 0.484 400 

4,286 398 107.5 107.6 8.5 0.348 

500 4,454 505 107.9 108.0 9.2 0.338 

4,242 

600 4,478 604 108.9 109.2 9.4 0.357 

4,848 207 106.6 106.4 4.5 0.372 200 

4,846 206 106.7 106.4 3.9 0.320 

4,859 315 107.9 107.9 4.9 0.406 300 

4,852 313 107.5 107.5 4.8 0.390 

4,867 407 110.3 110.5 5.5 0.601 400 

5,000 401 107.4 107.2 9.6 0.365 

500 5,014 506 108.1 108.0 9.7 0.353 

4,949 

600 5,027 602 109.1 109.1 9.4 0.356 

5,435 201 107.4 107.5 3.8 0.408 200 

5,595 216 107.1 106.9 9.5 0.361 

5,539 315 109.1 109.3 6.0 0.488 300 

5,539 308 108.5 108.6 6.0 0.497 

5,561 413 108.8 108.8 7.5 0.610 400 

5,586 424 109.2 109.2 5.6 0.550 

500 5,642 510 109.0 109.0 10.8 0.411 

5,656 

600 5,664 604 108.8 108.9 11.9 0.422 

6,200 204 108.5 108.6 4.8 0.523 200 

6,155 196 107.7 107.7 5.8 0.567 

6,197 316 108.7 108.8 5.7 0.616 300 

6,137 304 109.1 109.1 6.0 0.598 

6,219 405 110.7 110.8 6.5 0.710 400 

6,213 408 109.8 110.0 5.7 0.618 

500 6,334 508 109.4 109.4 17.9 0.675 

6,323 598 110.2 110.2 17.1 0.657 

6,363 

600 

6,346 604 110.7 110.7 14.0 0.529 
68

Table 5.10 Sound Power Level Testing – Mist Drilling Method (3 qt/min), 1-inch bit, Round 

Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 2,418 214 105.3 104.6 4.05 0.1580 

300 2,432 307 106.5 105.8 4.84 0.1910 

400 2,445 402 107.4 106.7 5.53 0.2180 

500 2,458 507 107.5 107.4 6.60 0.2600 

2,121 

600 2,472 593 107.7 107.7 5.58 0.2220 

200 2,978 216 105.0 104.5 6.93 0.2730 

300 2,993 301 107.4 107.1 8.85 0.3510 

400 3,004 408 108.4 107.9 8.99 0.3590 

500 3,004 510 108.7 108.5 8.05 0.3190 

2,828 

600 3,012 605 109.4 109.2 8.45 0.3280 

200 3,685 213 106.5 106.3 9.16 0.3610 

300 3,700 306 108.6 108.5 9.93 0.3920 

400 3,716 404 109.1 109.1 12.06 0.4690 

500 3,734 509 109.9 109.7 11.36 0.4520 

3,535 

600 3,758 607 110.1 110.1 11.70 0.4600 

200 4,335 216 100.2 107.9 10.85 0.4270 

300 4,350 305 109.3 109.2 13.96 0.5410 

400 4,364 407 110.5 110.5 14.83 0.5910 

500 4,381 508 110.9 111.1 14.22 0.5610 

4,242 

600 4,397 606 111.1 111.2 14.94 0.5770 

200 4,928 210 109.1 108.9 14.11 0.5640 

300 4,947 307 110.2 110.2 16.39 0.6440 

400 4,966 405 110.8 110.9 17.50 0.6900 

500 4,994 502 112.0 112.2 16.66 0.7300 

4,949 

600 4,825 584 112.4 112.5 23.19 0.9200 
69

Table 5.11 Sound Power Level Testing – Mist Drilling Method (3 qt/min), 1-inch bit, Hex Drill 

Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 2,347 216 105.4 104.6 3.77 0.1520 

300 2,357 307 106.8 106.5 4.93 0.1950 

400 2,370 405 107.8 107.9 4.72 0.1910 

500 2,387 508 108.0 108.1 4.73 0.1950 

2,121 

600 2,404 607 108.2 108.5 4.56 0.1850 

200 2,989 216 106.4 105.9 6.14 0.2460 

300 2,999 308 108.0 107.8 7.02 0.2840 

400 3,008 406 109.7 109.8 6.40 0.2800 

500 3,022 505 109.3 109.6 6.80 0.2730 

2,828 

600 3,036 606 110.0 110.3 5.50 0.2230 

200 3,686 218 107.1 106.7 8.53 0.3430 

300 3,699 302 108.6 108.5 10.11 0.4070 

400 3,709 404 110.9 110.9 9.66 0.3880 

500 3,723 501 111.0 111.3 9.28 0.3740 

3,535 

600 3,738 604 112.0 112.4 9.37 0.3790 

200 4,239 204 108.1 107.8 10.04 0.4170 

300 4,247 309 110.2 110.1 13.07 0.5380 

400 4,257 404 111.4 111.7 12.05 0.4880 

500 4,269 508 111.9 112.3 11.25 0.4650 

4,242 

600 4,278 606 111.8 112.2 12.60 0.5190 

200 4,899 212 109.3 109.3 11.52 0.4750 

300 4,916 310 111.2 111.4 12.21 0.4920 

400 4,909 403 111.3 111.6 13.21 0.5400 

500 4,929 506 113.4 113.9 12.39 0.5180 

4,949 

600 4,955 608 113.1 113.6 13.31 0.5440 
70

Table 5.12 Sound Power Level Testing – Mist Drilling Method (3 qt/min), 1-3/8-inch bit, Round 

Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 3,748 219 108.6 108.4 4.51 0.2050 

300 3,752 310 109.6 109.7 5.73 0.2190 

400 3,756 402 110.8 111.1 6.12 0.2360 

500 3,779 510 111.4 111.8 5.94 0.2310 

3,535 

600 3,789 606 112.1 112.6 5.78 0.2240 

200 4,352 214 110.8 110.9 6.66 0.2580 

300 4,361 311 111.7 112.0 7.03 0.2730 

400 4,371 406 112.2 112.5 7.88 0.3060 

500 4,383 510 112.3 112.7 8.09 0.3140 

4,242 

600 4,396 609 112.6 113.1 6.94 0.2700 

200 4,953 218 111.3 111.5 7.62 0.2910 

300 4,965 309 111.2 111.3 9.33 0.3580 

400 4,967 401 111.7 112.1 7.93 0.3050 

500 4,986 512 112.2 112.6 8.83 0.3350 

4,949 

600 5,007 607 112.9 113.4 8.26 0.3140 

200 5,523 216 111.6 111.8 9.14 0.3580 

300 5,528 312 110.3 110.4 9.91 0.3820 

400 5,942 403 113.3 113.6 10.88 0.4160 

500 5,558 510 113.1 113.6 10.60 0.4120 

5,656 

600 5,569 608 114.5 114.8 9.93 0.3760 

200 6,244 218 109.9 109.8 10.17 0.3970 

300 6,256 309 111.1 111.2 12.39 0.4850 

400 6,275 401 112.6 112.9 13.91 0.5370 

500 6,294 509 113.8 114.3 13.58 0.5240 

6,363 

600 6,317 608 113.0 113.4 12.44 0.4830 
71

Table 5.13 Sound Power Level Testing – Mist Drilling Method (3 qt/min), 1-3/8-inch bit, Hex 

Drill Steel 

SET POINTS AVERAGE SOUND POWER PENETRATION 

THRUST SPEED THRUST SPEED LINEAR A-WGT DEPTH RATE 

(lbs) (rpm) (lbs) (rpm) (dB) (dBA) (in) (in/sec) 

setthrst setspd avthrust avspeed spdb spdba pendepth penrate 

200 3,680 213 107.9 107.9 4.64 0.2110 

300 3,692 305 110.1 109.9 5.43 0.2500 

400 3,717 403 111.2 111.7 4.05 0.1850 

500 3,736 509 112.5 112.9 3.84 0.1730 

3,535 

600 3,752 606 113.2 113.3 4.14 0.1880 

200 4,298 213 108.5 108.7 4.98 0.2290 

300 4,310 314 111.2 111.6 5.78 0.2640 

400 4,326 402 112.0 112.5 5.95 0.2740 

500 4,338 508 113.4 114.0 4.76 0.2160 

4,242 

600 4,357 607 114.2 114.8 4.88 0.2720 

200 4,977 212 107.3 107.3 6.34 0.2910 

300 4,998 303 108.0 108.0 7.12 0.3270 

400 5,013 398 111.8 112.3 6.56 0.3000 

500 5,037 511 113.7 114.2 5.13 0.2370 

4,949 

600 5,060 606 115.6 116.2 5.78 0.2670 

200 5,617 211 110.3 110.5 7.87 0.3990 

300 5,632 306 112.7 113.1 9.10 0.4110 

400 5,646 404 113.2 113.6 8.92 0.4020 

500 5,671 512 116.3 117.0 8.09 0.3660 

5,656 

600 5,686 595 115.5 116.1 8.20 0.3740 

200 6,260 212 111.7 111.9 9.36 0.4320 

300 6,287 312 113.2 113.6 10.41 0.4810 

400 6,317 404 114.5 114.9 10.00 0.4620 

500 6,347 507 115.4 115.9 11.78 0.5380 

6,363 

600 6,306 598 116.3 116.9 9.05 0.4030 

Nomenclature within tables 5.2 thru 5.13 include: 

SET POINTS – these represent the settings for thrust and rotational speed prior to the drilling 

procedure 

o Thrust (lbs) – setthrst – thrust setting prior to drilling 

o Speed (rpm) – setspd – rotational speed setting prior to drilling 

AVERAGE – represents the average thrust and speed measured during the drilling portion of the 

test 

o Thrust (lbs) – avthrust – average thrust during the test 
72

o Speed (rpm) – avspeed – average rotational speed during the test 

SOUND POWER – represents the total noise energy emitted from machine during the test 

o Linear (dB) – spdb – linear sound power determined for test 

o A-WGT (dBA) – spdba – a-weighted sound power determined for test 

PENETRATION – the length of run the drill bit encountered during a test 

o Depth (in) – pendepth – The depth, in inches, the bit penetrated the rock media during a 

test 

o Rate (in/sec) – penrate – The rate, in inches per second, the bit traveled thru the rock 

media during the test. 

5.3 Experimental Test Results – Sound Power Levels 

 The data, represented graphically, listed in the following discussion are the average sound 

power levels (LwA) expressed in A-weighted decibels (dBA) and the penetration rates (in/sec) 

monitored at a given test configuration. Furthermore, all similar tests (e.g., same steel shape and 

bit size) were averaged for a given thrust or rotation speed. This approach facilitated the 

illustrating of trends showing the affects of thrusts or rotation speeds on the data. As a result, 

relationships were determined for sound power, penetration rate, thrust and rotational speed 

related to the different types of drilling methods (vacuum, wet and mist). The laboratory data 

was characterized and plotted for each test configuration as shown below. 
73

5.3.1 Round Drill Steel Compared to Hexagonal Drill Steel (Penetration Rate and 

 Sound Power)

 

 Figure 5.1 below represents plots of thrust vs. penetration rate for one-inch round and oneinch hex drill steel given differing rotational speeds. 

Figure 5.1 Drill Steels - Round and Hex (1-inch) – Thrust vs. Penetration Rate 
74

In most cases, for both the one-inch round and hex drill steel, the data represents higher penetration 

rates when utilizing a wet, mist and dry drilling system respectively. However, for the one-inch 

round drill steel, penetration rates were higher using a mist system of drilling as compared to a wet 

system when the rotational speed was higher, specifically at 600 rpm. The data also shows that 

penetration rates did increase as the thrust was increased for both the one-inch round and hex drill 

steel with the exception of the one-inch hex drill steel at the higher rotational speed of 600 rpm. The 

penetration rate for this remained fairly constant as the thrust was increased. 

 Figure 5.2 represents plots of penetration rates vs. sound power for one-inch round and oneinch hex drill steel given differing rotational speeds. 
75

Figure 5.2 Drill Steels - Round and Hex (1-inch) – Penetration Rate vs. Sound Power 
76

For all cases, sound power levels were highest during vacuum or dry drilling tests and the levels 

decreased during mist and wet system type of drilling respectively as shown in figure 5.2. In 

general, for all configurations, as the penetration rate increased, the sound power level increased as 

well. Additionally, sound power levels for the round drill steel were lower than compared to the hex 

type drill steel. Figure 5.3 below represents plots of thrust vs. penetration rate for 1.375-inch round 

and hex drill steel given differing rotational speeds. 
77

Dry

Wet

Mist

1 3/8 Round

Linear Regression

0.00

0.20

0.40

0.60

Penetration rate (inches/sec)

W W WW W

W W

W

W

WW

W WW

W

W

W

W

W W

W

W

W W

W

W

W W

W W

200 rpm 300 rpm 400 rpm

500 rpm 600 rpm

W

WW

WW WW W

W W

W

W W WW

W

W

WW

W

W

W WW

W

W

W

W

W

W

W

W

W W

W

W

W

W

W W

W

W W W

W W W

W WW

W

W

W W

WW

W

W

W

W

W

W W

W W

W

W W

W

W

3000 4000 5000 6000

Average thrust (lbs)

0.00

0.20

0.40

0.60

Penetrat oi n rate (inches/sec)

W W W W

W

W W W

W

W

W

W W

W

W

3000 4000 5000 6000

Average thrust (lbs)

W W

W W

W W

W

W

W

W

W

W

W W

W WW

W

W

W

W

W

Figure 5.3 Drill Steels - Round and Hex (1.375-inch) – Thrust vs. Penetration Rate 
78

As seen earlier with the one-inch round and hex drill steel in figure 5.1, the data represented for the 

1.375-inch round and hex drill steel also presents higher penetration rates when using a wet, mist and 

dry drilling system respectively. However, penetration rates are significantly decreased when 

utilizing a dry or vacuum drilling system and operating at higher rotational speeds, specifically, 400 

thru 600 rpm. Additionally, penetration rates did increase as the thrust was increased for both the 

1.375-inch round and hex drill steel until a vacuum type of drilling system was used and rotational 

speeds were higher. Figure 5.4 displays plots of penetration rates vs. sound power for 1.375-inch 

round and hex drill steel given differing rotational speeds. 
79

Figure 5.4 Drill Steels - Round and Hex (1.375-inch) – Penetration Rate vs. Sound Power 
80

In general, sound power levels were lowest during wet drilling tests and highest when utilizing a 

vacuum or dry method of drilling. Additionally, the penetration rates for the vacuum drilling 

method were much lower as compared to the mist or wet systems of drilling. Minimal penetration 

rates were observed at higher rotational speeds utilizing the dry or vacuum method of drilling and 

sound power levels were higher utilizing the 1.375-inch hex drill steel as compared to the round steel 

and the one-inch hex results showed sound power levels less than one-inch round at lower rotational 

speeds but the advantage disappears at 500 and 600 rpm. 

5.3.2 One-Inch Diameter Compared to One and Three-Eighths Inch Diameter Drill Bits

 Figure 5.5 represents plots of penetration rates vs. thrust for comparing one-inch to 1.375-

inch round and hex drill steel given differing rotational speeds. 
81

Dry

Wet

Mist

1 3/8 Round

Linear Regression

0.00

0.20

0.40

0.60

Penetrat oi n rate ( ni ches s/ ec)

W W WW W

W W

W

W

WW

W WW

W

W

W

W

W W

W

W

W W

W

W

W W

W W

200 rpm 300 rpm 400 rpm

500 rpm 600 rpm

W

WW

WW WW W

W W

W

W W WW

W

W

WW

W

W

W

WW

W

W

W

W

W

W

W

W

W W

W

W

W

W

W W

W

W W W

W W W

W WW

W

W

W W

WW

W

W

W

W

W

W W

W W

W

W W

W

W

3000 4000 5000 6000

Average thrust (lbs)

0.00

0.20

0.40

0.60

Penetrat oi n rate ( ni ches s/ ec)

W W W W

W

W W W

W

W

W

W W

W

W

3000 4000 5000 6000

Average thrust (lbs)

W W

W W

W W

W

W

W

W

W

W

W W

W WW

W W

W

W

W

Figure 5.5 One-inch vs. 1.375-inch Drill Bit (Penetration Rate vs. Thrust) 

As shown in figure 5.5 above, the thrust has a significant affect on the penetration rate for most 

cases. The one-inch drill bit performance was on the order of two to three times that of the 1.375-

inch drill bit. However, the thrust had minimal influence relative to using a dry method of drilling at 

the higher rotational speeds, specifically, 500 and 600 rpm. The one-inch drill bit performed 

significantly better than the 1.375-inch drill bit relative to rotational speed. Figure 5.6 displays plots 

of penetration rates vs. sound power levels for comparing one-inch to 1.375-inch round and hex drill 

bits given differing rotational speeds. 
82

Figure 5.6 One-inch vs. 1.375-inch Drill Bit (Penetration Rate vs. Sound Power Level) 

Sound power levels experienced with the 1.375-inch diameter bit were observed to be higher than 

experienced with the one-inch diameter bit, varying approximately by 2.5 dBA. Additionally, sound 

power levels for either a one-inch or 1.375-inch diameter bit were lowest during the wet drilling 

method. Penetration rates using a one-inch diameter bit were typically higher than when using a 

1.375-inch diameter bit independent upon the type of drilling method used. As was the case with 

thrust, when using rotation speed as a comparative basis, the vacuum round drill steel results indicate 
83

a lower sound power than similar hex drill steel tests. For wet testing, there is no difference between 

the one-inch and 1.375-inch round and hex results. 

5.3.3 General Conclusions Regarding Data Collection

 When comparing round and hex drill steel, round drill steel should be used when utilizing the 

vacuum type of drilling method and hex drill steels when performing the wet or mist type of drilling 

method. While increasing the thrust does yield an increased sound power level for both of the round 

and hex drill steel, the differences are negligible. When comparing rotational speed affect relative to 

round or hex drill steel, the round drill steel, during vacuum type drilling, provides a lower sound 

power level than similar hex drill steel tests. For wet or mist system type of drilling, their appears to 

be no difference between the one-inch and 1.375-inch round and hex drill steel. Upon comparing 

penetration rates relative to round or hex drill steel in relation to thrust or rotational speed, their 

appears to be minimal affect attributed to thrust or rotational speeds. 

 When comparing the one-inch diameter bits to the 1.375-inch diameter bits, the one-inch 

diameter drill bits are slightly quieter than the 1.375-inch diameter drill bits. The penetration rates 

relative to the one-inch drill bits are noticeably higher than the 1.375-inch bits, on an order of two to 

three times higher. When comparing the 1-inch bit to the 1.375-inch bit relative to rotational speed, 

the one-inch bit performed significantly better than the 1.375-inch bit. For optimal performance and 

lower sound power levels, rotational speeds in the range of 200-400 rpm performed better and were 

quieter. 

 When comparing the different types of drilling methods, specifically vacuum, mist or 

wet, wet and mist drilling, penetration rates utilizing a wet or mist system drilling technique were 

much higher than using a dry or vacuum type drilling method. Additionally, utilizing a wet or 

mist system proved to emit less noise than similar tests conducted under vacuum or dry 
84

conditions. Much of the difference is attributable to the lubricating affect of the water or mist, 

which attenuates higher frequency noise. An example of this effect is given in figure 5.7 (17,22). 

Here, one-inch round data tested at a thrust of 4,949 pounds and a rotation speed of 200 rpm is 

given for testing under both vacuum and wet drilling system conditions. For all one-third octave 

band frequencies of 1,000 Hz and greater, it is clearly shown that the sound power levels are 

greater for vacuum drilling. Four examples of this are listed in table 5.14. For each case, the 

sound power level contributions for the one-third octave bands from 50 through 800 Hz are 

essentially the same for vacuum and wet drilling, e.g., for the one-inch round case they are 95 

dBA and 96 dBA respectively. There is a significantly larger difference in the frequency range 1 

kHz through 10 kHz. For the one-inch round example, there is a 5 dBA difference. Similar 

results are listed for the other three cases. 

40

50

60

70

80

90

100

110

120

5080

125200315500800

1,2502,0003,1505,0008,000

Overall

Frequency (Hz)

A Weighted Sound Power Level 

(dBA)

Vacuum Wet

Figure 5.7 One-inch Round Drill Steel - Vacuum and Wet – Sound Power Levels - 4,949 lbs Thrust, 

200 rpm Rotational Speed 
85

Table 5.14 - Sound Power Level Contributions of Two Frequency Bands 

Size & 

Shape 

Thrust (lbs) 

Speed (rpm) 

Frequency 

Band 

(Hz) 

Vacuum

LwA

Wet 

LwA

1-inch 50 through 800 95 96 

round 

4,949 

400 1 k through 10 k 113 108 

1-3/8 inch 50 through 800 96 96 

round 

6,363 

400 1 k through 10 k 115 109 

1-inch 50 through 800 93 96 

hex 

4,949 

400 1 k through 10 k 112 105 

1-3/8 inch 50 through 800 97 95 

hex 

5,656 

200 1 k through 10 k 114 107 

Further analysis indicated another key point. The overall A-weighted sound power levels are 

essentially unaffected by the sound power generated in the one-third octave bands below 1 kHz. 

For each example given, the overall A-weighted sound power level is the same as the 1 kHz 

through 10 kHz contributions, given rounding the sound power levels to the nearest dBA. 

5.4 Development of a Statistical Model for Determining Sound Power Levels 

5.4.1 Introduction

The next step of the research was to compile, summarize and statistically correlate all of the 

data collected (approximately 500 tests) for drilling into a high-compressive strength media 

(>20,000 psi) by developing one equation, which, would be used to determine sound power levels 

given any drilling method (vacuum, wet or mist) and utilizing differing drilling parameters or 

configurations related to thrust, rotational speed, bit size and type of drill steel used. A 

commercially available, statistical software package, SPSS was used to correlate all of the data. 

 In order to statistically correlate the data into one useful equation, the data from each test had 

to be organized into a useful form. The laboratory data is shown in table 5.15. Each individual test 

supplied the following independent data: 1) bit size; 2) drill steel type; 3) thrust utilized; 4) rotational 

speed and 5) type of drilling method (vacuum, mist or wet). The dependent information derived 
86

from the statistical approach was the sound power level generated from each test configuration. As 

shown in table 5.15, the independent variables utilized for the model were: 

Water = 0 gpm for the vacuum drilling method 

 0.75 gpm for the mist drilling method 

 3 gpm for the wet drilling method 

Thrust = average thrust level used for the individual test, in lbs. 

Speed = average rotational speed used for the individual test, in rpm 

Bit Size = 1 for 1-inch and 1.375 for 1.375-inch 

Drill Steel = 0 for hex drill steel and 1 for round drill steel 

It was determined the penetration rate measured for each test was not to be included as a specific 

independent variable when developing the one equation for predicting sound power. The penetration 

rates measured for each test were directly affected by all of the independent variables listed above. 

Therefore, a direct correlation between the dependent variable, sound power and the penetration rate 

cannot exist due to the contribution required by all of the independent variables (drilling method, 

thrust, speed, bit size and type of drill steel) in determining the penetration rate. 
87

Table 5.15 Laboratory Data Utilized for Input into the Statistical Model 

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

106.60 209.00 2239.00 .00 1.000 1.000

107.10 210.00 2228.00 .00 1.000 1.000

108.30 306.00 2282.00 .00 1.000 1.000

107.40 305.00 2272.00 .00 1.000 1.000

108.40 400.00 2324.00 .00 1.000 1.000

108.60 402.00 2280.00 .00 1.000 1.000

109.50 514.00 2220.00 .00 1.000 1.000

108.80 609.00 2241.00 .00 1.000 1.000

107.80 208.00 2711.00 .00 1.000 1.000

109.90 305.00 2696.00 .00 1.000 1.000

109.40 306.00 2705.00 .00 1.000 1.000

109.90 402.00 2701.00 .00 1.000 1.000

110.10 509.00 2865.00 .00 1.000 1.000

110.10 602.00 2882.00 .00 1.000 1.000

110.20 215.00 3435.00 .00 1.000 1.000

110.90 304.00 3451.00 .00 1.000 1.000

109.60 311.00 3620.00 .00 1.000 1.000

111.50 405.00 3487.00 .00 1.000 1.000

111.60 404.00 3483.00 .00 1.000 1.000

110.50 510.00 3628.00 .00 1.000 1.000

111.10 607.00 3653.00 .00 1.000 1.000

111.20 208.00 4085.00 .00 1.000 1.000

111.60 305.00 4097.00 .00 1.000 1.000

111.50 404.00 4111.00 .00 1.000 1.000

111.40 406.00 4283.00 .00 1.000 1.000

110.90 509.00 4291.00 .00 1.000 1.000

110.90 604.00 4314.00 .00 1.000 1.000

110.40 221.00 4744.00 .00 1.000 1.000

110.60 223.00 4778.00 .00 1.000 1.000

112.30 308.00 4769.00 .00 1.000 1.000

112.60 404.00 4800.00 .00 1.000 1.000

110.40 406.00 4821.00 .00 1.000 1.000

111.40 507.00 4870.00 .00 1.000 1.000

110.70 607.00 4822.00 .00 1.000 1.000

112.00 211.00 4745.00 .00 1.000 1.000

105.50 203.00 2268.00 .00 1.375 1.000

106.10 306.00 2285.00 .00 1.375 1.000

108.60 402.00 2293.00 .00 1.375 1.000

108.80 211.00 2915.00 .00 1.375 1.000

108.50 215.00 2908.00 .00 1.375 1.000

108.50 308.00 2925.00 .00 1.375 1.000
88

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

108.30 311.00 2923.00 .00 1.375 1.000

109.60 404.00 2952.00 .00 1.375 1.000

108.50 211.00 3527.00 .00 1.375 1.000

108.30 213.00 3522.00 .00 1.375 1.000

109.60 306.00 3545.00 .00 1.375 1.000

108.90 305.00 3545.00 .00 1.375 1.000

110.10 402.00 3580.00 .00 1.375 1.000

110.20 402.00 3567.00 .00 1.375 1.000

111.80 208.00 4183.00 .00 1.375 1.000

113.00 306.00 4181.00 .00 1.375 1.000

111.70 309.00 4228.00 .00 1.375 1.000

113.00 403.00 4239.00 .00 1.375 1.000

112.50 405.00 4360.00 .00 1.375 1.000

111.30 511.00 4303.00 .00 1.375 1.000

110.00 606.00 4405.00 .00 1.375 1.000

112.10 210.00 4842.00 .00 1.375 1.000

112.30 307.00 4865.00 .00 1.375 1.000

112.70 314.00 4923.00 .00 1.375 1.000

114.20 405.00 4886.00 .00 1.375 1.000

111.00 509.00 5082.00 .00 1.375 1.000

113.60 215.00 5415.00 .00 1.375 1.000

112.50 307.00 5438.00 .00 1.375 1.000

113.10 403.00 5446.00 .00 1.375 1.000

113.40 207.00 6195.00 .00 1.375 1.000

112.70 212.00 6242.00 .00 1.375 1.000

114.30 312.00 6234.00 .00 1.375 1.000

113.10 310.00 6218.00 .00 1.375 1.000

114.80 402.00 6167.00 .00 1.375 1.000

114.10 402.00 6237.00 .00 1.375 1.000

111.40 155.00 6225.00 .00 1.375 1.000

112.80 402.00 4180.00 .00 1.375 1.000

110.20 318.00 2979.00 .00 1.375 1.000

110.00 223.00 3609.00 .00 1.375 1.000

112.10 411.00 3625.00 .00 1.375 1.000

112.00 405.00 3628.00 .00 1.375 1.000

110.50 312.00 3623.00 .00 1.375 1.000

109.60 221.00 3615.00 .00 1.375 1.000

109.00 206.00 2334.00 .00 1.000 .000

110.20 303.00 2333.00 .00 1.000 .000

111.00 404.00 2344.00 .00 1.000 .000

110.20 506.00 2226.00 .00 1.000 .000

112.80 602.00 2241.00 .00 1.000 .000

111.30 208.00 2919.00 .00 1.000 .000
89

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

112.70 305.00 2933.00 .00 1.000 .000

112.30 401.00 2955.00 .00 1.000 .000

110.50 406.00 2840.00 .00 1.000 .000

111.10 508.00 2877.00 .00 1.000 .000

112.50 606.00 2890.00 .00 1.000 .000

112.70 207.00 3587.00 .00 1.000 .000

111.60 209.00 3588.00 .00 1.000 .000

112.80 307.00 3622.00 .00 1.000 .000

113.40 307.00 3607.00 .00 1.000 .000

113.20 400.00 3642.00 .00 1.000 .000

113.40 398.00 3660.00 .00 1.000 .000

113.60 508.00 3622.00 .00 1.000 .000

112.90 606.00 3651.00 .00 1.000 .000

112.50 218.00 4294.00 .00 1.000 .000

110.80 208.00 4238.00 .00 1.000 .000

113.30 305.00 4254.00 .00 1.000 .000

112.70 402.00 4258.00 .00 1.000 .000

114.00 508.00 4344.00 .00 1.000 .000

112.90 607.00 4362.00 .00 1.000 .000

112.30 209.00 4818.00 .00 1.000 .000

113.00 211.00 4916.00 .00 1.000 .000

113.20 306.00 4869.00 .00 1.000 .000

113.30 407.00 4898.00 .00 1.000 .000

114.30 510.00 4979.00 .00 1.000 .000

113.00 607.00 4995.00 .00 1.000 .000

106.30 212.00 2283.00 .00 1.375 .000

109.50 309.00 2302.00 .00 1.375 .000

110.40 402.00 2326.00 .00 1.375 .000

109.70 209.00 2892.00 .00 1.375 .000

110.40 308.00 2914.00 .00 1.375 .000

113.00 405.00 2943.00 .00 1.375 .000

109.60 208.00 3559.00 .00 1.375 .000

111.90 304.00 3575.00 .00 1.375 .000

112.50 313.00 3715.00 .00 1.375 .000

112.80 402.00 3591.00 .00 1.375 .000

113.30 405.00 3741.00 .00 1.375 .000

112.80 214.00 4321.00 .00 1.375 .000

114.10 309.00 4316.00 .00 1.375 .000

113.30 313.00 4342.00 .00 1.375 .000

114.60 402.00 4330.00 .00 1.375 .000

114.60 403.00 4357.00 .00 1.375 .000

114.70 505.00 4407.00 .00 1.375 .000

114.10 604.00 4420.00 .00 1.375 .000
90

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

113.80 212.00 4979.00 .00 1.375 .000

113.80 310.00 5001.00 .00 1.375 .000

113.70 309.00 4958.00 .00 1.375 .000

115.50 405.00 5047.00 .00 1.375 .000

114.30 409.00 4973.00 .00 1.375 .000

114.70 511.00 4982.00 .00 1.375 .000

113.90 604.00 4992.00 .00 1.375 .000

114.10 211.00 5558.00 .00 1.375 .000

113.30 218.00 5485.00 .00 1.375 .000

114.40 313.00 5497.00 .00 1.375 .000

114.30 310.00 5502.00 .00 1.375 .000

116.10 405.00 5576.00 .00 1.375 .000

115.20 408.00 5510.00 .00 1.375 .000

114.70 511.00 5523.00 .00 1.375 .000

113.40 600.00 5544.00 .00 1.375 .000

114.10 212.00 6342.00 .00 1.375 .000

114.60 211.00 6224.00 .00 1.375 .000

115.20 311.00 6360.00 .00 1.375 .000

115.70 309.00 6234.00 .00 1.375 .000

116.20 404.00 6382.00 .00 1.375 .000

115.30 402.00 6244.00 .00 1.375 .000

114.30 506.00 6256.00 .00 1.375 .000

113.20 603.00 6205.00 .00 1.375 .000

102.10 207.00 2313.00 3.00 1.000 1.000

102.00 211.00 2306.00 3.00 1.000 1.000

102.20 309.00 2321.00 3.00 1.000 1.000

104.00 308.00 2318.00 3.00 1.000 1.000

102.90 402.00 2335.00 3.00 1.000 1.000

105.50 405.00 2329.00 3.00 1.000 1.000

102.40 503.00 2448.00 3.00 1.000 1.000

103.60 605.00 2461.00 3.00 1.000 1.000

103.50 205.00 2909.00 3.00 1.000 1.000

104.30 311.00 3084.00 3.00 1.000 1.000

104.40 312.00 3005.00 3.00 1.000 1.000

103.90 402.00 2978.00 3.00 1.000 1.000

103.20 403.00 3098.00 3.00 1.000 1.000

105.40 508.00 3113.00 3.00 1.000 1.000

102.50 507.00 3012.00 3.00 1.000 1.000

105.70 605.00 3129.00 3.00 1.000 1.000

104.40 201.00 3591.00 3.00 1.000 1.000

106.30 308.00 3605.00 3.00 1.000 1.000

105.80 314.00 3601.00 3.00 1.000 1.000

106.80 401.00 3617.00 3.00 1.000 1.000
91

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

105.90 511.00 3815.00 3.00 1.000 1.000

107.70 604.00 3820.00 3.00 1.000 1.000

105.80 210.00 4275.00 3.00 1.000 1.000

105.70 213.00 4272.00 3.00 1.000 1.000

107.00 309.00 4285.00 3.00 1.000 1.000

106.50 315.00 4285.00 3.00 1.000 1.000

107.30 411.00 4288.00 3.00 1.000 1.000

108.60 411.00 4296.00 3.00 1.000 1.000

105.80 508.00 4411.00 3.00 1.000 1.000

106.70 595.00 4434.00 3.00 1.000 1.000

106.20 206.00 4888.00 3.00 1.000 1.000

106.30 205.00 4899.00 3.00 1.000 1.000

107.60 302.00 4898.00 3.00 1.000 1.000

108.20 307.00 4916.00 3.00 1.000 1.000

108.10 412.00 4927.00 3.00 1.000 1.000

108.90 412.00 4912.00 3.00 1.000 1.000

107.10 510.00 4876.00 3.00 1.000 1.000

106.20 607.00 4902.00 3.00 1.000 1.000

105.80 407.00 4398.00 3.00 1.000 1.000

105.00 212.00 4371.00 3.00 1.000 1.000

106.10 400.00 3028.00 3.00 1.000 1.000

103.40 304.00 2953.00 3.00 1.000 1.000

102.70 215.00 4368.00 3.00 1.000 1.000

103.50 305.00 2985.00 3.00 1.000 1.000

104.90 210.00 2335.00 3.00 1.375 1.000

103.90 208.00 2337.00 3.00 1.375 1.000

104.30 310.00 2340.00 3.00 1.375 1.000

105.00 311.00 2337.00 3.00 1.375 1.000

106.60 406.00 2351.00 3.00 1.375 1.000

105.50 407.00 2347.00 3.00 1.375 1.000

103.50 211.00 2916.00 3.00 1.375 1.000

103.60 209.00 2915.00 3.00 1.375 1.000

104.90 305.00 2937.00 3.00 1.375 1.000

104.50 305.00 2935.00 3.00 1.375 1.000

106.10 411.00 2959.00 3.00 1.375 1.000

106.70 411.00 2955.00 3.00 1.375 1.000

105.90 218.00 3611.00 3.00 1.375 1.000

105.30 214.00 3609.00 3.00 1.375 1.000

105.10 313.00 3623.00 3.00 1.375 1.000

106.00 311.00 3621.00 3.00 1.375 1.000

108.00 408.00 3709.00 3.00 1.375 1.000

108.50 411.00 3701.00 3.00 1.375 1.000

106.80 217.00 4187.00 3.00 1.375 1.000
92

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

106.00 215.00 4188.00 3.00 1.375 1.000

108.10 313.00 4210.00 3.00 1.375 1.000

107.60 307.00 4202.00 3.00 1.375 1.000

108.80 408.00 4233.00 3.00 1.375 1.000

108.90 407.00 4230.00 3.00 1.375 1.000

108.90 510.00 4456.00 3.00 1.375 1.000

109.20 603.00 4485.00 3.00 1.375 1.000

106.50 211.00 4833.00 3.00 1.375 1.000

106.30 217.00 4808.00 3.00 1.375 1.000

108.50 309.00 4816.00 3.00 1.375 1.000

107.40 310.00 4826.00 3.00 1.375 1.000

107.40 403.00 4839.00 3.00 1.375 1.000

108.30 403.00 4840.00 3.00 1.375 1.000

109.80 506.00 5110.00 3.00 1.375 1.000

110.80 604.00 5136.00 3.00 1.375 1.000

108.00 210.00 5649.00 3.00 1.375 1.000

107.30 212.00 5644.00 3.00 1.375 1.000

109.20 311.00 5662.00 3.00 1.375 1.000

108.60 310.00 5512.00 3.00 1.375 1.000

110.20 411.00 5669.00 3.00 1.375 1.000

108.70 401.00 5666.00 3.00 1.375 1.000

110.30 507.00 5740.00 3.00 1.375 1.000

110.40 604.00 5755.00 3.00 1.375 1.000

108.00 206.00 6298.00 3.00 1.375 1.000

109.40 178.00 6270.00 3.00 1.375 1.000

109.70 308.00 6307.00 3.00 1.375 1.000

109.00 307.00 6143.00 3.00 1.375 1.000

109.60 407.00 6320.00 3.00 1.375 1.000

109.30 402.00 6148.00 3.00 1.375 1.000

108.40 504.00 6161.00 3.00 1.375 1.000

109.40 601.00 6369.00 3.00 1.375 1.000

110.40 578.00 6311.00 3.00 1.375 1.000

108.60 310.00 6230.00 3.00 1.375 1.000

110.70 506.00 6009.00 3.00 1.375 1.000

109.90 562.00 6018.00 3.00 1.375 1.000

109.10 565.00 5692.00 3.00 1.375 1.000

108.80 571.00 5286.00 3.00 1.375 1.000

108.60 472.00 5270.00 3.00 1.375 1.000

108.30 415.00 5249.00 3.00 1.375 1.000

108.40 332.00 5229.00 3.00 1.375 1.000

110.00 544.00 4868.00 3.00 1.375 1.000

110.90 577.00 4554.00 3.00 1.375 1.000

109.40 579.00 4223.00 3.00 1.375 1.000
93

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

107.70 572.00 3987.00 3.00 1.375 1.000

109.40 582.00 3734.00 3.00 1.375 1.000

108.60 577.00 4892.00 3.00 1.375 1.000

109.10 408.00 3703.00 3.00 1.375 1.000

109.70 313.00 4210.00 3.00 1.375 1.000

110.30 413.00 4233.00 3.00 1.375 1.000

108.80 405.00 4841.00 3.00 1.375 1.000

106.10 214.00 5496.00 3.00 1.375 1.000

108.70 301.00 5653.00 3.00 1.375 1.000

108.70 310.00 5653.00 3.00 1.375 1.000

110.40 409.00 5661.00 3.00 1.375 1.000

109.30 300.00 5711.00 3.00 1.375 1.000

110.50 202.00 5057.00 3.00 1.375 1.000

100.60 207.00 2314.00 3.00 1.000 .000

100.50 315.00 2332.00 3.00 1.000 .000

103.80 404.00 2347.00 3.00 1.000 .000

105.60 508.00 2295.00 3.00 1.000 .000

105.90 607.00 2306.00 3.00 1.000 .000

101.50 214.00 2924.00 3.00 1.000 .000

104.20 198.00 2932.00 3.00 1.000 .000

102.80 306.00 2939.00 3.00 1.000 .000

104.80 406.00 2957.00 3.00 1.000 .000

105.70 403.00 3121.00 3.00 1.000 .000

107.70 507.00 3135.00 3.00 1.000 .000

107.20 602.00 3147.00 3.00 1.000 .000

103.80 215.00 3670.00 3.00 1.000 .000

103.90 204.00 3665.00 3.00 1.000 .000

105.30 316.00 3715.00 3.00 1.000 .000

105.90 304.00 3720.00 3.00 1.000 .000

108.20 409.00 3578.00 3.00 1.000 .000

107.90 402.00 3581.00 3.00 1.000 .000

107.50 517.00 3741.00 3.00 1.000 .000

108.30 504.00 3644.00 3.00 1.000 .000

108.30 606.00 3755.00 3.00 1.000 .000

106.90 605.00 3657.00 3.00 1.000 .000

101.70 202.00 4273.00 3.00 1.000 .000

105.20 216.00 4349.00 3.00 1.000 .000

103.80 310.00 4272.00 3.00 1.000 .000

106.10 412.00 4297.00 3.00 1.000 .000

104.80 398.00 4296.00 3.00 1.000 .000

108.10 511.00 4382.00 3.00 1.000 .000

108.40 614.00 4392.00 3.00 1.000 .000

105.10 215.00 4793.00 3.00 1.000 .000
94

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

104.70 209.00 4930.00 3.00 1.000 .000

105.60 306.00 4940.00 3.00 1.000 .000

105.50 314.00 4806.00 3.00 1.000 .000

105.70 414.00 4944.00 3.00 1.000 .000

108.10 509.00 4831.00 3.00 1.000 .000

108.30 578.00 4850.00 3.00 1.000 .000

105.20 409.00 3696.00 3.00 1.000 .000

104.00 201.00 4694.00 3.00 1.000 .000

106.70 401.00 3726.00 3.00 1.000 .000

103.70 319.00 3682.00 3.00 1.000 .000

106.60 403.00 2957.00 3.00 1.000 .000

104.30 307.00 3618.00 3.00 1.000 .000

106.20 400.00 3635.00 3.00 1.000 .000

104.20 209.00 2338.00 3.00 1.375 .000

105.00 311.00 2360.00 3.00 1.375 .000

106.10 403.00 2378.00 3.00 1.375 .000

104.20 213.00 2915.00 3.00 1.375 .000

106.30 309.00 2937.00 3.00 1.375 .000

107.00 402.00 2961.00 3.00 1.375 .000

104.90 209.00 3593.00 3.00 1.375 .000

105.00 312.00 3606.00 3.00 1.375 .000

106.10 400.00 3622.00 3.00 1.375 .000

104.90 212.00 4402.00 3.00 1.375 .000

105.70 208.00 4207.00 3.00 1.375 .000

106.80 302.00 4227.00 3.00 1.375 .000

106.40 309.00 4277.00 3.00 1.375 .000

107.50 411.00 4258.00 3.00 1.375 .000

107.60 398.00 4286.00 3.00 1.375 .000

108.00 505.00 4454.00 3.00 1.375 .000

109.20 604.00 4478.00 3.00 1.375 .000

106.40 207.00 4848.00 3.00 1.375 .000

106.40 206.00 4846.00 3.00 1.375 .000

107.90 315.00 4859.00 3.00 1.375 .000

107.50 313.00 4852.00 3.00 1.375 .000

110.50 407.00 4867.00 3.00 1.375 .000

107.20 401.00 5000.00 3.00 1.375 .000

108.00 506.00 5014.00 3.00 1.375 .000

109.10 602.00 5027.00 3.00 1.375 .000

107.50 201.00 5435.00 3.00 1.375 .000

106.90 216.00 5595.00 3.00 1.375 .000

109.30 315.00 5539.00 3.00 1.375 .000

108.60 308.00 5539.00 3.00 1.375 .000

108.80 413.00 5561.00 3.00 1.375 .000
95

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

109.20 424.00 5586.00 3.00 1.375 .000

109.00 510.00 5642.00 3.00 1.375 .000

108.90 604.00 5664.00 3.00 1.375 .000

108.60 204.00 6200.00 3.00 1.375 .000

107.70 196.00 6155.00 3.00 1.375 .000

108.80 316.00 6197.00 3.00 1.375 .000

109.10 304.00 6137.00 3.00 1.375 .000

110.80 405.00 6219.00 3.00 1.375 .000

110.00 408.00 6213.00 3.00 1.375 .000

109.40 508.00 6334.00 3.00 1.375 .000

110.20 598.00 6323.00 3.00 1.375 .000

110.70 604.00 6346.00 3.00 1.375 .000

112.20 556.00 6299.00 3.00 1.375 .000

110.50 453.00 6274.00 3.00 1.375 .000

108.50 436.00 6007.00 3.00 1.375 .000

109.00 561.00 6020.00 3.00 1.375 .000

108.60 543.00 5694.00 3.00 1.375 .000

108.90 428.00 5668.00 3.00 1.375 .000

108.10 428.00 5266.00 3.00 1.375 .000

109.30 579.00 5280.00 3.00 1.375 .000

109.00 453.00 6004.00 3.00 1.375 .000

108.40 596.00 4993.00 3.00 1.375 .000

108.10 481.00 4969.00 3.00 1.375 .000

107.50 401.00 4933.00 3.00 1.375 .000

107.30 403.00 4610.00 3.00 1.375 .000

107.70 484.00 4622.00 3.00 1.375 .000

109.00 590.00 4636.00 3.00 1.375 .000

108.50 586.00 4348.00 3.00 1.375 .000

110.20 473.00 4216.00 3.00 1.375 .000

106.10 376.00 4179.00 3.00 1.375 .000

107.90 475.00 3714.00 3.00 1.375 .000

110.10 555.00 3728.00 3.00 1.375 .000

109.60 510.00 3709.00 3.00 1.375 .000

109.00 213.00 4836.00 3.00 1.375 .000

109.80 304.00 4853.00 3.00 1.375 .000

107.90 304.00 5453.00 3.00 1.375 .000

110.40 405.00 5468.00 3.00 1.375 .000

106.30 403.00 4432.00 3.00 1.375 .000

105.20 205.00 4265.00 3.00 1.375 .000

105.60 213.00 4971.00 3.00 1.375 .000

106.30 210.00 5523.00 3.00 1.375 .000

108.00 401.00 5624.00 3.00 1.375 .000

106.90 405.00 6231.00 3.00 1.375 .000
96

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

107.30 218.00 6210.00 3.00 1.375 .000

104.60 214.00 2418.00 .75 1.000 1.000

105.80 307.00 2432.00 .75 1.000 1.000

106.70 402.00 2445.00 .75 1.000 1.000

107.40 507.00 2458.00 .75 1.000 1.000

107.70 593.00 2472.00 .75 1.000 1.000

104.50 216.00 2978.00 .75 1.000 1.000

107.10 301.00 2993.00 .75 1.000 1.000

107.90 408.00 3004.00 .75 1.000 1.000

108.50 510.00 3004.00 .75 1.000 1.000

109.20 605.00 3012.00 .75 1.000 1.000

106.30 213.00 3685.00 .75 1.000 1.000

108.50 306.00 3700.00 .75 1.000 1.000

109.10 404.00 3716.00 .75 1.000 1.000

109.70 509.00 3734.00 .75 1.000 1.000

110.10 607.00 3758.00 .75 1.000 1.000

107.90 216.00 4335.00 .75 1.000 1.000

109.20 305.00 4350.00 .75 1.000 1.000

110.50 407.00 4364.00 .75 1.000 1.000

111.10 508.00 4381.00 .75 1.000 1.000

111.20 606.00 4397.00 .75 1.000 1.000

108.90 210.00 4928.00 .75 1.000 1.000

110.20 307.00 4947.00 .75 1.000 1.000

110.90 405.00 4966.00 .75 1.000 1.000

112.20 502.00 4994.00 .75 1.000 1.000

112.50 584.00 4825.00 .75 1.000 1.000

108.40 219.00 3748.00 .75 1.375 1.000

109.70 310.00 3752.00 .75 1.375 1.000

111.10 402.00 3756.00 .75 1.375 1.000

111.80 510.00 3779.00 .75 1.375 1.000

112.60 606.00 3789.00 .75 1.375 1.000

110.90 214.00 4352.00 .75 1.375 1.000

112.00 311.00 4361.00 .75 1.375 1.000

112.50 406.00 4371.00 .75 1.375 1.000

112.70 510.00 4383.00 .75 1.375 1.000

113.10 609.00 4396.00 .75 1.375 1.000

111.50 218.00 4953.00 .75 1.375 1.000

111.30 309.00 4965.00 .75 1.375 1.000

112.10 401.00 4967.00 .75 1.375 1.000

112.60 512.00 4986.00 .75 1.375 1.000

113.40 607.00 5007.00 .75 1.375 1.000

111.80 216.00 5523.00 .75 1.375 1.000

110.40 312.00 5528.00 .75 1.375 1.000
97

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

113.60 403.00 5942.00 .75 1.375 1.000

113.60 510.00 5558.00 .75 1.375 1.000

114.80 608.00 5569.00 .75 1.375 1.000

109.80 218.00 6244.00 .75 1.375 1.000

111.20 309.00 6256.00 .75 1.375 1.000

112.90 401.00 6275.00 .75 1.375 1.000

114.30 509.00 6294.00 .75 1.375 1.000

113.40 608.00 6317.00 .75 1.375 1.000

107.20 216.00 2347.00 .75 1.000 .000

108.09 307.00 2357.00 .75 1.000 .000

109.04 405.00 2370.00 .75 1.000 .000

110.04 508.00 2387.00 .75 1.000 .000

111.00 607.00 2404.00 .75 1.000 .000

108.07 216.00 2989.00 .75 1.000 .000

108.86 308.00 2999.00 .75 1.000 .000

109.69 406.00 3008.00 .75 1.000 .000

110.54 505.00 3022.00 .75 1.000 .000

111.39 606.00 3036.00 .75 1.000 .000

109.02 218.00 3686.00 .75 1.000 .000

109.64 302.00 3699.00 .75 1.000 .000

110.38 404.00 3709.00 .75 1.000 .000

111.09 501.00 3723.00 .75 1.000 .000

111.83 604.00 3738.00 .75 1.000 .000

109.68 204.00 4239.00 .75 1.000 .000

110.34 309.00 4247.00 .75 1.000 .000

110.93 404.00 4257.00 .75 1.000 .000

111.58 508.00 4269.00 .75 1.000 .000

112.19 606.00 4278.00 .75 1.000 .000

110.63 212.00 4899.00 .75 1.000 .000

111.14 310.00 4916.00 .75 1.000 .000

111.59 403.00 4909.00 .75 1.000 .000

112.11 506.00 4929.00 .75 1.000 .000

112.63 608.00 4955.00 .75 1.000 .000

107.90 213.00 3680.00 .75 1.375 .000

109.90 305.00 3692.00 .75 1.375 .000

111.70 403.00 3717.00 .75 1.375 .000

112.90 509.00 3736.00 .75 1.375 .000

113.30 606.00 3752.00 .75 1.375 .000

108.70 213.00 4298.00 .75 1.375 .000

111.60 314.00 4310.00 .75 1.375 .000

112.50 402.00 4326.00 .75 1.375 .000

114.00 508.00 4338.00 .75 1.375 .000

114.80 607.00 4357.00 .75 1.375 .000
98

Sound Power 

dBA 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

107.30 212.00 4977.00 .75 1.375 .000

108.00 303.00 4998.00 .75 1.375 .000

112.30 398.00 5013.00 .75 1.375 .000

114.20 511.00 5037.00 .75 1.375 .000

116.20 606.00 5060.00 .75 1.375 .000

110.50 211.00 5617.00 .75 1.375 .000

113.10 306.00 5632.00 .75 1.375 .000

113.60 404.00 5646.00 .75 1.375 .000

117.00 512.00 5671.00 .75 1.375 .000

116.10 595.00 5686.00 .75 1.375 .000

111.90 212.00 6260.00 .75 1.375 .000

113.60 312.00 6287.00 .75 1.375 .000

114.90 404.00 6317.00 .75 1.375 .000

115.90 507.00 6347.00 .75 1.375 .000

116.90 598.00 6306.00 .75 1.375 .000

Utilizing the sound power level as the dependent variable and the rotational speed, thrust, drilling 

method, bit size and drill steel type as the independent variables, a statistical approach utilizing a 

multiple linear regression analysis, was performed to fit the data and to provide an accurate 

representation for obtaining one equation to determine the sound power level given any drilling 

method or drilling configuration used. Table 5.16 represents the regression coefficients determined 

from the statistical model run. 

Table 5.16 Regression Coefficients Determined from the Statistical Model 

(Constant) 101.708

Water -1.766

Thrust .001

Speed .007

Bit Size 2.568

Drill Steel -.640

5.4.2 Statistical Accuracy of the Model

 The statistical accuracy of the data fit is shown in the histogram below (figure 5.8) and 

tabulated in table 5.17. Additionally, R2

, the coefficient of determination, or the measure of the 
99

goodness of fit of a linear model, was equal to .849, indicating the model to be a good fit or 

representation of the data set. 

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0

Unstandardized Residual (dBA)

90

85

80

75

70

65

60

55

50

45

40

35

30

25

20

15

10

5

0

Frequency

1 3 5

10

38

57

73

81

67

57

47

21

10

6 6 4

Figure 5.8 Histogram Representing the Fit Accuracy of Statistical Run of Model 

As shown in figure 5.8, the data follows a nice “bell-shaped” curve, indicating the data set is 

normally distributed. Also, figure 5.8 displays, graphically, the residuals (laboratory minus model 

values of sound power) from the data set. As shown, five residuals were determined to be plus or 

minus 3.5 to 4.0 dBA and nine residuals at plus or minus 3.0 to 3.5 dBA. The remaining 472 

residuals all fell within plus or minus 0 to 3.0 dBA. Therefore, 97% of the data fell within a residual 
100

of 0 to 3.0 dBA and would be well received within the acoustical community, particularly during 

prediction exercises. 

Table 5.17 Comparing Laboratory Results to Model Results (Sound Power Level) 

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

106.60 209.00 2239.00 .00 1.000 1.000 107.75978 -1.15978

107.10 210.00 2228.00 .00 1.000 1.000 107.75385 -.65385

108.30 306.00 2282.00 .00 1.000 1.000 108.40316 -.10316

107.40 305.00 2272.00 .00 1.000 1.000 108.38604 -.98604

108.40 400.00 2324.00 .00 1.000 1.000 109.02700 -.62700

108.60 402.00 2280.00 .00 1.000 1.000 108.99101 -.39101

109.50 514.00 2220.00 .00 1.000 1.000 109.61354 -.11354

108.80 609.00 2241.00 .00 1.000 1.000 110.22048 -1.42048

107.80 208.00 2711.00 .00 1.000 1.000 108.27164 -.47164

109.90 305.00 2696.00 .00 1.000 1.000 108.85136 1.04864

109.40 306.00 2705.00 .00 1.000 1.000 108.86739 .53261

109.90 402.00 2701.00 .00 1.000 1.000 109.45304 .44696

110.10 509.00 2865.00 .00 1.000 1.000 110.29067 -.19067

110.10 602.00 2882.00 .00 1.000 1.000 110.88093 -.78093

110.20 215.00 3435.00 .00 1.000 1.000 109.10923 1.09077

110.90 304.00 3451.00 .00 1.000 1.000 109.67380 1.22620

109.60 311.00 3620.00 .00 1.000 1.000 109.90230 -.30230

111.50 405.00 3487.00 .00 1.000 1.000 110.33409 1.16591

111.60 404.00 3483.00 .00 1.000 1.000 110.32355 1.27645

110.50 510.00 3628.00 .00 1.000 1.000 111.13419 -.63419

111.10 607.00 3653.00 .00 1.000 1.000 111.75781 -.65781

111.20 208.00 4085.00 .00 1.000 1.000 109.77955 1.42045

111.60 305.00 4097.00 .00 1.000 1.000 110.38891 1.21109

111.50 404.00 4111.00 .00 1.000 1.000 111.01276 .48724

111.40 406.00 4283.00 .00 1.000 1.000 111.21381 .18619

110.90 509.00 4291.00 .00 1.000 1.000 111.85566 -.95566

110.90 604.00 4314.00 .00 1.000 1.000 112.46480 -1.56480

110.40 221.00 4744.00 .00 1.000 1.000 110.58269 -.18269

110.60 223.00 4778.00 .00 1.000 1.000 110.63229 -.03229

112.30 308.00 4769.00 .00 1.000 1.000 111.14485 1.15515

112.60 404.00 4800.00 .00 1.000 1.000 111.76891 .83109

110.40 406.00 4821.00 .00 1.000 1.000 111.80425 -1.40425

111.40 507.00 4870.00 .00 1.000 1.000 112.47880 -1.07880

110.70 607.00 4822.00 .00 1.000 1.000 113.04075 -2.34075

112.00 211.00 4745.00 .00 1.000 1.000 110.52232 1.47768

105.50 203.00 2268.00 .00 1.375 1.000 108.65847 -3.15847
101

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

106.10 306.00 2285.00 .00 1.375 1.000 109.31019 -3.21019

108.60 402.00 2293.00 .00 1.375 1.000 109.90901 -1.30901

108.80 211.00 2915.00 .00 1.375 1.000 109.41770 -.61770

108.50 215.00 2908.00 .00 1.375 1.000 109.43460 -.93460

108.50 308.00 2925.00 .00 1.375 1.000 110.02486 -1.52486

108.30 311.00 2923.00 .00 1.375 1.000 110.04110 -1.74110

109.60 404.00 2952.00 .00 1.375 1.000 110.64453 -1.04453

108.50 211.00 3527.00 .00 1.375 1.000 110.08935 -1.58935

108.30 213.00 3522.00 .00 1.375 1.000 110.09615 -1.79615

109.60 306.00 3545.00 .00 1.375 1.000 110.69300 -1.09300

108.90 305.00 3545.00 .00 1.375 1.000 110.68685 -1.78685

110.10 402.00 3580.00 .00 1.375 1.000 111.32145 -1.22145

110.20 402.00 3567.00 .00 1.375 1.000 111.30718 -1.10718

111.80 208.00 4183.00 .00 1.375 1.000 110.79084 1.00916

113.00 306.00 4181.00 .00 1.375 1.000 111.39098 1.60902

111.70 309.00 4228.00 .00 1.375 1.000 111.46100 .23900

113.00 403.00 4239.00 .00 1.375 1.000 112.05082 .94918

112.50 405.00 4360.00 .00 1.375 1.000 112.19591 .30409

111.30 511.00 4303.00 .00 1.375 1.000 112.78486 -1.48486

110.00 606.00 4405.00 .00 1.375 1.000 113.48070 -3.48070

112.10 210.00 4842.00 .00 1.375 1.000 111.52637 .57363

112.30 307.00 4865.00 .00 1.375 1.000 112.14780 .15220

112.70 314.00 4923.00 .00 1.375 1.000 112.25447 .44553

114.20 405.00 4886.00 .00 1.375 1.000 112.77318 1.42682

111.00 509.00 5082.00 .00 1.375 1.000 113.62749 -2.62749

113.60 215.00 5415.00 .00 1.375 1.000 112.18594 1.41406

112.50 307.00 5438.00 .00 1.375 1.000 112.77664 -.27664

113.10 403.00 5446.00 .00 1.375 1.000 113.37546 -.27546

113.40 207.00 6195.00 .00 1.375 1.000 112.99280 .40720

112.70 212.00 6242.00 .00 1.375 1.000 113.07511 -.37511

114.30 312.00 6234.00 .00 1.375 1.000 113.68096 .61904

113.10 310.00 6218.00 .00 1.375 1.000 113.65110 -.55110

114.80 402.00 6167.00 .00 1.375 1.000 114.16059 .63941

114.10 402.00 6237.00 .00 1.375 1.000 114.23741 -.13741

111.40 155.00 6225.00 .00 1.375 1.000 112.70612 -1.30612

112.80 402.00 4180.00 .00 1.375 1.000 111.97993 .82007

110.20 318.00 2979.00 .00 1.375 1.000 110.14559 .05441

110.00 223.00 3609.00 .00 1.375 1.000 110.25309 -.25309

112.10 411.00 3625.00 .00 1.375 1.000 111.42615 .67385

112.00 405.00 3628.00 .00 1.375 1.000 111.39257 .60743

110.50 312.00 3623.00 .00 1.375 1.000 110.81548 -.31548
102

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

109.60 221.00 3615.00 .00 1.375 1.000 110.24738 -.64738

109.00 206.00 2334.00 .00 1.000 .000 108.64027 .35973

110.20 303.00 2333.00 .00 1.000 .000 109.23536 .96464

111.00 404.00 2344.00 .00 1.000 .000 109.86820 1.13180

110.20 506.00 2226.00 .00 1.000 .000 110.36562 -.16562

112.80 602.00 2241.00 .00 1.000 .000 110.97212 1.82788

111.30 208.00 2919.00 .00 1.000 .000 109.29458 2.00542

112.70 305.00 2933.00 .00 1.000 .000 109.90613 2.79387

112.30 401.00 2955.00 .00 1.000 .000 110.52031 1.77969

110.50 406.00 2840.00 .00 1.000 .000 110.42484 .07516

111.10 508.00 2877.00 .00 1.000 .000 111.09236 .00764

112.50 606.00 2890.00 .00 1.000 .000 111.70896 .79104

112.70 207.00 3587.00 .00 1.000 .000 110.02154 2.67846

111.60 209.00 3588.00 .00 1.000 .000 110.03493 1.56507

112.80 307.00 3622.00 .00 1.000 .000 110.67457 2.12543

113.40 307.00 3607.00 .00 1.000 .000 110.65811 2.74189

113.20 400.00 3642.00 .00 1.000 .000 111.26813 1.93187

113.40 398.00 3660.00 .00 1.000 .000 111.27559 2.12441

113.60 508.00 3622.00 .00 1.000 .000 111.90997 1.69003

112.90 606.00 3651.00 .00 1.000 .000 112.54414 .35586

112.50 218.00 4294.00 .00 1.000 .000 110.86505 1.63495

110.80 208.00 4238.00 .00 1.000 .000 110.74213 .05787

113.30 305.00 4254.00 .00 1.000 .000 111.35588 1.94412

112.70 402.00 4258.00 .00 1.000 .000 111.95646 .74354

114.00 508.00 4344.00 .00 1.000 .000 112.70234 1.29766

112.90 607.00 4362.00 .00 1.000 .000 113.33058 -.43058

112.30 209.00 4818.00 .00 1.000 .000 111.38481 .91519

113.00 211.00 4916.00 .00 1.000 .000 111.50465 1.49535

113.20 306.00 4869.00 .00 1.000 .000 112.03697 1.16303

113.30 407.00 4898.00 .00 1.000 .000 112.68957 .61043

114.30 510.00 4979.00 .00 1.000 .000 113.41153 .88847

113.00 607.00 4995.00 .00 1.000 .000 114.02528 -1.02528

106.30 212.00 2283.00 .00 1.375 .000 109.52491 -3.22491

109.50 309.00 2302.00 .00 1.375 .000 110.14195 -.64195

110.40 402.00 2326.00 .00 1.375 .000 110.73989 -.33989

109.70 209.00 2892.00 .00 1.375 .000 110.17483 -.47483

110.40 308.00 2914.00 .00 1.375 .000 110.80745 -.40745

113.00 405.00 2943.00 .00 1.375 .000 111.43547 1.56453

109.60 208.00 3559.00 .00 1.375 .000 110.90069 -1.30069

111.90 304.00 3575.00 .00 1.375 .000 111.50829 .39171

112.50 313.00 3715.00 .00 1.375 .000 111.71725 .78275

112.80 402.00 3591.00 .00 1.375 .000 112.12819 .67181
103

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

113.30 405.00 3741.00 .00 1.375 .000 112.31124 .98876

112.80 214.00 4321.00 .00 1.375 .000 111.77384 1.02616

114.10 309.00 4316.00 .00 1.375 .000 112.35225 1.74775

113.30 313.00 4342.00 .00 1.375 .000 112.40536 .89464

114.60 402.00 4330.00 .00 1.375 .000 112.93921 1.66079

114.60 403.00 4357.00 .00 1.375 .000 112.97499 1.62501

114.70 505.00 4407.00 .00 1.375 .000 113.65678 1.04322

114.10 604.00 4420.00 .00 1.375 .000 114.27953 -.17953

113.80 212.00 4979.00 .00 1.375 .000 112.48368 1.31632

113.80 310.00 5001.00 .00 1.375 .000 113.11016 .68984

113.70 309.00 4958.00 .00 1.375 .000 113.05682 .64318

115.50 405.00 5047.00 .00 1.375 .000 113.74453 1.75547

114.30 409.00 4973.00 .00 1.375 .000 113.68791 .61209

114.70 511.00 4982.00 .00 1.375 .000 114.32470 .37530

113.90 604.00 4992.00 .00 1.375 .000 114.90728 -1.00728

114.10 211.00 5558.00 .00 1.375 .000 113.11296 .98704

113.30 218.00 5485.00 .00 1.375 .000 113.07587 .22413

114.40 313.00 5497.00 .00 1.375 .000 113.67294 .72706

114.30 310.00 5502.00 .00 1.375 .000 113.65999 .64001

116.10 405.00 5576.00 .00 1.375 .000 114.32509 1.77491

115.20 408.00 5510.00 .00 1.375 .000 114.27110 .92890

114.70 511.00 5523.00 .00 1.375 .000 114.91843 -.21843

113.40 600.00 5544.00 .00 1.375 .000 115.48850 -2.08850

114.10 212.00 6342.00 .00 1.375 .000 113.97952 .12048

114.60 211.00 6224.00 .00 1.375 .000 113.84387 .75613

115.20 311.00 6360.00 .00 1.375 .000 114.60776 .59224

115.70 309.00 6234.00 .00 1.375 .000 114.45718 1.24282

116.20 404.00 6382.00 .00 1.375 .000 115.20350 .99650

115.30 402.00 6244.00 .00 1.375 .000 115.03976 .26024

114.30 506.00 6256.00 .00 1.375 .000 115.69214 -1.39214

113.20 603.00 6205.00 .00 1.375 .000 116.23236 -3.03236

102.10 207.00 2313.00 3.00 1.000 1.000 102.73010 -.63010

102.00 211.00 2306.00 3.00 1.000 1.000 102.74700 -.74700

102.20 309.00 2321.00 3.00 1.000 1.000 103.36580 -1.16580

104.00 308.00 2318.00 3.00 1.000 1.000 103.35636 .64364

102.90 402.00 2335.00 3.00 1.000 1.000 103.95277 -1.05277

105.50 405.00 2329.00 3.00 1.000 1.000 103.96462 1.53538

102.40 503.00 2448.00 3.00 1.000 1.000 104.69755 -2.29755

103.60 605.00 2461.00 3.00 1.000 1.000 105.33874 -1.73874

103.50 205.00 2909.00 3.00 1.000 1.000 103.37190 .12810

104.30 311.00 3084.00 3.00 1.000 1.000 104.21546 .08454

104.40 312.00 3005.00 3.00 1.000 1.000 104.13490 .26510
104

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

103.90 402.00 2978.00 3.00 1.000 1.000 104.65844 -.75844

103.20 403.00 3098.00 3.00 1.000 1.000 104.79628 -1.59628

105.40 508.00 3113.00 3.00 1.000 1.000 105.45810 -.05810

102.50 507.00 3012.00 3.00 1.000 1.000 105.34111 -2.84111

105.70 605.00 3129.00 3.00 1.000 1.000 106.07185 -.37185

104.40 201.00 3591.00 3.00 1.000 1.000 104.09578 .30422

106.30 308.00 3605.00 3.00 1.000 1.000 104.76880 1.53120

105.80 314.00 3601.00 3.00 1.000 1.000 104.80128 .99872

106.80 401.00 3617.00 3.00 1.000 1.000 105.35357 1.44643

107.70 604.00 3820.00 3.00 1.000 1.000 106.82405 .87595

105.80 210.00 4275.00 3.00 1.000 1.000 104.90176 .89824

105.70 213.00 4272.00 3.00 1.000 1.000 104.91691 .78309

107.00 309.00 4285.00 3.00 1.000 1.000 105.52122 1.47878

106.50 315.00 4285.00 3.00 1.000 1.000 105.55810 .94190

107.30 411.00 4288.00 3.00 1.000 1.000 106.15143 1.14857

108.60 411.00 4296.00 3.00 1.000 1.000 106.16021 2.43979

105.80 508.00 4411.00 3.00 1.000 1.000 106.88261 -1.08261

106.70 595.00 4434.00 3.00 1.000 1.000 107.44257 -.74257

106.20 206.00 4888.00 3.00 1.000 1.000 105.54993 .65007

106.30 205.00 4899.00 3.00 1.000 1.000 105.55585 .74415

107.60 302.00 4898.00 3.00 1.000 1.000 106.15094 1.44906

108.20 307.00 4916.00 3.00 1.000 1.000 106.20143 1.99857

108.10 412.00 4927.00 3.00 1.000 1.000 106.85886 1.24114

108.90 412.00 4912.00 3.00 1.000 1.000 106.84240 2.05760

107.10 510.00 4876.00 3.00 1.000 1.000 107.40522 -.30522

106.20 607.00 4902.00 3.00 1.000 1.000 108.02994 -1.82994

105.80 407.00 4398.00 3.00 1.000 1.000 106.24757 -.44757

105.00 212.00 4371.00 3.00 1.000 1.000 105.01941 -.01941

106.10 400.00 3028.00 3.00 1.000 1.000 104.70102 1.39898

103.40 304.00 2953.00 3.00 1.000 1.000 104.02866 -.62866

102.70 215.00 4368.00 3.00 1.000 1.000 105.03456 -2.33456

103.50 305.00 2985.00 3.00 1.000 1.000 104.06993 -.56993

104.90 210.00 2335.00 3.00 1.375 1.000 103.67642 1.22358

103.90 208.00 2337.00 3.00 1.375 1.000 103.66632 .23368

104.30 310.00 2340.00 3.00 1.375 1.000 104.29653 .00347

105.00 311.00 2337.00 3.00 1.375 1.000 104.29939 .70061

106.60 406.00 2351.00 3.00 1.375 1.000 104.89865 1.70135

105.50 407.00 2347.00 3.00 1.375 1.000 104.90040 .59960

103.50 211.00 2916.00 3.00 1.375 1.000 104.32019 -.82019

103.60 209.00 2915.00 3.00 1.375 1.000 104.30680 -.70680

104.90 305.00 2937.00 3.00 1.375 1.000 104.92099 -.02099

104.50 305.00 2935.00 3.00 1.375 1.000 104.91879 -.41879
105

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

106.10 411.00 2959.00 3.00 1.375 1.000 105.59664 .50336

106.70 411.00 2955.00 3.00 1.375 1.000 105.59225 1.10775

105.90 218.00 3611.00 3.00 1.375 1.000 105.12595 .77405

105.30 214.00 3609.00 3.00 1.375 1.000 105.09917 .20083

105.10 313.00 3623.00 3.00 1.375 1.000 105.72302 -.62302

106.00 311.00 3621.00 3.00 1.375 1.000 105.70853 .29147

108.00 408.00 3709.00 3.00 1.375 1.000 106.40130 1.59870

108.50 411.00 3701.00 3.00 1.375 1.000 106.41096 2.08904

106.80 217.00 4187.00 3.00 1.375 1.000 105.75195 1.04805

106.00 215.00 4188.00 3.00 1.375 1.000 105.74075 .25925

108.10 313.00 4210.00 3.00 1.375 1.000 106.36723 1.73277

107.60 307.00 4202.00 3.00 1.375 1.000 106.32157 1.27843

108.80 408.00 4233.00 3.00 1.375 1.000 106.97637 1.82363

108.90 407.00 4230.00 3.00 1.375 1.000 106.96693 1.93307

108.90 510.00 4456.00 3.00 1.375 1.000 107.84802 1.05198

109.20 603.00 4485.00 3.00 1.375 1.000 108.45145 .74855

106.50 211.00 4833.00 3.00 1.375 1.000 106.42403 .07597

106.30 217.00 4808.00 3.00 1.375 1.000 106.43347 -.13347

108.50 309.00 4816.00 3.00 1.375 1.000 107.00771 1.49229

107.40 310.00 4826.00 3.00 1.375 1.000 107.02483 .37517

107.40 403.00 4839.00 3.00 1.375 1.000 107.61070 -.21070

108.30 403.00 4840.00 3.00 1.375 1.000 107.61180 .68820

109.80 506.00 5110.00 3.00 1.375 1.000 108.54118 1.25882

110.80 604.00 5136.00 3.00 1.375 1.000 109.17205 1.62795

108.00 210.00 5649.00 3.00 1.375 1.000 107.31342 .68658

107.30 212.00 5644.00 3.00 1.375 1.000 107.32022 -.02022

109.20 311.00 5662.00 3.00 1.375 1.000 107.94846 1.25154

108.60 310.00 5512.00 3.00 1.375 1.000 107.77769 .82231

110.20 411.00 5669.00 3.00 1.375 1.000 108.57077 1.62923

108.70 401.00 5666.00 3.00 1.375 1.000 108.50601 .19399

110.30 507.00 5740.00 3.00 1.375 1.000 109.23873 1.06127

110.40 604.00 5755.00 3.00 1.375 1.000 109.85138 .54862

108.00 206.00 6298.00 3.00 1.375 1.000 108.00109 -.00109

109.40 178.00 6270.00 3.00 1.375 1.000 107.79826 1.60174

109.70 308.00 6307.00 3.00 1.375 1.000 108.63789 1.06211

109.00 307.00 6143.00 3.00 1.375 1.000 108.45175 .54825

109.60 407.00 6320.00 3.00 1.375 1.000 109.26063 .33937

109.30 402.00 6148.00 3.00 1.375 1.000 109.04114 .25886

108.40 504.00 6161.00 3.00 1.375 1.000 109.68232 -1.28232

109.40 601.00 6369.00 3.00 1.375 1.000 110.50679 -1.10679

110.40 578.00 6311.00 3.00 1.375 1.000 110.30177 .09823

108.60 310.00 6230.00 3.00 1.375 1.000 108.56567 .03433
106

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

110.70 506.00 6009.00 3.00 1.375 1.000 109.52780 1.17220

109.90 562.00 6018.00 3.00 1.375 1.000 109.88187 .01813

109.10 565.00 5692.00 3.00 1.375 1.000 109.54254 -.44254

108.80 571.00 5286.00 3.00 1.375 1.000 109.13384 -.33384

108.60 472.00 5270.00 3.00 1.375 1.000 108.50780 .09220

108.30 415.00 5249.00 3.00 1.375 1.000 108.13442 .16558

108.40 332.00 5229.00 3.00 1.375 1.000 107.60233 .79767

110.00 544.00 4868.00 3.00 1.375 1.000 108.50915 1.49085

110.90 577.00 4554.00 3.00 1.375 1.000 108.36738 2.53262

109.40 579.00 4223.00 3.00 1.375 1.000 108.01641 1.38359

107.70 572.00 3987.00 3.00 1.375 1.000 107.71438 -.01438

109.40 582.00 3734.00 3.00 1.375 1.000 107.49819 1.90181

108.60 577.00 4892.00 3.00 1.375 1.000 108.73832 -.13832

109.10 408.00 3703.00 3.00 1.375 1.000 106.39471 2.70529

109.70 313.00 4210.00 3.00 1.375 1.000 106.36723 3.33277

110.30 413.00 4233.00 3.00 1.375 1.000 107.00710 3.29290

108.80 405.00 4841.00 3.00 1.375 1.000 107.62519 1.17481

106.10 214.00 5496.00 3.00 1.375 1.000 107.17009 -1.07009

108.70 301.00 5653.00 3.00 1.375 1.000 107.87712 .82288

108.70 310.00 5653.00 3.00 1.375 1.000 107.93244 .76756

110.40 409.00 5661.00 3.00 1.375 1.000 108.54970 1.85030

109.30 300.00 5711.00 3.00 1.375 1.000 107.93463 1.36537

110.50 202.00 5057.00 3.00 1.375 1.000 106.61455 3.88545

100.60 207.00 2314.00 3.00 1.000 .000 103.52586 -2.92586

100.50 315.00 2332.00 3.00 1.000 .000 104.20941 -3.70941

103.80 404.00 2347.00 3.00 1.000 .000 104.77289 -.97289

105.60 508.00 2295.00 3.00 1.000 .000 105.35504 .24496

105.90 607.00 2306.00 3.00 1.000 .000 105.97559 -.07559

101.50 214.00 2924.00 3.00 1.000 .000 104.23834 -2.73834

104.20 198.00 2932.00 3.00 1.000 .000 104.14878 .05122

102.80 306.00 2939.00 3.00 1.000 .000 104.82026 -2.02026

104.80 406.00 2957.00 3.00 1.000 .000 105.45464 -.65464

105.70 403.00 3121.00 3.00 1.000 .000 105.61619 .08381

107.70 507.00 3135.00 3.00 1.000 .000 106.27076 1.42924

107.20 602.00 3147.00 3.00 1.000 .000 106.86783 .33217

103.80 215.00 3670.00 3.00 1.000 .000 105.06319 -1.26319

103.90 204.00 3665.00 3.00 1.000 .000 104.99010 -1.09010

105.30 316.00 3715.00 3.00 1.000 .000 105.73335 -.43335

105.90 304.00 3720.00 3.00 1.000 .000 105.66509 .23491

108.20 409.00 3578.00 3.00 1.000 .000 106.15460 2.04540

107.90 402.00 3581.00 3.00 1.000 .000 106.11487 1.78513

107.50 517.00 3741.00 3.00 1.000 .000 106.99729 .50271
107

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

108.30 504.00 3644.00 3.00 1.000 .000 106.81093 1.48907

108.30 606.00 3755.00 3.00 1.000 .000 107.55967 .74033

106.90 605.00 3657.00 3.00 1.000 .000 107.44597 -.54597

101.70 202.00 4273.00 3.00 1.000 .000 105.64506 -3.94506

105.20 216.00 4349.00 3.00 1.000 .000 105.81452 -.61452

103.80 310.00 4272.00 3.00 1.000 .000 106.30776 -2.50776

106.10 412.00 4297.00 3.00 1.000 .000 106.96212 -.86212

104.80 398.00 4296.00 3.00 1.000 .000 106.87498 -2.07498

108.10 511.00 4382.00 3.00 1.000 .000 107.66389 .43611

108.40 614.00 4392.00 3.00 1.000 .000 108.30793 .09207

105.10 215.00 4793.00 3.00 1.000 .000 106.29565 -1.19565

104.70 209.00 4930.00 3.00 1.000 .000 106.40912 -1.70912

105.60 306.00 4940.00 3.00 1.000 .000 107.01629 -1.41629

105.50 314.00 4806.00 3.00 1.000 .000 106.91840 -1.41840

105.70 414.00 4944.00 3.00 1.000 .000 107.68447 -1.98447

108.10 509.00 4831.00 3.00 1.000 .000 108.14436 -.04436

108.30 578.00 4850.00 3.00 1.000 .000 108.58930 -.28930

105.20 409.00 3696.00 3.00 1.000 .000 106.28411 -1.08411

104.00 201.00 4694.00 3.00 1.000 .000 106.10095 -2.10095

106.70 401.00 3726.00 3.00 1.000 .000 106.26786 .43214

103.70 319.00 3682.00 3.00 1.000 .000 105.71558 -2.01558

106.60 403.00 2957.00 3.00 1.000 .000 105.43620 1.16380

104.30 307.00 3618.00 3.00 1.000 .000 105.57158 -1.27158

106.20 400.00 3635.00 3.00 1.000 .000 106.16184 .03816

104.20 209.00 2338.00 3.00 1.375 .000 104.46823 -.26823

105.00 311.00 2360.00 3.00 1.375 .000 105.11929 -.11929

106.10 403.00 2378.00 3.00 1.375 .000 105.70451 .39549

104.20 213.00 2915.00 3.00 1.375 .000 105.12605 -.92605

106.30 309.00 2937.00 3.00 1.375 .000 105.74024 .55976

107.00 402.00 2961.00 3.00 1.375 .000 106.33818 .66182

104.90 209.00 3593.00 3.00 1.375 .000 105.84555 -.94555

105.00 312.00 3606.00 3.00 1.375 .000 106.49288 -1.49288

106.10 400.00 3622.00 3.00 1.375 .000 107.05131 -.95131

104.90 212.00 4402.00 3.00 1.375 .000 106.75184 -1.85184

105.70 208.00 4207.00 3.00 1.375 .000 106.51325 -.81325

106.80 302.00 4227.00 3.00 1.375 .000 107.11295 -.31295

106.40 309.00 4277.00 3.00 1.375 .000 107.21084 -.81084

107.50 411.00 4258.00 3.00 1.375 .000 107.81691 -.31691

107.60 398.00 4286.00 3.00 1.375 .000 107.76774 -.16774

108.00 505.00 4454.00 3.00 1.375 .000 108.60976 -.60976

109.20 604.00 4478.00 3.00 1.375 .000 109.24458 -.04458

106.40 207.00 4848.00 3.00 1.375 .000 107.21058 -.81058
108

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

106.40 206.00 4846.00 3.00 1.375 .000 107.20224 -.80224

107.90 315.00 4859.00 3.00 1.375 .000 107.88645 .01355

107.50 313.00 4852.00 3.00 1.375 .000 107.86647 -.36647

110.50 407.00 4867.00 3.00 1.375 .000 108.46068 2.03932

107.20 401.00 5000.00 3.00 1.375 .000 108.56977 -1.36977

108.00 506.00 5014.00 3.00 1.375 .000 109.23049 -1.23049

109.10 602.00 5027.00 3.00 1.375 .000 109.83480 -.73480

107.50 201.00 5435.00 3.00 1.375 .000 107.81791 -.31791

106.90 216.00 5595.00 3.00 1.375 .000 108.08570 -1.18570

109.30 315.00 5539.00 3.00 1.375 .000 108.63272 .66728

108.60 308.00 5539.00 3.00 1.375 .000 108.58970 .01030

108.80 413.00 5561.00 3.00 1.375 .000 109.25920 -.45920

109.20 424.00 5586.00 3.00 1.375 .000 109.35425 -.15425

109.00 510.00 5642.00 3.00 1.375 .000 109.94428 -.94428

108.90 604.00 5664.00 3.00 1.375 .000 110.54618 -1.64618

108.60 204.00 6200.00 3.00 1.375 .000 108.67591 -.07591

107.70 196.00 6155.00 3.00 1.375 .000 108.57735 -.87735

108.80 316.00 6197.00 3.00 1.375 .000 109.36100 -.56100

109.10 304.00 6137.00 3.00 1.375 .000 109.22140 -.12140

110.80 405.00 6219.00 3.00 1.375 .000 109.93216 .86784

110.00 408.00 6213.00 3.00 1.375 .000 109.94402 .05598

109.40 508.00 6334.00 3.00 1.375 .000 110.69144 -1.29144

110.20 598.00 6323.00 3.00 1.375 .000 111.23253 -1.03253

110.70 604.00 6346.00 3.00 1.375 .000 111.29465 -.59465

112.20 556.00 6299.00 3.00 1.375 .000 110.94805 1.25195

110.50 453.00 6274.00 3.00 1.375 .000 110.28754 .21246

108.50 436.00 6007.00 3.00 1.375 .000 109.89003 -1.39003

109.00 561.00 6020.00 3.00 1.375 .000 110.67258 -1.67258

108.60 543.00 5694.00 3.00 1.375 .000 110.20418 -1.60418

108.90 428.00 5668.00 3.00 1.375 .000 109.46882 -.56882

108.10 428.00 5266.00 3.00 1.375 .000 109.02764 -.92764

109.30 579.00 5280.00 3.00 1.375 .000 109.97109 -.67109

109.00 453.00 6004.00 3.00 1.375 .000 109.99123 -.99123

108.40 596.00 4993.00 3.00 1.375 .000 109.76061 -1.36061

108.10 481.00 4969.00 3.00 1.375 .000 109.02745 -.92745

107.50 401.00 4933.00 3.00 1.375 .000 108.49624 -.99624

107.30 403.00 4610.00 3.00 1.375 .000 108.15405 -.85405

107.70 484.00 4622.00 3.00 1.375 .000 108.66507 -.96507

109.00 590.00 4636.00 3.00 1.375 .000 109.33193 -.33193

108.50 586.00 4348.00 3.00 1.375 .000 108.99128 -.49128

110.20 473.00 4216.00 3.00 1.375 .000 108.15189 2.04811

106.10 376.00 4179.00 3.00 1.375 .000 107.51509 -1.41509
109

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

107.90 475.00 3714.00 3.00 1.375 .000 107.61325 .28675

110.10 555.00 3728.00 3.00 1.375 .000 108.12032 1.97968

109.60 510.00 3709.00 3.00 1.375 .000 107.82288 1.77712

109.00 213.00 4836.00 3.00 1.375 .000 107.23428 1.76572

109.80 304.00 4853.00 3.00 1.375 .000 107.81225 1.98775

107.90 304.00 5453.00 3.00 1.375 .000 108.47073 -.57073

110.40 405.00 5468.00 3.00 1.375 .000 109.10797 1.29203

106.30 403.00 4432.00 3.00 1.375 .000 107.95870 -1.65870

105.20 205.00 4265.00 3.00 1.375 .000 106.55846 -1.35846

105.60 213.00 4971.00 3.00 1.375 .000 107.38244 -1.78244

106.30 210.00 5523.00 3.00 1.375 .000 107.96980 -1.66980

108.00 401.00 5624.00 3.00 1.375 .000 109.25459 -1.25459

106.90 405.00 6231.00 3.00 1.375 .000 109.94533 -3.04533

107.30 218.00 6210.00 3.00 1.375 .000 108.77293 -1.47293

104.60 214.00 2418.00 .75 1.000 1.000 106.71231 -2.11231

105.80 307.00 2432.00 .75 1.000 1.000 107.29927 -1.49927

106.70 402.00 2445.00 .75 1.000 1.000 107.89744 -1.19744

107.40 507.00 2458.00 .75 1.000 1.000 108.55706 -1.15706

107.70 593.00 2472.00 .75 1.000 1.000 109.10101 -1.40101

104.50 216.00 2978.00 .75 1.000 1.000 107.33918 -2.83918

107.10 301.00 2993.00 .75 1.000 1.000 107.87808 -.77808

107.90 408.00 3004.00 .75 1.000 1.000 108.54780 -.64780

108.50 510.00 3004.00 .75 1.000 1.000 109.17472 -.67472

109.20 605.00 3012.00 .75 1.000 1.000 109.76739 -.56739

106.30 213.00 3685.00 .75 1.000 1.000 108.09665 -1.79665

108.50 306.00 3700.00 .75 1.000 1.000 108.68471 -.18471

109.10 404.00 3716.00 .75 1.000 1.000 109.30461 -.20461

109.70 509.00 3734.00 .75 1.000 1.000 109.96972 -.26972

110.10 607.00 3758.00 .75 1.000 1.000 110.59839 -.49839

107.90 216.00 4335.00 .75 1.000 1.000 108.82844 -.92844

109.20 305.00 4350.00 .75 1.000 1.000 109.39192 -.19192

110.50 407.00 4364.00 .75 1.000 1.000 110.03420 .46580

111.10 508.00 4381.00 .75 1.000 1.000 110.67363 .42637

111.20 606.00 4397.00 .75 1.000 1.000 111.29353 -.09353

108.90 210.00 4928.00 .75 1.000 1.000 109.44236 -.54236

110.20 307.00 4947.00 .75 1.000 1.000 110.05940 .14060

110.90 405.00 4966.00 .75 1.000 1.000 110.68259 .21741

112.20 502.00 4994.00 .75 1.000 1.000 111.30950 .89050

112.50 584.00 4825.00 .75 1.000 1.000 111.62803 .87197

108.40 219.00 3748.00 .75 1.375 1.000 109.10640 -.70640

109.70 310.00 3752.00 .75 1.375 1.000 109.67011 .02989

111.10 402.00 3756.00 .75 1.375 1.000 110.23995 .86005
110

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

111.80 510.00 3779.00 .75 1.375 1.000 110.92899 .87101

112.60 606.00 3789.00 .75 1.375 1.000 111.53001 1.06999

110.90 214.00 4352.00 .75 1.375 1.000 109.73854 1.16146

112.00 311.00 4361.00 .75 1.375 1.000 110.34461 1.65539

112.50 406.00 4371.00 .75 1.375 1.000 110.93948 1.56052

112.70 510.00 4383.00 .75 1.375 1.000 111.59186 1.10814

113.10 609.00 4396.00 .75 1.375 1.000 112.21461 .88539

111.50 218.00 4953.00 .75 1.375 1.000 110.42270 1.07730

111.30 309.00 4965.00 .75 1.375 1.000 110.99518 .30482

112.10 401.00 4967.00 .75 1.375 1.000 111.56284 .53716

112.60 512.00 4986.00 .75 1.375 1.000 112.26592 .33408

113.40 607.00 5007.00 .75 1.375 1.000 112.87287 .52713

111.80 216.00 5523.00 .75 1.375 1.000 111.03597 .76403

110.40 312.00 5528.00 .75 1.375 1.000 111.63150 -1.23150

113.60 403.00 5942.00 .75 1.375 1.000 112.64516 .95484

113.60 510.00 5558.00 .75 1.375 1.000 112.88138 .71862

114.80 608.00 5569.00 .75 1.375 1.000 113.49579 1.30421

109.80 218.00 6244.00 .75 1.375 1.000 111.83953 -2.03953

111.20 309.00 6256.00 .75 1.375 1.000 112.41201 -1.21201

112.90 401.00 6275.00 .75 1.375 1.000 112.99832 -.09832

114.30 509.00 6294.00 .75 1.375 1.000 113.68297 .61703

113.40 608.00 6317.00 .75 1.375 1.000 114.31669 -.91669

107.20 216.00 2347.00 .75 1.000 .000 107.44135 -.24214

108.09 307.00 2357.00 .75 1.000 .000 108.01163 .07535

109.04 405.00 2370.00 .75 1.000 .000 108.62823 .41334

110.04 508.00 2387.00 .75 1.000 .000 109.27995 .76261

111.00 607.00 2404.00 .75 1.000 .000 109.90709 1.09197

108.07 216.00 2989.00 .75 1.000 .000 108.14592 -.07862

108.86 308.00 2999.00 .75 1.000 .000 108.72235 .13419

109.69 406.00 3008.00 .75 1.000 .000 109.33456 .35732

110.54 505.00 3022.00 .75 1.000 .000 109.95841 .57811

111.39 606.00 3036.00 .75 1.000 .000 110.59454 .79825

109.02 218.00 3686.00 .75 1.000 .000 108.92314 .10098

109.64 302.00 3699.00 .75 1.000 .000 109.45370 .18855

110.38 404.00 3709.00 .75 1.000 .000 110.09159 .29003

111.09 501.00 3723.00 .75 1.000 .000 110.70314 .38187

111.83 604.00 3738.00 .75 1.000 .000 111.35267 .47389

109.68 204.00 4239.00 .75 1.000 .000 109.44399 .23960

110.34 309.00 4247.00 .75 1.000 .000 110.09813 .24184

110.93 404.00 4257.00 .75 1.000 .000 110.69300 .24097

111.58 508.00 4269.00 .75 1.000 .000 111.34538 .23574

112.19 606.00 4278.00 .75 1.000 .000 111.95760 .22768
111

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

Sound Power 

dBA 

Model 

Sound Power 

dBA 

Difference

110.63 212.00 4899.00 .75 1.000 .000 110.21749 .41267

111.14 310.00 4916.00 .75 1.000 .000 110.83848 .29710

111.59 403.00 4909.00 .75 1.000 .000 111.40240 .18382

112.11 506.00 4929.00 .75 1.000 .000 112.05742 .05347

112.63 608.00 4955.00 .75 1.000 .000 112.71287 -.08592

107.90 213.00 3680.00 .75 1.375 .000 109.78957 -1.88957

109.90 305.00 3692.00 .75 1.375 .000 110.36819 -.46819

111.70 403.00 3717.00 .75 1.375 .000 110.99796 .70204

112.90 509.00 3736.00 .75 1.375 .000 111.67032 1.22968

113.30 606.00 3752.00 .75 1.375 .000 112.28407 1.01593

108.70 213.00 4298.00 .75 1.375 .000 110.46780 -1.76780

111.60 314.00 4310.00 .75 1.375 .000 111.10174 .49826

112.50 402.00 4326.00 .75 1.375 .000 111.66017 .83983

114.00 508.00 4338.00 .75 1.375 .000 112.32485 1.67515

114.80 607.00 4357.00 .75 1.375 .000 112.95418 1.84582

107.30 212.00 4977.00 .75 1.375 .000 111.20683 -3.90683

108.00 303.00 4998.00 .75 1.375 .000 111.78919 -3.78919

112.30 398.00 5013.00 .75 1.375 .000 112.38955 -.08955

114.20 511.00 5037.00 .75 1.375 .000 113.11041 1.08959

116.20 606.00 5060.00 .75 1.375 .000 113.71955 2.48045

110.50 211.00 5617.00 .75 1.375 .000 111.90306 -1.40306

113.10 306.00 5632.00 .75 1.375 .000 112.50342 .59658

113.60 404.00 5646.00 .75 1.375 .000 113.12112 .47888

117.00 512.00 5671.00 .75 1.375 .000 113.81235 3.18765

116.10 595.00 5686.00 .75 1.375 .000 114.33896 1.76104

111.90 212.00 6260.00 .75 1.375 .000 112.61488 -.71488

113.60 312.00 6287.00 .75 1.375 .000 113.25914 .34086

114.90 404.00 6317.00 .75 1.375 .000 113.85752 1.04248

115.90 507.00 6347.00 .75 1.375 .000 114.52351 1.37649

116.90 598.00 6306.00 .75 1.375 .000 115.03782 1.86218

5.4.3 Development of An Equation for Determining a Sound Power Level

 The dependent variable, sound power level was then modeled by the following equation 

using the regression coefficients determined from table 5.16: 

 Sound Power Level (dBA) = 101.708 – 1.766(water) + .001(thrust) (8) 

 + .007(rotational speed) + 2.588(bit size) - .640(drill steel type) 
112

Utilizing equation (8) above, the mining community can now determine a sound power level, during 

the drilling cycle in high compressive rock media (>20,000 psi) for a roof bolting machine using a 

simple equation developed from laboratory testing and statistical modeling. 

Using equation (8) from above, an example is shown below illustrating the use of the equation and 

determining a sound power level given a specific drilling method (wet, mist or vacuum), thrust 

setting, rotational speed, bit size and type of drill steel. Assume a roof bolter operator is drilling into 

a high-compressive strength media (>20,000 psi), using the wet method of drilling, using a 1.375-

inch bit with round drill steel, a rotational speed set at 600 rpm and a thrust setting at 4,000 lbs. 

Using equation (8) above and inputting the specific drilling parameters, the mining community could 

then determine a sound power level with significant confidence as shown below: 

Sound Power Level (dBA) = 101.708 – 1.766(water) + .001(thrust) 

 + .007(rotational speed) + 2.588(bit size) - .640(drill steel type) 

Sound Power Level (dBA) = 101.708 – 1.766(3) + .001(4,000) + 0.007(600) + 2.588(1.375) - 

.640(1) 

 = 101.708 – 5.30 + 4 + 4.20 + 3.56 – 0.640 = 107.53 dBA 

By comparing the predicted sound power level of 107.53 dBA above to the measured sound power 

level from the laboratory measurement shown below is: 

Sound Power 

dBA 

Laboratory 

Speed 

rpm 

Thrust 

lbs 

Water 

gpm 

Bit Size 

in. 

Drill Steel 

(hex/round) 

107.70 572.00 3987.00 3.00 1.375 1.000
113

Sound Power Level (dBA) = 107.70 – 107.53 = 0.17 dBA, which, 

demonstrates a significant correlation between the measured and predicted (determined) sound 

power level from the statistical model. The statistical model equation (equation 8), provides the 

mining community with a simple and reliable approach in determining a sound power level for a 

roof bolting machine during the drilling operation in high compressive strength rock media, 

given any type of drilling method (vacuum, wet or mist) and drilling parameter configuration 

(thrust, rotational speed, bit size and type of drill steel). Chapter 6 will then offer and provide 

the mining community with two different approaches in predicting sound pressure levels at the 

operator position of a roof bolting machine. One method of prediction, will utilize overall sound 

power levels either measured from laboratory tests or determined (predicted) from equation (8). 

The other approach, a more sophisticated and reliable approach, would predict sound pressure 

levels at the operator position of the roof bolting machine, using full-octave band frequency 

measurements obtained from laboratory testing for input into a computer model for simulating 

and predicting sound pressure levels from sound power level measurements. 
114

Chapter 6 

DEVELOPMENT AND UTILIZATION OF MODELS FOR PREDICTING SOUND 

PRESSURE LEVELS FROM LABORATORY TESTS 

6.1 Introduction 

Underground mining machines are subject to many variables that can affect the noise 

levels measured. Some of these variables cannot be controlled while others can be influenced or 

even controlled by the machine operator. The acoustic environment in which the mining 

machines operate is a critical factor affecting the sound pressure levels measured. Underground 

mines are enclosed areas, which usually represent diffused fields. A diffuse sound field is a 

sound field in which the time average of the mean-square sound pressure is everywhere the same 

and the flow of acoustic energy in all directions is equally probable. The geometry and the 

composition of the surfaces influence the overall sound level by the number of rays (sound 

waves) being reflected or absorbed. Mine entries also have various shapes, rectangular, square, 

or arched, and various dimensions as well. These variations in shape and size affect the overall 

sound energy that is reflected or absorbed. These are the variables that cannot be controlled in 

the acoustic environment, and include geometry and composition of the surfaces, shape of the 

mine opening, and the compressive strength of the affected medium. Two methods of predicting 

the acoustic environment properties associated with underground coal mining machines and the 

sound pressure level experienced at the operator utilizing laboratory results are provided in this 

chapter. One model, demonstrates the prediction of sound pressure levels, given overall sound 

power levels and the second model, a more sophisticated and reliable modeling approach, 

utilizes full-octave band frequency measurements obtained from laboratory and mine testing for 

input, thereby, used for predicting sound pressure levels at the operator position. The objective 

for the development of the respective models is to provide a methodology for determining a 

miners’ effective noise dosage related to measured and determined engineering noise control 
115

tests determined from laboratory trials dependent upon overall and full-octave band sound power 

levels. Upon completion of the models, the measured sound power determined in the laboratory, 

with a calculated or predicted sound absorption coefficient, could then be entered into the model 

to determine an operator’s noise dosage relative to the drilling cycle of the roof bolting machine. 

The first model discussed will provide the mining community with a method to determine sound 

pressure levels experienced by the roof bolting operator, through inputting an overall sound 

power level. The second model presented will provide a more reliable approach in determining 

sound pressure levels experienced by the roof bolting machine operator utilizing full-octave band 

frequency sound power levels. This will be achieved using a ray-tracing program to predict the 

steady-state sound pressure level and the associated sound decay in a mine environment. This 

information will provide a snapshot of the environment and calculate the noise levels throughout 

the environment, additionally, it will account for the positions of an operator with respect to a 

machine and ultimately, provide the mining industry with a method to model a simple event 

within a mine section and determine the noise dosage to the roof bolting machine operator. 

6.2 Model for Predicting Sound Pressure Levels Using Overall Sound Power Levels 

6.2.1 Introduction

 It would be a time consuming and complex task to try to develop a model of all shapes 

and sizes of different mines. However, the acoustic differences are small and can be broken 

down into two shapes, a tunnel or a flat room. The acoustic properties of these two shapes are 

flexible enough to be applied to most other shapes. Underground noise travels both as a direct 

path and as multiple reflected paths. The number of reflections depends on the shape, 

dimensions, and the absorption property of the walls and roof. This absorption property is called 

the sabine absorption coefficient, α, and is used to describe the degree of reflectivity of the walls 

and roof. The sabine absorption coefficient ranges from zero to one, where zero is total 
116

reflection and one is total absorption. A low sabine absorption coefficient means the 

environment is highly reverberant and a sabine absorption coefficient that is near one such as 0.9 

means that most of the sound is absorbed upon reflection. In the case of a high sabine absorption 

coefficient a lower level of sound occurs as compared to a lower sabine absorption coefficient 

for that particular environment. 

6.2.2 Predicting Underground Sound Pressure Levels from Measurements Above Ground

 To predict underground sound levels from above ground measurements there are two 

basic techniques used. One method is the room acoustics method and the other is the imaging 

method. The room acoustic method describes the sound level in a large room where the sound 

undergoes a large number of reflections from the room’s walls, roof, and floor. The imaging 

method is used to describe the tunnel surfaces, where the sound rays are traced from the source 

to the receiver and the sound energy is summed. The imaging method is more complex then the 

room acoustic method. The imaging method models a tunnel which is “U” shaped rather than a 

square channel, however the modeling of the square channel is acoustically accurate. The reason 

being is that the individual sound rays differ only in a small and random manner. 

6.2.2.1 Differences Between the Room Acoustic Method and Imaging Method

 To illustrate the difference between the room acoustic method and the imaging method 

for predicting underground sound pressure levels, figure 6.1 provides an example for a tunnel 

200 ft long with a 10 ft-square cross-section. A sabine absorption coefficient of 0.2 is used for 

the walls with a source having a sound power of 100 dBA. 
117

10 100

Distance (ft)

100

90

80

70

60

Sound Pressure Level dB(A)

Room Acoustics 

 Method

Imaging 

 Method

Above ground 

 Level

Figure 6.1 Comparison of Imaging and Room Acoustics Method of Predicting Sound Pressure 

Levels 

The imaging and room acoustics predictive techniques are very close up to about 30 feet from 

the source of noise. Subsequent to 30 ft, the imaging method decreases at the same rate as the 

above ground sound level and the room acoustic method reaches some sound power value and 

does not decrease any further. The room acoustic method assumes a diffuse field throughout the 

tunnel where as the imaging method only assumes a diffuse field near the source, but not farther 

down the tunnel. The imaging method differs in sound levels as to where the location of the 

person is from the noise source. The room acoustics method differs in sound levels only until 30 

ft. from the noise source and does not decrease after 30 ft. While observing machine operators 

they are located typically close to the noise source or in the near field. The near field is the 

sound field close to the sound source (between the source and the far field) where the 

instantaneous sound pressure and particle velocity are not in phase with each other. Conversely, 

the far field is a portion of a sound field of a sound source in which the sound pressure level 

decreases by 6 dB for each doubling of the distance from the source. In the case of operators 

located in the near field, both the room acoustics and imaging method would work for predicting 
118

sound pressure levels. However, when examining other mine personnel away from the noise 

source or within the far field, the sound pressure levels in the far field would have greater 

accuracy with the imaging method. The reason for this is the imaging method assumes a diffuse 

field only near the source, and not further down the tunnel thus giving a better representation of 

the sound in a tunnel. 

6.2.2.2 Predicting Sound Levels at a Single Point

 Patterson, et.al (23), developed curves, plotting the correction factors for using above 

ground measurements to predict underground sound pressure levels for tunnels (figure 6.2) and 

flat rooms (figure 6.3). The curves plotted represent different sabine absorption coefficients and 

are plotted as a function of normalized distance from the acoustic center of the noise source. The 

correction factor is larger for tunnels as compared to flat rooms; this is due to the tunnels being 

more confined than the rooms, therefore, creating more reflections of sound. 

1 10 100

Distance (r/W)

30

20

10

0

Correction Factor (dB)

0.6

0.4

0.3

0.2

0.1

0.05

0.03

Figure 6.2 Correction Factors for Converting Above Ground Measurements to Underground 

 Sound Pressure Levels (Tunnels) 
119

1 10

Distance (r/H)

20

10

0

Correction Factor (dB)

0.6

0.4

0.2

0.1

0.03

0.01

Figure 6.3 Correction Factors for Converting Above Ground Measurements to Underground 

 Sound Pressure Levels (Flat Rooms) 

The limitation of figures 6.2 and 6.3 is they only provide correction factors at a single point, 

relative to a measured distance from the source as measured above ground for determining sound 

pressure levels underground. To determine sound pressure levels below ground at any point, one 

would have to know the exact distances mine personnel are from the noise source and then 

measure sound pressure levels above ground from the specific distances to provide correction 

factors for determining sound pressure levels underground at the relative distances, a very 

cumbersome and unfriendly approach. 

6.2.2.3 Predicting Sound Levels at Multiple Points

 A more direct method in determining the underground sound pressure level at any point 

underground without having to conduct or measure all the above ground sound pressure level 

measurements would be to know or determine the sound power of the noise source above 

ground. Patterson, et.al (24), developed curves to determine the A-weighted sound pressure 

level at any point underground, using the measured or known sound power level of the machine. 

Figures 6.4 and 6.5 represent plots for determining two correction factors, namely G and F, for 

determining the underground A-weighted, sound pressure level at a specific location for tunnels 

and flat rooms, respectively if you can identify the sabine absorption coefficient and the sound 

power of the noise source. 
120

The following equation is used to determine the underground A-weighted, sound pressure level. 

 

 Lp (underground) = Lw (above ground) – (G + F) (9) 

where: 

Lp (underground) = A-weighted sound pressure level, dBA – predicted underground 

Lw (above ground) = A-weighted sound power level, dBA – measured above ground 

G and F = Correction factors 

Using the statistical model equation developed in the previous section, Development of An 

Equation for Determining a Sound Power Level, one could then predict the sound pressure level, 

experienced by a roof bolting machine operator utilizing this modeling approach. For example, 

assume a roof bolter operator is drilling into a high-compressive strength media (>20,000 psi), 

using the wet method of drilling, using a 1.375-inch bit with round drill steel, a rotational speed 

set at 600 rpm and a thrust setting at 4,000 lbs. Using the statistical model equation and 

inputting the specific drilling parameters, the sound power level is shown below: 

Sound Power Level (dBA) = 101.708 – 1.766(water) + .001(thrust) + .007(rotational speed) + 

2.588(bit size) - .640(drill steel type) 

Sound Power Level (dBA) = 101.708 – 1.766(3) + .001(4,000) + 0.007(600) + 2.588(1.375) - 

.640(1) 

 = 101.708 – 5.30 + 4 + 4.20 + 3.56 – 0.640 = 107.5 dBA 

Determining a sound power level of 107.5 dBA, one could then use figure 6.4 to determine the 

sound pressure level at a specific distance from the noise source, for example 30 ft. Assuming 

the tunnel width is 16 ft and the sabine absorption coefficient is 0.2, therefore, r would equal 30 
121

ft and W would equal 16 ft and the normalized source-to-distance, r/W, would equal 30ft/16ft, or 

1.9. Using figure 6.4, G would equal -2.5 dBA and F would equal 23 dBA and then using 

equation (9): 

Lp (underground) = Lw (above ground) – (G + F) 

Lp (underground) = 107.5 dBA – (-2.5 + 23) = 107.53 – (20.5) = 87.0 dBA, 30 ft from the 

noise source. 
122

1 10 100

Distance (r/W)

30

20

10

0

-10

G (dB)

0.03

0.05

0.1

0.2

0.3

0.4

0.6

5 10 15 20 25 30 35 40

Width (W)

30

25

20

15

F (dB)

Figure 6.4 Correction Factors for Determining Underground Sound Pressure Levels from Sound 

Power Measurements Above Ground (Tunnels) 
123

5 10 15 20 25 30

Distance (r/H)

30

20

10

0

-10

G (dB)

0.01

0.03

0.1

0.2

0.4

0.6

5 10 15 20 25 30 35 40

Width (W)

30

25

20

15

F (dB)

Figure 6.5 Correction Factors for Determining Underground Sound Pressure Levels from Sound 

Power Measurements Above Ground (Tunnels) 
124

6.2.2.4 Predicting Sound Levels in the Near-Field

 Determining an underground sound pressure level near the machine or the noise source is 

a more difficult task, due to encountering the geometric near field. The shape and size of the 

machine and the location of the noise source on the machine plays an important role in the 

behavior of sound pressure levels. For example, two machines may have far field sound pressure 

levels equal to each other, but could have very different sound pressure levels near the machine. 

For example, when measuring sound pressure levels close to the noise source, an error of one or 

two-feet can be much more significant than measuring a sound pressure level 40-50 ft away from 

the noise source. 

 To address the near field issue relative to sound pressure level measurements, Patterson 

(20), developed correction factor curves, which are used for calculating sound pressure levels 

close to the noise source for tunnels and flat rooms (figure 6.6). Several assumptions were 

determined when using the correction curves and consisted of: 1) the machine shape and size can 

influence the results and the curves are only approximations; 2) the location of the acoustic 

center of the noise source must be accurate and 3) the curves are on the conservative side and the 

predicted sound pressure levels may be 1-2 dBA greater than would be measured underground. 
125

0.20 0.40 0.60 0.80 1.00

r/W

15

10

5

0

Correction Factor (dB)

0.6

0.4

0.3

0.2

0.1

0.05

0.03

0.20 0.40 0.60 0.80 1.00

r / H

10

5

0

Correction Factor (dB)

0.8

0.6

0.4

0.2

0.1

0.03

Figure 6.6 Correction Factors for Determining Sound Pressure Levels Underground in the Near 

 Field (Top-Tunnel and Bottom-Flat Room) 

 As mentioned above, the acoustic center of a noise source has to be measured accurately. 

One can locate the acoustic center of a noise source by: 1) assuming all measurements for sound 

power are made at 25 ft from the geometric center of the machine; 2) record the sound pressure 

level 25 ft from the front of the machine; 3) move the microphone at the rear and move the 

microphone in and out until the same sound pressure level is experienced as in the front of the 

machine, the halfway distance between the two measurements is the acoustic center and 4) repeat 

the process on the left and right sides of the machine to find the acoustic center along that 

particular axis. For utilization of this model, knowledge of sound power level and the acoustic 

center are necessary information in predicting underground sound pressure levels. 
126

 Using figure 6.6 above, one could then determine or predict the underground sound 

pressure level at the operator position of a roof bolting machine taking into account the 

assumptions used for the development of the curves in figure 6.6 mentioned above. However, 

this type of approach for predicting sound pressure levels underground utilizes numerous 

assumptions and adopts a very conservative approach. Additionally, locating the acoustic center 

of the piece of equipment can also be very difficult, dependent upon the type, location and the 

number of noise sources associated with the particular machine. The location of the acoustic 

center depends upon numerous parameters and can be strongly influenced by minimal details of 

a machine, such as, the machine having a reflective surface behind a noise source, in which, 

would provide additional sound energy towards the operator, therefore the acoustic center would 

be closer than typically measured from the operator to the noise source. For the reasons 

mentioned above, this type of modeling approach, determining sound pressure levels in the nearfield, is a very approximate approach. Section 6.3 provides a more reliable approach for 

determining sound pressure levels in the near-field. 

6.2.3 Limitations of Model Utilizing Overall Sound Power Levels

 Section 6.2 provided several methods for determining sound pressure levels underground 

using overall sound power levels measured. However, the approach contained several 

limitations. As mentioned in section 6.2.2.4, Predicting Sound Levels in the Near-Field, 

numerous assumptions were required and a conservative approach was used to predict sound 

pressure levels in the near-field. More importantly, the model predictions utilized absorption 

coefficients, which, were determined using the suitable methods available 30 years ago. The 

authors did mention that a more thorough investigation relative to the dependence of acoustic 

absorption on ore type and mine environment was needed to be conducted and many more 

measurements would be needed to obtain extreme confidence in the results of the model. 
127

Section 6.3 provides a more reliable modeling approach, utilizing measured absorption 

coefficients, for predicting sound pressure levels underground using laboratory results. 

Additionally, the model developed in section 6.3, provides a more accurate description of the 

sound pressure levels experienced by operators of roof bolting machine equipment in the nearfield. 

6.3 Model for Predicting Sound Pressure Levels Using Full-Octave Band Frequency 

 Sound Power Levels

6.3.1 Ray-tracing Technique

 

 Ray-tracing is a technique that can be used to predict sound fields in mines of various 

shapes and sizes. A computer program will simulate rays that are emitted from each noise 

source in a random or deterministic fashion. Each ray in the program is then reflected and 

scattered by surfaces, barriers and objects until it reaches a receiver. The great potential of raytracing techniques is the ability to display contour maps of noise levels of various mining 

machines and then using the information to determine a noise dosage of operators in a particular 

mine environment. 

6.3.2 Raynoise Computer Program

The Raynoise program was the noise modeling software utilized for displaying and 

predicting sound pressure levels experienced by roof bolter operators (figure 6.7). 
128

Figure 6.7 Sound Pressure Level Contour Plot Using the Raynoise Program 

The Raynoise program uses a ray-tracing based technique to calculate the noise characteristics of 

a given source/room configuration. A key aspect of the package is that the noise sources and 

material properties are defined in terms of full octave-band, not one-third octave-band format. 

The program also has the capability of importing model information in AutoCAD DXF format. 

Additionally, the package has command file capabilities that allow complete model and test 

definitions to be written and processed. This capability is extremely helpful for processing a 

variety of tests in bulk and for varying parameters for a single test. The program also has 

command-line operation capabilities that allow it to be used as a ‘black box’ by other software. 

For example, “Rayserve” is an in-house package developed at the Pittsburgh Research 

Laboratory. Rayserve creates a shell around the Raynoise package that allows it to act as a noise 

profile engine, or “black box”. The benefit is that many tests can be processed in bulk using the 
129

Rayserve program (25). This is extremely beneficial because when Raynoise is running it takes 

a lot of processor time, making a computer unusable until model run completion. Rayserve also 

automatically calculates the overall sound pressure level results for a given test setup by running 

the test at each octave band frequency and combining the results. However, Raynoise does have 

some limitations. One limitation is the package can only make calculations for a specific 

frequency and to generate overall results, a model needs to be run at each octave band 

frequencies and the resultant sound pressure level for each frequency band is then combined 

interdependent of the Raynoise package. 

6.3.3 Absorption Coefficients

 Classic absorption/reverberation estimation using T60 measurements (measuring how 

sound decays over a period of time and distance) will not work well in the underground mining 

environment because the classic absorption theory assumes (1) a finite room, (2) a diffuse field 

and (3) relatively uniform absorption. None of these factors is true in an open ended mine entry. 

The assumption then is to treat the mine entry as an “infinite” duct, i.e. very little of the acoustic 

power traveling down the duct is ever reflected back into the source area. In order to determine 

the absorption coefficient, the measurements are matched to a ray model (or image source 

model) of the acoustic field radiated from the source in an “infinite” duct. The entry is modeled 

as a finite entry with an absorption coefficient of α = 1 at both ends to make it appear infinite. 

The ray model (Figure 6.8) is used to calculate the sound pressure level at the measurement 

positions based on varying absorption coefficients relative to the acoustic environment. 
130

α=1 α=1

α=0.01, 0.02, 0.04, ... 1

Source

Measurement 

planes

Figure 6.8 Illustration of Ray Tracing for Analyzing 

the Acoustic Environment

Rays *

Since the entry, associated with underground coal mining, is fairly wide (>15ft across), this 

method will work well, even at low frequencies within the frequency spectrum. The procedure 

used for collecting acoustical data in the mine environment for estimating the absorption 

coefficients for utilization in the ray tracing model, is provided in section 6.3 below. 

6.3.4 Method for Determining Absorption Coefficients in an Underground Coal Mine

 The method utilized to determine the absorption coefficients in an underground coal mine 

is displayed below. 

6.3.4.1 Underground Measurements and Testing Parameters

 Figure 6.9 displays the measurement scheme used in determining the coefficients of 

absorption in an underground mine setting. 
131

- Microphone

- Noise source *

Width (w)

Height (h)

*

0 10 20 30 40 50 5

Measurement planes

View across one 

measurement plane 

Source

ft

Crosscut

Figure 6.9 Measurement Layout Used for Determining Absorption Coefficients in an 

Underground Coal Mine 

 The calibrated noise source (fan) was positioned near the end of a crosscut, or the edge of 

the mine entry as shown in figure 6.9 above. Figure 6.10 shows a picture of the calibrated noise 

source to be utilized for conducting the underground mine tests. 
132

Figure 6.10 Photograph of Calibrated Sound Source for Underground Testing 

The noise source (fan) was placed at the midway point of the crosscut and at a position halfway 

between the floor and roof of the crosscut. The actual position of the noise source was recorded 

and documented for analysis procedures to be performed in determining the absorption 

coefficients of the mine environment. The octave-band sound power levels for the calibrated 

noise source are shown in table 6.1 below. 
133

Table 6.1 One-Third Octave-Band Sound Power Levels for Calibrated Noise Source 

Octave-band

(Hz) 

Sound Power

(dB) 

63 72.8 

125 78.9 

250 80.1 

500 79.9 

1000 83.6 

2000 84.8 

4000 83.0 

8000 80.2 

Additionally, the actual dimensions of the crosscut were measured and recorded. The crosscut 

was divided into equal areas or sub-sections and the center of each sub-section represented a 

measurement location as shown in figure 6.9 above. Several measurement planes were 

developed and measured to collect the acoustical data across the measured planes within each 

subsection previously established. At each measurement location, the one-third octave band 

sound pressure level was measured due to the calibrated noise source and recorded at the 63-

hertz thru 8,000-hertz one-third octave bands. A Brüel and Kjaer 2260 Investigator was used to 

collect the one-third octave band data and shown in figure 6.11 below. The Brüel and Kjaer 

2260 Investigator is a handheld real-time one-third octave band device with frequency analysis, 

statistics and logging capabilities. 
134

Figure 6.11 Photograph of a Brüel and Kjaer 2260 Investigator 

Utilizing the measurement scheme from figure 6.9 for underground testing, the calibrated noise 

source (fan) was placed inside the right open end of a crosscut. A total of forty-eight, one-third 

octave band measurements were performed using the Brüel and Kjaer 2260 Investigator for 

characterization of the acoustical mining environment. Two measurements were conducted at 

each of the twenty-four monitoring points within the crosscut, therefore, accounting for fortyeight measurements. At each monitoring point, a measurement (bottom point) was conducted 

0.7 meters from the floor and the other measurement was performed at 1.4 meters (top point) 

from the floor. The length of the crosscut measured 22 meters. Figure 6.12 provides the location 

of the measuring points (twenty-four) and the position of the measurement planes with respect to 
135

the width and height of the crosscut, utilized for characterizing the acoustical properties of the 

mining environment. 

 22m 19m 16m 13m 10m 7m 4m 1m 

 22 19 16 13 10 7 4 1 

 23 20 17 14 11 8 5 2 source 

 24 21 18 15 12 9 6 3 

width 6.6m 6.0m 5.3m 5.6m 5.7m 5.6m 5.6m 5.1m 

height 2.3m 2.3m 2.2m 2.1m 2.3m 2.3m 2.2m 2.1m 

Figure 6.12 Measurement Locations for Determining Acoustical Properties Underground 

An example of the one-third octave data collected for all forty-eight measuring points is shown 

in table 6.2. 
136

Table 6.2 Example of the One-Third Octave Data Collected Underground 

Instrument: 2260 

Start Time: 08/06/2004 03:28:40 AM 

End Time: 08/06/2004 03:28:55 AM 

Elapsed Time: 0:00:15 

Bandwidth: 1/3 Octave 

Calibration Time: 11/04/2003 04:19:15 PM 

Calibration Level: 93.9 dB 

08/06/2004 03:28:40 AM - 03:28:55 AM 

Hz LLeq LLSMax LLSMin 

63 65.54 66.76 63.02 

80 64.3 65.54 62.53 

100 67.56 68.79 65.12 

125 74.08 74.55 72.75 

160 66.04 67.56 64.64 

200 62.93 63.53 62.25 

250 64.64 65.79 60.93 

315 66.06 66.88 63.42 

400 69.09 70.01 67.7 

500 68.58 70.31 67.53 

630 67.25 68.15 66.38 

800 69.44 70.33 68.2 

1000 72.41 73.18 70.13 

1250 73.39 73.95 70.66 

1600 73.86 74.46 71.57 

2000 72 72.48 70.25 

2500 71.18 71.54 68.81 

3150 69.72 70.19 67.8 

4000 68.36 68.59 66.33 

5000 67.96 68.16 65.92 

6300 66.32 66.6 64.32 

8000 64.58 64.78 62.72 

A 82.19 82.49 80.13 

L 83.43 83.68 81.45 

It should be noted that Table 6.2 represents data collected for one measuring point, for this case 

it was measurement location number one, bottom measurement (see figure 6.12), therefore, 

forty-seven additional tests were conducted representing a similar format for obtaining the 

necessary data for characterization of the mining environment and for input into the Raynoise 

program. 
137

6.3.4.2 Utilizing the Excelparse Program for Calculating Octave-Band Information

 As mentioned in section 6.3.4.1, data from underground testing was collected in one-third 

octave bands. The program, Raynoise, used for displaying and predicting sound pressure levels 

experienced by roof bolter operators requires full-octave band data. Therefore, a program was 

developed, referred to as Excelparse, to convert the one-third octave band data collected from 

underground testing to full-octave band data for input into the Raynoise program. 

 Upon completion of the underground testing, the data was downloaded to a portable 

computer. The data is in an Excel format with a separate file for each point measured as shown 

in section 6.3.4.1 (table 6.2). The Excelparse program extracts the sound pressure level 

information from each individual file and combines the results for all points measured into one 

file. Figure 6.13 displays a screenshot of the data from the Excelparse program. 
138

Figure 6.13 Screenshot of the Excelparse Program 

The program determines full-octave band data from the one-third octave band data collected 

from the underground measurements. The equation used in the program which converts onethird to full-octave band sound pressure levels is shown below. 

 SPL = 10 * LOG10 (temp) (9) 

where 

SPL = Sound Pressure Level (in respective full-octave band) 

(temp) = 10(Previous one-third octave/10) + 10(Actual one-third octave/10) + 10(Next one-third octave/10)
139

For example, by utilizing equation 8 and table 6.2 above, the full-octave band of 63 Hz could be 

obtained from one-third octave band data as shown below: 

 

 SPL (63 Hz-Octave Band) = 10 * LOG10 {10(65.44/10) + 10(65.54/10) + 10(64.3/10)} (10) 

yields the following: 

 SPL (63 Hz-Octave Band) – 10 * LOG10 {10(6.54) + 10(6.55) + 10(6.43)} 

 SPL (63 Hz-Octave Band) – 10 * LOG10 {3,467,368.50 + 3,548,133.89 + 2,691,534.80} 

 SPL (63 Hz-Octave Band) – 10 * LOG10 {9,707,037.19} 

 SPL (63 Hz-Octave Band) – 10 * 6.99 

 SPL (63 Hz-Octave Band) – 69.9 dB 

Table 6.3, shown below, represents the full-octave band data (for 63 Hz, 125 Hz, 250 Hz, 500 

Hz, 1000 Hz, 2,000 Hz, 4,000 Hz and 8,000 Hz), generated from the Excelparse program for all 

forty-eight measuring points within the crosscut in the underground coal mine as shown in figure 

6.12. 
140

Table 6.3 Measured Full-Octave Band Sound Pressure Levels from Underground Testing 

Point Number Full-Octave Bands 

63 125 250 500 1000 2000 4000 8000 

 dB dB dB dB dB dB dB dB

1 69.9 75.48 69.5 73.14 76.82 77.27 73.52 69.33 

2 69.9 75.48 69.5 73.14 76.82 77.27 73.52 69.33 

3 71.95 72.14 71.22 75.1 79.49 79.06 75.05 70.15 

4 71.95 72.14 71.22 75.1 79.49 79.06 75.05 70.15 

5 69.06 74.85 70.46 73.58 75.43 76.29 73.15 69.26 

6 69.06 74.85 70.46 73.58 75.43 76.29 73.15 69.26 

7 70.2 70.01 68.47 69.67 73.14 72.42 69.82 64.92 

8 70.2 70.01 68.47 69.67 73.14 72.42 69.82 64.92 

9 70.06 72.09 67.34 70 72.74 74 70.5 66.49 

10 70.06 72.09 67.34 70 72.74 74 70.5 66.49 

11 66.65 69.95 68.59 69.91 72.86 73.03 69.97 64.79 

12 66.65 69.95 68.59 69.91 72.86 73.03 69.97 64.79 

13 69.28 71.75 67.62 70.33 71.69 71.25 68.23 63.23 

14 69.28 71.75 67.62 70.33 71.69 71.25 68.23 63.23 

15 69.44 70.29 67.86 70.66 71.4 71.57 67.92 62.69 

16 69.44 70.29 67.86 70.66 71.4 71.57 67.92 62.69 

17 66.67 69.89 67.48 70.04 72 71.49 67.98 62.29 

18 66.67 69.89 67.48 70.04 72 71.49 67.98 62.29 

19 68.7 70.73 67.81 67.51 68.42 69.02 65.4 59.53 

20 68.7 70.73 67.81 67.51 68.42 69.02 65.4 59.53 

21 69.87 69.62 68.83 68.64 70.7 69.87 66.2 59.82 

22 69.87 69.62 68.83 68.64 70.7 69.87 66.2 59.82 

23 66.98 73.25 67.85 68.34 70.01 69.19 65.75 60.09 

24 66.98 73.25 67.85 68.34 70.01 69.19 65.75 60.09 

25 68.68 72.64 66.57 67.26 69.28 68.18 64.92 58.12 

26 68.68 72.64 66.57 67.26 69.28 68.18 64.92 58.12 

27 70.27 74.89 67.77 68.55 69 68.38 64.35 58.33 

28 70.27 74.89 67.77 68.55 69 68.38 64.35 58.33 

29 67.68 70.5 68.16 67.9 69.37 68.71 64.47 58.29 

30 67.68 70.5 68.16 67.9 69.37 68.71 64.47 58.29 

31 67.63 68.81 65.75 67.2 67.02 66.64 62.24 56.68 

32 67.63 68.81 65.75 67.2 67.02 66.64 62.24 56.68 

33 68.92 71.99 66.8 67.43 67.99 66.82 63.08 56.85 

34 68.92 71.99 66.8 67.43 67.99 66.82 63.08 56.85 

35 67.89 69.57 68.24 66.78 68.06 66.64 62.53 56.69 

36 67.89 69.57 68.24 66.78 68.06 66.64 62.53 56.69 

37 67.24 70.63 65.12 66.65 66.32 64.99 60.93 55.36 

38 67.24 70.63 65.12 66.65 66.32 64.99 60.93 55.36 

39 67.59 70.58 65.24 66.98 65.87 65.17 60.36 55.49 

40 67.59 70.58 65.24 66.98 65.87 65.17 60.36 55.49 

41 67.63 68.89 67.42 65.77 66.1 64.52 60.41 55.19 

42 67.63 68.89 67.42 65.77 66.1 64.52 60.41 55.19 

43 64.84 69.52 64.85 64.69 63.02 62.58 58.19 54.77 

44 64.84 69.52 64.85 64.69 63.02 62.58 58.19 54.77 

45 66.79 72.14 63.97 63.53 64.85 63.72 58.62 54.77 

46 66.79 72.14 63.97 63.53 64.85 63.72 58.62 54.77 

47 69.33 72.9 65.59 64.33 64.86 63.65 59.51 54.88 

48 69.33 72.9 65.59 64.33 64.86 63.65 59.51 54.88 
141

6.3.4.3 Development of an Equivalent Model in Raynoise for Predicting Sound Pressure Levels

 The test conditions documented from the underground testing in figure 6.6 where then 

used to create an equivalent underground model utilizing the Raynoise package. The specific 

information used for input into the Raynoise package consisted of: 1) the height above the floor 

of the noise source and the X and Y coordinates relative to the placement and location of the 

calibrated noise source; 2) the height above the floor relative to the bottom and top measurement 

points as shown in figure 6.12; 3) the total length of the crosscut being examined; 4) the crosscut 

height and width at each measurement plane location and 5) the sound power output of the 

calibrated noise source in full-octave band format as displayed in table 6.1. Inputting the test 

conditions mentioned above, an equivalent Raynoise model was constructed (25). The structural 

information for the equivalent model was determined thru the development of an AutoCAD 

drawing of the crosscut and then inputted into the Raynoise package. The measurement points 

within the model are then defined utilizing the underground measurements collected relative to 

the height above the floor in relation to the top and bottom point measurements for input into the 

Raynoise model. The calibrated noise source is then placed in the position as performed for the 

underground measurements and the sound power output is set for input into the Raynoise model 

as shown in Figure 6.14 below. 
142

Figure 6.14 Test Layout for First Run in Raynoise Model 

Due to the geometric underground measurements conducted in figure 6.12, a total of four 

diffraction edges were added to the model to account for the changing geometry of the crosscut 

measured underground. These edges are shown as (F)1 thru (F)4 shown in figure 6.14. An 

initial set of absorption coefficients, in which, are full-octave band based, were then inputted into 

the model relative to the underground mining environment. The first set of absorption 

coefficients inputted into the Raynoise model for the first run were selected from previous 

research conducted by Patterson, et.al (24) are shown in table 6.4 below. 
143

Table 6.4 Absorption Coefficients Utilized for First Run of Raynoise Model 

Octave-band

(Hz) 

Absorption 

Coefficient 

63 .035 

125 .04 

250 .17 

500 .14 

1000 .21 

2000 .24 

4000 .33 

8000 .45 

The absorption coefficients were determined from a basic equation, where the volume, surface 

area and decay time are inputted as shown below: 

α = 0.05 * V/S * 1/T60 (11) 

where V represents the volume, S is the surface area and T60 represents the decay time. The 

decay time is determined by the amount of time it takes for sound to dissipate by 60 dB in each 

octave band for a given position. 

 A full-octave band test of the model, utilizing the absorption coefficients from table 6.4 

was then processed utilizing the Raynoise program and Rayserve package, mentioned 

previously. For example, figure 6.15 displays graphically, the results for sound pressure levels 

experienced at the 1,000 Hz octave band relative to the absorption coefficients utilized in table 

6.4. Seven additional plots for each of the other full-octave bands were processed and 

constructed, in which, were utilized for comparing the results from the actual underground 

testing displayed in table 6.3. 
144

Figure 6.15 Sound Pressure Levels at 1,000 Hz Full-Octave Band 

The linear sound pressure level information for each of the full-octave bands were also 

organized into a file and imported into Excel for comparing the calculated sound pressure 

level results to the measured sound pressure levels from table 6.3. The calculated sound 

pressure level results are shown in table 6.5 below. 
145

Table 6.5 Calculated Full-Octave Band Sound Pressure Levels – First Run of Model 

Point 

Number 

Octave Band (Hz) 

63 125 250 500 1000 2000 4000 8000 Sound Pressure Level 

dB 

1 70 74.1 73.5 74.1 75.9 75.9 73.2 70.2 82.9 

2 70.1 74.1 73.5 74.1 76 76 73.2 70.2 82.9 

3 72 76 76 76.5 78.6 78.8 76.4 73.8 85.5 

4 71.5 75.6 75.5 76 78.1 78.2 75.9 73.3 85.0 

5 70 74.1 73.5 74.1 75.9 75.9 73.2 70.2 82.9 

6 70.1 74.1 73.5 74.1 76 76 73.2 70.2 82.9 

7 66.8 70.9 69.9 70.6 72.2 72.2 69.1 65.7 79.2 

8 66.9 70.9 70 70.7 72.3 72.2 69.2 65.8 79.3 

9 67.3 71.3 70.4 71.1 72.7 72.7 69.7 66.2 79.7 

10 67.6 71.6 70.6 71.3 72.9 72.8 69.8 66.3 79.9 

11 66.8 70.9 69.9 70.6 72.2 72.2 69.1 65.7 79.2 

12 66.9 70.9 70 70.7 72.3 72.2 69.2 65.8 79.3 

13 65.8 69.8 68.3 69.1 70.4 70.2 66.8 62.9 77.5 

14 65.9 69.9 68.4 69.1 70.5 70.3 66.9 63 77.6 

15 65.9 69.9 68.4 69.2 70.6 70.4 67 63.1 77.7 

16 66.1 70.1 68.6 69.4 70.8 70.6 67.1 63.2 77.9 

17 65.8 69.8 68.3 69.1 70.4 70.2 66.8 62.9 77.5 

18 65.9 69.9 68.4 69.1 70.5 70.3 66.9 63 77.6 

19 65.1 69.1 67.1 68 69.1 68.8 65.1 60.9 76.3 

20 65.3 69.3 67.3 68.2 69.3 69 65.3 61 76.5 

21 65.8 69.8 67.9 68.8 69.9 69.6 65.9 61.6 77.1 

22 65.7 69.7 67.7 68.6 69.7 69.4 65.7 61.5 76.9 

23 65.1 69.1 67.1 68 69.1 68.8 65.1 60.9 76.3 

24 65.3 69.3 67.3 68.2 69.3 69 65.3 61 76.5 

25 65.3 69.2 67.2 68.1 69.1 68.8 65 60.5 76.4 

26 65.4 69.4 67.2 68.1 69.2 68.8 65 60.6 76.4 

27 64.9 68.8 66.5 67.5 68.4 68 64.2 59.7 75.7 

28 65 69 66.7 67.7 68.6 68.3 64.4 59.9 76.0 

29 65.3 69.2 67.2 68.1 69.1 68.8 65 60.5 76.4 

30 65.4 69.4 67.2 68.1 69.2 68.8 65 60.6 76.4 

31 64.4 68.4 66 67 67.9 67.5 63.5 58.9 75.2 

32 64.3 68.2 65.9 66.9 67.8 67.4 63.4 58.8 75.1 

33 64.3 68.3 66 66.9 67.8 67.4 63.5 59 75.2 

34 64.4 68.4 65.8 66.8 67.6 67.2 63.1 58.5 75.1 

35 64.4 68.4 66 67 67.9 67.5 63.5 58.9 75.2 

36 64.3 68.2 65.9 66.9 67.8 67.4 63.4 58.8 75.1 

37 62.3 66.3 63.8 64.8 65.6 65.1 61.1 56.4 73.0 

38 62.6 66.6 64.2 65.1 66 65.6 61.5 56.8 73.4 

39 62.5 66.5 64.3 65.2 66.2 65.8 61.9 57.4 73.5 

40 63.4 67.4 65.1 66 66.9 66.5 62.5 57.8 74.3 

41 62.3 66.3 63.8 64.8 65.6 65.1 61.1 56.4 73.0 

42 62.6 66.6 64.2 65.1 66 65.6 61.5 56.8 73.4 

43 61.2 65.1 62.5 63.6 64.3 63.8 59.7 54.9 71.7 

44 61 65 62.5 63.5 64.3 63.9 59.8 55 71.7 

45 61.2 65.2 62.9 63.8 64.8 64.4 60.6 56.1 72.1 

46 61.4 65.4 63.1 64 65 64.6 60.8 56.5 72.3 

47 61.2 65.1 62.5 63.6 64.3 63.8 59.7 54.9 71.7 

48 61 65 62.5 63.5 64.3 63.9 59.8 55 71.7 
146

Both files (measured and calculated) were then utilized to compare differences in sound 

pressure levels. Charts were generated plotting measured vs. calculated sound pressure level 

at each measurement point for each octave band (63 Hz, 125 Hz, 250 Hz, 500 Hz, 1,000 Hz, 

2,000 Hz, 4,000 Hz and 8,000 Hz) sound pressure level for comparison purposes as shown in 

figures 6.16 thru 6.23 below (25). 

Octave Comparison

50

55

60

65

70

75

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.16 Comparing Calculated vs. Measured Sound Pressure Levels for 63-Hz Octave 

Band. 
147

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.17 Comparing Calculated vs. Measured Sound Pressure Levels for 125-Hz Octave 

Band. 

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.18 Comparing Calculated vs. Measured Sound Pressure Levels for 250-Hz Octave 

Band. 
148

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.19 Comparing Calculated vs. Measured Sound Pressure Levels for 500-Hz Octave 

Band. 

Octave Comparison

50

55

60

65

70

75

80

85

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.20 Comparing Calculated vs. Measured Sound Pressure Levels for 1,000-Hz Octave 

Band. 
149

Octave Comparison

50

55

60

65

70

75

80

85

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.21 Comparing Calculated vs. Measured Sound Pressure Levels for 2,000-Hz Octave 

Band. 

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.22 Comparing Calculated vs. Measured Sound Pressure Levels for 4,000-Hz Octave 

Band. 
150

Octave Comparison

50

55

60

65

70

75

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.23 Comparing Calculated vs. Measured Sound Pressure Levels for 8,000-Hz Octave 

Band. 

The calculated results at each of the eight full-octave bands were then compared to the 

measured results. The modeled absorption coefficients were then adjusted to bring the sound 

pressure level results closer to the measured sound pressure levels and the model was then 

processed again. Consequently, after five model runs, the error between the measured and 

calculated sound pressure levels were minimized and a set of full-octave band absorption 

coefficients for the mine cross-section were determined. Plots comparing the measured and 

calculated sound pressure levels for each of the eight full-octave bands are shown below in 

figures 6.24 thru 6.31. Additionally, table 6.6 displays the calculated sound pressure levels 

after the fifth model run in determining the absorption coefficients thru comparing sound 

pressure levels (measured and calculated). Table 6.7 provides the difference in dB, between 

the measured and calculated sound pressure levels for all forty-eight monitoring points and 

full-octave band frequencies. 
151

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.24 Comparing Calculated vs. Measured Sound Pressure Levels for 63-Hz Octave 

Band (Model Run 5) 

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.25 Comparing Calculated vs. Measured Sound Pressure Levels for 125-Hz Octave 

Band (Model Run 5) 
152

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.26 Comparing Calculated vs. Measured Sound Pressure Levels for 250-Hz Octave 

Band (Model Run 5) 

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.27 Comparing Calculated vs. Measured Sound Pressure Levels for 500-Hz Octave 

Band (Model Run 5) 
153

Octave Comparison

50

55

60

65

70

75

80

85

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.28 Comparing Calculated vs. Measured Sound Pressure Levels for 1,000-Hz Octave 

Band (Model Run 5) 

Octave Comparison

50

55

60

65

70

75

80

85

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.29 Comparing Calculated vs. Measured Sound Pressure Levels for 2,000-Hz Octave 

Band (Model Run 5) 
154

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.30 Comparing Calculated vs. Measured Sound Pressure Levels for 4,000-Hz Octave 

Band (Model Run 5) 

Octave Comparison

50

55

60

65

70

75

80

1 5 9 13 17 21 25 29 33 37 41 45

Point #

SPL (Lin)

Calculated

Measured

Figure 6.31 Comparing Calculated vs. Measured Sound Pressure Levels for 8,000-Hz Octave 

Band (Model Run 5) 
155

Table 6.6 Calculated Full-Octave Band Sound Pressure Levels – Fifth Run of Model 

Point Number 63 125 250 500 1000 2000 4000 8000 Sound Pressure Level, dB

1 70.7 74.1 72.6 73.5 75.9 75.7 72.6 68.8 82.5

2 70.8 74.2 72.6 73.6 76 75.8 72.7 68.9 82.6

3 72.2 75.8 75.2 75.8 78.3 78.3 75.8 73 85.0

4 72.2 75.8 75.3 75.9 78.4 78.4 75.9 73.1 85.1

5 70.7 74.1 72.6 73.5 75.9 75.7 72.6 68.8 82.5

6 70.8 74.2 72.6 73.6 76 75.8 72.7 68.9 82.6

7 68.9 71.8 69.9 71 73.4 73 69.8 65.4 80.0

8 68.9 71.9 69.9 71 73.4 73.1 69.8 65.4 80.0

9 68.9 71.9 70 71.1 73.5 73.2 70 65.7 80.1

10 68.9 71.9 70 71 73.4 73.1 69.9 65.7 80.1

11 68.9 71.8 69.9 71 73.4 73 69.8 65.4 80.0

12 68.9 71.9 69.9 71 73.4 73.1 69.8 65.4 80.0

13 67.5 70.1 67.7 68.8 71.2 70.8 67.3 62.5 77.9

14 67.4 70 67.7 68.8 71.2 70.8 67.3 62.5 77.9

15 67.7 70.3 67.9 69.1 71.4 71 67.5 62.6 78.1

16 67.2 69.7 67.1 68.3 70.7 70.2 66.7 61.8 77.4

17 67.5 70.1 67.7 68.8 71.2 70.8 67.3 62.5 77.9

18 67.4 70 67.7 68.8 71.2 70.8 67.3 62.5 77.9

19 66.8 69.1 66 67.3 69.6 69.1 65.1 59.4 76.4

20 67 69.3 66.4 67.7 70 69.5 65.7 60.3 76.8

21 66.8 69.1 66.1 67.4 69.7 69.2 65.5 60.1 76.5

22 67.1 69.5 66.9 68.1 70.4 69.9 66.3 61.2 77.1

23 66.8 69.1 66 67.3 69.6 69.1 65.1 59.4 76.4

24 67 69.3 66.4 67.7 70 69.5 65.7 60.3 76.8

25 66.3 68.4 65.1 66.4 68.7 68.1 64.2 58.6 75.6

26 66.3 68.3 65 66.4 68.7 68.1 64.2 58.5 75.5

27 66.2 68.2 64.5 66 68.3 67.6 63.5 57.7 75.2

28 65.9 67.7 64 65.4 67.6 67 63 57.3 74.6

29 66.3 68.4 65.1 66.4 68.7 68.1 64.2 58.6 75.6

30 66.3 68.3 65 66.4 68.7 68.1 64.2 58.5 75.5

31 65.3 66.6 62.5 63.9 66.1 65.4 61.3 55.2 73.3

32 65.3 66.6 62.5 63.9 66.2 65.4 61.1 54.8 73.3

33 65.8 67.6 64.1 65.4 67.7 67.1 63.2 57.6 74.7

34 65.9 67.7 63.9 65.4 67.6 66.9 62.8 56.6 74.6

35 65.3 66.6 62.5 63.9 66.1 65.4 61.3 55.2 73.3

36 65.3 66.6 62.5 63.9 66.2 65.4 61.1 54.8 73.3

37 65.1 66.4 62.2 63.6 65.8 65.1 60.9 54.5 73.0

38 65.1 66.4 62.3 63.7 65.9 65.2 61.1 54.9 73.1

39 65.3 66.6 62.5 63.9 66.2 65.4 61.2 55.1 73.3

40 65 66.2 62.1 63.4 65.6 65 60.9 55 72.9

41 65.1 66.4 62.2 63.6 65.8 65.1 60.9 54.5 73.0

42 65.1 66.4 62.3 63.7 65.9 65.2 61.1 54.9 73.1

43 64.9 65.9 61.5 62.9 65.1 64.4 60.1 53.6 72.5

44 65 66.1 62 63.3 65.6 64.9 60.8 54.5 72.8

45 64.7 65.5 60.8 62.2 64.4 63.6 59.2 52.7 71.9

46 64.5 65.2 60.6 61.9 64.1 63.4 59.3 53.3 71.7

47 64.9 65.9 61.5 62.9 65.1 64.4 60.1 53.6 72.5

48 65 66.1 62 63.3 65.6 64.9 60.8 54.5 72.8

Full-Octave Band, Hz
156

Table 6.7 Differences Relative to the Measured and Calculated Sound Pressure Levels 

 Full-Octave Band, Hz 

Point Number 63 125 250 500 1000 2000 4000 8000 

1 1.6 1.13 -1.17 1.64 1.17 1.78 3.25 4.12 

2 -1.3 -3.02 -1.13 0.07 0.58 1.79 1.99 1.81 

3 3.62 0.36 -1.64 0.73 0.51 1.15 1.99 1.94 

4 -0.61 -4.1 -3.27 0.14 -0.03 0.74 0.04 -1.57 

5 -0.83 -1.44 -1.85 -1.17 -0.55 0.35 0.26 0.73 

6 -1.91 -0.47 -3.53 -1.14 -0.22 -0.19 0.44 0.22 

7 0 0 0 0 -0.7 -0.6 -0.7 -0.6 

8 -0.28 -1.51 -2.05 0.94 -0.32 -0.65 -0.16 -0.7 

9 -2.83 -0.98 0.48 -0.03 0.1 0.73 1.97 3.03 

10 -3.25 -1.62 -2.24 0.35 -0.25 0.27 0.1 -0.7 

11 -2.87 -1.77 0.2 0.97 1.26 0.73 1.12 2.46 

12 -3.8 -0.15 -2.33 0.13 0.06 1.32 1.41 0.73 

13 1.98 0.06 0.38 0.13 -0.61 0.06 0.96 2.78 

14 0.92 0.89 -0.83 -1.35 -0.14 -0.29 0.56 0.37 

15 0.84 -0.42 -1.33 1.04 -0.7 0.35 0.96 2.89 

16 0.15 -1.89 0.79 -0.11 -0.07 1.01 1.02 0.67 

17 0.84 -1.97 -1.39 0.84 0.32 1.16 1.48 2.98 

18 -0.02 -0.55 0.43 -0.13 1.14 -0.22 0.31 -0.41 

19 1.21 -0.38 -0.46 1.1 -0.1 0.72 1.11 3.48 

20 1.01 1.39 -0.44 -0.97 -0.49 -0.31 -0.14 -0.43 

21 1.82 1.17 2.18 0.39 -0.3 0.79 1.42 2.53 

22 1.35 -1.49 2.49 -0.02 -1.36 -0.78 -0.06 -0.91 

23 1.76 0.85 1.49 0.47 0.51 1.23 1.99 3.22 

24 1.74 -1.34 1.7 0.35 0.59 0.91 1 0.14 

25 0.84 0.97 -0.07 0.59 -0.03 -0.78 0.71 1.62 

26 -0.48 -0.14 -0.75 -0.08 -1.59 -1.18 -0.45 -0.71 

27 2.3 1.5 1.23 0.99 -0.07 0.5 1.76 3.19 

28 1.94 1.02 3.18 1.53 1 1.62 1.31 1.4 

29 2.2 3.36 1.65 1.48 -0.69 0.35 1.03 1.86 

30 1.81 0.28 2.31 0.77 0.5 0.77 0.9 -0.02 

31 1.08 2.29 2.71 2.72 1.44 1.12 2.73 3.28 

32 -0.28 1.42 2.14 1.24 0.29 0.32 1.92 1.8 

33 2.09 2.36 0.76 1.6 -0.18 -0.66 0.71 1.48 

34 1.79 3.41 1.75 -0.05 -0.66 -0.38 -0.42 0.03 

35 4.29 3.05 4.03 3.05 1.78 0.85 2.39 3.37 

36 3.74 1.74 4.83 1.22 1.6 1.35 1.4 1.76 

37 1.96 2.94 2.49 2.16 0.29 -0.18 0.27 1.87 

38 1.44 2.32 3.09 1.04 0.29 -0.47 -0.82 0.31 

39 2.39 2.87 2.23 1.85 0.7 -0.31 0.84 1.89 

40 2.79 4.04 3.22 2.28 0.29 -0.11 0.72 0.78 

41 3.8 2.47 3.61 2.39 0.77 0.36 0.7 2.46 

42 3.58 3.06 4.04 2.07 0.31 -0.35 -0.65 0.45 

43 0.48 3.5 4.72 1.75 -1.21 -1.36 -0.69 1.82 

44 0.42 2.32 2.18 1.04 -1.07 -1.75 -2.12 0.27 

45 4.76 4.43 4.43 2.67 0.66 0.22 0.92 3.13 

46 4.54 3.7 4.29 2.64 0.55 0.48 -0.51 1.49 

47 5.61 3.52 4.2 2.27 0.56 -0.66 0.58 2.44 

48 5.49 1.24 0.94 1.26 -0.12 0.2 -0.75 0.58 
157

As shown in table 6.7 and figures 6.24 thru 6.27, the differences between the measured and 

calculated sound pressure levels for the 63 Hz, 125 Hz, 250 Hz and 500 Hz full-octave bands are 

typically larger as compared to the other full-octave bands. It should be noted that the measured 

and calculated sound pressure levels are displayed as linear values in the tables and figures. 

Once the data was filtered, utilizing an A-weighting of the data, the differences in the lower 

frequency bands was negligible due to the type of filtering. Additionally, the frequency bands of 

major interest relative to the drilling portion of a roof bolting machine are the 1,000 Hz to 4,000 

Hertz full-octave bands. Therefore, the differences in measured and calculated sound pressure 

levels after the fifth run of the model relative to the full-octave bands of interest, provided a good 

fit and the final absorption coefficients determined from the model are shown in table 6.8. 

Table 6.8 Final Absorption Coefficients Determined from Model Runs 

Octave-band

(Hz) 

Absorption 

Coefficient 

63 .03 

125 .04 

250 .20 

500 .14 

1000 .15 

2000 .19 

4000 .28 

8000 .45 

The absorption coefficients determined, were then inputted into the Raynoise program to predict 

sound pressure levels at the operator position of the roof bolting machine as described in the next 

section. 
158

6.3.5 Predicting Sound Pressure Levels Underground Due to Drilling Cycle of Roof 

 Bolting Machine

 Once the absorption coefficients were determined from section 6.3.4 and displayed in 

table 6.8, several other pieces of information were required for input into the model to determine 

or predict the sound pressure levels underground. Namely, the full-octave band sound power 

level information received from the laboratory testing for a specific test, the specific roof bolting 

machine characteristics designed from the drafting package, AutoCAD, the geometry of the 

section of the underground mine to be modeled and a measurement grid within the geometric 

section representing the point locations for determining the sound pressure levels. 

6.3.5.1 Full-Octave Band Sound Power Levels from Laboratory Testing

 Table 6.9, illustrated below, provides the one-third octave-band as well as full-octave 

band sound power levels as an example for input into the Raynoise modeling program for 

predicting sound pressure levels. This example illustrates the octave-band and one-third octave 

band information from one of the laboratory test conducted for high-compressive strength media 

(>20,000 psi), using a 1.375-inch drill bit, round drill steel, a rotational speed of 600 rpm and a 

thrust setting of 4,242 lbs. 
159

Table 6.9 Full-Octave and One-Third Octave Band Sound Power Levels From Laboratory Test 

(1.375-inch drill bit, round drill steel, rotational speed of 600 rpm and thrust setting of 4,242 lbs.) 

 dBA dBA 

50 78.4 63 81.6 

63 76.9 125 88.5 

80 74.0 250 96.5 

100 87.0 500 96.9 

125 78.8 1,000 96.1 

160 81.0 2,000 100.8 

200 93.1 4,000 105.9 

250 93.0 8,000 101.4 

315 85.9 

Octave band Center 

Frequency (Hz) 

Overall 109.0 

400 90.2 

500 92.7 

630 93.1 

800 91.8 

1,000 89.8 

1,250 92.0 

1,600 93.8 

2,000 96.2 

2,500 97.3 

3,150 100.6 

4,000 102.0 

5,000 100.7 

6,300 98.9 

8,000 96.9 

10,000 90.4 

One-Third Octave band Center Frequency (Hz) 

Overall 109.0 

Therefore, the octave-band sound power levels from any of the tests conducted in the laboratory 

can be used as input for determining sound pressure levels utilizing the Raynoise modeling 

program. 

6.3.5.2 Specific Characteristics of the Roof Bolting Machine

 AutoCAD is a standard drafting package that is used to create the structural and machine 

models used to create testing environments for the Raynoise program. Due to input constraints 

with the Raynoise program, the drawings were limited to using the 3DPolyline entities to create 

the models (25). Objects with different material properties in a given model or structure drawing 

can be placed on different layers within AutoCAD and this can be read in as SET information by 

the Raynoise package where specific absorption, diffusion, transmission coefficients for each set 
160

can be assigned. Figures 6.32 and 6.33 listed below are drawings developed from the AutoCAD 

drafting package for two types of roof bolting machines. Figure 6.32 represents a Fletcher Roof 

Ranger II roof bolting machine and figure 6.33 illustrates a Fletcher HDDR roof bolting 

machine. Figures 6.32 and 6.33 were used as input to the Raynoise program relative to machine 

characteristics of the roof bolting machine. 

Figure 6.32 AutoCAD drawing of a Roof Ranger II Roof Bolting Machine 
161

Figure 6.33 AutoCAD drawing of a HDDR Roof Bolting Machine 

6.3.5.3 Establishment of a Measurement Grid for the Underground Mine Section

 Section 6.3.4.3, discussed earlier, provided the geometric configuration of an 

underground mine section, which was developed from in-mine measurements. To determine or 

predict sound pressure levels at specific points within the underground mine section, a 

measurement grid or mesh was required to be constructed for input into the Raynoise program. 

The measurement grid was developed and the associated measuring points were determined. 

The grid was developed utilizing measuring points that were on one-meter centers relative to the 

width of the entry or crosscut and located five-feet above the floor surface. The height 

measurement of five-feet was selected because this distance, on average, represents the average 
162

ear-height of an individual. Figures 6.34 thru 6.36, shown below, illustrate the measurement 

grids developed for a roof bolting machine located at the working face, crosscut and intersection, 

respectively. Figures 6.34 thru 6.36 were generated and required for input into the Raynoise 

program. 

Figure 6.34 Measurement Grid Developed for a Roof Bolting at the Mine Face 
163

Figure 6.35 Measurement Grid Developed for a Roof Bolting Machine at a Crosscut 

Figure 6.36 Measurement Grid Developed for a Roof Bolting Machine at an Intersection 
164

6.3.5.4 Development of a Command File for Input into Raynoise Program

 The construction of a command file (CMD) is necessary for using the Raynoise program 

(25). The command file provided properties related to the sound power of the noise source or 

sources, the type of noise source, e.g. line source or point source and the absorption or sabine 

coefficients relative to the acoustic properties associated with the underground mine section, 

equipment, etc. A point source is defined as a single noise source at a given location and a line 

source is a group of point sources along a straight line with the same acoustical characteristics. 

Research results have shown the dominant noise sources of a roof bolting machine are the drill 

bit, the drill steel, and the drill chuck. These noise sources would correspond to three point 

sources on a line source extending from the bit to the chuck, with the drill bit/contact surface as 

one source, the drill steel another and the third source being the drill chuck. A line source was 

chosen from the drill chuck to the drill bit/contact surface for the model run. Figure 6.37, shown 

below, provides a screenshot of a typical command file for input into the Raynoise program. 
165

Figure 6.37 Screenshot of a Command File for Input into Raynoise Program
166

6.3.5.5 Sound Pressure Levels Determined from Raynoise Program

 Once all of the required input parameters for the Raynoise program are constructed, 

determined and entered as discussed in sections 6.3.5.1 thru 6.3.5.4, the predicted or determined 

underground sound pressure levels can then be determined and viewed using the Raynoise 

program. An example of this view is shown in Figure 6.38, displaying the sound pressure levels 

attributed to a Roof Ranger II roof bolting machine drilling a bolt hole at the face of 6-foot-high 

underground coal mine. 

Figure 6.38 Determined Sound Pressure Level Contours in an Underground Coal Mine 

The sound pressure levels can be viewed or displayed as contour plots, as shown in figure 6.38, 

or interpreted numerically as shown in figure 6.39. 
167

Figure 6.39 Determined Sound Pressure Levels (Numerical) in an Underground Coal Mine 

Additionally, the program can provide a “zoom” view, relative to the determined sound pressure 

levels. Figure 6.40 shows a closer, or “zoom” view of the numerical sound pressure levels near 

and around a roof bolting machine. 
168

Figure 6.40 Zoom-view of Determined Sound Pressure Levels Near a Roof Bolting Machine 
169

6.3.5.6 Comparing Sound Pressure Levels - Model Prediction vs. Underground Measurements

 Sound pressure level measurements were conducted at the operator position of a Roof 

Ranger II roof bolting machine in an underground coal mine. The underground mine height 

varied from approximately 4 to 5 feet and the thickness of the coal seam varied from 32-40 

inches. The mine operator provided the opportunity to measure sound pressure levels relative to 

two bolting machines utilizing a vacuum system and mist system drilling method respectively. 

The roof bolting plan for the section is illustrated in figure 6.41 below. 

80ft. X 80 ft.

19 ft.

80ft. X 80 ft.

X X XX

X = Drill Holes

XX XX

X

X

X XX

XX X

Vacuum Drilling

Noise Measurement 

Mist Drilling

Noise Measurement

Figure 6.41 Roof Bolting Plan at the Underground Coal Mine 

Each roof bolting machine utilized a 1-inch drill bit, hex drill steel and drilled to a depth of 5 feet 

into the immediate roof. The roof consisted of a highly fractured shale rock consistent of a rock 

type with a low compressive strength (approximately 6,000 psi). The drilling configurations for 

both machines were set at a rotational speed of 500 rpm and a thrust of approximately 6,500 lbs. 
170

Sound pressure level measurements were conducted at the operator position of each machine. 

Table 6.10, illustrated below provides the results of the sound pressure level testing. 

Table 6.10 Sound Pressure Level Measurements at Operator Position of Roof Bolting Machine 

Operation of Roof 

Bolting Machine 

Roof Ranger II 

(Vacuum) 

dBA

Roof Ranger II 

(Mist System) 

dBA

Idling 82 82 

Mist System On 

No drilling 

NA 88 

Drilling 101 96 

The sound pressure levels experienced at the operator position during drilling utilizing the 

vacuum system of drilling was 101 dBA. Utilizing a mist system type of drilling, the operator 

was exposed to a sound pressure level of 96 dBA, resulting in a 5 dBA difference in sound 

pressure level. 

 The next step was to utilize the Raynoise program to compare the measured underground 

sound pressure level experienced at the operator position to the predicted sound pressure level 

determined thru the modeling approach. The first step was to characterize the geometric 

configuration of the mine layout in AutoCAD as shown in figure 6.41, secondly the specific 

characteristics of the roof bolting machine were then processed in AutoCAD and placed within 

the mine layout. A measurement mesh or grid was then developed to characterize sound 

pressure levels at specific locations within the mine section. Figure 6.42 displays the geometric 

configuration of the mine section, the location of the roof bolting machine and the measurement 
171

mesh used for predicting sound pressure levels. A total of 246 measurement locations within the 

mine section were selected and shown below. 

Figure 6.42 Model Simulation for Predicting Sound Pressure Levels 

Additionally, full-octave band sound power levels, obtained from the reverberation room testing, 

were then utilized for input into the program. Table 6.11 below provides the full-octave band 

sound power levels based on a test in the reverberation room relative to a rock media with a 

compressive strength equal to 6,000 psi, a 1-inch drill bit, hex drill steel, a rotational speed of 

500 rpm and a thrust setting of 6,363 lbs. 
172

Table 6.11 Full-Octave Band Sound Power Levels - Compressive strength-6,000 psi, hex drill 

steel, 1-inch bit, rotational speed-500 rpm, and Thrust setting-6,363 lbs 

Octave-band

(Hz) 

Sound Power Level

dBA 

63 85.6 

125 89.4 

250 101.1 

500 96.5 

1000 97.4 

2000 103.3 

4000 103.7 

8000 97.1 

Therefore, the mine configuration or layout, the roof bolting machine characteristics, a 

measurement grid or mesh, the full-octave band sound power levels and the sabine or absorption 

coefficients determined from section 6.3.4 were then inputted into the Raynoise program for 

predicting or determining sound pressure levels within the mine section and at the operator 

position of the roof bolting machine. The results of the model run are displayed graphically, as 

sound pressure level contours, shown in figure 6.43 below. 
173

Figure 6.43 Sound Pressure Level Contours for Model Run 

Furthermore, table 6.12 provides the results of the model run in numerical form for each of the 

246 measurement positions as displayed in figure 6.42. The table provides the predicted or 

determined sound pressure levels for each full-octave band (63 Hz, 125 Hz, 250 Hz, 500 Hz, 

1,000 Hz, 2,000 Hz, 4,000 Hz and 8,000 Hz) relative to each of the 246 measurement positions. 

The table also provides the overall linear and a-weighted sound pressure level at each 

measurement position. 
174

Table 6.12 Sound Pressure Level Results (Numerically) of the Model Run 

Location 63 Hz 125 Hz 250 Hz 500 Hz 1 kHz 2 kHz 4 kHz 8 kHz dBA dB 

1 65.3 68.8 77.4 74.0 74.6 79.8 78.5 69.0 84.1 84.7 

2 66.1 69.6 78.2 74.7 75.4 80.5 79.2 69.6 84.8 85.4 

3 66.6 70.2 78.7 75.3 75.9 81.1 79.8 70.2 85.4 86.0 

4 66.8 70.3 79.0 75.5 76.2 81.4 80.1 70.5 85.6 86.3 

5 67.1 70.7 79.3 75.8 76.5 81.7 80.4 70.8 85.9 86.6 

6 67.6 71.2 79.8 76.3 77.0 82.2 80.8 71.2 86.4 87.0 

7 67.6 71.2 79.9 76.4 77.0 82.3 80.9 71.4 86.5 87.1 

8 68.2 71.7 80.3 76.9 77.5 82.7 81.4 71.8 86.9 87.6 

9 68.8 72.4 81.1 77.6 78.2 83.4 82.1 72.7 87.7 88.3 

10 69.5 73.1 81.7 78.2 78.9 84.1 82.8 73.2 88.3 89.0 

11 70.4 73.9 82.5 79.1 79.7 84.9 83.6 74.1 89.1 89.8 

12 71.0 74.5 83.1 79.7 80.3 85.5 84.2 74.6 89.7 90.4 

13 71.4 74.9 83.7 80.2 80.8 86.1 84.8 75.3 90.3 91.0 

14 71.8 75.3 84.1 80.6 81.3 86.5 85.3 75.9 90.8 91.4 

15 72.2 75.7 84.7 81.1 81.8 87.0 85.9 76.6 91.3 91.9 

16 72.9 76.4 85.4 81.8 82.5 87.8 86.6 77.3 92.1 92.7 

17 73.6 77.2 86.3 82.7 83.4 88.7 87.6 78.4 93.0 93.6 

18 74.5 78.1 87.3 83.6 84.3 89.7 88.6 79.5 94.0 94.6 

19 65.0 68.6 77.2 73.7 74.4 79.6 78.2 68.7 83.8 84.4 

20 65.2 68.8 77.4 74.0 74.6 79.8 78.5 69.0 84.0 84.7 

21 65.5 69.1 77.8 74.3 75.0 80.2 78.9 69.5 84.4 85.1 

22 65.7 69.2 78.0 74.5 75.2 80.4 79.2 69.8 84.7 85.3 

23 66.1 69.7 78.6 75.0 75.7 80.9 79.7 70.4 85.2 85.8 

24 67.0 70.6 79.4 75.9 76.5 81.8 80.5 71.1 86.1 86.7 

25 67.9 71.5 80.3 76.7 77.4 82.6 81.4 72.0 86.9 87.5 

26 68.8 72.3 81.0 77.5 78.2 83.4 82.1 72.6 87.6 88.3 

27 69.7 73.3 81.9 78.4 79.1 84.3 83.0 73.3 88.5 89.2 

28 70.5 74.1 82.6 79.2 79.8 85.0 83.6 73.9 89.3 89.9 

29 71.2 74.7 83.3 79.8 80.5 85.7 84.3 74.6 89.9 90.5 

30 71.5 75.0 83.6 80.1 80.8 86.0 84.6 74.8 90.2 90.8 

31 71.7 75.3 83.8 80.4 81.0 86.2 84.8 75.1 90.4 91.1 

32 72.4 76.0 84.7 81.2 81.9 87.1 85.7 76.1 91.3 91.9 

33 72.6 76.1 84.9 81.4 82.0 87.3 86.0 76.5 91.5 92.2 

34 72.8 76.4 85.3 81.7 82.4 87.7 86.5 77.2 92.0 92.6 

35 73.5 77.0 86.2 82.5 83.2 88.6 87.5 78.5 92.9 93.5 

36 74.5 78.1 87.3 83.6 84.3 89.7 88.7 79.7 94.0 94.6 

37 64.7 68.3 77.0 73.5 74.2 79.4 78.1 68.5 83.6 84.3 

38 64.6 68.2 77.1 73.5 74.2 79.5 78.3 68.8 83.8 84.4 

39 64.6 68.2 77.3 73.7 74.3 79.6 78.5 69.2 84.0 84.5 

40 65.0 68.6 77.7 74.1 74.7 80.1 78.9 69.6 84.4 85.0 

41 65.6 69.1 78.2 74.6 75.2 80.5 79.4 70.0 84.8 85.4 

42 67.0 70.5 79.4 75.8 76.5 81.8 80.5 71.0 86.1 86.6 

43 67.8 71.4 80.1 76.6 77.3 82.5 81.2 71.5 86.7 87.4 

44 69.1 72.7 81.2 77.8 78.4 83.6 82.2 72.4 87.8 88.5 

45 70.1 73.6 82.0 78.6 79.3 84.4 82.9 73.0 88.6 89.2 

46 70.9 74.4 82.9 79.5 80.1 85.3 83.8 73.9 89.5 90.1 

47 71.5 75.0 83.6 80.1 80.8 85.9 84.5 74.8 90.2 90.8 
175

Location 63 Hz 125 Hz 250 Hz 500 Hz 1 kHz 2 kHz 4 kHz 8 kHz dBA dB 

48 71.8 75.4 83.8 80.4 81.1 86.2 84.8 74.9 90.4 91.1 

49 72.3 75.9 84.4 81.0 81.6 86.8 85.4 75.7 91.1 91.7 

50 72.5 76.1 84.8 81.3 81.9 87.2 85.8 76.2 91.4 92.0 

51 72.5 76.0 84.9 81.4 82.0 87.3 86.2 77.0 91.6 92.2 

52 73.0 76.6 85.6 82.0 82.7 88.0 86.9 77.7 92.3 92.9 

53 73.1 76.6 85.8 82.1 82.8 88.1 87.1 78.0 92.4 93.1 

54 73.8 77.4 86.7 83.0 83.7 89.1 88.1 79.2 93.4 94.0 

55 64.7 68.3 77.0 73.5 74.2 79.4 78.1 68.4 83.6 84.3 

56 64.9 68.5 77.3 73.8 74.4 79.7 78.4 68.9 83.9 84.6 

57 64.7 68.3 77.2 73.6 74.3 79.6 78.3 68.9 83.9 84.4 

58 65.2 68.8 77.7 74.1 74.8 80.0 78.8 69.4 84.4 84.9 

59 66.0 69.6 78.5 74.9 75.6 80.9 79.7 70.3 85.2 85.8 

60 66.7 70.2 79.1 75.5 76.2 81.5 80.2 70.8 85.8 86.4 

61 67.6 71.2 79.9 76.4 77.1 82.3 81.0 71.4 86.5 87.2 

62 68.5 72.1 80.7 77.3 77.9 83.1 81.8 72.2 87.3 88.0 

63 69.9 73.5 82.0 78.6 79.2 84.4 83.0 73.2 88.6 89.3 

64 70.9 74.4 82.8 79.5 80.1 85.2 83.8 73.8 89.5 90.1 

65 71.4 74.9 83.4 80.0 80.6 85.8 84.3 74.3 90.0 90.6 

66 71.8 75.3 83.8 80.4 81.0 86.2 84.7 74.8 90.4 91.0 

67 72.3 75.8 84.4 80.9 81.6 86.8 85.3 75.6 91.0 91.6 

68 72.3 75.9 84.5 81.0 81.7 86.9 85.5 75.9 91.1 91.7 

69 72.6 76.2 84.9 81.4 82.1 87.3 86.0 76.5 91.6 92.2 

70 72.9 76.5 85.4 81.8 82.5 87.8 86.6 77.3 92.1 92.7 

71 72.9 76.5 85.5 81.9 82.6 87.9 86.7 77.4 92.2 92.8 

72 73.5 77.1 86.1 82.5 83.2 88.5 87.3 77.8 92.8 93.4 

73 65.4 68.9 77.3 73.9 74.6 79.7 78.3 68.5 84.0 84.6 

74 65.4 69.0 77.4 74.0 74.6 79.8 78.4 68.7 84.0 84.7 

75 65.7 69.2 77.9 74.4 75.1 80.3 79.0 69.4 84.5 85.2 

76 65.8 69.3 78.2 74.6 75.3 80.5 79.3 69.9 84.8 85.4 

77 66.1 69.7 78.6 75.0 75.7 81.0 79.8 70.5 85.3 85.9 

78 66.8 70.4 79.3 75.8 76.4 81.7 80.5 71.2 86.0 86.6 

79 67.4 71.0 79.8 76.3 77.0 82.2 81.0 71.6 86.5 87.1 

80 68.3 71.9 80.6 77.1 77.7 83.0 81.7 72.2 87.2 87.9 

81 69.3 72.8 81.4 77.9 78.6 83.8 82.4 72.8 88.0 88.6 

82 70.3 73.8 82.4 79.0 79.6 84.8 83.5 73.8 89.0 89.7 

83 71.2 74.7 83.3 79.9 80.5 85.7 84.3 74.6 89.9 90.6 

84 71.7 75.3 83.9 80.4 81.0 86.2 84.9 75.2 90.5 91.1 

85 71.9 75.5 84.1 80.6 81.3 86.5 85.1 75.4 90.7 91.3 

86 72.1 75.6 84.4 80.9 81.5 86.7 85.4 75.9 91.0 91.6 

87 72.4 75.9 84.7 81.2 81.9 87.1 85.8 76.2 91.3 92.0 

88 72.8 76.4 85.3 81.7 82.4 87.7 86.5 77.2 92.0 92.6 

89 73.4 77.0 86.2 82.5 83.2 88.5 87.4 78.3 92.8 93.4 

90 74.0 77.6 86.8 83.1 83.8 89.1 88.0 78.8 93.4 94.0 

91 65.0 68.5 77.1 73.6 74.3 79.5 78.1 68.5 83.7 84.3 

92 65.8 69.3 77.9 74.4 75.1 80.3 78.9 69.3 84.5 85.1 

93 66.3 69.9 78.5 75.0 75.7 80.9 79.6 70.0 85.1 85.8 

94 66.5 70.1 78.8 75.3 76.0 81.2 79.9 70.4 85.5 86.1 

95 66.7 70.3 79.0 75.5 76.1 81.4 80.1 70.5 85.6 86.3 

96 67.7 71.2 79.8 76.3 77.0 82.2 80.8 71.1 86.4 87.0 
176

Location 63 Hz 125 Hz 250 Hz 500 Hz 1 kHz 2 kHz 4 kHz 8 kHz dBA dB 

97 67.5 71.1 79.7 76.2 76.9 82.1 80.8 71.3 86.3 87.0 

98 67.8 71.4 80.1 76.6 77.3 82.5 81.2 71.8 86.7 87.4 

99 68.5 72.1 80.8 77.3 78.0 83.2 82.0 72.6 87.5 88.1 

100 69.4 73.0 81.7 78.2 78.9 84.1 82.8 73.3 88.3 89.0 

101 70.5 74.1 82.7 79.3 79.9 85.1 83.8 74.2 89.3 90.0 

102 71.0 74.5 83.2 79.7 80.4 85.6 84.3 74.7 89.8 90.5 

103 71.4 75.0 83.7 80.2 80.8 86.1 84.7 75.1 90.3 90.9 

104 71.6 75.2 83.9 80.4 81.1 86.3 85.0 75.6 90.6 91.2 

105 72.1 75.7 84.6 81.0 81.7 87.0 85.8 76.6 91.3 91.9 

106 72.6 76.1 85.2 81.6 82.3 87.6 86.5 77.3 91.9 92.5 

107 73.1 76.7 85.9 82.3 82.9 88.3 87.3 78.2 92.6 93.2 

108 73.9 77.5 86.7 83.0 83.7 89.1 88.1 79.1 93.4 94.0 

109 79.2 82.8 92.6 88.7 89.4 94.9 94.2 86.0 99.4 99.9 

110 78.3 81.9 91.3 87.5 88.2 93.7 92.8 84.3 98.1 98.6 

111 77.6 81.1 90.4 86.7 87.4 92.7 91.8 83.2 97.1 97.7 

112 76.8 80.4 89.5 85.8 86.5 91.8 90.8 81.9 96.1 96.8 

113 76.3 79.8 88.7 85.1 85.8 91.1 90.0 80.9 95.4 96.0 

114 75.8 79.4 88.1 84.6 85.2 90.5 89.3 80.1 94.8 95.4 

115 75.4 78.9 87.6 84.1 84.7 89.9 88.7 79.4 94.2 94.8 

116 75.0 78.5 87.2 83.7 84.3 89.5 88.3 79.1 93.8 94.4 

117 74.4 78.0 86.4 83.0 83.6 88.8 87.5 78.1 93.1 93.7 

118 73.9 77.4 85.9 82.5 83.1 88.3 86.9 77.5 92.5 93.2 

119 73.0 76.5 85.0 81.6 82.2 87.4 86.1 76.8 91.7 92.3 

120 71.9 75.5 84.1 80.6 81.2 86.4 85.2 75.9 90.7 91.3 

121 71.0 74.5 83.1 79.6 80.2 85.5 84.2 74.9 89.7 90.4 

122 70.1 73.6 82.1 78.7 79.3 84.5 83.2 73.8 88.8 89.4 

123 69.6 73.1 81.7 78.2 78.9 84.1 82.8 73.6 88.3 89.0 

124 69.3 72.9 81.6 78.0 78.7 83.9 82.7 73.6 88.2 88.8 

125 68.6 72.1 80.9 77.4 78.0 83.3 82.0 72.8 87.6 88.2 

126 68.3 71.8 80.6 77.0 77.7 82.9 81.7 72.4 87.2 87.8 

127 68.1 71.6 80.3 76.8 77.4 82.7 81.4 72.0 86.9 87.6 

128 67.7 71.2 79.9 76.4 77.0 82.2 81.0 71.6 86.5 87.1 

129 67.5 71.0 79.6 76.2 76.8 82.0 80.8 71.5 86.3 86.9 

130 80.0 83.6 93.9 89.8 90.5 96.1 95.8 88.2 100.7 101.3 

131 78.7 82.3 92.1 88.1 88.9 94.4 93.8 85.7 98.9 99.5 

132 77.9 81.5 91.0 87.2 87.9 93.3 92.5 84.1 97.7 98.3 

133 77.1 80.7 89.9 86.2 86.9 92.3 91.4 82.7 96.7 97.3 

134 76.8 80.3 89.5 85.8 86.5 91.8 90.8 82.1 96.2 96.8 

135 76.1 79.7 88.6 85.0 85.6 90.9 89.8 80.8 95.2 95.8 

136 75.4 79.0 87.7 84.1 84.8 90.1 88.9 79.8 94.4 95.0 

137 75.0 78.6 87.1 83.7 84.3 89.5 88.3 79.0 93.8 94.4 

138 74.6 78.1 86.6 83.2 83.8 89.0 87.7 78.3 93.2 93.9 

139 74.3 77.8 86.3 82.8 83.5 88.7 87.3 78.0 92.9 93.6 

140 73.8 77.3 85.7 82.3 83.0 88.1 86.8 77.3 92.4 93.0 

141 73.0 76.5 85.1 81.6 82.2 87.4 86.1 76.7 91.7 92.3 

142 72.1 75.7 84.3 80.8 81.5 86.7 85.4 76.1 91.0 91.6 

143 71.2 74.8 83.5 80.0 80.6 85.9 84.7 75.4 90.2 90.8 

144 70.3 73.9 82.7 79.1 79.8 85.0 83.8 74.7 89.3 89.9 

145 69.5 73.0 81.9 78.3 79.0 84.3 83.1 74.0 88.6 89.2 
177

Location 63 Hz 125 Hz 250 Hz 500 Hz 1 kHz 2 kHz 4 kHz 8 kHz dBA dB 

146 68.7 72.3 81.1 77.6 78.2 83.5 82.4 73.3 87.8 88.4 

147 68.2 71.8 80.5 77.0 77.6 82.9 81.7 72.6 87.2 87.8 

148 68.0 71.5 80.1 76.7 77.3 82.5 81.2 72.0 86.8 87.4 

149 67.8 71.4 79.9 76.5 77.1 82.3 81.0 71.6 86.5 87.2 

150 67.7 71.3 79.7 76.3 76.9 82.1 80.7 71.3 86.3 87.0 

151 82.5 86.2 97.1 92.8 93.6 99.4 99.4 92.4 104.1 104.6 

152 79.4 83.0 93.1 89.1 89.8 95.4 94.9 87.1 99.9 100.5 

153 78.4 82.0 91.6 87.7 88.5 93.9 93.3 85.1 98.4 99.0 

154 77.5 81.1 90.5 86.7 87.4 92.8 92.0 83.5 97.2 97.8 

155 77.0 80.5 89.7 86.0 86.7 92.0 91.1 82.4 96.4 97.0 

156 76.3 79.9 88.9 85.2 85.9 91.2 90.2 81.3 95.5 96.2 

157 75.9 79.5 88.3 84.7 85.4 90.6 89.5 80.5 95.0 95.6 

158 75.4 78.9 87.6 84.1 84.8 90.0 88.8 79.7 94.3 94.9 

159 75.0 78.5 87.1 83.6 84.3 89.5 88.3 79.0 93.8 94.4 

160 74.4 77.9 86.4 83.0 83.6 88.8 87.5 78.2 93.1 93.7 

161 74.0 77.5 86.0 82.5 83.2 88.4 87.0 77.6 92.6 93.3 

162 73.3 76.9 85.4 81.9 82.6 87.8 86.4 77.0 92.0 92.7 

163 72.4 76.0 84.6 81.1 81.8 87.0 85.7 76.4 91.3 91.9 

164 71.2 74.8 83.5 80.0 80.7 85.9 84.7 75.5 90.2 90.8 

165 70.5 74.0 82.9 79.3 80.0 85.2 84.1 75.0 89.6 90.2 

166 70.0 73.5 82.4 78.8 79.5 84.8 83.6 74.5 89.1 89.7 

167 69.4 73.0 81.8 78.3 78.9 84.2 83.0 73.9 88.5 89.1 

168 68.8 72.4 81.2 77.7 78.3 83.6 82.5 73.4 87.9 88.5 

169 68.5 72.0 80.8 77.3 77.9 83.2 82.0 72.8 87.5 88.1 

170 68.0 71.6 80.3 76.8 77.4 82.7 81.5 72.2 87.0 87.6 

171 67.7 71.3 79.9 76.4 77.1 82.3 81.0 71.7 86.5 87.2 

172 82.5 86.2 97.1 92.8 93.5 99.3 99.3 92.3 104.0 104.6 

173 79.4 83.1 93.1 89.1 89.8 95.4 94.9 87.1 99.9 100.5 

174 78.4 82.0 91.7 87.8 88.5 94.0 93.3 85.2 98.5 99.0 

175 77.5 81.1 90.5 86.7 87.4 92.8 92.0 83.5 97.2 97.8 

176 76.9 80.4 89.6 85.9 86.6 91.9 91.0 82.2 96.3 96.9 

177 76.3 79.9 88.8 85.2 85.9 91.2 90.1 81.3 95.5 96.1 

178 75.9 79.4 88.2 84.7 85.3 90.6 89.4 80.4 94.9 95.5 

179 75.4 78.9 87.6 84.1 84.7 90.0 88.8 79.6 94.3 94.9 

180 74.9 78.5 87.1 83.6 84.2 89.5 88.2 79.0 93.7 94.4 

181 74.5 78.0 86.5 83.1 83.7 88.9 87.6 78.3 93.2 93.8 

182 74.0 77.5 86.0 82.5 83.2 88.3 87.0 77.5 92.6 93.2 

183 73.3 76.8 85.3 81.9 82.5 87.7 86.4 76.9 92.0 92.6 

184 72.4 75.9 84.6 81.1 81.7 87.0 85.7 76.4 91.2 91.9 

185 71.3 74.9 83.6 80.1 80.7 86.0 84.8 75.5 90.3 90.9 

186 70.5 74.1 82.9 79.3 80.0 85.2 84.1 74.9 89.6 90.2 

187 69.8 73.4 82.2 78.6 79.3 84.5 83.3 74.2 88.8 89.4 

188 69.3 72.8 81.6 78.1 78.7 84.0 82.8 73.6 88.3 88.9 

189 68.7 72.2 81.0 77.5 78.2 83.4 82.3 73.2 87.7 88.3 

190 68.3 71.8 80.6 77.0 77.7 83.0 81.8 72.6 87.3 87.9 

191 68.0 71.5 80.2 76.7 77.4 82.6 81.4 72.2 86.9 87.5 

192 67.5 71.1 79.7 76.2 76.8 82.0 80.8 71.5 86.3 86.9 

193 80.0 83.6 93.9 89.8 90.5 96.2 95.9 88.3 100.8 101.3 

194 78.7 82.3 92.0 88.1 88.8 94.3 93.7 85.5 98.8 99.4 
178

Location 63 Hz 125 Hz 250 Hz 500 Hz 1 kHz 2 kHz 4 kHz 8 kHz dBA dB 

195 77.9 81.5 90.9 87.1 87.8 93.2 92.4 83.9 97.6 98.2 

196 77.2 80.7 89.9 86.2 86.9 92.3 91.3 82.7 96.7 97.2 

197 76.7 80.3 89.3 85.7 86.4 91.7 90.7 81.8 96.0 96.6 

198 76.1 79.6 88.5 84.9 85.6 90.8 89.7 80.7 95.1 95.8 

199 75.5 79.1 87.8 84.2 84.9 90.1 88.9 79.8 94.4 95.0 

200 75.1 78.6 87.2 83.7 84.4 89.6 88.3 79.1 93.8 94.5 

201 74.7 78.2 86.7 83.3 83.9 89.1 87.8 78.4 93.3 94.0 

202 74.3 77.8 86.3 82.8 83.5 88.7 87.3 78.0 92.9 93.6 

203 73.7 77.3 85.7 82.3 82.9 88.1 86.7 77.3 92.4 93.0 

204 72.8 76.4 84.9 81.4 82.1 87.3 86.0 76.6 91.5 92.2 

205 71.9 75.5 84.1 80.6 81.3 86.5 85.2 75.9 90.7 91.4 

206 71.0 74.5 83.2 79.7 80.3 85.6 84.4 75.1 89.9 90.5 

207 70.0 73.6 82.3 78.8 79.4 84.6 83.4 74.2 88.9 89.5 

208 69.2 72.8 81.5 78.0 78.6 83.8 82.6 73.5 88.2 88.7 

209 68.5 72.0 80.7 77.2 77.8 83.1 81.9 72.7 87.4 88.0 

210 68.1 71.7 80.3 76.8 77.4 82.7 81.4 72.2 86.9 87.6 

211 68.0 71.5 80.0 76.6 77.2 82.4 81.1 71.9 86.7 87.3 

212 67.9 71.4 79.9 76.5 77.1 82.3 81.0 71.6 86.5 87.2 

213 68.0 71.5 80.0 76.5 77.2 82.4 81.0 71.6 86.6 87.3 

214 79.4 83.0 92.8 88.9 89.6 95.1 94.5 86.3 99.6 100.2 

215 78.4 82.0 91.5 87.7 88.4 93.8 93.0 84.5 98.2 98.8 

216 77.6 81.2 90.5 86.7 87.4 92.8 91.9 83.2 97.2 97.8 

217 76.9 80.5 89.5 85.9 86.6 91.9 90.9 82.0 96.2 96.8 

218 76.3 79.9 88.8 85.2 85.9 91.2 90.1 81.0 95.5 96.1 

219 75.7 79.3 88.0 84.5 85.2 90.4 89.2 80.0 94.7 95.3 

220 75.3 78.8 87.5 84.0 84.6 89.9 88.6 79.3 94.1 94.8 

221 74.9 78.4 87.0 83.5 84.2 89.4 88.1 78.8 93.6 94.3 

222 74.3 77.9 86.4 82.9 83.6 88.8 87.4 78.0 93.0 93.7 

223 73.8 77.3 85.7 82.3 83.0 88.1 86.8 77.3 92.4 93.0 

224 72.6 76.1 84.6 81.1 81.8 87.0 85.7 76.3 91.2 91.9 

225 71.2 74.7 83.2 79.8 80.4 85.6 84.2 74.9 89.8 90.5 

226 70.5 74.1 82.5 79.1 79.7 84.9 83.6 74.2 89.1 89.8 

227 69.8 73.4 81.9 78.4 79.1 84.3 83.0 73.7 88.5 89.2 

228 69.4 72.9 81.5 78.0 78.7 83.9 82.6 73.4 88.2 88.8 

229 69.4 73.0 81.6 78.1 78.8 84.0 82.8 73.6 88.3 88.9 

230 68.4 72.0 80.8 77.2 77.9 83.2 82.0 72.8 87.5 88.1 

231 68.3 71.9 80.7 77.1 77.8 83.1 81.9 72.7 87.4 88.0 

232 68.1 71.7 80.4 76.9 77.5 82.8 81.5 72.3 87.1 87.7 

233 67.7 71.2 80.0 76.5 77.1 82.4 81.2 71.9 86.7 87.3 

234 67.3 70.9 79.6 76.1 76.7 82.0 80.8 71.6 86.3 86.9 

235 79.5 83.1 93.1 89.1 89.9 95.4 94.9 86.8 99.9 100.5 

236 80.3 83.9 94.2 90.1 90.9 96.5 96.1 88.3 101.0 101.6 

237 82.3 86.0 96.8 92.5 93.3 99.1 99.0 91.7 103.7 104.3 

238 78.9 82.5 92.4 88.5 89.2 94.8 94.1 85.9 99.2 99.8 

239 79.6 83.3 93.4 89.4 90.1 95.7 95.3 87.3 100.3 100.8 

240 79.8 83.4 93.7 89.6 90.3 95.9 95.5 87.6 100.5 101.0 

241 78.8 82.4 92.3 88.4 89.1 94.6 94.1 85.9 99.1 99.7 

242 79.3 82.9 93.1 89.0 89.8 95.3 94.9 86.9 99.9 100.4 

243 79.6 83.2 93.4 89.3 90.1 95.7 95.3 87.5 100.2 100.8 
179

Location 63 Hz 125 Hz 250 Hz 500 Hz 1 kHz 2 kHz 4 kHz 8 kHz dBA dB 

244 79.6 83.2 93.3 89.3 90.0 95.6 95.1 87.0 100.1 100.7 

245 80.3 83.9 94.3 90.2 91.0 96.6 96.3 88.6 101.2 101.7 

246 82.5 86.1 97.1 92.7 93.5 99.3 99.3 92.2 104.0 104.5 

In determining the validity of the model approach relative to comparing the actual underground 

measurements to the predicted or determined sound pressure levels when utilizing the model 

approach, measurement positions 235 thru 237, shown in figure 6.42, were examined to provide 

the predicted or determined sound pressure levels at the operator position of the roof bolting 

machine. Figure 6.44 displays a “snapshot” of the sound pressure level contours, along with the 

A-weighted sound pressure levels at measuring points 235 thru 237 of the model. 

235 236 237

99.9 dBA

101.0 dBA 103.7 dBA

Figure 6.44 A-Weighted Sound Pressure Levels Near Operator Position of Roof Bolting 

 Machine 
180

Table 6.10 provided a sound pressure level of 101 dBA at the operator position of the roof 

bolting machine from underground measurements. The location of the measurement 

underground was the same location as measuring point number 236 utilized for the model 

approach. The determined or predicted sound pressure level using the modeling approach was 

101 dBA, the same sound pressure level as measured underground. It should be noted, in order 

for model validation, data was collected in an actual underground mine environment. Due to 

mine accessibility, characterization of the acoustic environment, along with measuring sound 

pressure levels associated operators of roof bolting machines occurred in a mine with low 

compressive strength rock media during drilling operations. However, the research effort has 

proven that measuring laboratory sound power level results of the roof bolting machine given 

any compressive strength rock media, along with proper characterization of the acoustic and 

geological environment underground, one could predict the sound pressure level experienced by 

a roof bolting machine operator with confidence. 

 Therefore, this section provided the mining community with an approach, which utilizes 

sound power levels acquired from laboratory tests and measured absorption coefficients from 

underground testing to accurately predict or determine sound pressure levels, at any location in a 

mine section. The approach as compared to the modeling approach in section 6.2, provides a 

more reliable and accurate determination of sound pressure level at any position or location 

within a mine section without the limitations relative to absorption coefficients and near-field 

limitations as discussed in section 6.2. Section 6.3.6 below will demonstrate and provide an 

approach for determining the noise dosage of a roof bolting machine operator utilizing the 

predicted or determined sound pressure levels obtained from the modeling approach addressed 

from this section. 
181

6.3.6 Determining Noise Dosage of a Roof Bolter Operator from Predicted Sound Pressure 

 Levels

The noise dosage a worker receives can be expressed by the following equation: 

 % (100 / )[ 2 ] ( ) /

0

Dose TC dt LS CL ER RTime −

∫ = (12) 

and % (100 / )(2 )[ ] 0

( ) / Dose TC dt

RTime LS CL ER ∫ − =

therefore ) % (100 / )(2 )( ( ) / Dose TC RTime LS −CL ER =

where 

 Dose% = workers’ noise dosage, percent 

 

 TC = criterion time, 8 hours or 28,800 seconds 

 LS = Sound pressure level, dBA 

 CL = Criterion level, dBA 

 ER = Exchange rate, dBA 

 RTime = Run time, seconds 

Using equation (12) above, with a predicted or determined sound pressure level at the operator 

position of a roof bolting machine, the machine operators’ noise dosage could then be 

determined. For instance, if we use the example illustrated above in section 6.3.5.6, where the 

compressive strength of the rock media was 6,000 psi and the roof bolting machine operator 

utilized the vacuum drilling method, with a 1-inch bit, hex drill steel, a rotational speed of 500 

rpm and a thrust setting of 6,363 lbs, the measured and validated predicted sound pressure level 

was determined to be 101 dBA at the operator position of the machine. Using equation (12), the 

mining community can then determine the operators’ noise dosage, relative to the MSHAPermissible Exposure Limit (MSHA-PEL) (90 decibels, A-weighted, as an 8-hour time-weighted 
182

average [90 dBA as an 8-hr TWA]), with a 5 dBA exchange rate) or the NIOSH-Recommended 

Exposure Limit (NIOSH-REL) (85 decibels, A-weighted, as an 8-hour time-weighted average 

[85 dBA as an 8-hr TWA]), with a 3 dBA exchange rate (26) received per drilling an individual 

hole during the drilling cycle of the roof bolting machine as shown below. 

 ) % (100 / )(2 )( ( ) / Dose TC RTime LS −CL ER =

where 

TC = 28,800 seconds 

LS = 101 dBA 

CL = 90 dBA 

ER – 5 dBA 

RTime = 50 seconds (based on a penetration rate of 1.2 inches/second and a hole depth of 5 ft) 

therefore, the dose percentage of the roof bolter operator for this particular example would be: 

 ) % (100 / 28,800)(2 )(50 (101−90) / 5 Dose = = (.00347)(4.59)(50) = 0.80% 

Additionally, assuming similar rock media (compressive strength of 6,000 psi) and the operator 

of the roof bolting machine drilling 78 drill holes per shift for installation of roof bolts, the 

operator’s noise dosage relative to only utilizing the roof bolting machine for drilling would be: 

 0.8% x (78 drill holes) = 62.4 % of the MSHA-PEL of 100% 

In comparison, the NIOSH-REL noise dosage for the same situation mentioned above would be 

546%, based on a criterion level of 85 dBA and an exchange rate of 3 dBA. Table 6.13 below, 

provides the noise dosage of a roof bolter operator (per hole and per shift), relative to a 

respective sound pressure level and based on a run time of each hole consisting of 50 seconds 

and assuming the operator will drill 78 holes per his working shift. 
183

Table 6.13 Noise Dosage (MSHA and NIOSH) of Roof Bolting Machine Operator 

Sound 

Pressure Level 

dBA 

Run Time 

(per hole) 

(sec) 

MSHA-Dose 

(per hole) 

(%) 

NIOSH-Dose 

(per hole) 

(%) 

Drill Holes 

(per shift) 

MSHA-Dose 

(per shift) 

(%) 

NIOSH-Dose 

(per shift) 

(%) 

80 50 0.0 0.1 78 3.4 4.3 

82 50 0.1 0.1 78 4.5 6.8 

85 50 0.1 0.2 78 6.8 13.5 

86 50 0.1 0.2 78 7.8 17.1 

87 50 0.1 0.3 78 8.9 21.5 

88 50 0.1 0.3 78 10.3 27.1 

89 50 0.2 0.4 78 11.8 34.1 

90 50 0.2 0.6 78 13.5 43.0 

91 50 0.2 0.7 78 15.6 54.2 

92 50 0.2 0.9 78 17.9 68.2 

93 50 0.3 1.1 78 20.5 86.0 

94 50 0.3 1.4 78 23.6 108.3 

95 50 0.3 1.7 78 27.1 136.5 

96 50 0.4 2.2 78 31.1 172.0 

97 50 0.5 2.8 78 35.7 216.7 

98 50 0.5 3.5 78 41.1 273.0 

99 50 0.6 4.4 78 47.2 343.9 

100 50 0.7 5.6 78 54.2 433.3 

101 50 0.8 7.0 78 62.2 546.0 

102 50 0.9 8.8 78 71.5 687.9 

103 50 1.1 11.1 78 82.1 866.7 

104 50 1.2 14.0 78 94.3 1091.9 

105 50 1.4 17.6 78 108.3 1375.7 

106 50 1.6 22.2 78 124.4 1733.3 

Chapter 6 has provided the mining community with proven approaches to predict sound pressure 

levels, with relative certainty, at the operator position of a roof bolting machine and at differing 

locations within a mine section, utilizing laboratory testing results relative to the roof bolting 

machine. Additionally, the mining community was presented with an approach to characterize 

the noise dosage a roof bolting machine operator will receive, based on laboratory results. These 

approaches provide the mining industry with the opportunity to predict sound pressure levels and 

noise dosage to machine operators without the laborious effort of conducting numerous 

underground measurements. 
184

CHAPTER 7 

CONCLUSIONS 

 The evaluation of differing noise control technologies relative to a roof bolting 

machine was possible utilizing the acoustically controlled reverberation room at the 

Pittsburgh Research Laboratory, along with installing thrust, rotational speed and penetration 

sensors on the machine as discussed in Chapter 4. Chapter 5 of the research effort provided 

testing results related to using differing drilling configurations (thrust, rotational speed, 

penetration rate, bit size, type of drill steel) and drilling methods (vacuum or dry, wet, mist) 

in high compressive strength rock media (>20,000 psi) relative to sound power levels 

measured from the roof bolting machine. When comparing round and hex drill steel, round 

drill steel should be used when utilizing the vacuum type of drilling method and hex drill 

steel should be utilized when performing the wet or mist type of drilling method. While 

increasing the thrust does yield an increased sound power level for both of the round and hex 

drill steel, the differences are negligible. When comparing rotational speed affect relative to 

round or hex drill steel, the round drill steel, during vacuum type drilling, provides a lower 

sound power level than similar hex drill steel tests. For the wet or mist system type of 

drilling, there appears to be no difference between the one-inch and 1.375-inch round and 

hex drill steel. Upon comparing penetration rates relative to round or hex drill steel in 

relation to thrust or rotational speed, their appears to be minimal affect attributed to thrust or 

rotational speeds. 

 When comparing the one-inch diameter bits to the 1.375-inch diameter bits, the oneinch diameter drill bits are slightly quieter than the 1.375-inch diameter drill bits. The 

penetration rates relative to the one-inch drill bits are noticeably higher than the 1.375-inch 
185

bits, on an order of two to three times higher. When comparing the 1-inch bit to the 1.375-

inch bit relative to rotational speed, the one-inch bit performed significantly better than the 

1.375-inch bit. For optimal performance and lower sound power levels, rotational speeds in 

the range of 200-400 rpm performed better and were quieter. 

 When comparing the different types of drilling methods, specifically vacuum, wet 

and mist drilling, penetration rates utilizing a wet or mist system drilling technique were 

much higher than using a dry or vacuum type drilling method. Additionally, utilizing a 

wet or mist system proved to emit less noise than similar tests conducted under vacuum 

or dry conditions. Much of the difference is attributable to the lubricating affect of the 

water or mist, which attenuates the higher frequency noise during the drilling process. 

 The individual test data collected (approximately 500 tests) from the research effort 

was then compiled, summarized and statistically correlated for drilling into a highcompressive strength media (>20,000 psi) by developing one equation, in which, could be 

used to determine or predict overall sound power levels given any type of drilling method 

(vacuum, wet or mist) and using varying types of drilling parameters or configurations 

related to thrust, rotational speed, bit size and type of drill steel. The statistical model 

equation, provided the mining community with a simple and reliable approach to predict a 

sound power level for a roof bolting machine during the drilling operation in high 

compressive strength rock media, given any type of drilling method (vacuum, wet or mist) 

and drilling parameter configuration (thrust, rotational speed, bit size and type of drill steel). 

The coefficient of determination for the test data, R2

, or the measure of the goodness of fit of 

a linear model, was equal to .849, indicating the statistical model to be a good fit or a 

representation of the data set. Furthermore, the residuals of the data set (laboratory minus 
186

model values of sound power) provided an excellent correlation with each other. Five 

residuals out of 486, were determined to be plus or minus 3.5 to 4.0 dBA and nine residuals 

at plus or minus 3.0 to 3.5 dBA. The remaining 472 residuals all fell within plus or minus 0 

to 3.0 dBA. Therefore, 97% of the data fell within a residual of 0 to 3.0 dBA and would be 

well received within the acoustical community, particularly during prediction exercises. 

 Chapter 6 then offered the mining community with two different approaches in 

predicting sound pressure levels at the operator position of a roof bolting machine. One 

method of prediction, utilized overall sound power levels either measured from 

laboratory tests or determined (predicted) from the statistical model equation. The other 

approach, a more sophisticated and reliable approach, predicted sound pressure levels at 

the operator position of the roof bolting machine as well as other locations within the 

underground mining section, using full-octave band frequency measurements obtained 

from laboratory testing for input into a computer model for simulating and predicting 

sound pressure levels from sound power level measurements. This approach, predicted 

the same sound pressure level at the operator position of a roof bolting machine, when 

compared to the actual sound pressure level from underground measurements. The 

approach, proved especially reliable, utilizing: 1) underground measurements to 

characterize the acoustic properties of an underground coal mine section in determining 

the correct sabine or absorption coefficients; 2) laboratory testing in the reverberation 

room to determine full-octave band sound power levels of the roof bolting machine and 

3) the use of an acoustical ray-tracing computer model program for predicting sound 

pressure levels from the required input data as mentioned above. 
187

 The research effort has provided the mining community with: 1) an 

understanding on how differing drilling configurations and drilling methods attribute to 

the sound power levels generated from a roof bolting machine while drilling into a high 

compressive rock media; 2) optimal drilling configurations and drilling methods in 

reducing sound power levels of the roof bolting machine; 3) a statistically valid equation 

for determining sound power levels of a roof bolting machine given differing drilling 

configurations and drilling methods; 4) a method for predicting sound pressure levels at 

the operator position and multiple locations in an underground mine related to the drilling 

cycle of a roof bolting machine and 5) a method for determining an operators’ noise 

dosage relative to a roof bolting machine given any type of drilling configuration or 

drilling method utilized. 
188

CHAPTER 8 

RECOMMENDATIONS FOR FUTURE RESEARCH 

 This research effort has provided the mining industry with: 1) a complete 

understanding on how differing drilling configurations and drilling methods attribute to 

the sound power levels generated from a roof bolting machine while drilling into a high 

compressive rock media; 2) optimal drilling configurations and drilling methods in 

reducing sound power levels of the roof bolting machine; 3) a statistically valid equation 

for determining sound power levels of a roof bolting machine given differing drilling 

configurations and drilling methods; 4) a method for predicting sound pressure levels at 

the operator position and multiple locations in an underground mine related to the drilling 

cycle of a roof bolting machine and 5) a method for determining an operators’ noise 

dosage relative to a roof bolting machine given any type of drilling configuration or 

drilling method utilized. 

 Initially, this research program focused on the related sound power and sound 

pressure levels attributed to roof bolting machines when drilling into high compressive 

strength rock media (>20,000 psi). Additional research efforts should be performed to 

characterize sound power and sound pressure level emissions of roof bolting machines 

when drilling into either low or medium compressive strength rock media. A similar 

testing plan should be developed and performed comparable to the plan conducted for 

determining sound power levels while drilling into high compressive strength rock media 

(>20,000 psi). Sound power levels should be determined in the laboratory relative to 

utilizing differing drilling parameters (thrust, rotational speed, drill bit size and type of 

drill steel) and drilling methods (vacuum, wet or mist) while drilling into low or medium 
189

compressive strength rock media. Additionally, the data collected from each individual 

test in the laboratory should then be compiled and analyzed for comparing sound power 

levels relative to the differing drilling parameters and drilling methods. Furthermore, a 

statistical analysis should be conducted on the collected data to determine if a statistically 

valid equation could then be developed, in which, will provide the mining community 

with a reliable and valid equation for predicting overall sound power levels relative to 

differing drilling parameters and methods used in low or medium compressive strength 

rock media. 

 Secondly, further research should be conducted to continue to characterize and 

define the acoustical properties related to differing geometrical configurations in 

underground coal mines. The research program presented, only characterized 

underground coal mines with roof to floor heights of five and six feet, mine heights lower 

than five feet and greater than six feet should be investigated to verify if differing mine 

heights have an affect on the acoustical properties in underground coal mines, as well as 

examining the affect shotcrete or rock dust usage might have relative to the acoustical 

properties in underground coal mines. 

 Additionally, research efforts relative to absorption coefficient determination 

should span outside the underground coal industry into underground metal and non-metal 

operations. Eventually, the results of the research effort could possibly be a handbook, in 

which, would provide the mining industry with the appropriate absorption coefficients 

relative to the mine type, geometry and geological characteristics for predicting and 

determining sound power and sound pressure levels underground. 
190

 Finally, the research presented here only focused on the drilling cycle of the roof 

bolting machine, additional research should be conducted to characterize and monitor the 

sound power and sound pressure levels attributed to the bolting cycle of the machine and 

the corresponding noise dosage to the operator. Obtaining this information, would 

provide the mining industry with a complete understanding relative to the overall noise 

dosage presented to the operator of the roof bolting machine relative to both, the drilling 

and bolting cycle of the machine. Acquiring this additional information, would provide 

extremely useful in the development of engineering noise controls during the bolting 

cycle of the machine, thereby, reducing the noise exposure to the operator. 
191

References 

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1-7. 

3. International Standard ISO 1999.2 [1990]. Acoustics - determination of 

occupational noise exposure and estimation of noise-induced hearing impairment. 

Geneva, Switzerland. 

4. Mine Safety and Health Administration. Health Standards for Occupational 

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