IMBSIR 76-1001 O

An Evaluation and Assessment of

Existing Data and Procedures for

the Measurement of Noise from

Motorcycles

Applied Acoustics Section

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

February 1 976

Final Report

Prepared for

Office of Noise Abatement and Control

U.S. Environmental Protection Agency

Washington, D. C. 20460

NBSIR 76-1001

AN EVALUATION AND ASSESSMENT OF

EXISTING DATA AND PROCEDURES FOR

THE MEASUREMENT OF NOISE FROM

MOTORCYCLES

Applied Acoustics Section

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

February 1976

Final Report

Prepared for

Office of Noise Abatement and Control

U.S. Environmental Protection Agency

Washington, D. C. 20460

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Table of Contents

Page

Executive Summary ii

1. Introduction and Scope 1

2. Motorcycle Description and Design 2

2.1. Definition 2

2.2. Industry Structure 3

2.3. Design Characteristics and Product Classification 3

3. Effects of Noise and Parties Affected 6

4. Major Noise Sources 7

5. Modes of Operation for Motorcycles 8

6. Existing Measurement Procedures 9

6.1. Environmental Noise .......................... 9

6.2. Operator At-Ear Noise 14

7. Data Base and Correlation * » 17

8. Overview of Motorcycle Noise Measurement Difficulties 17

8.1. Classification , 20

8.2. Relation of Physical Measures to Effects/Normal Use..,,... 21

8.3. Quantity Measured , * 22

8.4. Acoustic Environment . . . . , ............ , 23

8.5. Instrumentation 24

8.6. Alternative Test Procedure , 24

9. Appendix A. A Discussion of Motorcycle Subsource Noise ........ 26

10. Appendix B. Existing and Proposed Motorcycle Noise Measurement

Procedures 29

11. References 53

12. Bibliography 55

i
EXECUTIVE SUMMARY

The Environmental Protection Agency (EPA) is charged with taking strong,

comprehensive action to protect public health and welfare from increasing

noise. Accordingly, the Agency initially identified medium and heavy trucks

and portable air compressors as major noise sources and promulgated noise

emission regulations covering these products. Additional products have

recently been identified as major noise sources, including motorcycles. For

the purposes of this discussion motorcycles can be defined as two or three

wheeled vehicles (excluding tractors) with a propelling engine and a seat or

saddle for the use of the operator.

Motorcycle noise can be categorized as the noise produced by the power

plant (including the engine, transmission, intake, exhaust, etc.) and by

aerodynamic flow and tire-road interaction. The noise from the power plant

increases as the engine speed (and power) increases while the noise from

aerodynamic flow/tires increases as the vehicle speed increases. Maximum

power-plant noise usually occurs when the engine is delivering maximum

power at its maximum operating speed. The percentage of time a motorcycle

spends at maximum noise conditions is determined by the vehicles power-to-weight

ratio and operating conditions such as acceleration, speed, load (weight of

operator), and to a great extent, the manner in which the motorcycle is

operated

.

This report reviews existing motorcycle noise measurement procedures

with regard to their usefulness in the regulation of motorcycle noise as

well as the availability, extent and applicability of existing data. On

the basis of this review, the following probable or potential measurement

difficulties have been identified that could hinder promulgation and/or

enforcement of future EPA regulations to control the noise emission from

motorcycles

.

AN INSUFFICIENT DATA BASE . Data exist in only limited quantity in the

public domain on the noise levels associated with motorcycle operations.

NEED TO DETERMINE QUANTITY TO BE REGULATED . Need to develop a philosophy

regarding the quantity to be regulated, i.e., maximum noise potential,

maximum noise under normal operating conditions, or average noise. If

average noise is selected, there is the need to develop a typical

operating cycle.

LACK OF TYPICAL USAGE DATA . In order to develop an appropriate, reliable

and repeatable test procedure, it is necessary to consider the range of

possible motorcycle operational modes and the noise emission associated

with each mode. What is needed is definition of the percentage of time

which a motorcycle typically spends accelerating, decelerating, at low

speed cruise, at high speed cruise, at wide open throttle, etc. Such

data could serve as the basis for logical decisions on whether a

multi-modal test procedure or simply a few selected modes of operation

should be specified as part of the test procedure. Such typical usage
data do not presently exist for motorcycles.

NEED TO DEVELOP AN OPERATOR-AT- EAR NOISE TEST . There exists a need to

develop an operator-at-ear noise test to assess potential hearing

impairment that may be incurred by the operator.

NEED TO ACCOUNT FOR ENVIRONMENTAL/ SITE EFFECTS . There is a need for the

various environmental and test site effects on noise generation, radiation and/or propagation to be systematically investigated and correction

factors developed so that measurements made under any conditions may be

corrected to a single standard set of conditions. If correction factors

are feasible then there is a need for a site calibration procedure or

definition of limiting test conditions.

NEED FOR SIMPLER TEST PROCEDURE . There exists a need to develop a test

procedure that is simpler to perform and is less dependent on weather and

test site variables than those specified in current standards. Correlation should be established between the results obtained utilizing such

a test and human response to motorcycle noise.

A NEED TO BETTER SPECIFY TRANSIENT RESPONSE OF INSTRUMENTATION . There

exists a need to evaluate the response of existing instrumentation to

actual transient signals, e.g., a motorcycle passby, in order to

establish the relationships among the various precision instruments, to

supply data to strengthen existing standards, and to establish a data

base so that the technical community, manufacturers, lawmakers and

enforcement agencies will have a common basis for comparison of results

obtained using supposedly comparable equipment.

In summary, it is doubtful that the data in the open literature are

extensive enough to provide EPA with the information needed for a comprehensive

analysis of the economic costs and technical feasibility associated with a given regulation. Furthermore, there are insufficient data available upon

which to base an evaluation of alternative motorcycle noise measurement

procedures or to establish correlations between the noise associated with

various operational modes and the noise measured utilizing various test

procedures

.

Thus, it appears that EPA will have to generate a rather extensive

physical data base and investigate alternative measurement procedures prior

to formulation of the Notice of Proposed Rule Making.

iii

AN EVALUATION AND ASSESSMENT OF EXISTING DATA AND PROCEDURES

FOR THE MEASUREMENT OF NOISE FROM MOTORCYCLES

This report reviews existing motorcycle noise measurement procedures

with regard to their usefulness in the regulation of motorcycle noise as

well as the availability, extent and applicability of existing data. On

the basis of this review, probable or potential measurement difficulties are

identified that could hinder the promulgation and/or enforcement of future

EPA regulations to control the noise emission from motorcycles.

Key Words: Acoustics (sound); measurement methodology; motorcycle; noise

emission standard; noise measurement.

1. Introduction and Scope

The National Bureau of Standards (NBS) , under the sponsorship of the

Office of Noise Abatement and Control (ONAC), U. S. Environmental Protection

Agency (EPA), has attempted in this report to identify probable or potential

measurement difficulties that could hinder the promulgation and/or enforcement

of future noise regulations to control the noise emissions from motorcycles.

A search of the open literature in conjunction with numerous industrial and

private sector contacts established the basis for discussion of:

1. The basic characteristics of motorcycle design and construction.

2. The effects of motorcycle noise and the parties affected.

3. The major component noise sources for motorcycles.

4. The normal or typical modes of operation characteristic of the

various classes of motorcycles.

5. The usefulness of existing measurement procedures for use in regulation of the noise from motorcycles, considering the viewpoint of

EPA, manufacturers and enforcement personnel.

6. The availability, extent and applicability of existing data that

could be utilized by EPA in their efforts to promulgate noise

emission regulations for motorcycles.

This report is limited to those factors related to the measurement of

motorcycle noise. EPA/ONAC will independently investigate the technical

feasibility and economic implications of motorcycle noise regulation.

Also, it is assumed that the strategy followed during the development of the

new truck regulation — namely, that tires will be identified separately as

a major noise source — will apply to all vehicular noise sources, therefore,

this report concentrates on procedures for measuring the noise of motorcycles,

excluding tires.

One factor which makes detailed discussion of this source unique and

more difficult than for other vehicle noise sources is the extreme state of

1
flux of the motorcycle field in general. This is due, in part, to the

relative newness and rate of growth of the motorcycle population. Lightweight

motorcycles were first introduced into the United States in the early 1960 's.

Since then, motorcycle registrations have been doubling every four to five

years (with some recent flattening of this trend).

The initial geographic area of widespread acceptance was in California

and other West Coast states. For this reason, the early legislation in

terms of motorcycle noise regulations was promulgated by the State of

California. In response to this legislation, which establishes maximum

allowable noise levels of motorcycles sold in California, noise levels of

new motorcycles have been changing significantly. For example, typical

maximum A-weighted sound levels at 50 feet (15.2 m) have been reduced from

approximately 93-106 dB in 1971 to approximately 71-88 dB in 1974.

The continuing pressure from existing and/or future legislation for

lower noise levels will force a continuing state of change. This places

a great burden on the measurement methodology development in that it

requires the procedure to be such that it provides data which will be

meaningful in the implementation and evaluation of noise control measures

in addition to determining compliance with a regulated level.

2. Motorcycle Description and Design

2.1. Definition

The Task Forje on Noise to the State of Illinois, Institute for Environmental Quality [1]— defined a motorcycle as "every motor vehicle having a seat

or saddle for the use of the rider and designed to travel with not more than

3 wheels in contact with the ground, but excluding a tractor." A somewhat

modified definition was given by the Society of Automotive Engineers (SAE)

Recommended Practice J213a[2] - Definitions-Motorcycles. They defined a motorcycle as "any two wheeled vehicle with a propelling engine having a

piston displacement ranging from less than 50 cubic centimeters to more than

170 cubic centimeters and weighing less than 1000 pounds curb weight (the

total weight of a vehicle, including a full load of fuel, oil, and water but

without any passengers or cargo) or any three-wheeled vehicle with a propelling

engine and weighing less than 1500 pounds curb weight." This definition

includes only those vehicles which are intended at least partially for public

road use and excludes vehicles which do not meet common legal requirements for

public road use. However, the most comprehensive description of a motorcycle

was given in a report entitled "Control of Motorcycle Noise, Volume I,

Technology and Cost Information" [3] , prepared by Wyle Laboratories, which

stated: "with few exceptions, the motorcycle is a two wheeled vehicle powered

by a carbureted, spark ignition, air cooled, reciprocating, two or four stroke

engine driving through a manual clutch and multi-ratio gearset."

— Numbers in brackets indicate literature references at the end of this report.

2
It should be noted that in addition to motorcycles, there are also

vehicles termed "motor driven cycles." These vehicles are normally treated

separately from other vehicles in state and municipal vehicle codes. For

example, the state of California classifies separately those vehicles

with a horse power rating of 15 hp or less and an engine displacement of

200 cc or less as being a motor driven cycle. However, for the purpose of

this report, when the term motorcycle is used, motor driven cycle is

implied

.

2.2. Industry Structure

The motorcycle industry is comprised primarily of foreign manufacturers.

Eighty-eight percent of the motorcycles sold in the United States are manufactured in Japan, shipped to Japanese-owned distributors in the United States,

retailed by independent dealers who typically carry only a single manufacturer's

line, and subsequently equipped and serviced with parts or accessories made by

U. S. suppliers. European manufacturers supply about 5 percent of the market.

The largest U. S. Motorcycle manufacturer is AMF/Harley-Davidson which provides

about 5 percent of the U. S. unit sales. Since both European and American firms

sell smaller numbers of motorcycles, they either market through distributors

or sell directly to franchise dealers. The market is concentrated, in the

sense that six manufacturers supply approximately 95 percent of American unit

sales. See Table 1 for a listing of principal suppliers of motorcycles to the

United States.

2.3. Design Characteristics and Product Classification

Design characteristics and product classification are important interactive parameters for noise regulation in that these factors may differentially

influence noise output and usage In a manner that would require accommodation in

order to produce fair and equitable measurement methodology and/or regulation.

In the case of automobiles, for example, experience in California has clearly

indicated that a maximum noise regulation does not imply uniformly controlled

noise in typical use.

Four different classes of motorcycles can be readily identified according

to their end use, including:

1. Highway motorcycles

2. Off road motorcycles

3. Dual-purpose motorcycles

4. Mini bikes.

Further classification of highway and dual-purpose motorcycles can be made

according to engine displacement, or horsepower, according to their legally

permitted use. California, for example does not permit motorcycles of less

than 15 horsepower (motor driven cycles) to use certain high speed, limited

3
Table 1

Percent of Market Share by Motorcycle

Manufacturers in the U. S. Market as of 1973 [3]

Manufacturer

Percent of Units

Sold in

United States Location

Honda Motor Company 48.6 Japan

Yamaha Motor Co., Ltd. 18.9 Japan

Suzuki Motor Corporation 12.2 Japan

Kawasaki Motors Corporation 8.2 Japan

AMF/Harley-Davidson Motor Co., Inc. 4.6 U. S. A.

1 The Birmingham Small Arms Co

.

3.2 England

Ltd. (BSA, Triumph)

Bavarian Motor Works 0.6 Germany

Bultaco Motors 0.6 Spain

Hodaka Industrial Co., Ltd 0.4 Japan

OSSA 0.4 Spain

Husquarna 0.3 Czechoslovakia

Benelli 0.2 Italy

98.2%

4
access highways. This limitation may be translated into engine displacement,

since with current state-of-the-art of production motorcycles, this implies

an engine of 150-200 cc. displacement.

For the purposes of further discussion, the four major classifications

will be identified as follows (from reference [3])

• Highway motorcycles are produced in the entire size and performance

range and are standard transportation models produced for licensing

and use on public highways. They contain all required safety equipment (lights, horn, passenger seat and handhold, turn signals, etc.,)

and have the least critical weight and size requirements.

• Dual purpose motorcycles are a design compromise including features

which allow reasonable operation both on the highway and in nonpaved

or natural areas. Differences from pure highway machines include

generally smaller components for less weight, increased ground clearance

usually requiring a high mounted and smaller exhaust, changes in frame

geometry, suspension, engine output characteristics, and occasionally

different tire size and tread type.

• Off road motorcycles are designed for use over natural terrain only, and

contain no features oriented toward highway use. Performance demands

for off road use, which often includes racing and other competitive

events, require extreme light weight, balance and agility. Thus, items

such as seat, fuel tank, fenders, intake, and exhaust systems are of

minimal functional dimensions. Dual purpose and off road motorcycles

are available in engine displacements of 500 cc or less.

• Minibikes exist in many forms, from accurately scaled down motorcycles

to simple tube frames on small tires powered by lawn mower type engines.

Intended for general off road use by children, some high developed

minibikes produced by large manufacturers also contain the equipment

necessary for highway licensing.

Table 2 shows the range of design parameters of currently (1974 model)

manufactured highway motorcycles[3] . Of particular interest is the

relatively low machine weight (compared to transported weight) and the large

range in power (reflected in the wide range of power to weight ratio)

.

In view of the different purposes of the products as sold, different end

uses, and widely different sizes, it would appear that equitable regulation

would require different operational procedures for the different classes of

motorcycles — unless data are available, or can be generated, that indicate

that all classes generate a given noise condition, e.g., maximum noise, under

the same operating conditions.

5
Table 2

Manufacturer Specification Ranges for

Standard Highway Motorcycles and

Motor-Driven Cycles[3]

Displacement, cc 50 to 1200

Maximum Power, hp 4.9 to 82

Maximum Engine Speed, rpm 5900 to 10,000

Specific Power Output, hp/100 cc 4.5 to 12.7

Weight, lb 143 to 722

Power to Weight Ratio, hp/ lb 0.039 to .17

Wheelbase, in 43.3 to 61.5

Number of Gear Ratios 3 to 10

Top speed, mph 50 to 130

Fuel Consumption, mpg 20 to 90

3. Effects of Noise and Parties Affected

Motorcycles are used in a wider range of places for a wider range of

purposes — e.g., basic transportation, recreation, off-highway, etc. —

than any other type of motor vehicle; therefore, the noise produced by these

devices can affect the community in a wide range of ways. One study [4] has

noted that motorcycles are second only to automobiles (out of all motor vehicle

sources) in terms of the number of annoying situations created, and they were

found to produce more intensely annoying situations than all other vehicular

sources except buses. Since the time of that report, there has been some

progress in motorcycle noise control resulting from enforcement of regulations

at the state and local level which may reduce the intensity of annoyance;

however, it should also be noted that nationwide motorcycle registrations have

increased by approximately 80 percent during that period, which probably

resulted in a corresponding increase in the extensity of annoyance. For example,

use of off road vehicles in park lands has created such a noise problem that

the USDA, Forest Service has proposed noise limits[5] for motorcycles operated

on National Forest Lands. Estimates of the "vanishing distance" (distance to

inaudibility) for 1973 and 1974 off highway motorcycles in the 125-250 cc

displacement range was estimated to be 1400-3900 feet (427-1189 m)[6].

6

i i
Assuming a mean "vanishing distance" of about 2500 ft. (762 m) (and ignoring

terrain effects), this implies that with a density of 4-5 motorcycles per

square mile of parkland, visitors to the nation's parklands are never (on the

average) out of earshot of a motorcycle. These examples are cited to indicate

that the potential for annoyance from motorcycle noise is widespread. As noted

in several reports, the annoyance response arises from the many possible interferences due to noise with everyday activities ranging from interruption with

sleep or listening activities [4 , 7 ] to simply the information carried implying

that a motorcycle is present where its use may be inappropriate[8]

.

In addition to annoyance and task interference, the motorcycle may

represent a potential source of hearing damage in the exposed out-of-doors

community, and certainly represents a strong potential source for hearing

damage to the operator. Maximum A-weighted sound levels at 25 ft (7.6 m)

can exceed 90 dB, while mean A-weighted sound levels at the operator's ear — at least for trail riding — are in the range of 85-98 dB. The motorcycle

is unique among highway transportation noise sources with respect to potential

operator hearing damage, and the regulation and/or measurement methodology

should address this problem.

4. Major Noise Sources

Because of possible impact on the test procedure, it is useful to identify

the major sources of noise in motorcycles and the effect of normal operation

on the noise levels associated with each of these sources. Basically the

sources are as follows:

Exhaust Noise - is created when high pressure exhaust gases, released

through the engine exhaust valves or parts, excite oscillations in

the exhaust system which are radiated to the atmosphere at the tail

pipe, through the pipe surfaces and through the muffler shell at an

amplitude determined by the system configuration. The noise is a function of engine type, timing, load and speed (rpm) , intake

system type, muffler type and size, pipe diameter, pipe bends, dual

or single system, etc.

Air-Intake Noise - is created by the opening and closing of the intake

valve which causes the volume of air in the intake system to

pulsate. Associated noise levels are dependent upon whether the

engine is 2-cycle or 4-cycle, load and speed (rpm), the number of

cylinders, the engine displacement, etc.

Engine (Mechanical) Noise - is primarily produced by the combustion

process which produces rapid changes in pressure in the cylinder

which in turn results in excited mechanical impact and vibration in

the engine structure. Some of this vibrational energy is

subsequently radiated to the atmosphere as acoustic energy.

7
Transmission and Drive Noise - arises from the meshing and movements of

gears and bearings within the gear ratio assembly and may be apparent

under load or no load conditions. The noise may be aggravated by

resonance of the gearbox casing or by structure-borne components that

excite body surfaces that act as efficient radiators. Most motorcycles

employ a chain drive for conveying power from the gearbox to the driven

wheel. The attendant noise is a function of the type and state of chain

lubrication, chain loading, and speed of chain motion.

Tire-Road Interaction Noise - is related to tire and tread configuration,

road surface texture, vehicle speed, load, and state of tire wear.

Vibration of the tire carcass and the entrapment and release of air

from tread/pavement interstices appear to be the major mechanisms for

tire noise generation.

Aerodynamic Noise - is created by turbulent passage of air in and around

the motorcycle components and rider. The magnitude of aerodynamic noise

depends primarily on vehicle speed, vehicle aerodynamics, and wind

velocity.

Noise from Accessories - is created by vibration of fenders, fuel tank

and side panels due to the various engine, drive, and road excitations.

Appendix A contains a more detailed discussion of the component noise sources.

5. Modes of Operation for Motorcycles

The current literature provides very little information on the manner in

which motorcycles are typically used. However, there is some information, in

the form of a social surveyI4], on motorcycle use patterns which cause annoyance. Survey results indicate that 68% of the respondents who indicated that

motorcycles were annoying suggested that the annoying vehicle was

accelerating (as opposed to steady speed (17%), decelerating (0%), or not

relevant (13%)). This may be interpreted as a loudness judgment, however,

since an acceleration usually does create higher noise levels.

The only bounds that can be placed on modes of operation at this time are

the physical and legal limitations of operation. Thus, cruise speed will be

typically limited by aerodynamic drag and horsepower, to the extent that many

low power highway and dual purpose machines are incapable of speeds in excess

of 65 mph under optimum conditions and are in fact designed to cruise at

speeds at or below 45 mph. Larger highway machines are easily capable of

maintaining posted speed limits on any road surface. Minibikes are typically

smaller than off highway machines and face similar off highway terrain

limitations so that operating speeds are more frequently in the range of

10-25 mph.

8
6. Existing Measurement Procedures

In this section, the existing measurement procedures, relevant to determination of the noise emission from motorcycles, are presented and compared.

In addition, the feasibility of an operator-at-ear noise level measurement

procedure is discussed.

6.1. Environmental Noise

There are six existing measurement procedures which may be applicable to

the measurement of the environmental impact noise level produced by motorcycles.

They are:

(1) Society of Automotive Engineers (SAE) Standard J331a — Sound

Levels for Motorcycles[9]

,

(2) California Highway Patrol (CHP) Noise Measurement

Procedure[10]

,

(3) Society of Automotive Engineers (SAE) Standard J47 — Maximum

Sound Level Potential for Motorcycles[ll]

,

(4) International Organization for Standardization (ISO) Recommendation

R362 — Measurement of Noise Emitted by Vehicles[12]

,

(5) ASA STD 3-1975 — Test-Site Measurement of Maximum Noise Emitted

by Engine-Powered Equipment [ 13 ]

, and

(6) U. S. Forest Service Proposal — Sound Level Standard and Test

Procedure for Motorcycles [5 ]

.

To better facilitate a discussion of these measurement procedures a table — Table 3 — has been prepared which outlines the pertinent sections of each

of the test methods. This table permits rapid comparison among the six procedures. With the exception of ASA STD 3-1975 (permission to reprint this

standard was not granted by ASA), complete texts of the finalized measurement

procedures are reproduced in Appendix B.

The SAE J331a and CHP procedures are presently the most widely used

standards in the United States for establishing motorcycle noise levels for

legal compliance. Practically all reported noise level data are based on these

two procedures [17] . The SAE standard was designed to measure maximum noise

produced by motorcycles under typical highway operation without considering

the influence of tire noise. The noise level produced during such a test is

intended to represent the worst case noise level for motorcycles operating

under urban driving conditions. This standard is intended as a design tool

and, as such, the standard recommends that a maximum A-weighted sound le/vel

of 82, 84 or 86 dB dependent on the vehicle engine displacement (169 cm or

9
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less, 170 through 500 cm or more than 500 cm respectively), when measured in

accordance with J331a procedures, be used as a reference in the design and

development of motorcycles. In addition a 2 dB allowance is recommended for

variations in test site temperature gradients, test equipment, and inherent

differences in nominally identical vehicles[9, 17]

.

The CHP procedure (implementing Section 27160 of the California Vehicle

Code which applies to the measurement of noise from new motor vehicles,

including motorcycles, offered for sale in the state of California) is very

similar to the SAE J331a procedure. However, since the vehicles covered by

the CHP test include passenger cars and light trucks, medium and heavy trucks

and buses, in addition to motorcycles, the specification of the test site

geometry in the CHP procedure differs from that specified in SAE J331a. The

CHP test site is basically a compromise combination of the test sites specified in SAE J986a (passenger cars and light trucks), SAE J366b (heavy trucks

and buses) and SAE J331a (motorcycles). Another difference occurs in the

instrumentation requirements. The CHP allows the use of type 2 of S2A instrumentation in lieu of Type 1 (precision) equipment for enforcement purposes.

A second SAE measurement procedure — SAE J47 — was developed in addition

to SAE J331a. It is intended primarily to be a manufacturing tool for determination of the maximum sound level potential for motorcycles (without considering the influence of tires), and was in no way Intended to represent the way a

motorcycle is driven on the public highways or in urban areas [17]. This test

procedure is considered by many to be unsafe, and even dangerous, since it

requires a test vehicle to operate in its lowest gear (first gear) under maximum acceleration, resulting in front wheel lift off on most machines. Such

operation requires a skilled operator to maintain some margin of control over

the vehicle. Since this test requires vehicles to accelerate more rapidly

than normal, the specification of the test site geometry differs from that

specified in the SAE J331a and CHP procedures. The SAE J47 test site specifications require that the maximum rated engine speed be reached just beyond the

microphone point on the vehicle path (a minimum distance of 25 ft (7.5 m)).

The instrumentation and recommended 2 dB allowance for uncontrollable conditions is identical to that specified by the SAE J331a procedure.

ISO R362 is the applicable International standard for the measurement

of exterior motor vehicle noise, including motorcycles. The use of this

standard is especially widespread in Europe. As was the case with the CHP

procedure, this standard covers all vehicles and allows the use of essentially

type 2 instrumentation. However, the test site geometry is very similar to

the SAE J47 site specification. The major difference, which is a common one

between domestic and international standards, is the fact that measurements

are made at 7.5 m (25 ft.) instead of 15.2 m (50 ft.).

The ASA standard specifies methods for determining the maximum noise emitted

by a variety of engine powered equipment, including motorcycles. The procedures

stipulated are intended as a tool for certification testing by manufacturers,

conformance testing by community agencies, and survey testing for community

noise intrusion. As was the case with the CHP and ISO R362 procedures, the

12
standard covers all motor vehicles; however, the test site geometry is similar

to that specified in the SAE J47 and ISO R362. In addition, the instrumentation

requirements are identical to those specified in the CHP procedure, with the

exception that type 1 (precision) equipment is required for certification tests

while type 2 equipment is allowed for survey or enforcement purposes.

It should also be noted that the ASA standard specifies, in addition to a

passby test procedure, a stationary test procedure. However, the stationary

test methods only apply to construction, industrial and residential equipment,

highway and off-highway equipment having auxiliary powered equipment, and

auxiliary equipment separately.

The United States Forest Service (USFS) Proposal establishes measurement

methodologies and describes sound level limits for motorcycles used on

National Forest lands. This standard is designed to extract the maximum noise

produced by motorcycles under typical off-road operations, without considering

the influence of tire noise. It is also intended as a design tool and as such

the standard recommends the following maximum A-weighted sound levels — when

measured in accordance with U.S.F.S. Proposal procedures — be used as a reference in the design and development of motorcycles operated on National Forest

lands

(1) All presently constructed motorcycles — not to exceed a maximum

sound level of 86 dB,

(2) All new motorcycles sold after January 1, 1975 — not to exceed

a maximum sound level of 82 dB, and

(3) All new motorcycles sold after January 1, 1980 — not to exceed

a maximum sound level of 75 dB.

In addition a 3 dB allowance is recommended (instead of the 2 dB allowance

recommended by the SAE procedures) for variations in test site, vehicle

operation, temperature gradients, wind velocity gradients, test equipment, and

inherent differences in nominally identical vehicles. However, the test site

geometry is very similar to the SAE J47 and ISO R362 site specifications,

while the instrumentation specifications are identical to those required by

SAE J331a.

There is one other test procedure that should be discussed due to its

simplicity of application. It is not listed in Table 3 due to the lack of

necessary data required for a fair comparison of this test procedure to the

other six test procedures. The test procedure referred to is the Federal

International Motorcyclist (FIM) Recommended Noise Testing Method designed

exclusively for measuring the noise emission from racing bikes (motorcycles)

.

This method employs a very simplified test procedure which consists of utilizing a sound level meter located 50 ft. (15.2 m) directly behind the vehicle

while it operates at some pre-determined engine speed (at a stationary position) in order to obtain the A-weighted sound level of the vehicle. A maximum

A-weighted sound level of 92 dB is recommended for all vehicles. See

13
Appendix B for the entire text of this test procedure.

It should also be noted that there are additional motorcycle measurement

procedures in the various stages of development. For example, the Motorcycle

Industry Council (MIC) has recently proposed a measurement procedure that is

intended strictly for racing and competition machines.

All of the procedures discussed above measure the same acoustic quantity;

namely, the maximum A-weighted sound level with fast meter response. Also

each of the procedures utilize the wide open throttle acceleration mode of

operation as the primary test although procedures for closed throttle deceleration (SAE J331a/CHP/SAE J47/ASA) and stationary acceleration (ISO R362) tests

are also outlined. However, there is one crucial factor that may affect the

acceleration mode of the vehicle —— that is the test weight specifications as

outlined by the SAE J331a procedure. Since weight is a critical element in

smaller vehicles' ability to accelerate, the SAE J331a procedure recommends

that the driver's weight be not less than 165 lbs (74.8 kg) and not more than

175 lbs (79.4 kg). This weight requirement includes all necessary test

equipment which might be attached to the vehicle[9,17]

.

Currently within ISO, a revision of R362 is being considered. Review of

a recent draft points out only two significant differences between the original

and revised standard — (1) the revised standard requires the use of precision

instrumentation meeting the requirements of IEC Publication 179 and (2) the

provisions for a stationary acceleration test and a constant speed passby test

have been deleted. In addition to the revision to ISO R362, a second document

is being developed which outlines a survey method for measurement of noise

emitted by stationary motor vehicles. This document provides specifications

for instrumentation, test site, microphone locations and vehicle operating

conditions as part of a procedure for making near-field measurements of

exhaust and engine noise.

As stated earlier in this section, the FIM test procedure is a simplified

procedure that utilizes a stationary acceleration (or "run-up") test method

for determining the noise output of motorcycles. This test method deserves

further evaluation, especially since such a test is also prescribed in the

Federal Interstate motor carrier noise emission standards pertaining to trucks.

In the Federal Standard this test specifies that the vehicle should be

accelerated at wide-open throttle to its governed engine speed as rapidly as

possible while the vehicle is stationary with its transmission in neutral.

One problem with this test procedure is that its application is limited to

vehicles with governed engines.

6.2. Operator At-Ear Noise

There are no standardized measurement procedures directly applicable to

the measurement of noise produced at the ear of the motorcycle operator; and,

as a consequence, there is practically a non-existent data base available in

the public domain on the noise levels normally "heard" by the operator. Unlike

most vehicle operators, the motorcyclist is constantly exposed to unobstructed

14
noise levels by virtue of his unshielded condition during vehicle operations.

The noise level produced at the operator's position (ear level) can be highly

annoying as well as pose a serious threat of possible hearing loss or damage as

a result of prolonged exposure. The sound levels generated are generally

dependent on two factors— , (1) vehicle type and operational procedure, and

(2) vehicle speed. Although most motorcycle operators normally wear protective

helmets, these devices are considered to have only a nominal effect on noise

reduction at the ear of the operator depending on the style, fit and type of

eye protection afforded by the helmet and the speed of the vehicle[18].

Not until recently, however, have any efforts been made to develop a test

procedure which could be used to evaluate the potential for hearing damage of

motorcycle operators. In reports entitled "Motorcycle Noise" and "Operator's

At-Ear Noise Exposure for Off-Road Recreational Vehicles", by Robin Harrison,

U. S. Department of Agriculture, Forest ServiceI8 , 19] , a test procedure was

devised to measure the noise level produced at the operator's ear — in order

to assess the noise level present at this position that may cause possible

hearing damage. To better facilitate a discussion of this test procedure

Table 4 has been developed which outlines the pertinent areas of the test

method

.

Drivers utilized several motorcycles typically designed for off-road

purposes (i.e., dual purpose or competitive type vehicles) to evaluate this

test procedure. These vehicles were tested at three different sites which were

consistent with normal motorcycle operation — i.e., 1) an area that consisted

of rough terrain and steep hills which required low speed operation to

negotiate, 2) an area that consisted of a large, open, flat smooth surface

that was conducive to high speed operation, and 3) an area that was somewhat

restricted in nature that required average or moderate speeds to negotiate.

See Table 5 for a description of each motorcycle used and the type of test

site utilized.

The riders of these vehicles were fitted with a helmet-mounted microphone

which was coupled to a tape recorder that was carried by the operator in a

backpack. The sound levels recorded at the operator's ear were analyzed in

terms of two parameters — (1) A-weighted sound level distribution with time

(to determine the time distribution of at-ear intensities), and (2) spectral

content (to determine the frequency of the noise signal at the time of

occurrence of the maximum A-weighted level experienced during normal operation

at the operator's ear). The instrumentation used in the data gathering and

analysis process is given in Figures 1 and 2.

— Vehicle type and operational procedures are the determinant factors of

operator-at-ear noise levels for motorcycles traveling under 40 mph. An

A-weighted sound level of 100 dB has been reported at the operator's ear

for motorcycles traveling at 20 mph (32 km/hr) . At speeds greater than 40

mph (64 km/hr), operator-at-ear noise levels are considered to be strictly

a function of vehicle speed alone and completely determined by aerodynamic

noises (although a narrow portion of the frequency range radiated by the

components of the motorcycle may also be heard by the operator) — an

A-weighted sound level of 110 dB has been reported at the operator's ear

for motorcycles traveling at 70 mph (112 km/hr) [3].

15
Table 4

Operator-at-ear Noise Test Procedure

Type of Vehicles Used Off-road Motorcycles

Ins trumentat ion (1) B & K Microphone, type 4117—

C2) Kudelski Nagra III tape recorder

(3) B & K Spectrum Shaper

(4) B & K 166 environmental noise monitor

(5) Hewlet-Packard real-time 1/3 octave band

analyzer

(6) PDP-8 Computer

Test Site (1) Rough ground and steep hills

(2) Vast open expanse of smooth, flat, hard

lake bed

(3) Forest trail

Microphone Location Adjacent to operator's ear inside of helmet

Vehicle Operation (1) Low speed operation

(2) Full-throttle accelerations

(3) Moderate speed operation

Quantity Measured (1) A^-weighted level distribution in time

(2) Maximum A-weighted noise spectra — Commercial instruments are identified in this report to adequately specify

the experimental procedure. In no case does such identification imply

recommendation or endorsement by the National Bureau of Standards, nor

does it imply that the equipment identified Is necessarily the best

available for the purpose.

16

1
However, these data represent only a first attempt to establish an

appropriate measurement procedure for at-ear operator noise. Thus, it appears

that EPA should generate an extensive physical data base that can serve as the

basis for development of an at-ear measurement methodology, prior to the formulation of the Notice of Proposed Rule Making.

7. Data Base and Correlation

Motorcycle noise data exist in limited quantity in the public domain.

Since 1969, the application of noise control technology to motorcycles has

been necessitated by the enactment and enforcement of noise emission regulations by various state and municipal governments. These regulations for the

most part have adopted existing motorcycle measurement procedures. The

regulations in general apply to new and older motorcycles; thus, industry

has been evaluating alternative approaches to noise control for the last five

or six years in order to ensure that their products are in compliance with

the regulations.

Although there is probably some proprietary data which has been obtained

by the motorcycle industry and data resulting from state and local compliance

testing— , it appears doubtful that the existing data is sufficiently

extensive to provide EPA with even a nominal fraction of the information

needed for a comprehensive analysis of the economic costs and technical

feasibility associated with a given regulation. Furthermore, it is evident

that there is very little data upon which to base an evaluation of alternative

motorcycle noise measurement procedures or to establish correlations between

the noise associated with various operational modes and the noise measured

according to the various test procedures.

Thus it appears that EPA will have to generate a rather extensive

physical data base and investigate alternative measurement procedures prior

to formulation of the Notice of Proposed Rule Making.

8. Overview of Motorcycle Noise Measurement Difficulties

The information discussed in Sections 2 through 7 of this report serves

as the basis for an overview of motorcycle noise measurement problems.

Utilizing this information, potential noise measurement problems that could

hinder the promulgation and/or enforcement of future noise regulations to

control noise emission from motorcycles are identified.

Prior to the establishment of an appropriate measurement procedure that

can be utilized for determining the environmental impact and at-ear noise

level of motorcycles, certain informational requirements must be satisfied.

These include: (1) a product classification scheme, (2) typical usage data

(normal use conditions and range) and the effects of operation and environment on generated noise levels, and (3) the effects of motorcycle noise on — Due to the disparities among state and local jurisdictions in implementing

standardized noise measurement techniques the resultant data may be difficult

to compare

.

17
Table 5

Test Motorcycles and Site Location

Motorcycles used over Rough Terrain, Steep

Hills and Open Flat Smooth Surfaces

Year Engine

Displacement

Type Classification

Early

1973 250 cc 2-stroke Dual purpose

1973 100 cc 2 stroke Dual purpose

1973 125 cc 2 stroke Dual purpose, Pro to-type

1973 250 cc 4 stroke Dual purpose

1973 500 cc 4 stroke Dual purpose

1973 250 cc 2 stroke Professional racer

Motorcycles Used Ove r Forest Trails

Late

1973 250 cc 2 stroke Dual purpose

1974 250 cc 2 stroke Dual purpose

1974 125 cc 2 stroke Dual purpose

1974 125 cc 4 stroke Trials competition motorcycle

people, including the operator, and the nature of the effects. Such data

allows one to select, with confidence, the acoustic quantity to be measured,

the operational mode(s) of the vehicle during measurement and the appropriate

acoustic measurement procedure(s) which need to be specified in the regulation. Test site and operational limitations, and instrumentation requirements

also hinge on the availability of this fundamental information.

It must be borne in mind throughout the following discussions that the

motorcycle as a noise source is a rapidly changing subject, and for this

reason, any data with respect to the problems raised, must be reviewed for

18
Helmetmounted

microphone

Kudelski Nagra

Recorder

(record mode)

DATA GATHERING

INSTRUMENTATION

B&K 166 Envir. Noise

Mon it or

Kudelski Nagra

Recorder

(playback mode)

B&K Spectrum

Shaper

Amplitude

distribution

in time

OR

H-P Real- PDP-8

Time Analyzer Computer

DATA REDUCTION INSTRUMENTATION

1/3 octave band

spectra

Figure 1 . Operator at—ear noise measuring instrument system (schematic)

Figure 2. Helmet-mounted microphone and backpack tape recorder.

19
their currency. As has been noted, the pressure from state and local legislation has significantly altered the acoustic output of the typical motorcycle

as sold today. At this juncture, it is reasonable to treat data on physical

characteristics of motorcycle noise as obsolete if taken on vehicles manufactured prior to 1973, and old (with possibly questionable applicability) if

more than one year old.

The fact that the bulk of motorcycles are imported creates some unique

problems for selection of appropriate measurement methodologies, due to the

interaction with the group likely to perform the measurements. It can be

expected that an assembly plant or a distributorship will not have readily

available, the engineering staff required to supervise and maintain an extensive

or sophisticated acoustic measurement program, even though such expertise may

be expected at the design and manufacturing site. On the other hand, it is

also reasonable to expect that the foreign manufacturer might not permit the

verification of data at his foreign test site that recent proposed source

regulations have required of the domestic manufacturer. Successful regulation will require recognition of these unique nonacoustic problems. Since it

may be expected that such testing will be performed in the U. S., the attendant

requirements of the regulation for skilled test personnel — in light of the

limited pool of such personnel presently available — must also be considered.

Another unique factor in this industry is the existance of a large after

market accessory industry which is primarily U. S. based. Since this industry

produces a significant number of components which may alter the mechanical

and/or acoustic performance of the product, this regulation should identify

labeling requirements and measurement techniques which would ensure maintenance

of new product noise levels consistent with community needs.

8.1. Classification

Some of the factors associated with the establishment of motorcycle classes

have been discussed in Section 2. There are actually two major purposes for

motorcycle classification in conjunction with noise regulations.

1. In order to establish different measurement procedures, or variations

of the same measurement procedure, for motorcycles which have different operational characteristics or which exhibit important variations

in their acoustical characteristics.

2. In order to set different noise limits on different categories of

motorcycles, either because they are used differently and thus affect

people in different ways, or because of economic cost and technological

feasibility of noise control as applied to the various classes of

motorcycles

.

Although motorcycle noise data is relatively abundant compared to other

vehicular noise sources, sufficient data to allow adequate correlation between

the classes of motorcycles — categorized by engine displacement, weight and

size, intended usage, etc. — and the resultant noise levels characteristic

20
of each class over the range of normal operation (as opposed to maximum acceleration) does not exist in any meaningful quantity.

8.2. Relation of Physical Measures to Effects/Normal Use

It is likely that the test procedure established for motorcycle

environmental impact and operator at-ear noise measurements should be such

that the measured noise levels are representative of typical operation and

not necessarily maximum levels.

At least three types of measurements come to mind when one considers

measurement procedures which will permit adequate assessment of the noise

exposures of the several groups affected:

Sideline "far-field" noise, representative of the noise which is

radiated to listeners located back from the side of a road, trail or

highway in a rather open and/or wooded area.

Sideline "near-field" noise, representative of that which is heard

by passing pedestrians and motorists and by those working or living, or

utilizing recreational facilities within close proximity to vehicle

paths (i.e., streets or off-road trails).

That noise experienced at the operator's ear during exposure to airflow

past the head. All of these exposure conditions occur for various

operational modes of the motorcycle.

In general, products have a range of possible operational modes with noise

emission characteristics dependent on how they operate. The key to deciding

upon the mode or modes of operation of a vehicle that should be specified for

noise test purposes hinges on the knowledge of how the vehicle is "normally"

operated. In order to determine "normal operation" a usage survey should be

conducted. Such data providing the correspondence between acoustic output of

various motorcycles under various operations do not presently exist.

In selecting appropriate operating procedures for use in motorcycle noise

tests, it is important to consider which of the major noise sources — engine

(including exhaust, intake and mechanical factors), transmission (including

internal and external drive system components — gearset, clutch and chain

or gear linkage, etc.) and aerodynamic flow/tires — are important during the

various modes of operation of motorcycles, in order to be sure that the measurement methodology and operating limitations provide equitable tests. For

instance, at low speed acceleration, as indicated by most of the test procedures, engine noise and that part of transmission noise associated with the

particular gear in which the vehicle is operated is predominant. Although it

is normally assumed that the results of these test procedures are essentially

unaffected by tire/road interaction noise, at higher speeds aerodynamic flow/tire

noise levels may become the dominate source of noise (especially in and around

the motorcycle and the rider). Knowledge of the controlling source (s) is also

important in this case for selecting microphone height, etc.

O 1
There is also a need to establish correlations between the noise emitted

by motorcycles in various operational modes and the noise emitted during

simulated operations which may be much more convenient from a testing point

of view — for example, a stationary run-up test instead of the acceleration

passby test specified by most of the existing measurement procedures.

As previously noted, a number of parameters can affect the mechanical

performance of these lightweight vehicles, which may in turn affect the

results of acoustic measurements, particularly measurements made during

maximum performance maneuvers such as acceleration passbys.

In the acceleration test for example, the speed of the vehicle (and hence

the engine) at any time (in a particular gear) is determined by engine power

output, the mass being accelerated and frictional losses in the system. Thus,

equitable tests of acoustic output can be made only when engine performance,

accelerated mass and frictional losses are comparable with "in use" expectations.

It should be expected then, that the vehicle operation portion of the methodology must incorporate specifications or rider limitations which will yield

suitable vehicle operation.

8.3. Quantity Measured

The EPA "levels document" utilizes the equivalent A-weighted sound level

as the appropriate quantity to use in characterizing community noise exposure.

Thus, it is necessary that (one of) the quantity (or quantities) measured

in a regulation on a specific noise source, e.g., a motorcycle, could be

easily and directly related to the contribution which the source makes to the

equivalent A-weighted sound level for typical listeners. Therefore, it seems

appropriate to measure the A-weighted sound level at a particular microphone

location during a vehicle passby. This measure of source strength can then

be used to estimate the contribution which that source makes to the equivalent

sound level at some other location. For example, data obtained on trucks and

automobiles indicate that the sound level 50 feet (15.2 m) to the side of the

vehicle centerline can be used fairly reliably to predict noise levels further

from the vehicle. This is expected to be the case for motorcycles as well.

However, it should be noted that since motorcycle noise producing components

are exposed, they may generate a more complex acoustical field with potentially

greater directivity which may make estimation of noise in the community more

difficult.

There is a hazard associated with the use of A-weighted level only in the

measurement procedure and/or regulation. The A-weighting filter places very

little emphasis on low frequency sounds; therefore, the noise control treatment

which is designed to control mid and high frequency sounds may or may not

change low frequency sound levels — thus, creating a dominance of low frequency

noise levels. For this reason, considerations of other weighting networks, in

addition to the A-weighted system, should be made prior to regulation of the

source output.

22
It is questionable as to whether or not the maximum noise level at 50

feet (15.2 m) can be used to infer the contribution which a motorcycle passby

makes to the equivalent sound level at distances much closer to the

motorcycle — distances which correspond to the vehicle operator and other

pedestrians. Some attempts to measure noise at the operator's ear, for

example, have indicated that aerodynamic noise is a very significant factor,

even at moderate speeds (30-40 mph) . If this is the case, then factors which

affect flow around the operator's head, such as helmet design and fit,

windshield, etc., can be expected to be significant in this measurement,

although of course they would not affect a measurement at 50 ft. (15.2 m)

.

In order to ascertain the contribution which motorcycles make to the

"reverberant level" in city streets with tall buildings on either side, it is

necessary to consider whether or not the noise emission from motorcycles is

highly directional. If so, It might be necessary to measure the noise level

in several directions from the motorcycle.

Hopefully, adequate correlations can be established to enable collapsing

the number of measurement positions to a very few. Similarly, it may be hoped

that only maximum noise levels need to be measured for the several operational

modes of interest. However, it seems evident that a comprehensive experimental

program is needed to guide and justify such simplification.

The motorcycle (considering present typical levels and use periods) presents a potentially serious hearing damage threat to the rider and passenger.

As a result, it is expected that regulation of noise output will have to consider this aspect of the problem. In the event that it is concluded in the

regulatory process that a level for noise at the operator's ear must be determined, then considerable investigation of measurement techniques will be

required. In particular, it should be noted that wind, which may or may not

represent a significant source to the operator, will certainly represent a

significant measurement problem, if the vehicle is in motion.

8.4. Acoustic Environment

There is general agreement that the noise emission from motor vehicles

should be measured in a free field over a reflecting plane. If a 50 foot

(15.2 m) measurement distance is utilized a rather large open area is needed

plus a roadway of sufficient length to accommodate the specified operational

mode(s) of the vehicle.

Although considerable uniformity has been achieved by the SAE, CHP and

ISO in defining standard noise measurement procedures, there remain significant variations between noise measurements made at different sites, or at

different times at the same site. Experience to date with measurement of

motor vehicle noise at 25 to 50 foot (7.5 to 15.2 m) distances, for typical

microphone heights, indicates that the levels measured are sensitive to the

characteristics of surrounding ambient conditions (air temperature, humidity,

atmospheric pressure), to the characteristics of the reflecting plane

(acoustic impedance, flatness), to temperature gradients above the ground

23
plane (which depend on present and past air temperatures, sunlight, and wind

velocities as well as the emittance and absorptance of the reflecting plane)

,

and to atmospheric inhomogenieties (wind velocity, wind gradients, and local

turbulance) . All of these factors may influence the generation of noise by

the propulsion system and associated auxiliary equipment, the radiation from

the source into the surrounding atmosphere and/or the propagation from the

immediate vicinity of the vehicle to the measurement location.

Since these factors influence reliable measurements of many of the sources

which EPA is, or will be, regulating, there is a need for the various environmental and site effects to be systematically investigated so that: (1) noise

measurements taken at a given site can be corrected to standard environmental

conditions, (2) noise measurements taken at different sites under the same

environmental conditions can be correlated and, therefore (3) noise measurements taken at different sites under any environmental conditions can be

correlated. If correction factors can not be demonstrated to be feasible then

there is a need for a site calibration procedure and/or definition of limiting

test conditions.

8.5. Instrumentation

The instrumentation section of the regulation should require equipment

meeting the Type 1 requirements of American National Standard Specifications

for Sound Level Meters, Si .4-1971[14] . In addition, pertinent sections of

American National Standard Methods for the Measurement of Sound Pressure Levels,

SI . 13-1971 [20] should be Incorporated. For instruments for which standards do

not exist, or where existing standards are not sufficient, the regulation

should include specific criteria for evaluating the performance of such devices.

For example, a critical deficiency in existing standards is that the response

of instrumentation to transient signals, e.g., vehicle passbys, is not well

defined. Further, the exhaust signature of many small engines produces a very

high crest-factor signal for which many commercially available detection circuits

have notably deficient response. Suitable standards defining these characteristics do not exist.

It is important to clearly state in the regulation the allowable tolerance

for frequency response, environmental effects, harmonic distortion, etc., which

the instruments are required to meet. These specifications should be applied

not only to specific components of the system but to the overall system as well.

The overall system measurement error should not be degraded below that allowed

for direct measurements made with sound level meters regardless of the instrumentation configuration.

In addition, overall system calibration should be required at frequent

stipulated intervals. The fact that each component of a system appears

satisfactory does not ensure that the system performance will be acceptable.

8.6. Alternative Test Procedures

It is not seriously suggested that a motorcycle noise regulation should

explicitly require measurements corresponding to all possible exposure conditions coupled with all possible motorcycle operational modes. However, it

24
is important to consider the prevalance of each condition, perhaps in terms of

its contribution to L or when evaluating the effects of motorcycle

noise on the populace?*^ If several exposure conditions are found to be

important, hopefully correlations can be developed which will enable collapsing

the several cases into one or two measurements.

Because of the space, weather and other constraints associated with the

existing low speed acceleration test procedures, it seems appropriate to

investigate alternative procedures which would be simpler to perform yet

correlatable with the "real world" situation. The Federal International

Motorcyclist presently utilizes a stationary motorcycle test procedure with

the engine stablized at some pre-determined rpm level as the basis for

determining permissible noise levels for racing motorcycles. The Bureau of

Motor Carrier Safety also has a similar stationary test procedure except

that the engine is stabilized at its maximum rated or governed engine speed

(high idle) as the basis for regulating truck and bus (interstate) interior

cab noise. In addition, present Federal noise certification procedures for

interstate motor carriers specifies a stationary run-up test — the engine

is accelerated as rapidly as possible to its governed speed at wide open

throttle (transmission in neutral) . One of the main difficulties with

stationary test procedures is the fact that gear train associated noise is

not evaluated. Also, stationary procedures such as the stationary run-up

test are limited in their applicability — in this case the test can only be

utilized on vehicles with governed engines. Although stationary tests

probably take less time to perform and require less space (smaller test sites)

,

all of the weather constraints which limit testing when the passby method is

utilized would also be a problem with the stationary test. Further, recent

data indicates an extremely poor correlation between stationary run-up tests

and either passby or in use tests for racing cycles.

Since the weather is a major limiting factor for all outdoor tests, it

would seem logical to investigate the feasibility of Indoor testing. If

indoor testing were to be chosen as part of a standard or regulation, a testing facility would have to be specified in great detail and identical

facilities would have to be constructed by each manufacturer — be he small

or large. It would appear to be prohibitively expensive to construct a

facility to allow for 15.2 meter measurements; yet, measurements any closer

than 15.2 meter would be questionable without extensive research to

provide insight into the near field/far field effects and to establish the

correlation between the results obtained according to such procedures with

the community noise exposure from motorcycle operation. Also, the practical

problem of removing the heat and exhaust fumes from the operating vehicle

would have to be dealt with.

Any alternative procedure will have pros and cons associated with them;

but, they will have almost no data base or experience base to back them up.

Much research would be necessary before such procedures could be utilized

as a measurement methodology for regulating the environmental impact or

operator-at-ear noise produced by motorcycles.

25
9. Appendix A: A Discussion of Motorcycle Subsource Noise

Exhaust System Noise

Exhaust noise is generated by the rapid release of high temperature and

pressure combustion gases when the exhaust valve or port opens. In addition

to the discharge noise — noise radiated to the atmosphere at the tail pipe

outlet — this rapid release of pressure excites oscillations of the muffler

shell and exhaust and tail pipe surfaces which are radiated into the atmosphere as noise. A running engine can repeat this process over a hundred times

per second, with the resultant perceived noise appearing as a staccato or

smooth tone depending on engine type and speed. Transmission loss through the

pipes is an additional noise source.

The primary frequency components of exhaust noise are dependent upon

engine speed, number of cylinders, exhaust system configuration (single or

dual exhausts) and whether the engine is a 2-cycle or 4-cycle engine. For

2-cycle engines high frequency spectra are typical, while the 4-cycle engine

exhibits more low frequency content. The amplitude of exhaust noise is

directly dependent upon ignition timing, throttle setting and engine load

(pressure in the cylinder when the valve opens)

.

Mufflers or resonators are typically utilized to control exhaust discharge noise. The performance of these devices is very dependent upon other

acoustic elements within the system such as the engine and the length and

diameter of both the exhaust and tail pipe. A major consideration in engine

performance for 4-cycle motorcycle engines over a specific rpm range is

exhaust pipe length. By virtue of their design constraints, these machines

must emphasize lightweight, compact construction — such requirements are not

directly compatible with the basic principle of 4-cycle muffler tuning which

equates the degree of silencing to gross muffler volume. Performance and

economy are directly affected by silencing, as these machines rely on low

back pressure to achieve competitive horsepower/weight ratios. Thus,

mufflers, in addition to providing effective noise reduction must also be

designed to provide a tolerable back pressure on the engine.

Two-stroke motorcycle engines present less of an exhaust silencing problem

since they are designed to incorporate an expansion chamber system, in which

much of the acoustic energy is reflected back into the engine. A well designed

2-cycle exhaust muffler system will actually increase power while at the same

time reduce noise levels.

Most of the early success in exhaust noise reduction involved improvements

in exhaust silencing. Techniques involving using large volume, more restrictive

sound baffles in the mufflers, multiple mufflers, and the interconnection of

header pipes on multicylinder engines have reduced exhaust outlet noise

appreciably. — The material in this appendix was mainly derived from Wyle Laboratory

reports to EPA [3, 21] on transportation noise and a technology and cost

information study on control of motorcycle noise.

26
• Air Intake Noise

Engine air-intake noise is produced by the opening and closing of the

intake valve which causes the volume of air in the system to pulsate.

Intake systems are similar to exhaust systems in that the components and

problems are much the same; however, each intake system must be treated

individually since both the frequency and amplitude of intake noise varies with

engine type.

With the reduction of exhaust noise over the past few years, noise radiated through the intake system is nearly equal to the noise radiated through

the exhaust system for all motorcycle sizes. They both correspond to throttle

opening, engine speed, number of cylinders, engine displacement and engine

load, and are the two predominant noise sources for most modes of operation.

Two-cycle engines which, for a given speed, induct nearly twice the volume of

air as four-cycle engines of equivalent size, have traditionally generated high

intake levels, but recent improvements in silencing practice have reduced intake

levels to those of the exhaust. Also, there is some indication that, as exhaust

muffler "back pressure" increases, intake noise levels may also increase.

The reduction of intake noise is affected in a manner similar to that

employed for the exhaust. Techniques such as the reduction of the inlet crosssectional area to the minimum required for adequate intake supply, the use of

noise baffles along the intake tract, large rubber enclosed plenum volumes

along the intake tract, and positioning of inlet apertures behind filtration

elements in acoustically shielded portions of the machine are but a few of

the methods used in intake noise reduction.

• Engine (mechanical)

The engine and transmission drive system form a complex acoustical system

composed of a large number of sources, the most important of which is the

characteristic mechanical clatter and ringing of an air cooled engine. Mechanical noise directly transmitted from within the engine results from the combustion process which produces rapid changes in pressure in the cylinder which

in turn causes the actual striking together of engine parts, such as piston

slap, valve and valve train clatter (present in four-cycle engines only), gear

meshing, and noise from the roller and ball bearings widely used in motorcycle

engines. Secondary mechanical noise is radiated from vibrating engine surfaces,

such as cooling fins and casings, which become excited by internal engine

operation and combustion pulses. A final source of engine noise is directly

transmitted combustion noise which is considered to be of an insignificant

level in relation to the other major sources for most modes of operation.

Transmission noise originates from the internal and external drive system

components. Internal sources consist of the gearset and primary drive. The

gearset noise originates with the meshing and movements of gears and bearings

within the gear ratio assembly. This may be apparent under both load and no

load conditions. The primary drive system, comprised of the clutch and chain

27
or gear linkage between engine crankshaft and gear set, creates additional

noise which is at times coupled with vibration noise from clutch components.

The noise generated by the primary drive system is usually lower than that

produced by the external drive chain. The transmission system subsources tend

to excite the external gearset cases, primary cases, and other vehicle parts

which radiate additional sound. A disproportionate reduction of mechanical

noise may be necessary when considering reduction of total motorcycle noise in

order to prevent conditions such as the "bolt-in-a-canM effect.

To reduce total noise levels for the majority of large machines requires

significant reduction of mechanical noise from both the engine and transmission

drive system components. Techniques involving encapsulation of engine, elastic

isolation of engine and drive units, increased damping of engine and transmission cases and drive chain enclosures have been but a few of the many

methods considered for quieting engine mechanical noise.

Aerodynamic Noise

This source of noise is most prevalent at high vehicle speed and is created

by turbulent passage of air in and around the motorcycle and its rider. Aerodynamic sources along with tire/roadway interactions are somewhat negligible

in overall contributions to present day total motorcycle noise levels, but

future requirements for reduced noise levels may require serious investigation

of these sources.

Turbulence caused by the motion of the machine through air may be reduced

in a number of ways — such as utilizing solid or thick spoked cast alloy

wheels instead of wire spoked wheels and streamlining or routing the maze of

cables, levers, and wires through the vehicle components.

Tire-Road Interaction Noise

The physical mechanisms of the production of noise by the tire-road

interaction process are not well understood. The general consensus is that

air pumping (entrapment and release of air from the tire tread cavities)

and vibration of the tire carcass are the major mechanisms contributing to

the generation and radiation of acoustic energy. Even though the effects of

tread design (rib, cross bar), road surface, wear, and load on the noise

levels produced are known, the existing data do not provide the basis for the

design of quieter tires. Little research has been specifically conducted

regarding motorcycle tire noise due to the low significance of the problem.

28
10. Appendix B. Existing and Proposed Noise Measurement Procedures

Pertinent to Motorcycles

SOUND LEVELS FOR

MOTORCYCLES - SAE J331a SAE Reoorrmended Practice 13/

Report of Vehicle Sound Level Ccnmittee and Motorcycle Committee

Approved May 1975.

1. SCOPE - This SAE Reconmended Practice establishes the test procedure,

environment, and instrumentation for

determining sound levels typical of normal

motorcycle operation.

2. INSTRUMENTATION

2.1 The following instrumentation

shall be used, where applicable:

2.1.1 A sound level meter which meets

the Type 1 or S1A requirements of American

National Standard Specification for Sound

Level Meters, SI. 4-1971. As an alternative to making direct maasurorients using

a sound level meter, a microphone or

sound level meter may be used with a magnetic tape recorder and/or a graphic

level recorder or indicating instrument

provided that the system meets the

requirements of SAE Recamiended Practice,

Qualifying a Sound Data Acquisition

System - J184.

2.1.2 An acoustic calibrator with an

accuracy of + 0.5 dB (see paragraph

7.4.4)

.

2.1.3 A calibrated engine speed

tachometer having the following characteristics:

(a) Steady-state accuracy of better

than 1%.

(b) Transient response: Response to

a step input will be such that within 10

engine revolutions the indicated rpm will

be within 2% of the actual rpm.

2.1.4 A speedometer with steady-state

accuracy of at least + 10%.

2.1.5 An anemometer with steady-state

accuracy of at least + 10% at 19 km/h

U2 mph)

.

2.1.6 An acceptable wind screen may be

used with the microphone. To be acceptable, the screen must not affect the

microphone response more than + 1 dB for

frequencies of 20-4000 Hz or + 1-1/2 dB

for frequencies of 4000-10,000 Hz.

3. TEST SITE

3.1 The test site shall be a flat

open space free of large sound-reflecting

surfaces (other than the ground) , such as parked vehicles, signboards, buildings or

hillsides, located within 30m (100 ft)

radius of the microphone location and the

following points on the vehicle path:

(a) The microphone point

(b) A point 15m (50 ft) before

the microphone point.

(c) A point 15m (50 ft) beyond

the microphone point.

3.2 The measurement area within the

test site shall meet the following

requirements and be laid out as described:

3.2.1 The surface of the ground within

at least the triangular area formed by the

microphone location and the points 50 ft

(15. 2m) prior to and 50 ft (15. 2m) beyond the

microphone point shall be dry concrete or

asphalt, free from snow, soil or other

extraneous material.

3.2.2 The vehicle path shall be of

relatively smooth, dry concrete or asphalt,

free of extraneous materials such as gravel, and of sufficient length for safe

acceleration, deceleration and stopping of

the vehicle.

3.2.3 The microphone shall be located

15m (50 ft) from the centerline of the

vehicle path and 1.2m (4 ft) above the

ground plane.

3.2.4 The following points shall be

established on the vehicle path:

(a) Microphone point-a point on the

centerline of the vehicle path where a normal through the microphone location

intersects the vehicle path.

(b) End point-a point on the vehicle

path 30m (100 ft) beyond the microphone

point.

(c) Acceleration point-a point on

the vehicle path 7.5m (25 ft) prior to the

microphone point.

3.2.5 The test area layout in Fig. 1 shows a directional approach from left to

right with one microphone location, for

purposes of clarity. Sound level measurements are to be made on both sides of the

vehicle; therefore, it will be necessary

to establish either a second microphone

point on the opposite side of the vehicle

path with a corresponding clear area or end points and acceleration points for

approaches from both directions.

4. TEST WEIGHT

4.1 At the start of the test series,

the vehicle shall be filled with fuel and

lubricant to not less than 75% of capacity.

4.2 The combined weight of the test

13/Reprinted with permission, "Copyright © Society of Automotive Engineer'

Inc., 1975, All rights reserved."

29
rider and test equipment used on the

vehicle shall be not more than 79 kg

(175 lb) nor less than 75 kg (165 lb)

.

Weights shall be placed on the vehicle

saddle behind the driver to compensate

for any difference between the actual

driver/equipment load and the required

75 kg (165 lb) minimum.

S

FIG. 1

5. PROCEDURE

5.1 The vehicle shall use second gear

unless during the test under acceleration

the engine speed at maximum rated net

horsepower is reached before the vehicle

reaches a point 7.5m (25 ft) beyond the

microphone point, in which case the

vehicle shall be tested in third gear.

5.2 For the test under acceleration,

the vehicle shall proceed along the

vehicle path at a constant approach speed

which shall correspond to either an engine

speed of 60% of the engine speed at

maximum rated net horsepower or a vehicle

speed of 48 km/h (30 mph) , whichever is

slower. When the front of the vehicle

reaches the acceleration point, rapidly

and fully open the throttle and accelerate

until the front of the vehicle is 30 m

(100 ft) beyond the microphone point, or

until the engine speed at maximum rated

horsepower is reached, at which point

the throttle shall be closed. Wheel slip

which effects the maximum sound level

shall be avoided.

5 . 3 When excessive or unusual noise

is noted during deceleration, the

following test shall be performed with

sufficient runs to establish maximum

sound level under deceleration:

5.3.1 For the test under deceleration,

the vehicle shall proceed along the

vehicle path at an engine speed at

maximum rated net horsepower in the gear

selected for the test under acceleration.

At the end point, the throttle shall be

rapidly and fully closed, and the vehicle

allowed to decelerate to an engine speed

of one-half of the rpm at maximum rated

net horsepower.

5.4 Sufficient preliminary runs to

familiarize the driver and to establish

the engine operating conditions shall be

made before measurements begin. The

30
engine temperature shall be within the

normal operating range prior to each run.

6. MEASUREMENTS

6.1 The sound level meter shall be

set for fast response and for the Aweighting network.

6.2 The meter shall be observed while

the vehicle is accelerating or decelerating. Record the highest sound level

obtained for the run, ignoring unrelated

peaks due to extraneous ambient noises.

All values shall be recorded.

6.3 At least six measurements shall

be made for each side of the vehicle.

Sufficient measurements shall be made

until at least four readings from each

side are with 2 dB of each other. The

highest and the lowest readings shall be

discarded; the sound level for each side

shall be the average of the four, which

are within 2 dB of each other. The sound

level reported shall be for that side of

the vehicle having the highest sound

level.

6.4 The ambient sound level (including wind effects) at the test site due to

sources other than the vehicle being

measured shall be at least 10 dB lower

than the sound level produced by the

vehicle under test.

6 . 5 Wind speed at the test site

during tests shall be less than 19 km/h

(12 mph)

.

7. GENERAL COMMENTS

7.1 Technically competent personnel

should select equipment and the tests

should be conducted only by trained and

experienced persons familiar with the

current techniques of sound measurement.

7.2 While making sound level

8. REFERENCES

Suggested reference material is as follows:

8.1 ANSI Sl.l - 1960, Acoustical

Terminology.

8.2 ANSI SI. 2 - 1962, Physical

Measurement of Sound.

8.3 ANSI SI. 4 - 1971, Specification

Copyright © Society of Automotive Engineers, Inc. 1 975

All rights reserved.

SAE Technical Board Rule* and Regulations

All technical reports, including standard! approved and practices recommended, are advisory only. Their use by anyone

engaged in industry or trade is entirely voluntary. There is no

agreement to adhere to any SAE Standard or SAE Recom- mended Practice, and no commitment to conform to or be

guided by any technical report.

measurements, not more than one person

other than the rider and the observer

reading the meter shall be within 15m

(50 ft) of the vehicle or microphone, and

that person shall be directly behind the

observer reading the meter, on a line

through the microphone and the observer.

7.3 The test rider should be fully

conversant with and qualified to ride the

machine under test and be familiar with

the test procedure.

7.4 Proper use of all test instrumentation is essential to obtain valid

measurements. Operating manuals or other

literature furnished by the instrument

manufacturer should be referred to for

both recommended operation of the

instrument and precautions to be

observed. Specific items to be

considered are: 7.4.1 The type of microphone, its

directional response characteristics, and

its orientation relative to the ground

plane and source of noise.

7.4.2 The effects of ambient weather

conditions on the performance of all

instruments (for example, temperature,

humidity and barometric pressure)

.

7.4.3 Proper signal levels, terminating

impedances, and cable lengths on multiinstrument measurement systems.

7.4.4 Proper acoustical calibration

procedure to include the influence of

extension cables, etc. Field calibration

shall be made immediately before and after

each test sequence. Internal calibration means is acceptable for field use,

provided that external calibration is

accomplished iirmediately before or after

field use.

for Sound Level Meters.

8.4 ANSI SI. 13 - 1971, Method of

Measurement of Sound Pressure Levels.

8.5 SAE J184, Qualifying a Sound

Data Aquisition System.

8.6 SAE J47, Maximum Sound Level

Potential for Motorcycles.

In formulating and approving technical reports, the Technical Board, its Councils and Committees mill not investigate or consider patents which may apply to the subject matter. Pros- pective users of the report are responsible for protecting themselves against liability for infringement of patents.Printed in U.S.A.

31
CALIFORNIA HIGHWAY PATROL NOISE MEASUREMENT PROCEDURE

EDITED FOR NEW VEHICLES

ORDER ADOPTING, AMENDING, OR REPEALING

REGULATIONS OF THE DEPARTMENT OF THE

CALIFORNIA HIGHWAY PATROL

After proceedings had in accordance with the provisions of the

Administrative Procedure Act (Gov. Code, Title 2, Div. 3, Part 1, Chapter h.5)

and pursuant to the authority vested by Section 2^02 of the Vehicle Code, and

to implement, interpret, or make specific Sections 23130 and 27160 of the

Vehicle Code, the Department of the California Highway Patrol hereby adopts,

amends, or repeals regulations in Chapter 2, Title 13, California

Administrative Code, as follows:

(l) Amends Article 10, Subchapter k to read:

Article 10. Vehicle Noise Measurement

lOHO. Scope of Regulations . This article contains procedures

implementing Section 23130 of the Vehicle Code which applies to the

measurement of noise from motor vehicles and combinations of vehicles subject

to registration when operated on a highway and Section 27160 of the Vehicle

Code which applies to the measurement of noise from new motor vehicles offered

for sale.

lOUl. Definitions The following definitions shall apply -wherever the

terms are used in this article:

(a) First Gear . The "first gear" is the highest numerical gear ratio of

the transmission which is commonly referred to as low gear.

(b) Maximum RPM . The "maximum rpm" is the maximum governed engine

speed, or if ungoverned, the rpm at maximum engine horsepower as determined by

the engine manufacturer in accordance with the procedm*es in SAE J2h5 , April

1971.

(c) Vehicle Reference Point . The "vehicle reference point" is the

location on the vehicle used to determine when the vehicle is at any of the

points on the vehicle path. The vehicle reference point shall be the front of

the vehicle unless such position is more than 16 ft from the exhaust outlet,

in which case both the front of the vehicle and the exhaust outlet shall be

used as reference points.

10^2. Personnel . Persons selected to conduct noise measurement testing

or to measure noise level of vehicles operated on a highway shall have been

trained and qualified in the techniques of sound measurement and the operation

of sound measuring instruments.

10^3. Instrumentation . Equipment used in making vehicle noise

measurements shall be selected by technically trained personnel and shall meet

32
the following requirements:

(a) Sound Level Meter . The sound level meter shall meet the requirements

of A2ISI Standard Sl.U-1971 for Types 1, 2, or S2A.

(b) Sound Level Calibrator . The sound level calibrator shall calibrate

the entire sound level meter with an acoustic calibrator of the coupler-type.

(c) Tachometer . A calibrated engine speed tachometer shall be used to

determine when maximum rated rpm is attained in conducting the tests specified

in Section 10U6 of this code.

(d) Anemometer . An anemometer shall be used to measure the wind speed

at the test site when conducting tests specified in Section 10k6 of this code.

lOUU. Noise Measurement Sites . Noise measurement sites shall be

selected to meet location, ground condition, and roadway surface requirements

in the following subsections (a) and (b)

(a) Measurement Sites for Vehicles on the Highway .

(b) Measurement Sites for New Motor Vehicles . Sites for measuring noise

from new motor vehicles to determine compliance with Section 27l60 of the

Vehicle Code shall meet the following conditions:

(1) Location . The location shall be a flat open space free of

large vertical sound-reflecting surfaces such as signboards,

buildings hillsides, or trees within 100 ft of the microphone and

within 100 ft of the centerline of the path of the vehicle from the

point where the throttle is opened to the point where the throttle

is closed.

(2) Ground Condition . The ground surface between the

microphone and the path of the vehicle shall be asphalt or concrete

free of powdery snow, 1 o e soil, or ashes.

(3) Roadway Surface . The surface over which the vehicle

travels shall be dry and relatively smooth concrete or asphalt

pavement free of extraneous material.

IOU5. Microphone and Personnel Positions . The microphone for the sound

level meter and the personnel involved in all types of vehicle noise

measurements shall be positioned as follows

(a) Microphone Location . The microphone shall be located 50 + 1 ft from

the centerline of the lane of travel of the vehicle at a height of k + 1/2 ft

above the plane of the roadway surface.

(b) Microphone Orientation . The microphone shall be oriented in

relation to the source of the sound in accordance with the instrument

33
manufacturer 1 s instructions. Where the instruction manual is vague or does

not include adequate information, a specific recommendation shall he obtained

from the manufacturer.

(c) Technician Location . The technician making direct readings of the

meter shall be positioned in relation to the microphone in accordance vith the

instrument manufacturer's instructions. Where the instruction manual is vague

or does not include adequate information, a specific recommendation shall be

obtained from the manufacturer.

(d) Bystander Location . During noise measurements, bystanders shall

remain at least 50 ft from the microphone and the vehicle being measured,

except for a witness or trainee, who may be positioned beyond the technician

on a line with the technician and the microphone.

10U6. Operation of New Motor Vehicles . New motor vehicles tested to

determine compliance with Section 2

r(i60 of the Vehicle Code shall be operated

in conjunction with any auxiliary equipment that would be in use while the

vehicle is operated on the highway, including but not limited to cement

mixers, refrigerator units, and garbage compactors.

(a) Heavy Trucks, Truck Tractors, and Buses .

(b ) Light Trucks, Truck Tractors, Buses, and Passenger Cars .

(c) Motorcycles . The test procedure for motorcycles shall be as

follows

(1) Test Area layout . The test area layout for motorcycles

shall be the same as specified in subsection (b) (l) and Figure 3

for light trucks, truck tractors, buses, and passenger cars. (See

next page .

)

(2) Gear Selection . Motorcycles shall be operated in second

gear. Vehicles which reach maximum rpm at less than 30 mph or

before a point 25 ft bevond the microphone point shall be operated

in the next higher gear.

(3) Acceleration . The vehicle shall proceed along the test

path at a constant approach speed which corre ponds either to an

engine speed of 60% of maximum rpm or to 30 mph, whichever is lower.

When the vehicle reference point reaches the acceleration point, the

throttle shall be fully opened. The throttle shall be held open

until the rear of the vehicle is approximately 100 ft beyond the

microphone or until the maximum rpm is obtained, at which point the

throttle shall be gradually closed. Wheel slip shall be avoided

during this test.

(h) Engine Temperature . The engine tempera.ture shall be

within normal operating range before each test run.

34
Test Area Layout . The test area shall include a vehicle path of

sufficient length for safe acceleration, deceleration, and stopping of the

vehicle. The vehicle pat>i (shown with only one directional approach in Figure

3 for purposes of clarification) shall he marked with the following zone and

points

(A) Microphone point - the location on the centerline of the

vehicle path that is closest to the microphone.

(B) Acceleration point - a location 25 ft before the microphone

point.

(C) End point - a location 100 ft beyond the microphone point.

(D) End zone - the last 75-ft distance between the microphone point

and the end point.

Figure 3. Test Area Layout for Light Trucks, Truck Tractors, Buses, Passenger

Cars and Motorcycles

.

35
(d) Deceleration . Tests during deceleration shall be conducted when

deceleration noise appears excessive. The vehicle shall approach the end

point from the reverse direction a maximum rpm in the same gear selected for

the tests during acceleration. At the end point, the throttle shall be closed

and the vehicle shall be allowed to decelerate to 1/2 of maximum rpm.

10U7. Meter Operation . The sound level meter shall be operated in

accordance with the instrument manufacturer's instructions and as follows:

(a) Meter Setting . The A-weighting network and the fast meter response

shall be used.

(b) Calibration Check . An external calibration check shall be made

before and after each period of use and at intervals not exceeding 2 hr when

the instrument is used longer than a 2-hr period.

(c) Meter Reading . The reading recorded shall be the highest sound

level obtained as the vehicle passes by, disregarding unrelated peaks due to

extraneous ambient noises.

(d) Ambient Sound . Measurements shall be made only when the A-weighted

ambient sound level, including wind effects, due t<-> all sources other than the

vehicle being measured, is at least 10 dB(A) lower than the sound level of the

vehicle.

(e) Wind . Measurements shall be made only when the wind velocity is

less than 12 mph.

10^8. Vehicle Noise Level . The measured noise level of a vehicle shall

be reported as follows:

( a ) Vehicles on the Highway .

(b) New Motor Vehicles . The sound leve1 readings for determining

compliance of new motor vehicles with Section 27160 of the Vehicle Code shall

be obtained after sufficient preliminary runs to enable the test driver to

become familiar with the operation of the vehicle and to stabilize engine

operating conditions.

(1) At least four measurements shall be made from each side of

the vehicle. When the exhaust outlet is more than 16 ft from the

driver's position, at least two runs in each direction shall be

performed with each of the reference points described in Section

lOUl (c) of this code.

(2) The A-weighted sound level for each side of the vehicle

shall be the average of the two highest read.'ngs on that side which

are within 2 dB(A) of each other. The noise level reported for the

vehicle shall be the sound level of the loudest side.

36
MAXIMUM SOUND LEVEL

POTENTIAL FOR MOTORCYCLES - SAE J47 SAE Recommended Practice^/

Report of Vechile Sound Level Oommittee and

Motorcycle Conmittee approved May 1975.

1. SCOPE

This SAE Recorrmended Practice establishes the test procedure, environment and

instrumentation for determining maximum

sound level potential for motorcycles.

2. INSTRUMENTATION

2.1 The following instrumentation

shall be used, where applicable:

2.1.1 A sound level meter which meets

the Type 1 or S1A requirements of American

National Standard Specification for Sound

Level Meters, SI. 4-1971. As an alternative

to making direct measurements using a

sound level meter, a microphone or sound

level meter may be used with a magnetic

tape recorder and/or a graphic level re- corder or indicating instrument provided

that the system meets the requirements of

SAE Recommended Practice, Qualifying a

Sound Data Acquisition System -J184.

2.1.2 An acoustic calibrator with an accuracy of +0.5 dB (see paragraph 6.4.4)

2.1.3 A calibrated engine speed tachometer having the following characteristics:

(a) Steady-state accuracy of better

than 1%

(b) Transient response: Response to a step input will be such that within 10

engine revolutions the indicated rpm will

be within 2% of the actual rpm.

2.1.4 An anemometer with steady-state

accuracy within + 10% at (19 km/h) 12 mph.

2.1.5 An acceptable wind screen may be

used with the microphone. To be acceptable, the screen must not affect the microphone response more than +1 dB for frequencies of 20-4000 Hz or +1-1/2 dB for

frequencies of 4000-10,000 Hz.

3. TEST SITE

3.1 The test site shall be a flat

open space free of large sound-reflecting

surfaces (other than the ground) such as parked vehicles, signboards, buildings or hillsides, located within (30.4m) (100ft)

radius of the microphone location and the

following points on the vehicle path:

(a) The microphone point.

(b) A point (15.2m) (50 ft) before

the microphone point.

(c) A point (15.2m) (50 ft) beyond

the microphone point.

3.2 The measurement area within the

test site shall meet the following re- quirements and be laid out as described:

3.2.1 The surface of the ground within

at least the triangular area formed by

the microphone location and the points

(15.2m) 50 ft prior to and (15.2m) 50 ft

beyond the microphone' point shall be dry

concrete or asphalt, free from snow, soil or other extraneous material.

3.2.2 The vehicle path shall be of

relatively smooth, dry concrete or asphalt, free of extraneous materials such

as gravel, and of sufficient length for

safe acceleration, deceleration, and

stopping of the vehicle.

3.2.3 The microphone shall be located

(15.2m) (50 ft) from the centerline of

the vehicle path and (1.2m) (4 ft) above

the ground plane.

3.2.4 The following points shall be

extablished on the vehicle path:

(a) Microphone point-a point on the

centerline of the vehicle path where a normal through the microphone location

intersects the vehicle path.

(b) End point-a point on the vehicle path (7.6m) (25 ft) beyond the microphone point.

(c) Acceleration point-a point on

the vehicle path at least (7.6m) (25 ft)

prior to the microphone point established by the method described in paragraph

4.1.

3.2.5 The test area layout in Fig. 1 shows a directional approach from left to

right with one microphone location for

purposes of clarity. Sound level measurements are to be made on both sides of the

vehicle; therefore, it will be necessary

to establsh either a second microphone

location on the opposite side of the ve- hicle path with a corresponding clear

area or end points, and acceleration

points for approaches from both directions.

4. PROCEDURE

4.1 To establish the acceleration

point, the end point shall be approached

in low gear from the reverse direction

at a constant road speed obtained from

60% of the engine speed at maximum rated

— Reprinted with permission, "Copyright © Society of Automotive Engineers,

Inc., 1975, All rights reserved."

37
net horsepower. When the front of the

vehicle reaches the end point, the throttle shall be rapidly and fully opened to

accelerate past the microphone point under

wide-open throttle. By trail, the lowest

transmission gear shall be selected that

will result in the vehicle traveling the

shortest distance from the end point to

the place where the engine speed at maximum rated net horsepower is reached, but

which is not less than (7.6mm) (24ft) past

the microphone point. The location of the

front of the vehicle on the vehicle path

when the engine speed at rnaximum rated net

horsepower is attained shall be the acceleration point for test runs to be made in

the opposite direction.

I

i"" fUdlua

100- Itadlui — 30* <*• K

4 i

f A

- Ulcropnon*

' • - |nd point

/ C - AcceWratti

0 • Center of •

21- - 7 6 IMtraa

JO' -IS 2 M(r*«

100 -30 t Mttraa

100' Ridiua

FIG. 1

4.1.1 When the procedure described in

paragrah 4.1 results in a dangerous or

unusual operating condition such as wheel

spin, front wheel lifting, or other unsafe conditions, the next higher gear

shall be selected for the test and the

procedure rerun to establish the acceleration point. In any event, the procedure

shall result in the vehicle being at the

end point when the engine speed at maxi- mum rated net horsepower is attained.

4.2 For the test under acceleration,

the vehicle shall proceed along the vehicle path at a constant approach speed in

the gear selected in paragraph 4.1 and at

60% of the engine speed at maximum rated

net horsepower. When the front of the vehicle reaches the acceleration point, the

throttle shall be rapidly and fully opened. Full acceleration shall continue until

the engine speed at maximum rated net

horsepower is reached, which shall be at

the end point, at which tine the throttle

shall be closed. Wheel slip which affects

the maximum sound level shall be avoided,

and the manufacturer's safe maximum engine speed shall not be exceeded.

4 . 3 When excessive or unusual noise

is noted during deceleration, the following test shall be performed with sufficient runs to establish maximum sound

level under deceleration.

4.3.1 For the test under deceleration,

the vehicle shall approach the end point

from the reverse direction at the engine

speed at maximum rated horsepower in the

gear selected for the test under acceleration. At the end point, the throttle

shall be rapidly and fully closed and the

vehicle shall be allowed to decelerate to an engine speed of 1/2 the rpm at maximum

rated net horsepower.

4.4 Sufficient preliminary runs to

familiarize the driver and to establish

the engine operating conditions shall be

made before measurements begin. The engine

temperature shall be within the normal

operating range prior to each run.

5. MEASUREMENTS

5.1 The sound level meter shall be

set for fast response and for the Aweighting network.

5.2 The meter shall be observed while

the vehicle is accelerating or decelerating. The highest sound level obtained for

each run shall be recorded, ignoring unrelated peaks due to extraneous ambient

noises

.

5.3 At least six measurements shall

be made for each side of the vehicle.

Sufficient measurements shall be made until at least four readings from each side

are within 2 dB of each other. The highest and lowest readings shall be discarded; the sound level for each side shall

be the average of the four, which are within 2 dB of each other . The sound level

reported shall be for that side of the

vehicle having the highest sound level.

5.4 The ambient sound level (including

wind effects) at the test site due to

sources other than the vehicle being meas- ured shall be at least 10 dB lower than

the sound level produced by the vehicle

under test.

5.5 Wind speed at the test site during tests shall be less the 19 km/h (12

mph)

.

6. GENERAL COMMENTS

6.1 Technically competent personnel

should select equipment, and the tests

should be conducted only by trained and

38
experienced persons familiar with the

current techniques of sound measurement.

6.2 While making sound level measurements, not more than one person other than

the rider and the observer reading the

meter shall be within 15.2 m (50 ft) of

the vehicle or microphone, and that person

shall be directly behind the observer

reading the meter, on a line through the

microphone and the observer.

6.3 The test rider should be fully

conversant with and qualified to ride the

machine under test and be familiar with

the test procedure.

6.4 Proper use of all test instrumentation is essential to obtain valid

measurements. Operating manuals or other

literature furnished by the instrument

manufacturer should be referred to for

both recommended operation of the instrument and precautions to be observed.

Specific items to be considered are: 6.4.1 The type of microphone, its directional response characteristics, and

its orientation relative to the ground

plane and source of noise.

6.4.2 The effects of ambient weather

conditions on the performance of all instruments (for example, temperature, humidity, and barometric pressure)

.

6.4.3 Proper signal levels, terminating impedances, and cable lengths on

multi-instrument measurement systems.

6.4.4 Proper acoustical calibration

procedure, to include the influence of

extension cables, etc. Field calibration

shall be made immediately before and

after each test sequence. Internal calibration is acceptable for field use,

provided that external calibration is ' accomplished immediately before or after

field use. 6.5 Vehicles used for tests must not

be operated in a manner such that the

break-in procedure specified by the manufacturer is violated.

7. REFERENCES

Suggested reference material is as follows

7.1 ANSI SI. 1-1960, Acoustical Terminology.

7.2 ANSI SI. 2-1962, Physical Measurement of Sound.

7.3 ANSI SI. 4-1971, Specification

for Sound Level Meters.

7.4 ANSI SI. 13-1971, Method of Measurement of Sound Pressure Levels.

7.5 SAE J184, Qualifying a Sound

Data Aquisition System.

7.6 SAE J331, Sound Levels for

Motorcycles.

Copyright © Society of Automotive Engineers, Inc. 1975

All rights reserved.

SAE Technical Board Rules and Regulations

All technical reports, including standards approved and practices recommended, are advisory only. Their use by anyone

engaged in Industry or trade is entirely voluntary. There is no

agreement to adhere to any SAE Standard or SAE Recom- mended Practice, end no commitment to conform to or be

guided by any technical report.

In formulating and approving technical reports, the Technical Board, its Councils and Committees mill not investigate or consider patents which may apply to the subject matter. Pros- pective users of the report are responsible for protecting themselves against liability for infringement of patents.Printed in U.S.A.

39
ISO RECOMMENDATION R362

15/

MEASUREMENT OF NOISE EMITTED BY VEHICLES -

I. SCOPE

This ISO Recommendation describes methods of determining the noise emitted by motor vehicles,

these being intended to meet the requirements of simplicity as far as is consistent with reproducibility of results and realism in the operating conditions of the vehicle.

2. GENERAL REQUIREMENTS

2. 1 Test conditions

This ISO Recommendation is based primarily on a test with vehicles in motion, the ISO

reference test. It is generally recognized to be of primary importance that the measurements

should relate to normal town driving conditions, thus including transmission noise etc. Measurements should also relate to vehicle conditions which give the highest noise level

consistent with normal driving and which lead to reproducible noise emission. Therefore, an acceleration test at full throttle from a stated running condition is specified.

Recognizing, however, that different practices already exist, specifications of two other

methods used are also given in the Appendix. These relate to:

(a) a test with stationary vehicles (see Appendix Al) and

(b) a test with vehicles in motion, under vehicle conditions which (in the case of certain

vehicles) are different from those in the ISO reference test (sec Appendix A2).

When either of these tests is used, the relation between the results and those obtained by

the ISO reference test should be established for typical examples of the model concerned.

2.2 Test site

The test methods prescribed call for an acoustical environment which can only be obtained

in an extensive open space. Such conditions can usually be provided

for type-approval measurements of vehicles,

for measurements at the manufacturing stage, and

for measurements at official testing stations.

It is desirable that spot checking of vehicles on the road should be made in a similar

acoustical environment. If measurements have to be carried out on the road in an acoustical

environment which does not fulfil the requirements stated in this ISO Recommendation,

it should be recognized that the results obtained may deviate appreciably from the results obtained using the specified conditions.

2.3 Interpretation of results

The results obtained by the methods specified give an objective measure of the noise emitted

under the prescribed conditions of test. Owing, however, to the fact that the subjective

appraisal of the annoyance or noisiness of different classes of motor vehicles is not simply

related to the indications of a sound level meter, it is recognized that the correct interpretation of results of the measurements in this ISO Recommendation may require different

limits to he set for the corresponding annoyance of different classes of vehicles.

This material is reproduced with permission from International

Organization for Standardization Recommendation 362^1964, Measurement

of Noise Emitted by Vehicles, copyrighted by the American National

Standards Institute, 1430 Broadway, New York, N. Y. 10018.

40
3. MEASUREMENT EQUIPMENT

A high quality sound level meter should be used. The weighting network and meter time constant employed should be curve " A " and " fast response " respectively, as specified in Recommendation No. 123 of the International Electrotechnical Commission for Sound Level Meters. A

detailed technical description of the instrument used should be supplied.

NOTBS

1 . The sound level measured using sound level meters having the microphone close to the instrument

case may depend on the orientation of the instrument with respect to the sound source, as well as on

the position of the observer making the measurement. The instructions given by the manufacturer

concerning the orientation of the sound level meter with respect to the sound source and the observer should therefore be carefully followed.

2. If a wind shield is used for the microphone, it should be remembered that this may have an influence on the sensitivity of the sound level meter.

3. To ensure accurate measurements, it is recommended that before each series of measurements the

amplification of the sound level meter be checked, using a standard noise source and adjusting as necessary.

4. It is recommended that the sound level meter and the standard noise source be calibrated periodically

at a laboratory equipped with the necessary facilities for free-field calibration. Any peak which is obviously out of character with the general sound level being read should be

ignored.

4. ACOUSTICAL ENVIRONMENT

The test site should be such that hemispherical divergence exists to within ± 1 dB.

Note.—A suitable test site, which could be considered ideal for the purpose of the measurements, would

consist of an open space of some 50 m radius, of which the central 20 m, for example, would consist of

concrete, asphalt or similar hard material.

In practice, departure from the so-called " ideal " conditions arises from four main causes

(a) sound absorption by the surface of the ground

;

(b) reflections from objects, such as buildings, and trees, or from persons;

(c) ground which is not level or of uniform slope over a sufficient area

;

(d) wind.

It is impracticable to specify in detail the effect produced by each of these influences. It is considered important, however, that the surface of the ground within the measurement area be free from powdery snow, long grass, loose soil or ashes.

To minimise the effect of reflections, it is further recommended that the sum of the angles subtended at the position of the test vehicle by surrounding buildings within 50 m radius should not

exceed 90° and that there be no substantial obstructions within a radius of 25 m from the vehicle.

Acoustical focussing effects and sites between parallel walls should be avoided.

Wherever possible, the level of ambient noise (including wind noise and—for stationary tests

roller stand and tyre noise) should be such that the reading produced ou the meter is at least 10 dB below that produced by the test vehicle. In other cases, the prevailing noise level should be

stated in terms of the reading of the meter.

Note.—Care should be taken that gusts of wind do not distort the results of the measurements.

The presence of bystanders may have an appreciable influence on the meter reading, if such

persons are in the vicinity of the vehicle or the microphone. No person other than the observer

reading the meter should therefore remain in the neighbourhood of the vehicle or the microphone.

Note.—Suitable conditions exist, if bystanders are at a distance from the vehicle which is at least twice

the distance from vehicle to microphone.

41
5. MEASUREMENTS WITH VEHICLES IN MOTION

1 Testing ground

The testing ground should be substantially level, and its surface texture such that it does

not cause excessive tyre noise.

2 Measuring positions

The distance from the measuring positions to the reference line CC (Fig. 1) on the road

should be 7.5 m. The path of the centre line of the vehicle should follow as closely as possible the line CC.

The microphone should be located 1.2 m above the ground level.

3 Number of measurements

At least two measurements should be made on each side of the vehicle as it passes the measuring positions.

Note.—It is recommended that preliminary measurements be made for the purpose of adjustment.

Such preliminary measurements need not be included in the final result.

Microphone © Microphone

Fig. 1 . — Meowing positions for measurement with vehicles in motion

4 Test procedure

5.4.1 General conditions

The vehicle approaches the line AA in the appropriate conditions specified below:

When the front of the vehicle reaches the position, in relation to the microphone,

shown as A A in Figure 1, the throttle is fully opened as rapidly as practicable and held

there until the rear of the vehicle reaches position BB in Figure 1 , when the throttle is closed as rapidly as possible.

Trailers, including the trailer portion of articulated vehicles, are ignored when considering the crossing of line BB.

Note.—If the vehicle is specially constructed with equipment (such as concrete mixers, compressors, pumps, etc.), which is used whilst the vehicle is in normal service on the road, this equipment should also be operating during the test.

42
.4.2 Particular conditions

5.4.2.1 Vehicle with no giak-box. The vehicle should upproach the line A A at a stcudy

speed corresponding

either to an engine speed of three quarters of the speed at which the engine

develops its maximum power,

or to three quarters of the maximum engine speed permitted by the governor,

or to 50 km/h,

whichever is the lowest.

5.4.2.2 Vehicle with a manually operated gear-box. If the vehicle is fitted with a two-,

three-, or four-speed gear box, the second gear should be used. If the vehicle has more than four speeds, the third gear should be used. Auxiliary step-up ratios

(" overdrive ") should not be engaged. If the vehicle is fitted with an auxiliary

reduction gear box, this should be used with the drive allowing the highest vehicle

speed.

The vehicle should approach the line A A at a. steady speed corresponding

either to an engine speed of three quarters of the speed at which the engine

develops its maximum power,

or to three quarters of the engine speed permitted by the governor,

or to 50 km/h,

whichever is the lowest.

5.4.2.3 Vehicle with an automatic gear-box. The vehicle should approach the line AA

at a steady speed of 50 km/h or at three quarters of its maximum speed, whichever

is the lower. Where alternative forward drive positions are available, that position

which results in the highest mean acceleration of the vehicle between lines A A

and BB should be selected.

The selector position which is used only for engine braking, parking or similar

slow manoeuvres of the vehicle should be excluded.

5.4.2.4 Agricultural tractors, self-propelled agricultural machines and motor cultivators. The vehicle should approach the line A A at a. steady speed of three

quarters of the maximum speed which can be achieved, using the gear-box ratio

which gives the highest road speed.

Statement of results

All readings taken on the sound level meter should be stated in the report.

The basis of horsepower rating, if appropriate, should be stated in the report.

The state of loading of the vehicle should also be specified in the report.

43
a p p r n o i c i: s

Al. MEASUREMENTS WITH STATIONARY VEHICLES

A l.l Measuring positions

Measurements are made in each of the four main directions at a distance of 7.0 m from

the nearest surface of the vehicle. The actual positions used for the measurements arc shown in Figure 2. If measurements arc required in more than the four measuring

positions shown in Figure 2, they should be taken from chosen positions on the circles shown — i.e. the circles with radius 7.0 m,

The microphone should be located 1.2 m above the ground le\cl.

MOTORCYCLE WITH OR CAR WITH OR WITHOUT

WITHOUT SIDE-CAR TRAII FR

Fig. 2. — Measuring positions for measurement with stationary vehicles

A 1.2 Number of measurements

At least two measurements should be made in each measuring position.

A 1 .3 Vehicle conditions

The engine of the vehicle without a speed governor should be run at three quarters of

the number of revolutions per minute at which, according to the manufacturer, it develops its maximum power. The engine speed, expressed in revolutions per minute,

is measured by means of an independent instrument, e.g. by the use of free-running

rollers and a tachometer. A governed engine should be run at maximum speed.

The engine should be brought to its usual working temperature before measurements

are carried out.

A 1 .4 Statement of results

All the sound level readings observed in each measuring position should be stated in

the report.

44
A2. MEASUREMENTS WITH VEHICLES IN MOTION (MODIFIED METHOD)

A 2.1 Testing ground

The testing ground should be substantially level, and its surface texture such that it does not cause excessive tyre noise. A2.2 Measuring positions

The distance from the measuring positions to the reference line CC (Fig. 1) on the

road should be 7.5 m. The path of the centre line of the vehicle should follow as closely as possible the line CC.

The microphone should be located 1 .2 m above the ground level.

A2.3 Number of measurements

At least two measurements should be made on each side of the vehicle as it passes the measuring positions.

Note.—It is recommended that preliminary measurements be made for the purpose of adjust- ment. Such preliminary measurements need not be included in the final result. A 2.4 Test procedure

A2.4.1 General conditions

The vehicle approaches the line AA in the appropriate conditions specified below:

When the front of the vehicle reaches the position, in relation to the microphone,

shown as AA in Figure 1, the throttle is fully opened as rapidly as practicable and

held there until the rear of the vehicle reaches position BB in Figure 1, when the

throttle is closed as rapidly as possible.

Trailers, including the trailer portion of articulated vehicles, are ignored when

considering the crossing of line BB.

Note.—If the vehicle is specially constructed with equipment (such as concrete mixers, compressors, pumps, etc.), which is used whilst the vehicle is in normal service on the road, this equipment should also be operating during the test.

A2.4.2 Particular conditions

Vehicles should be driven in such a manner as to comply with either of the following

conditions

A2.4.2.1 Vehicle with a manually operated gear box, with or without automaticclutch. The vehicle should approach the line AA (Fig. 1) at a steady speed

corresponding to three quarters of the revolutions per minute at which the engine (according to the manufacturer) develops its maximum power. The

gear ratio should be chosen such that the road speed most closely approaches

50 km/h at this engine speed. However, if the vehicle has more than three

forward gears, the first gear should not be used.

A2.4.2.2 Vehicle with an automatic gear box. The vehicle should approach the line AA

at a steady speed of 50 km/h or at three quarters of its maximum speed, whichever

is the lower. Where alternative forward drive positions are available, the position

which results in the highest sound level of the vehicle should be selected.

The selector position which is used only for engine braking, parking or similar

slow manoeuvres of the vehicle should be excluded.

A 2.5 Statement of results

All readings taken on the sound level meter should be stated in the report.

The basis of horsepower rating, if appropriate, should be stated in the report.

The state of loading of the vehicle should also be specified in the report.

45
U.S.D.A. PROPOSED

SOUND LEVEL STANDARD AND TEST PROCEDURE FOR MOTORCYCLES

1. INTRODUCTION

This standard describes sound level limits for motorcycles used on

National Forest lands. This test procedure establishes methods and describes

the test environment and instrumentation for determining these sound levels.

2. SOUND LEVEL LIMITS

2.1 All motorcycles operated on National Forest lands must be equipped

at all times with an exhaust muffler equivalent in performance to

at least the manufacturer's original equipment. When a motorcycle

has been sold without an exhaust muffler, silencing equipment must

be installed, including but not limited to an exhaust muffler, so

as the total sound level, measured by the method described herein,

does not exceed 86 dBA.

2.2 All motorcycles operated on National Forest lands, which are sold

new after January 1, 1975, must not produce more than 82 dBA when

measured by the method described herein.

2.3 All motorcycles operated on National Forest lands, which are sold

new after January 1, 1980, must not produce more than 75 dBA, when

measured by the method described herein.

3. INSTRUMENTATION

The following instrumentation shall be used for the measurement required:

3.1 A sound level meter which meets the requirements of American National

Standards Institute SI. ^-1971, General Purpose Sound Level Meters.

3.1.1 Alternately, a microphone/magnetic tape recorder/indicating

meter system whose overall response meets SAE Recommended Practice Jl8U,

"Qualifying a Sound Data Acquisition System".

3.2 A sound level calibrator (see paragraph 5-5)«

3.3 A calibrated windscreen or nose cone (see paragraph 5-H).

k . PROCEDURE

k.l TEST SITE - A test site suitable for the purpose of measurements

shall consist of a flat open space free of large reflecting surfaces such

as signboards, buildings, or hillsides located within 50 ft. of either the

vehicle or the microphone. Other site limitations shall be as shown in

figure 1.

46
U.l.l The surface of the ground within the measurement area shall be

paved. If this is not possible, then at least the vehicle path shall be

paved, or well-packed earth or gravel.

k.1.2 Because bystanders may have an appreciable influence on meter

response when they are in the vicinity of the vehicle or the microphone,

not more than one person other than the observer reading the meter shall be

within 50 ft of the vehicle or microphone, and that person shall be directly

behind the observer reading the meter, on a line through the microphone

and the observer.

l+.l. 3 The ambient sound level (including wind effects) due to sources

other than the vehicle being measured shall be at least 10 dBA lower than

the level of the tested vehicle.

U . 1 . i+ The path of vehicle travel shall be relatively smooth.

i+.1.5 The microphone shall be located 50 ft from the centerline of

the vehicle path at a height of k ft above the ground plane.

h.1.6 An acceleration point (point A) shall be established on the

vehicle path 25 ft before a line through the microphone and normal to the

vehicle path.

k.2 VEHICLE OPERATIONS

h.2.1 The vehicle shall proceed along the test path at a constant

approach speed. The vehicle engine shall be run at 60% of the engine speed

at maximum rated net horsepower. The vehicle tachometer shall be used to

determine this speed. If the vehicle is not equipped with a tachometer,

then the appropriate vehicle speed must be calculated by the following

formula

Approach vehicle speed= [ (0-6)X(maximum hp engine speed)!

x

overall gear ratio

jrear wheel measured circumference, ftj X ^O.Olluj

The lowest gear which does not permit maximum rated net horsepower engine rpm

to be developed within 50 ft of point A shall be used. When the front of the

vehicle reaches the acceleration point, the throttle shall be opened wide,

and maintained until the front of the vehicle is 25 ft beyond the microphone.

U.3 MEASUREMENTS

U.3.1 The meter shall be set for "fast" response and for the A-weighted

network. If the meter is equipped with "hold" it may be used, provided the

response time is identical to that used on "fast." ("impulse" may not be

used.

)

U.3.2 The meter shall be observed while the vehicle is accelerating.

The applicable reading shall be the highest sound level obtained for the run,

ignoring unrelated peaks due to extraneous ambient noises. Sufficient

47
preliminary runs to familiarize the driver and to stabilize the engine

operating conditions shall be made before measurements begin. Immediately

after the preliminary runs, at least two measurements shall be made for

each side of the vehicle. All of the values shall be recorded.

U.3.3 The sound level for each side of the vehicle shall be the average

of the two highest readings which are within 2 db of each other. The sound

level reported shall be that of the louder side of the vehicle.

5. GENERAL COMMENTS

5.1 It is strongly recommended that technically trained personnel

select equipment and that tests be conducted only by qualified persons

trained in the current techniques of sound measurement.

5.2 An additional 3 dBA allowance over the sound level limit is

recommended to provide for variations in test site, vehicle operation,

temperature gradients, wind velocity gradients, test equipment, and inherent

differences in nominally identical vehicles.

5.3 Instrument manufacturer's specification for orientation of the

microphone relative to the source of sound and the location of the observer

relative to the meter should be adhered to.

5.^+ When a windscreen is required, a previously calibrated windscreen

should be used. It is recommended that measurements be made only when wind

velocity is below 12 mph.

5.5 Instrument manufacturer's recommended calibration practice should be

followed. Field calibration should be made immediately before and after

each test sequence. Either an external calibrator or internal calibration

means is acceptable for field use, provided that external calibration is

accomplished immediately before or after field use.

6. REFERENCE MATERIAL

Suggested reference material is as follows:

ANSI SI. 1-1960, Acoustical Terminology

ANSI SI. 2-1962, Physical Measurement of Sound

ANSI Sl.U-1971, Standard Specification for Sound Level Meters

SAE Jl84 - Qualifying a Sound Data Acquisition System

(Applications for copies of these documents should be addressed to

American National Standards Institute, 1^30 Broadway, New York,

N. Y. 10018, and the Society of Automotive Engineers, 2 Pennsylvania

Plaza, New York, N.Y. 10001.)

48
COURSE REQUIREMENTS

Course flat between Points A & B.

No obstructions within boundary shown.

No obstructions higher than 3 ft within 50 ft of

Points A, B, & C, or Microphone

Ground cover within the boundary shown shall not

be more than six inches high.

Figure 1

49
NOISE MEASUREMENT PROCEDURE USED FOR QUALIFICATION IN

AMERICAN MOTORCYCLE ASSOCIATION SANCTIONED OFF-ROAD COMPETITION

/

/

/ /

/ /

50 7

T

/ /

/ / /

i i i i L l

1 1

/

N

RECOMMENDED NOISE

TESTING METHOD

During the FIM spring, 1972, congress held

in Geneva, Switzerland, the world governing

body for the sport of motorcycling adopted noise

standards and testing methods based on proposals by

the delegates of the American federation. After

experiencing difficulties with various methods

designed for technical accuracy and sophistication,

the FIM turned to the American Motorcycle

Association for suggestions with the hope that

a world-wide noise abatement program could be

established, based on a practical, easilyadministered method of noise testing.

The FIM method provides that all machines under

examination be measured at a distance of 50 feet

(15.2m). They should be running in neutral with

the noise level reading taken at a pre-determined

motor speed, depending upon the size of the motor -

cycle

.

50
A hand-held meter, such as that available from the AMA, should be

held about 4 feet (1.2m) from the ground (a comfortable posture with

the elbows bent) with the microphone pointing at a right angle to the

motorcycle. The individual holding the meter, preferably the referee

in charge or someone appointed by him, takes the reading of each motorcycle and reports it to a clerk who should record it beside the contestant's

number on a entry list.

With the motorcycle started and running in neutral, the motor is

accelerated to a certain rpm and held there just long enough for the reading

to be taken. Care should be taken not to over-rev the motor or to hold it

at speed too long.

Below are the reading speeds established by the FIM:

50cc to 75cc 6000rpm

lOOcc to 125cc 5500rpm

175cc to 250cc 5000rpm

350cc to 500cc 4500rpm

over 500cc 4000rpm

Note that these recommendations are based on traditional FIM class

designations. If a motor size falls between categories, it should be moved

to the next larger class. For example, a 150cc machine should be measured

at 5000 rpm, falling into the class of motorcycles up to 250cc.

If the motorcycle has no tachometer, the testing crew may want to use

a counter which attaches to the electrical system, a method suggested by

the FIM. If no such device is available, the motor speed should be estimated

at 2/3 maximum safe revolutions.

No motorcycle, tested at the motor speed designated for its motor class,

may exceed 92 decibels (92 dB(a)) and be * legal for AMA amateur competition

or professional mo to-cross.

Common sense should be followed in administering this test. For example,

only the motorcycle being tested should be running. An open area should be

chosen so that the contestant will not be jeopardized by noise echoing from

walls or other large objects.

* This level is now set at 90 dBA.

51
This method is designed for its simplicity. More sophisticated and

accurate methods are available but they are more complicated, difficult

and expensive to administer. Furthermore, with the more complicated

methods, the individual being tested can usually find more ways to

manipulate the noise level of his machine and control the results to

his benefit.

For those interested in improving the sport of motorcycling by reducing

offensive noise, this simple method, administered in a spirit of cooperation

by official and contestant alike, is a most convenient and effective

technique

.

52

i
11. References

[I] Control of Noise from Motor Vehicles, Report of the Task Force on Noise,

June 1974, Illinois Institute for Environmental Quality, Chicago,

Illinois

.

[2] Society of Automotive Engineers, Inc., J213a - Definitions - Motorcycles

SAE Recommended Practice (SAE, New York, New York, 1972).

[3] Control of Motorcycle Noise, Volume I, Technology and Cost Information,

EPA Report No. 550/9-74-001-A, June 1974, U. S. Environmental Protection

Agency, Washington, D. C. (available from the National Technical

Information Service, Springfield, Virginia).

[4] A Study of Annoyance from Motor Vehicle Noise, Bolt Beranek and Newman,

Inc., Report No. 2112 (Bolt Beranek and Newman, Inc., Cambridge,

Massachusetts, June 1971).

[5] Proposed Forest Service Sound Level Standard and Test Procedure for

Motorcycles, U. S. Department of Agriculture Forest Service, San Dimas,

California, 1974.

[6] Harrison, R. T. , Off-Road Vehicle Noise-Effects on Operators and

Bystanders, SAE Paper 740687 (Society of Automotive Engineers, Inc.,

Warrendale, Pa. September 1974).

[7] Theissen, G. , Community Noise - Surface Transportation, Sound and

Vibration, _2, 14-16, April 1968.

[8] Harrison, R. T. , Motorcycle Noise, ED and T Report 2428 (USDA Forest

Service Equipment Development Center, San Dimas, California, February

1974).

[9] Society of Automotive Engineers, Inc., J331a - Sound Levels for

Motorcycles SAE Recommended Practice (SAE, New York, New York, 1975)

.

[10] California Administrative Code, Title 13, Chapter 2, Subchapter 4,

Article 10, Vehicle Noise Measurement (Department of the California

Highway Patrol, California, December 1973).

[II] Society of Automotive Engineers, Inc., J47 - Maximum Sound Level

Potential for Motorcycles, SAE Recommended Practice (SAE, New York, New

York, 1975).

[12] Measurement of Noise Emitted by Vehicles, ISO Recommendation R362

(International Organization for Standardization, Geneva, Switzerland,

1974). Available from the American National Standards Institute, New

York, New York.

53
[13] Acoustical Society of America Standard 3-1975, Test-Site Measurement of

Maximum Noise Emitted by Engine-Powered Equipment, Acoustical Society of

America, New York, New York, 1975.—

[14] American Standard Specifications for Sound Level Meters, SI. 4-1971,

American National Standards Institute, New York, New York (April 1971).

[15] Society of Automotive Engineers, Inc., J184 - Qualifying a Sound Data

Acquisition System, SAE Recommended Practice (SAE, Pittsburg,

Pennsylvania, 1970).

[16] Recommendation for Sound Level Meters, IEC Publication 123

(International Electrotechnical Commission, Geneva, Switzerland, 1961).

[17] Little, R. A., Motorcycle Noise Test Procedure Evaluation: SAE XJ331a

and XJ47, SAE Paper 740686 (Society of Automotive Engineers, Inc., New

York, New York, September 1974).

[18] Harrison, R. T., The Effectiveness of Motorcycle Helmets as Hearing

Protectors, Project Record ED & T 2210 (USDA Forest Service Equipment

Development Center, San Dimas, California, September 1973).

[19] Harrison, R. T. Operator's At-Ear Noise Exposure for Off-Road

Recreational Vehicles, in Proc. 1973 National Conference on Noise

Control Engineering (Noise-Con 73), D. R. Tree, Ed. (Institute of Noise

Control Engineering, Poughkeepsie, New York, 1973).

[20] American National Standard Methods for the Measurement of Sound Pressure

Levels, SI. 13-1971, American National Standards Institute, New York, New

York (July 1971).

[21] Transportation Noise and Noise from Equipment Powered by Internal

Combustion Engines, Report No. NTID 300.13 (U. S. Environmental

Protection Agency, Washington, D. C, December 1971).

— ASA 3-1975 was submitted to the American National Standards Institute

as ANS SI. 19 but was rejected in its present form.

54
12. Bibliography

1. Hare, C. T., Springer, K. J., Oliver, W. R. , Houtman, W. H. and Huls, T.

A., Motorcycle Emissions, Their Impact, and Possible Control Techniques,

SAE Paper 740627 (Society of Automotive Engineers, Inc., New York, New

York, August 1974)

.

2. Singh, J. and Renner, R. A., The Impact of Noise Abatement Standards

upon the Motorcycle Industry, IRT-344-R (International Research and

Technology Corporation, Arlington, Virginia, March 1974).

3. Harrison, R. T. , Sound Propagation and Annoyance under Forest

Conditions, ED&T Report 7120-6 (USDA Forest Service Equipment

Development Center, San Dimas, California, March 1974).

4. A Study of the Magnitude of Transportation Noise Generation and

Potential Abatement, Submitted to the Department of Transportation,

Office of Noise Abatement Under Contract No. DOT-OS-A9-018 , (Serendipity

Incorporated, Arlington, Virginia, September 1969).

5. Urban Traffic Noise: Strategy for an Improved Environment, Report of

the Consultative Group on Transportation Research to the Governments of

Member Countries, Organization for Economic Cooperation and Development,

Paris, France, October 1969.

6. Hager, W. L., A Proposal for Mocorcycle Noise Abatement, Proceedings of

the Technical Program, NOISEXPO (National Noise and Vibration Control

Conference, Atlanta, Georgia, May 1975).

USCOMM-NBS-DC 55
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1001

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

An Evaluation and Assessment of Existing Data and

Procedures for the Measurement of Noise from Motorcycles

5. Publication Date

November 1975

6. Performing Organization Code

7. author(S) B< R> Fuller, C. I. Holmer, W. A. Leasure, Jr. o. Performing Urgan. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

2000451

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Office of Noise Abatement and Control

U. S. Environmental Protection Agency

Washington, D. C. 20460

13. Type of Report & Period

Covered

final

14. Snnn q r> r in o Aopnru v. onp

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

This report reviews existing motorcycle noise measurement procedures with regard to

their usefulness in the regulation of motorcycle noise as well as the availability,

extent and applicability of existing data. On the basis of this review, probable or

potential measurement difficulties are identified that could hinder the promulgation

and/or enforcement of future EPA regulations to control the noise emission from

motorcycles.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Acoustics (sound); measurement methodology; motorcycle; noise emisson standard;

noise measurement.

18. AVAILABILITY '^J Unlimited

fx] For Official Di stribution. Do Not Release to NTIS

I | Order From Sup. of Doc, U.S. Government Printing Office

Washington, D.C. 20402, SD Cat. No. CH

| | Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

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60

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