Naval Submarine Medical Research Laboratory

NSMRL REPORT 1197 27 JUNE 1995

Sonar Headphone Selection for Optimum Performance

An Overview

Joseph S. RussottI

20031216 197

Released by

Steven F. Blacke, CDR, MSC, USN

Acting Commanding Officer

Naval Submarine Medical Research Laboratory

Approved for public release; distribution unlimited
Sonar Headphone Selection for Optimum Performance

An Overview

Joseph S. Russotti

Naval Submarine Medical Research Laboratory

Report No. 1197

Naval Medical Research and Development Command

Research Work Unit 65856N-M0100.001-5001

Approved and released by

S. F. Blacke, MSC, USN

Acting Commanding Officer

Approved for public release; distribution unlimited
Summary Page

The Problem

To improve the real-time auditory detection and aural analysis capability of passive broadband sonar systems.

The Findings

The most blatant source of acoustic signal degradation on auditory sonar systems is in the

acoustic performance of headsets. Recent detection performance data have shown the need for

upgrading sonar headsets to reproduce electrical energy accurately over a wider bandwidth.

Headphone measurement data on commercially available headphones have shown that headphones ofmore appropriate bandwidth and frequency-response accuracy have not been ofsealedcircumaural design. Headphones designed to completely seal around the listener's ear exhibit

low-finequency variations with placement on the head and with deterioration of ear-cushion as a

result of a less than perfect seal. Unfortunately, current noise levels preclude use ofthe more accurate, less variable, open-air types. Reduction of noise levels in sonar spaces to permit use of

better headphone designs is a highly desu^ble solution. Recent developments in active noise

canceling headsets show promise as an interim solution. A commercial model having adequately flat frequency response has been found and improved through active equalization. A prototype version of this improved headset has been evaluated.

Application

Advanced auditory sonar system design. Aural analysis and tactical sonar headphone requirements.

Administrative Information

This research was carried out under Naval Medical Research and Development Command Work

Unit 65856N-M0100.(X)1-5001. It was approved for publication on 27 Jun 95, and designated as

NSMRL Report 1197.

u
Abstract

Real-time auditory detection and aural analysis capability of passive broadband sonar

systems needs improvement. A weak link in these systems is the use of communicationsbandwidth low-fidelity headsets. Unfortunately, no procedure for headphone (earphone element

inside headshell) frequency response measurement exists in military headset specifications. An

accurate technique for headphone calibration was devised which provides the earphone element

with an acoustic load similar to the one provided by a human wearer. Using this technique,

headphone measurement data on commercially available headphones was collected and

compared to the current sonar headsets. The advantages and disadvantages of open and sealed

circumaural headsets and recent developments in noise canceling headsets are discussed, along

with the possibility ofreducing noise levels in sonar spaces to permit use of higher fidelity

headphone designs.

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IV
Sonar Headphone Selection for Optimum Performance

An Overview

This research on headset measurement came

about as a result of our interest in making full

use of auditory perceptual abilities in passive

sonar applications including the use of interaural cues for detecting and discriminating

acoustic target information. For optimum

aural signal presentation, all perceptually useful acoustic information present in the ocean

should be delivered to the ear. This broadband transfer of energy is essential since it is

the combination ofmany frequencies (not necessarily harmonically related) all time varying

in amplitude, which provide auditory cues to

the listener about the presence and character

of non-random energy in the listening channel.

Harris et. al. (1979) demonstrated that lowpass filtering that removes frequencies above

3 kHz, 4 kHz, or 6 kHz leads to significant

reduction in sonar target discrimination in

sea-state-noise.

Research also has shown that extending the

low-frequency cutoff downward an additional

4(X) Hz significantly improved auditory detection perfomiance (Russotti, 1987). More recent

research on digital sample rate reinforces the

critical need for an adequate reproduction of

upper frequencies. Both detection (Russotti,

et al., 1993) and discrinaination (Russotti, et

al. in press) were significantiy degraded when

sample rates used in digitizing the signal were

reduced from 12.5 kHz to 6.25 kHz.

As a first step to optimizing the energy

transfer, the frequency response accuracy of

the operator's headset needs major improvement. As an example, the ANWIC HI57-158

sonar headset used for BQQ-5 sonar systems

is an aircraft pilot's voice communications

headset, intentionally band-limited for that

purpose and designed within the constraints

of 1957 technology under specifications set

forth in the original MIL E-25670 specification

(U. S. Air Force, 1957). Headset technology

is far improved nearly 40 years later, but appropriate techniques for measurement of such

headsets are not specified.

Unfortunately, the current (1986) American

National Standards Institute (ANSI) method

for coupler calibration of earphones is not intended for such circumaural (around the ear)

phones. It is intended only for supra-aural (on

the ear) or insert earphones. Work by Shaw

and others (Shaw & Thiessen, 1962; Shaw,

1966) showed that probe-tube microphone

sound pressures measured under circumaural

earphones on real ears were not in agreement

witii similar measurements made on such earphones using simple couplers. Until such discrepancies could be resolved, a standard for

circumaural headphone measurement could

not be written.

Research on the acoustic impedance ofthe

human ear by Zwislocki (1957), Ithell (1963),

and Delaney (1964) led to the development of

several ear simulators. In these simulators,

accurate impedance loading ofthe earphone

was attempted using multiple resonant cavities

(Zwislocki, 1970,1971; Record & Hixson,

1972).

The measurement technique we devised in

1985 and proposed for use in earphone calibration in 1986 uses a laboratory type Zwislocki

earsimulator which includes multiple cavities

to model the acoustic load that an average

human wearer would place on the earphone

element. In standard form, this coupler uses a

machined surface and fifth resonant cavity to

simulate the external ear (or pinna). In developing a test and evaluation tool for hearing

aid performance, Burkhard and Sacks (1975)

incorporated the eardrum simulator portion of
Figure 1. Headphone under test on KEMAR manikin.

the Zwislocki coupler into the anthropometrically average manikin KEMAR. They accurately substituted flexible pinnae and metal

ear canals for the conesponding portions of

the Zwislocki coupler. Acoustic measurements

on this version ofthe KEMAR manikin are in

close agreement with similar measurements

on human subjects (Burkhard, 1975), and the

KEMAR manikin now conforms to ANSI

(1985) standards intended for airborne sound

measurement

Figure 1 shows the KEMAR manikin as

used in our application. The measurement

procedure is outlined in detail in Russotti, et

al., 1988. The Zwislocki coupler, modified in

the KEMAR manikin, has decided advantages

for headset evaluation over a hard surfaced

machined plate, in that any wearable headset

can be tested. For a real ear, and also for the

simulator, the acoustic signal that arrives at

the eardmm has had its frequency response

modified by the external ear structure, by

resonances created by the pinna, and by the
complex loading ofthe ear canal and eardrum

with its ossicular chain. A conversion function

is necessary. This converted response should

correctly reference the signal measured in the

coupler back to the external sound field.

The required conversion function shown

in Figure 2 references the earphone element

response back to the diffuse field. This transformation is the response of the human ear, or

in this case the manikin-mounted ear simulator, without regard to any one direction.

Earmuff shape, size, seal, headband effectiveness and placement of headset on the head

and against the ear are all major contributors

to the variability one finds in earphone response

measurements. Our technique samples these

variables taking 5 measurements each, of 4

earphone elements. All ofthe xy plots ofsound

pressure as a function of frequency are stored

using an A/D converter. They are averaged

and the diffuse-field conversion function

applied.

As a comparison, the upper left curve in

Figure 3 shows a prototype supra-aural (on

the ear) earphone teilored to have flat response

on a standard 6 cc ANSI volummelric coupler.

Below it is the averaged response of the same

earphone element measured on the ear simulator. This is the diffuse-field corrected response of the earphone. Figure 4 shows an

averaged response for one of our 24 tested

models from a 1985 paper (Russotti, et al.)

This Sennheiser 430 shows a total variation of

11 dB firom 40 Hz to 10 kHz. We previously

recommended these headsets for SSEP Code

60 Subschool New London, our land based

aural target analysis facility, where they have

been in use since 1985. Unfortunately, they

are open air headphones.

For purposes of comparison, we have

included some current headsets used in sonar

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Figure 2. Conversion function used for diffuse-Held transformation.
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Figure 3. Prototype audiometric headphone designed to produce a flat frequency

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Figure 5. Averaged diffuse-field frequency response for the Grey H157-158/AIC Federal Stock Headset.

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Figure 6. Averaged diffuse-field frequency response for the DAVID CLARK 12507G-20 Federal Stock

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systems along with some proposed headsets.

Figure 5 is the averaged and corrected response

of the previously mentioned H157-158 AIC

headset which shows a 35 dB total variation

in response over the 40 Hz to 10 kHz measurement range and a 29 dB variation over the

narrower 100 Hz to 10 kHz range. Figure 6

shows the David Clark federal-stock sonar

headset currently used, with a 31 dB response

variation in the 40 Hz to 10 kHz range and a

23 dB variation from 100 Hz to 10 kHz.

Figure 7, which plots the individual 20

corrected response curves for the David Qaik,

shows clearly why we sample the responses

of 4 earphone elements over 5 placements of

that element on the ear. The 4 distinct groupings in the 1 to 2 kHz region and the single

element's unique response in the 4 to 8 kHz

region are representative of many manufacturers' quality control. Headset specifications

can reduce this variability by defining tolerances required from sample to sample over a

specified frequency range. In addition these

individual curves reveal the major problem

with most sealed circumaural phones. There

is an inconsistent low-frequency response

found in sealed circumaural phones as a result

oftheir inherent need for a proper pressure

seal against the head. By its' very design, the

earphone element in a sealed circumaural

headphone must operate as a pressure

transducer. Acoustic leaks will change its

sound pressure output - in this case exhibiting

a measurement variation of 15 dB at 100 Hz.

Of course, such variations increase with deteriraation or hardening oftiie vinyl ear cushions.

A more logical solution to the problem would

be the overall reduction of airborne noise in

sonar workspaces. Such a solution would be

in line with a general need to reduce radiated

energy and would allow use of more accurate,

far more comfortable headphones. In our testing since 1985, we have yet to find a sealed

circumaural passive noise-occluding headset

that was not oflimited bandwidth.

Figure 8 shows tiie airborne sonar operator's

headset, the Astrocom H173/AIC, a closed

circumaural headset which shows a 34 dB

response variation from 40 Hz to 10 kHz and

a 25 dB variation from 100 Hz to 10 kHz.

Figure 9 shows the diffuse-field response of

the Joyce Telectronics Corporation JTC57-275

headset available through federal stock. This

is a communication headset having a response

variation of 36 dB from 40 Hz to 10 kHz and

28.5 dB variation firom 100 Hz to 10 kHz. It

has been included for reference purposes

since many sonar personnel have requested

information regarding its suitability for sonar

operator use.

For the same reasons we are including the

response characteristics ofthe Hughes Aircraft

model 4506408 military headset as Figure 10.

This federal stock headset produces a diffusefield response variation of 26.5 dB from 40

Hz to 10 kHz, with a 21.5 dB variation from

100 Hz to 10 kHz and is not appropriate as a

wideband sensor operator headset.

Figure 11 depicts the diffuse-field frequency

response of the headset originally specified

for BSY-1, the Sennheiser HMD 414. Since it

is a supra-aural headset, it provides minimal

attenuation of airborne noise and is far less

comfortable in extended use than circumaural

designs. As seen in the figure, there is a response variation of 22 dB from 40 Hz to 10

kHz. It has a 10 dB per octave slope just

under 200 Hz and, although not shown here

(the measurement device serves as an earphone coupler not an ear simulator above 10

kHz), appears to drop offrapidly by 20 dB

from 10 to 14 kHz.

We have also tested nine new conventional

broadband (high fidelity) headsets. The best

model tested to date is the Sennheiser model

HD250 shown in Figure 12. A closed circumaural model, though with minimal noise reduction, it has a total variation of 11 dB over the
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Figure 9. Averaged diffuse-field frequency response for the JOYCE TELECmONICS CORP. JTC

57-275 Federal Stock Headset.

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Figure 12. Averaged diffuse-field frequuency response for the SENNHEISER HD 250 Headphone.
Figure 13. SENNHEISER HMD 250.MIL Headset prototyped with NSMRL.

10
40 Hz to 10 kHz range. BSY 2 sonar system

design calls for reduced noise in sonar spaces.

This Sennheiser headset is the model we

recommend for the BSY-2 system given the

reduced noise levels in BSY-2 sonar spaces

(Commanding Officer NSMRL, 1990). At

our suggestion, a boom microphone was

added to the headband to isolate it from the

earcup shell and to allow boom placement on

either side of the head with simple rotation of

the boom on its mount. The new model has

been designated the HMD250.MIL. This

microphone equipped headset is shown in

Figure 13. It is extremely lightweight yet

rugged, with high tensile-strength stainless

steel signal cables dressed down vertically

from the boom side ofthe headband. The

small diameter smooth cabling is exceptionally well implemented and unobtrusive to the

user, especially when terminated in a Nexus

U-384/U five conductor phone-style plug.

Diffuse-field frequency response curves for

the eight remaining high fidelity models

tested, are presented in an appendix for

reference purposes.

We have tested several active noise canceling

(ANC) headset prototypes. One of these, the

Sennheiser HMEC 45 (an HME 1410 Series

headset), looks somewhat like the supra-aural

BSY 1 headset (HMD 414) externally but

employs electret microphones mounted outward on each earpiece which pick up airborne

noise and then generate an inverse of the

noise using an external processor. Figure 14

shows tiie averaged diffuse referenced response

ofthe prototype which produced a 21 dB

variation fix)m 40 Hz to 10 kHz with ANC "off."

Figure 15 shows the interactive effects of

active noise cancellation on the fii^equency

response of the headset. The notch at 450 Hz

would render this headset less than ideal for

passive sonar purposes. A second prototype

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supra-aural ANC Headset

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Figure 15. Averaged diffuse-field frequency response for the SENNHEISER HM#C 45 prototype headset

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Figure 16. Averaged diffuse-field frequency response for the SENNHEISER LHIC prototype supra-aural

ANC Headset, "ANC on" vs "ANC off{.

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circumaural ANC Headset

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Figure 19. Averaged diffuse-field frequency response for the BOSE AVIATION/NSMRL prototytpe

sealed ciicumaural ANC Headset.

Figure 20. BOSE AVIATION HEADSET.

14
active noise cancellation model was made

available for testing. This model, designated

the LHIC 45, used substantially smaller supraaural earphone elements with self-contained

electret microphones and noise cancellation

circuitry. The two curves shown in Figure 16

represent the averaged diffuse-field frequency

response to a swept tone set to produce 80 dB

SPL at the headphone at 1 kHz. The upper

curve is the measured response with no cancellation, and the lower is with cancellation on.

Unlike the previously mentioned HMEC-45,

no artifacts were introduced into the fiequency

response by tfie operation ofthe ANC circuitry.

While the real time noise cancellation was extremely effective, the earphone element was

of a communication bandwidth and, therefore,

not currcntiy useful for passive sonar application.

Figme 17 presents the diffuse-field-referenced fijequency response data (ANC "on") of

a Sennheiser HMEC 200 ANC headset which

uses a Peltor passive noise occluding headshell for additional noise attenuation. This

headset produces an averaged diffuse-fieldreferenced frequency response variation of

14.5 dB fi-om 40 Hz to 10 kHz.

Figure 18 depicts the Bose Aviation ANC

headset in a non standard configuration (a low

fi:equency filter has been removed). Total

fijequency response variation from 40 Hz to

10 kHz is 15 dB. This sealed circumaural

headset and the Sennheiser/Peltor mentioned

above use an internal microphone in each

earcup whose signal is compared against the

instantaneous electrical signal. The difference

signal is inverted and added to the electrical

signal sent to the earphone element to actively

null any unintended acoustic energy found in

the earcup. Subsequent to our frequency

response measiu-ements on the Aviation headset, we conferred with the manufacturer and

suggested that active equalization might be

added to further enhance the measured diffusefield response. The result of their efforts is

shown in Figure 19. This alteration known as

the Dan Gager/NSMRL prototype exhibits an

improved frequency response (11.5 dB total

variation 40 to 10k Hz) that competes favorably with high fidelity headsets, with the

added benefit ofsuperior noise attenuation.

Most importandy, die fact that its' ANC

circuitry compares the acoustic signal in the

headshell to tiie intended electrical signal automatically corrects for dinainished soundpressure output related to a less than perfect

seal. The Bose Aviation Headset is shown in

Figure 20. No external changes to the headshell ofthis commercial model are caused by

the modifications for our prototype.

Concurrent with our headset research, a

military aviation ANC headset was developed

for the Air Force with newly designed earcups

of smaller size for use inside flight helmets.

The headset also meets TEMPEST requirements

for radiated energy. Figure 21 depicts the

diffuse-field response ofthis communications

headset Total firequency response variation

was measured at 23.5 and 24 dB for right and

left earphone assemblies in the 40 to 10k Hz

range. Subsequent to a Naval Air Warfare

Center Aircraft Division request for added

active equalization as implemented in our

collaboration, Bose has prototyped an inproved

sensor operator version of that military headset as shown in Figure 22. Total frequency

response variation averaged across earphone

elements is 18.5 dB over the 40 to 10k Hz

range, with a 12 dB variation within the

narrower 40 to 8.5k Hz range.

For our submarine sonarrequirements the

higher fidelity commercial aviation headset

modified as the Dan Gager/NSMRL prototype

shown in Figure 19 is the better and far less

expensive choice. This headset has been taken

out-to-sea by Acoustic Intelligence (ACINT)

specialists and was given a very positive

evaluation (Russotti, 1993). Following that

evaluation these prototype headsets were

15
100

20Hz 500 I KHz

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Figure 21. Averaged diffuse-field frequency response for the BOSE AVIATION MILITARY HEADSET

prototype ANC Flight Helmet Communications Headset for USAF.

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Figure 22. Averaged diffuse-field frequency response for the BOSE AVIATION MILITARY HEADSET

rototype ANC Flight Helmet Headset with enhanced response.

16
recommended to Office of Naval Intelligence,

Code 25, for ACINT use (Commanding Officer NSMRL, 1993). They were given an

extended at-sea evaluation by two BSY-1

equipped submarines (Commanding Officer

USS San Juan, 1993), and were also used in

shorter deployment aboard two BQQ-5

equipped submarines (Benedetto et al, 1995).

Comments by the crews ofthese boats were

highly favorable in terms ofthe added information provided and positive in their acceptability and comfort, but expressed a desire for

more durable earcushions and a lighter overall

weight. The easily replaceable earcushions

are soft silicone gel-filled pads formed as two

concentric rings and covered by a thin urethane

membrane skin. Initially designed for a life

cycle of 1000 hours of intermittent use in aircraft, the cushions managed to survive under

continuous use and longer duration, but at-sea

1000 hours translates to 41.6 days. Their

condition following an extended deployment

far in excess of 1000 hours indicated that earcushion replacement was necessary. Although

the urethane membrane skin remained intact,

siUcone gel had migrated under and around a

foam substrate and the concentric ring appearance had been obliterated. Once new cushions

were snapped into place all headsets were in

excellent operation. No component failures

occurred. Work is underway to produce a

more durable earcushion with the same excellent comfort and noise reduction characteristics.

Given its aural capabilities, we strongly recommend this headset prototype be required

for the broadband search operator and sonar

supwvisor. Our second choice for all other

operators is the Sennheiser HD 250 (ruggedized) or the microphone equipped HMD 250-

MIL. This headset also was given highly

favorable evaluations by the same four sonar

crews that evaluated the ANC headsets, and

all HD 250 and HMD 250-MlL headsets

survived their extended at-sea deployment

without any earphone element failure. While

the microphone equipped HMD 250-MIL

version has a single-sheathed shielded cord of

high tensile-strength stainless steel with strainrelieved connection to the headshell at the

microphone boom, the commercial version

HD 250 has not been equally ruggedized. As

a consequence the less durable copper conductor "Y" cords failed on 2 headsets. Earlier

version HD 250 headsets used by ACINT

specialists had a stainless steel conductor "Y"

cord and no failures were encountered. The

solution was to modify the copper conductor

"Y" cord as was done on the 250-MIL version

so that the cord is not being pulled at its connection to the headshell. No further cord failure problems were encountered. However,

we would strongly recommend that the stainless steel cords be specified and that they be

installed configured as in the HMD 250-MIL

version. These headsets are the most accurate

headsets we have tested to date and are lightweight and extremely comfortable. Though

nominally of "closed" circumaural design they

incorporate tiny capillary tube vents which

limit the pressure seal and appear to reduce

the low fiequency variabihty normally encountered with closed headsets. Although these

circumaural headsets provide some noise

attenuation (Williams, 1992), we cannot recommend them for critical use such as passive

broadband (PBB) and sonar supervisor in

current sonar spaces on BQQ5 and BSYl due

to ambient noise levels. They are the headsets

we have specified for the quieter environment

designed for BSY2 (Commanding Officer

NSMRL, 1990).

Future iterations of submarine command

control centers may require concentrations of

operators in close proximity. To eliminate the

inevitable problems of battie station operating

conditions interfering with critical listening,

ANC headsets may be essential to specific

sensor operators in such environments.

As general purpose operator headsets both

are ideal in that the sound pressure output

17
across frequency is predictable and flat. This

is ofparticular importance in the implementation of narrow bandwidth or single ftequency

auditory alarms which would vary in amplitude

at different selected frequencies on headsets

of poorer fidelity. Both headsets exhibit a

sufficiently flat diffuse-field response which

make them suitable for virtual reality threedimensional auditory presentations, since the

necessary head-related transfer functions required for different source locations can be

imposed on their known non-directional

response.

In summary, we have found, and have overseen modifications on, two highly useful wideband sensor operator headsets which can be

selected according to noise environment.

There will always be some degree of discomfort associated with closed-shell noise-reducing

headsets. Temperatures at the eardrum are at

body core-temperature. Even the lightest,

best fitting, noise barriers cannot overcome

the heat and moisture buildup they create by

virtue oftheir seal around the external ear.

Unfortunately, open-air ANC headsets do not

attenuate enough across the necessary spectrum.

By far, the best solution to noise reduction is

to eliminate its source. For the present however, the most cost-effective solution is through

use of appropriate noise attenuating headsets.

References

American National Standard Method for

Coupler Calibration of Earphones." ANSI

S3.7-1973 (R1986), American National

Standards Institute, New York, 1973.

American National Standards Institute.

(1985). Specificationfor a Manikinfor

Simulated In-Situ Airborne Acoustic Measurements (ANSI S3.36-1985). New York:

American National Standards Institute,

Benedetto, J. L., Russotti, J. S., Harvey, J. T.,

and Hanna, T. E. (1995). At-sea tests of

headphones and activefilters (NSMRL

Report 1195). Groton,CT: Naval

Submarine Medical Research Laboratory.

Benson, R. W., Charan, K. K., Day, J. W.,

Harris, J. D., Niemoeller, A. R, Rudmose,

W., Shaw, E. A., and Weissler, P. G.

(1967). Limitations on the Use of

Circumaural Earphones. Journal ofthe

Acoustical Society ofAmerica, 41,713-

714.

Burkhard, M. D., and Sachs, R. M. (1975).

Anthropometric Manikin for Acoustic

Research. Journal ofthe Acoustical

Society ofAmerica, 58,214-222.

Burkhard, M. D. (Ed) (1978). Manikin

Measurements. Elk Grove Village, IL:

Industrial Research Products.

Conmianding Officer, NSMRL. (1990).

Sonar Headset Evaluation and Recommendation. Naval Submarine Medical Research

Laboratory Itr, 3960, Ser 50/459 dtd 13

April 1990.

Commanding Officer, NSMRL. (1993).

Sonar Headset Evaluation and Recommendation for ACINT use. Naval Submarine

Medical Research Laboratory Itr, 3960,

Ser 40/418 dtd 12 October 1993.

Commanding Officer, USS SAN JUAN, SSN

751. (1993). Evaluation of Noise Canceling Headset for AN/BSY-1 Sonar Suite.

3900, Ser 622 dtd 14 December 1993.

Delaney, M. E. (1964). The Acoustical

Impedance ofHuman Ears. Journal of

Sound Vibration, 1,455-467.

Delaney, M. E., Whittle, L. S., Cook, J. P.,

and Scott, V. (1967). Performance

18
Studies on a New Artificial Ear. Acustica,

75,231-237.

Harris, J. D., Kerivan, J. E., and Russotti, J. S.

(1979). The necessity for high frequency

hearing in passive sonar listening (NSMRL

Report 862). Groton, CT: Naval Submarine Medical Research Laboratory and

Military Medicine, 144, 3 33-336.

Ithell, A. H. (1963). The Measurement ofthe

Acoustical Input Impedance ofHuman

Ears. Acustica, 13,140-145.

Ithell, A. H. (1963). A Determination ofthe

Acoustical Input Impedance Characteristics ofHuman Ears. Acustica, 13,

311-314.

Killion, M. C. (1979). Equalization Filter for

Eardrum-Pressure Recording Using a KEMAR Manikin. Journal ofthe Audio Engineering Society, 27,13-16.

Record, H. L., and Hixson, E. L. (1972). The

Design and Evaluation ofan Artificial

Ear (Tech. Memo 32). Austin, TX:

Acoustics Research Lab, Electronics

Research Center, University of Texas.

Russotti, J. S., Haskell, G. B., Neal, R.,

Santoro, T. P., and Carpenter, S. M.

(1985). Frequency response and distortion measurement ofheadsetsfor use in

auditory displays (Repdort 1066). Groton, CT: Naval Submarine Medical Research Laboratory.

Russotti, J. S. (1987). (U) Effects ofsystem

bandwidth on passive sonar target detection using normal and experimental auditory displays (Report 1103). Groton, CT:

Naval Submarine Medical Research

Laboratory

Russotti, J. S., Santoro, T. P., and Haskell, G.

B. (1988). Proposed technique for earphone calibration. Audio Engineering

Society Journal, 36,643-650.

Russotti, J.S. (1993). At-Sea Evaluation of a

Prototype Active-Noise Canceling Headset

(Memorandum for the Record). Groton,

CT: Naval Submarine Medical Research

Laboratory.

Russotti, J.S., Santoro, T.P., Hanna, T.E.,

Wojtowicz, J.J. (1993). Effects ofdigital

sampling rate and bit quantization on

passive auditory sonar target detection

performance (Report 1184). Groton, CT:

Naval Submarine Medical Research

Laboratory.

Russotti, J.S., Santoro, T.P., Hanna, T£., and

Leo, T. (In Review). Effects of digital

sampling rate and bit quantization on the

auditory discrimination of passive sonartargets. Groton, CT: Naval Submarine

Medical Research Laboratory.

Shaw, E. A. G., and Thiessen, G. J. (1962).

Acoustics of Circumaural Earphones.

Journal ofthe Acoustical Society of

America, 34,1233-1246.

Shaw, E. A. G. (1966). Ear Canal Pressure

Generated by Circumaural and SupraAural Earphones. Journal ofthe Acoustical

Society ofAmerica, 39,471-479.

Shaw, E. A. G. (1974). Transformation of

Sound Pressure from Free Field to the

Eardrum in the Horizontal Plane. Journal

ofthe Acoustical Society ofAmerica, 56,

1848-1860.

Williams, C. E. (1992). Sound Attenuation

Evaluation of Sennheiser Model HD250

Headset (NAMRL-26-5720 Ser 26/0457

19
dtd 03 June 1992). Naval Aerospace

Medical Research Laboratory

Zwislocki, J, J. (1957). Some Measurements

ofthe Impedance at the Eardrum. Journal

ofthe Acoustical Society ofAmerica, 29,

349-356.

Zwislocki, J. J. (1970). Acoustic Couplerfor

Earphone Calibration (Spec. Rep. LS(5-S7). Syracuse, NY: Laboratory of Sensory

Communication.

Zwislocki, J. J. (1971). An Ear-Like Coupler

for Earphone Calibration (Spec. Rep.

LSC-S-9). Syracuse, NY: Laboratory of

Sensory Communication.

Acknowledgement

The author would like to thank Thomas P.

Santoro and Cindy Burgess-Russotti for their

programming efforts on the original Digital

Equipment Hardware and later IBM based

versions. Special thanks are extended to

Matthew Kosakowski for programming

changes to automate the data collection and

calibration process and for conducting the

major portion of data collection. Additional

thanks to John Benedetto for data collection

and for his significant contribution in modifying hardware and software to automate the

newest version of the data collection system.

Also, the editorial assistance of Susan Monty

is greatly appreciated.

20
APPENDIX

loo-

(O^ 1

GRADO

HP.IOOC

I

^^

SUPRA-AURAL HEADPHONE

1 1 se—

< ^., _^N P' 80-

a. /

\/vJ

m

/

r—

70-

60-

1 1 1 1 1 1 1 -.1 1 1 1 1—

50- H- Mil i— 1 1

20Hr 50 100 200 500 I KHz 2

FREQUENCY

10 20

100- 1 f—

YAMAHA

RH-5M

SUPRA-AURAL HEADPHONE

90-

c®

80-

a.

(O

m•o

70-

/IX

/

-l

60-

50- t--H4+ \—\ 1- \ 1 I I I H \

20Hz 50 100 200 500 I KHz 2

FREQUENCY

5 10 20

21
100-

90-

Q.

m

CD

a

70-

60-

50-

20Hz

++44

so 100

+-HSENNHEISER

HD 560

CRCUMAUMl. HEAM>HONE

^

i

200 500 I KHz 2

FREQUENCY

+—IA

/ 1

-K+F

10 20

100-

90-

1 1

SENNHEISER

HDS40

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80-

-I

Q.

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m

70-

ri>.

60-

50- 1—I++H—y +—f- i—I H-H- 1

20Hz SO 100 200 500 I KHz

FREQUENCY

10 20

22
100-

90-

80-

a.

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70-

60-

50-

20Hz

++H

50

-f-H

SENNHEISER

HDS20

CnCUMAURAL HEAOPHONi

AV

^.

100 200 500 I KHz 2

FREQUENCY

+-+ +++i

10 20

100-

90-

<>-"V\

SENNHEISER

HD480

CmCUMAURAL HEADPHONE

0.

v>

09

o

^

70-

60-

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FREQUENCY

23
100

20 Hz SOO IK Hz

FREQUENCY

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<n

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•o

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10 20

24
UNCLASSIFIED

SECUHIIVCUSSIUCAIIUNOF IHISHAGf

REPORT DOCUMENTATION PAGE

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Naval Submarine Medical

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11. TITLE (Include Security Classification)

IfliprovemeHfes-feo aural--sonar; headphones and acti^re filtors

12. PERSONAL AUTHOR(S)

Joseph S. Russotti

13a. TYPE OF REPORT

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95 JUN 27

15. PAGE COUNT

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16. SUPPLEMENTARY NOTATION

17. COSATI CODES

FIELD GROUP SUB-GROUP

18. SUBJECTTERMS (Continue on reverse ifnecessary and identify t>y block nunDber)

Headphones; Performance

19. ABSTRACT (Continue on reverse ifnecessary and identify by block number)

Real-time auditory detection and aural analysis capability of passive broadband sonar systems needs

improvement. A weak link in these systems is the use of communications-bandwidth low-fidelity headsets.

Unfortunately, no procedure for headphone (earphone element inside headshell) frequency response

measurement exists in military headset specifications. An accurate technique for headphone calibration was

devised which provides the earphone element with an acoustic load similar to the one provided by a human

wearer. Using this technique, headphone measurement data on commercially available headphones was

collected and compared to the current sonar headsets. The advantages and disadvantages of open and sealed

circumaural headsets and recent developments in noise canceling headsets are discussed, along with the

possibility ofreducing noise levels in sonar spaces to permit use of higher fidelity headphone designs.

20. DISTRIBUTION/AVAILABILITY OF ABSTRACT

UNCLASSIFIED/UNLIMITED [^SAME AS REPORT I IDTIC USERS

21. ABSTRACT SECURITY CLASSIFICATION

22a. NAME OF RESPONSIBLE INDIVIDUAL

Susan D. Monty

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(203) 449-3967

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