1lacllo Headsets
`Penonal
`Beuing Loss Ruic
`A1ldlometrlc EvaluatlOll
`
`s
`
`ISSN 0038- 1810
`
`May1985
`
`sound and vibration
`
`1
`
`APPLE 1076
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`

`

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` EDITOR AND PUBLISHER
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`dack K, Mowry
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`Donald R. Houser
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`THE NOISE AND VIBRATION CONTROL MAGAZINE
`Noise and Vibration Control ¢ Structural Analysis
`Dynamic Measurements © Dynamic Testing
`Hearing Conservation ¢ Architectural Acoustics
`
`MAY 1985
`
`VOLUME 19/NUMBER 5
`
`Editorial
`Should the Walkman Take a Walk?
`Larry H. Royster
`
`_ Features
`Do Personal Radio Headsets
`Provide Hearing Protection?
`S. F. Skrainar, L. H. Royster, E. H. Berger and R. G. Pearson
`Altematives for
`Hearing Loss Risk Assessment
`John Erdreich
`Audiometric Evaluations for
`Industrial Hearing Conservation
`Julia Doswell Royster
`
`
`Departments
`S)V News ~ 1
`S)V Observer - 6
`Our Authors - 6
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`Products and Literature — 30
`Professional Services - 32
`Advertiser's Index - 34
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`5
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`16
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`22
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`24
`
`Cover
`One method of assessing the attenuation of circumaural hearing protection
`devices is the dummy head specified in the supplemental physical method of
`ANSI S3,.19-1974. An 8-kg version of that head, machined from cast alu-
`minum and covered with an experimentalartificial flesh, is shown here during
`the testing of the insertion loss of a setoflightweight plastic earmuffs. (Photo
`courtesy of E-A-R Division, Cabot Corporation, Indianapolis, IN.)
`
`
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`Sound and Vibration « May 1085
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` ‘| This material may be protected by Copyright law (Title 17 U.S. Code)
`
`Provide Hearing Protection?
`
`Stephen F. Skrainar, North Carolina State University, Raleigh, North Carolina
`Larry H. Royster,North Carolina State University, Raleigh, North Carolina
`E. H. Berger, E-A-R Division, Cabot Corporation, Indianapolis, Indiana
`Richard G. Pearson, North Carolina State University, Raleigh, North Carolina
`A laboratory investigation was conducted to determine the
`acoustic attenuation of 18 personal radio headsets. Sixteen
`supre-aural, two semi-aural, and two circumaural headsets
`
` Do Personal Radio Headsets
`
`
`rgure 1. Orientation coordinates for sound sources relative to the
`manikin.
`AR
`ik
`
`
`
`
`
`
`tion indicate that, in general, personal radio headsets do not
`significantly modify external soundfields as perceived at the
`eardrum.
`
`Today it is almost impossible to miss seeing someone walk-
`ing, running, cycling, driving, and in some instances, working
`while listening to a personal radio. Since their introduction to
`the commercial marketin 1979 by the Sony Corporation,these
`devices, commonly referred to as “Walkmans,” have become
`exceedingly popular.
`In the past two fo three years several articles have been writ-
`ten on personal radios andtheir potential dangers.'* The gen-
`eral tone of these articles is that these units may present
`hazards in the following areas:1. they distract the user's atten-
`tion; 2.they interfere with the perceptionofincoming auditory
`information such as communication and warning signals; and
`3. they may cause noise-induced hearing loss.
`:
`In 1982 the town ofWoodbridge, New Jersey passedlegisla-
`tion prohibiting the use of personal radios on thestreets of
`theirtown. The township council President was quoted as say-
`ing “I think it's a distraction.”* The danger,they feel, is that
`users of personal radios will be oblivious to traffic hazards.’
`The UnitedStates Postal Service, in a similar action, banned
`the use of personal radios, with few exceptions, by postal
`employees while on the job.’® They contended that an
`individual's “concentration to traffic conditions can be com-
`promised by headphones,” andthat “they (headsets) can also
`be a hazard when performing jobs where an auditory alarm or
`feedback is essential...”
`Werecently investigated" the potential for personal radios
`to contribute to noise-induced hearing damage. The study
`concludedthat, at least for the one industrial noise environ-
`mentinvestigated,the use of personal radiosby employees did
`not present a significant additional health hazard and that
`their use should be allowed. However, the study did recom-
`mendcertain criteria be followed to educate the employee
`population to the potential dangers of extended use of per-
`sonal radios played at high volume levels, and to insure that
`potentially noise-sensitive employees are identified and
`refused permission to continue the use of personal radios
`while on the job.
`Whendiscussing the potential danger of personal radios
`interfering with incoming auditory information, one consider-
`ation is the attenuation characteristics of personal radio head-
`sets. Huber strongly advocatesthat “noneofthe units on the
`market can reduce sound, nor could any of these headsets be
`rated able to attenuate sond as supplemental hearing protec-
`tion.”* Unfortunately, Huber did not supply objective data to
`substantiate his claim.
`
`_
`
`Figure 2. Supra-aural, semi-aural, and circumaural headsets.
`
`The purpose ofthis study, therefore, was to provide objec-
`tive data concerning the insertion loss characteristics of per-
`sonal radio headsetsto facilitate management decision-mak-
`ing policy regarding personalradio use in industrial settings.
`Meth
`Theinsertion loss, defined as the difference between the
`eardrum sound pressure levels (SPLs) with and without the
`headphones in place, was measured using KEMAR.'? '
`KEMAR was specifically designed to simulate the acoustic
`characteristics of the human ear, head, and uppertorso, in-
`cluding a Zwislocki coupler to model eardrum impedance,
`KEMAR includes geometrically accurate pinnas but was not
`designed to reproduce the dynamic properties ofaural and cir-
`cumaural flesh, nor the bone conduction pathwaysto the inner
`ear. Therefore,it was deemed important tojustify the insertion —
`loss data obtained using KEMAR with the results of real-ear
`attenuation at threshold valuesderived via the methodology of
`ANSI $3.19-1974.'4
`Measurements Using KEMAR. Measurements were taken in
`a semi-free field. KEMAR was exposedto white noise generat-
`ed by a Calrad miniculve air-suspension speaker powered bya
`Realistic SA100B amplifier driven by a GenRad 1382 random
`noise generator. Measurements were taken at 0° and 90° inci-
`dence angles. These incidence angles follow Burkhard’s con-
`vention'® (reference Figure 1).
`Eighteen headsets which commonly accompany personal
`
`16
`Sound and Vibration « May 1985
`
`3
`
`

`

`
`
`%
`Table 1..A comparisonofthe insertion loss characteristics aPickering
`
`radio units were evaluated to determine their insertion loss
`OA-101P(annenbLethemeasured in a diffusecae ld in ac-
`characteristics. The labelling of headset style generally fol-
`cordance with ANSI$3.19 and in a directionalsoundfield(0°
`incidence)
`lows thedefinitions set forth in ANSI S3.19-1974."* In total,
`usingKEMAR.
`twenty
`test reco.
`| were completed, sixteen using supra-
`One-Third Octave
`aural headsets(having aheadband andfoam pads fitting light-
`Band Center
`ly against the pinna), two using semi-aural headsets (ear-
`Frequency (Hz)
`phones supported inthe conchaofthe ear canal), and twotests
`using circumaural headsets (the earphone enclosesthe entire
`pinna) (referenceFigure 2). Two of the headset units had
`removableheadbands allowingthe earphonesto be used in the
`concha (semi-aural), oras typical openair headsets (supra-
`aural). For the purpose ofthis research the two dual-use head-
`sets were tested as both supra-aural and semi-aural devices.
`A-weighted, C-weighted,and one-third octave band SPLs at
`the center bandfrequencies from125 Hz to 8 kHz were mea-
`sured with and without the headphonesin place. An initial
`recording of the “no headphones” condition was conducted,
`followed by three repetitions of the “headphones on” proce-
`dure. A final recording of the “no headphones” condition
`concluded the measurements. All headsets were evaluatedat
`each of the two incidence angles previously mentioned.
`The average SPL valuesfor the two test conditions (“no
`ue tn
`headphones” and “headphones on”) at the two incidence
`
`
`RaSenEaneeshtiestealWgeeeCoteeseguesetCR
`angles forall the one-third octave band SPL recordings were
`Table 2. A comparison ofthe insertion loss characteristics eg
`_ determined. The average value for the “headphones on” con-
`OA-88 (supra-aural) headset measured in a diffuse sound
`field in
`|
`dition was then subtracted from the average valuefor the “no
`ancenakANSIS3.19andin adirectionalsoundfield(0°incidence) using
`headphones” condition at each test frequency. The resulting
`values established the insertion loss characteristics of the
`One-Third Octave
`Insertion Loss (dB)
`headphones(in dB) at one-third octave band center frequen-
`Center
`ANSI
`cies.
`Frequency (Hz)
`Mean Std.
`Comparison to Real-Ear Attenuation at Threshold Data.
`|b 2B year ep ee ea Pp 1.0
`3.1
`Although KEMAR has been utilized to measure the insertion
`loss ofhearing protection devices,it was not intendedforthat
`purpose andresults with certain types of devices have shown
`significant disagreement with real-ear data.'* '* We did not
`expect such problems with devicesof the type includedin this
`study due to their presumed low inherent attenuation and
`their method of interface to the ear. However, we decided to
`confirm the acceptability of using KEMAR for our purpose by
`measuring a circumaural and two supra-aural devices by the
`standardized real-ear threshold method of ANSI $3.19 and
`comparing the data to KEMAR measuredinsertionloss values.
`The KEMAR datafora 0° angle of incidence are compared to
`the ANSI $3.19 values in Tables 1-3 and Figures 3-5. Theslight
`differences observed in the measuredinsertion loss values by
`the two methods are probably primarily attributable to the
`directional sound field used for the KEMAR measurements
`versus the diffuse sound field required by the ANSI $3.19
`"methodology. These data confirm the suitability ofKEMAR for
`measuring the insertion loss for the style of personal radio
`headsets investigated. The S3.19 testing was conductedatthe
`E-A-R Div., Cabot ‘Corp. acoustical labs, and the KEMAR stu-
`dies were conducted at North Carolina State University.
`Findings of Study
`The predominant style of headphones accompanyingper-
`sonal radios are the supra-aural variety. The insertion loss
`characteristics of the sixteen supra-aural headsets are pre-
`sented in Figures 6 and 7 along with the results from the two
`circumaural and two semi-aural headsets for comparison.
`From Figure 6 (the 0° incidence angle)it is apparent that a
`small negative insertion loss (amplification effect) is evident
`in the 1 to 2 kHz region for the supra-aural headsets. This
`trend peaks at -2.1 dB at 2 kHz before beginningto dropoffand
`show a positive insertion loss (attenuationeffect) throughout
`the rangefrom 4 to 6.3 kHz. At the 8 kHzbandcenterfrequency,
`a shift from a maximum positive insertion loss level ofroughly
`8 dB to a negative insertion loss level ofapproximately -5 dBis
`observed. However,dueto the significant differences between
`the data obtained using KEMAR andthe ANSI S3.19test fin-
`dings (displayed in Figures 3-5), the values at the 8 kHztest
`frequency should be questioned until further verification can
`
`Mean
`
`Table 3. A comparison of the insertion loss characteristics ofa Tandy 12-
`185 (circumaural)
`measured in a diffuse sound eid in accord-
`ance_ ANSIS3.19andinadirectionalsoundfield(0°
`using
`One-Third Octave
`
`Band Center
`
`Frequency (Hz)
`
`Sound and Vibration * May 1985
`
`
`7
`
`be established.
`Theinsertion loss characteristics of the circumaural head-
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`INSERTIONLO
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`125 260 500
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`FREQUENCYIN HERTZ
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`Figure 3. Insertion loss characteristicsfora Pickering OA-101P supra-
`aural headset.
`oa
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`-_—- KEMAR.O*AZMUTH
`——s re ANSI S310
`
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`i 4. Insertion loss characteristicsforaPickering OA-88 supra-aural
`
`Figure Zn Insertion loss characteristics ofpersonal radio headsets at 90°
`azimuth,
`
`
`Frequency in Hertz
`
`
`
`the supra-aural headsets (1.25 kHz) providing a greater mag-
`nitude ofattenuation through the frequency rangeof1.25 to 5
`kHz than for the supra-aural headsets,
`Figure 6 also shows theinsertion loss characteristics of the
`two semi-aural headsets at the 0° incidence angle. There is a
`very slight trend towards negative insertion loss beginning at
`approximately 500 Hz, reaching a maximumofroughly -1.7 dB
`at 1.6 kHz. A crossover to a positive insertion loss occurs at
`roughly 2 kHz, reaching a maximumpositive insertion loss of
`approximately 5 dB at 3.15 kHz.
`Figure 7 showsagraphicillustration of the insertion loss
`characteristics for the supra-aural, circumaural, and semi-
`aural headsets at a 90° angle of incidence from the noise
`source. At the 90° orientation a slight increase in the magni-
`tude in soundtransmitted fo the eardrum is observedoverthe
`frequencies exhibiting amplification. This should be antici-
`pated since the sound wave can more effectively couple to the
`headsets atthis angle.A similar increase in the eardrum to the
`free-field transformation ratio is observed."
`The average overalleffect of the personal radio headsets on
`an individual's noise exposure was determined by assuming
`an exposure fo a flat (pink) noise spectrum. The reduction in
`this noise spectrum was calculated by subtracting the headset
`insertion loss values from it to determine the interior (under-
`the-headset) noise levels. The difference betweenthe exterior
`C-weighted andinterior A-weighted SPLs was then computed.
`These values are similar to Noise Reduction Ratings (NRR)."
`They do not include a spectral uncertainty contribution and
`are lacking a two standard deviation correction.
`
`Figure 5. Insertion loss characteristicsfor a Ley 12-185 circumaural
`headset (Note: change in seale in comparison to Figures 3 and 4),
`‘set variety at a 0° incidence angl are also presented for com-
`parison in Figure 6. Again, anegative insertion loss is observed
`through the frequency range of 500 Hz to 1 kHz. The magni-
`tude ofthis amplification, reaching -6 dB at roughly 630 Hz, is
`greater than that of the supra-auralvariety. A positive inser-
`tion loss is evident begining at a lower frequency than thal of
`
`1K 2K 4K BK
`128 260 600
`FREQUENCY IN HERTZ
`
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`
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`Sound andVibration * May 1985
`
`5
`
`5
`
`

`

`
`
`7.
`
`Conclusion
`Theresultsof this research indicate thatthe typical personal
`radio headsets studied (those which commonly accompany
`“Walkman” style radios) do notsignificantly alter the sound
`field reaching the eardrum,and they do notprovide anysignif-
`icant degree of hearing protection.
`
`Table 4. Modifed NRRs (see text), dB.
`New York vom July oneases, 19,
`its Flash forEarphone Users,” The
`2. Fantel, H. (1983), “Warn
`Modified NRR, dB
`Number of
`aHons, H. (1982), “Headphone Radios,” Professional Safety,
`0° Incidence 90° Incidence
`Samples
`Headset Style
`4. Huber,L. J. (1984), “Headsets are Hi-Fi Hazards,” NationalSafety
`0.3
`0.3
`Supra-Aural ..... 0.00.0 0e 00: 16
`News, June, 43-46.
`0.6
`2.6
`Seml-Auralics 3300695 vs oy eos
`2
`5. Katz, A. E., Gvrstman, H. L., Sanderson, R. G., and Buchanan, R.
`1.9
`1.2
`Circumaural ................
`2
`(1982), “Stereo Earphones and H
`Loss,” The New England
`JournalofMedicine, Vol. 307, 1460-1461.
`The predicted effect on an individual's noise exposure level
`6.
`. Kidder,
`M. (1982), ces the Walkman: Whal Does It
`as a result of the insertion loss characteristics for the three
`Mean?,” The Christian Science Monitor, Sept. 8, 22.
`_ headsetstyles investigated at both the0° and90° incidence
`. Lohr, S, (1982), “Headsets and Ear Damage,” TheNew York Times,
`~Suiy17, aE
`;
`ane
`es is presented in Table 4, The results of this analysis
`8. Anonymous (1984), “Warning
`of Irrepar
`to Hearing,”
`Journal he Commonneantl
`mentofHealth, Vol. 1,No.2, 1.
`indicate that the protection provided by the personal radio
`headsets from the external soundfield is insignificant. In
`9. Winter,C.(1982), “The Ear-to-Hear Controversy,” Chicago Trib-
`reviewingthe data presentedfor the semi-aural and circumau-
`une,
`8, Sec. 12, 3,
`ral headsets it must be remembered thatthese results were
`10. United States Postal Service (1982), “Personal Portable Radio or
`based on a small sample size. Nevertheless, no significant
`Tape Cassette Headphones,” Postal Bulletin 21379, United States
`Postal Service, Was’
`on, D.C., Nov. 25, 1-2.
`changein magnitude would be expectedifadditional units had
`- Skrainar, S, F. (1985),
`“The Effects on Hearing ofUsing a Personal
`beeninvestigated.
`RadioinanEnvironment where theDailyimevieigned Average
`is 87 dB,” Masters Thesis, De
`nt of Industrial Engineering,
`North Carolina State University, Raleigh, North Carolina.
`12. Burkhard, M. D. (1978), “Non-hearing Aid Uses of the KEMAR
`Manikin,” in Manikin Measurements, edited by Burkhard, M. D.,
`Knowles Electronics Inc., Elk Grove Village,I linois.
`13. Burkhard, M.D, and Sachs, R. M, (1978), ‘Anthropometric Mani-
`kin for Acoustic Research,” in Manikin Measurements, edieby
`Burkhard, M. D., Knowles Electronics Inc., Elk Grove Village,Illi-
`nois.
`14. American National Standards Institule (1974), “Measurements of
`Acknowledgements
`Real-earProtection ofHearingProtectors and PhysicalAttenuation
`This research was supportedin part by a traineeship award
`Earmuffs,” Standard $3.19-1974, ANSI, New York, New York.
`15. Burkhard, M. D. (1978), “Anthropometric Manikin for Acoustical
`in OccupationalSafety to the first author under training grant
`Research. Sarremeatey Design Information,” in Manikin Meas-
`5-I-15-OH-07101 from the NationalInstitute of Occupational
`urements, edited by Burkhard, M. D., Knowles Electronics Inc., Elk
`Safety and Health, CDC, DHHS.
`Grove V
`» Illinois.
`16. Berger, E.
`H. (1985) “Methods of Measu
`‘the Attenuation of
`References
`a Protection Devices,”submitted forpublication toJ, Acous.
`‘oc, Am.
`1. Bishop,J. E. (1982), “Researchers Say Portable Tape Players with
`17. Berger, E. H. (1979), “E-A-R Log 2: Single Number Measuresof
`Earphones can Cause Hearing Loss,” The Wall Street Journal,
`HearingProtectorNoise Reduction,”SoundandVibration, 13:8,BB
`December 2,14.
`12-13.
`:
`ee
`
`Sound and Vibration e May 1985
`
`18
`
`Hampton, VA Circle 112 on Reader-Service Card
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