Personal Radio Headsets
`Hearing Loss Risk
`Audiometric Evaluations
`
`May1985
`
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`sound and vibration wOeyy
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`ISSN 0038-1610
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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
`Alternatives for
`Hearing Loss Risk Assessment
`John Erdreich
`Audiometric Evaluations for
`Industrial Hearing Conservation
`Julia Doswell Royster
`
`
`5
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`16
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`22
`
`24
`
`Clifford R. Bragdon
`
`Aram Glorig
`
`Gregg K. Hobbs
`Donald R. Houser
`
`Anthony J. Schneider
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`Alice H. Suter
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`Richard H. Tuft
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` EDITOR AND PUBLISHER
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`Departments
`Products and Literature — 30
`S)V News - 1
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`S)V Observer - 6
`Advertiser's Index - 34
`Our Authors -— 6
`aeae
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`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 coveredwith an experimentalartificial flesh, isshown here during
`the testing of the insertion lossofa setof lightweight plastic earmuffs. (Photo
`courtesy of E-A-R Division, Cabot Corporation, Indianapolis, IN.)
`
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`‘this material may be protected by Copyright law (Title 17 U.S. Code)
`Do Personal Radio Headsets
`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
`
`supra-aural, two semi-aural, and two circumaural headsets
`were included. Insertion loss was measured for grazing and
`perpendicular incidence using KEMAR.The data were corrob-
`orated by comparing the results to real-ear attenuation at
`threshold values derived via the methodology ofANSI S3.19-
`1974. The results demonstrated a range of NRR-like numbers
`from 0.3 to 2.6 dB. Across devices and angles ofincidence, the
`circumaural devices provided up to 7 dB amplification at 800
`Hz and all ofthe devices significantly affected the sound spec-
`trum at frequencies above 2 kHz. The results ofthis investiga-
`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 to 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 followingareas:1.they distract the user's atten-
`tion;2. they interfere with the perception ofincomingauditory
`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 the streets of
`their town. 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 United States 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 whenperforming 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
`concluded that, at least for the one industrial noise environ-
`mentinvestigated, the use of personal radiosby employees did
`not presenta 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 advocates that “noneofthe units on the
`market can reduce sound, nor could any ofthese headsets be
`rated able to attenuate sound as supplemental hearing protec-
`tion.”* Unfortunately, Huber did not supply objective data to
`substantiate his claim.
`
`o°
`
`aX
`
`90°
`
`Fi ure I. Orientation coordinates for sound sources relative to the
`
`AR manikin.
`
`Figure 2. Supra-aural, semi-aural, and circumaural headsets.
`
`The purpose ofthis study, therefore, was to provide objec-
`tive data concerningthe insertion loss characteristics of per-
`sonalradio headsetsto facilitate management decision-mak-
`ing policy regarding personalradio use in industrial settings.
`Methodology
`The insertion loss, defined as the difference between the
`eardrum soundpressure 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 dynamicproperties ofaural and cir-
`cumaural flesh, nor the bone conduction pathwaysto the inner
`ear. Therefore,it was deemed importanttojustify the insertion
`loss data obtained using KEMAR with theresults of real-ear
`attenuation at threshold values derived via the methodology of
`ANSI$3.19-1974,'4
`Measurements Using KEMAR. Measurementswere taken in
`a semi-free field. KEMAR was exposedto white noise generat-
`ed by a Calrad mini cube air-suspension speaker powered bya
`Realistic SA100B amplifier driven by a GenRad 1382 random
`noise generator. Measurementswere takenat 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
`
`

`

` ‘
`
`insertion Loss (dB)
`ANSI
`
`Table 3. A comparison of the insertion loss characteristics ofa Tandy 12-
`185 (circumaural)
`t measured in a diffuse sound
`field in accord-
`ance with ANSI $3.19 and in adirectionalsoundfield (0°
`)using
`KEMAR,
`
`rn
`radio units were evaluated to determine their insertion loss
`Table 1. A comparisonofthe insertion loss characteristics ofa Pickering
`characteristics. The labelling of headsetstyle generally fol-
`OA-101P (supra-aural)
`measured in a diffuse sound
`field in ac-
`cordance with ANSIS3.19 and in a directionalsoundfield(0°
`incidence)
`lows the definitions set forth in ANSI S3,19-1974."* In total,
`using KEMAR.
`iwenly test reco.
`were completed, sixteen using supra-
`aural headsets (having aheadbandand foam pads fitting light-
`One-Third Octave
`Band Center
`ly against the pinna),
`two using semi-aural headsets (ear-
`Frequency (Hz)
`phones supported in the conchaofthe ear canal), and twotests
`using circumaural headsets (the earphoneenclosesthe entire
`pinna) (referenceFigure 2). Two of the headset units had
`removableheadbands allowing the earphonestobe used in the
`concha (semi-aural), or as typical open air 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 band frequencies from125 Hz to 8 kHz were mea-
`sured with and without the headphones in 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 values for the two test conditions (“no
`headphones” and “headphones on”) at the two incidence
`pouiehbanvirreitescssSte00seaaieceenanneCet
`angles forall the one-third octave band SPL recordings were
`Table 2, A comparison ofthe insertion loss characteristicsofa peering
`- determined. The average value for the “headphones on” con-
`OA-88 (supra-aural) headset measured in adiffuse sound
`fieldin
`5
`dition was then subtracted from the average value for the “no
`headphones” condition at each test frequency. The resulting
`values established the insertion loss characteristics of the
`headphones(in dB) at one-third octave band center frequen-
`cies,
`:
`Comparison to Real-Ear Attenuation at Threshold Data.
`Although KEMAR has beenutilized to measure theinsertion
`loss ofhearing protection devices,it was not intendedfor that
`purpose andresults with certain types of devices have shown
`Significant disagreement with real-ear data.'? '* We did not
`expect such problems with devices of 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 S3.19 and
`comparing the data to KEMAR measuredinsertionloss values.
`The KEMAR datafor a 0°angle of incidence are compared to
`the ANSI S3.19 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 soundfield 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 conductedat the
`E-A-R Div., Cabot Corp. acoustical labs. and the KEMAR stu-
`dies were conducted at North Carolina State University.
`
`Mean Std.Dev, Mean
`ance_ ANSIS3.19andin adirectionalsoundfield(0°incidence) using
`-0.7
`
`One-Third Octave
`Band Center
`Frequency (Hz)
`MEG ess saws ca vee sed enw oe
`ROO ein isc os sa ieasa a
`a WA ei eiclcie d's
`SOO evs wont laes bene ene aes
`
`Insertion Loss (dB)
`ANSI
`Mean
`Std. Dev, Mean
`1.2
`2.5
`0.0
`=
`-
`0.0
`-
`=
`
`Findings of Study
`The predominantstyle of headphones accompanying per-
`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 alongwith the results from the two
`circumaural and two semi-aural headsets for comparison.
`From Figure 6 (the 0° incidence angle)it is apparentthat a
`small negative insertion loss (amplification effect) is evident
`in the 1 to 2 kHzregion for the supra-aural headsets. This
`trend peaks at -2,1 dB at 2kHzbefore beginningto drop offand
`showapositive insertion loss (attenuation effect) throughout
`the range from 4 to 6.3 kHz. At the 8kHzbandcenterfrequency,
`a shift from a maximumpositive insertion loss level of roughly
`8 dB to a negative insertion loss level ofapproximately -5 dBis
`observed. However, dueto the significantdifferences between
`the data obtained using KEMAR andthe ANSI $3.19 test fin-
`dings (displayed in Figures 3-5), the values at the 8 kHztest
`frequency should be questioned until further verification can
`
`be established.
`The insertion loss characteristics of the circumaural head-
`
`Sound and Vibration « May 1985
`
`
`
`
`17
`
`

`

`FREQUENCY IN HERTZ
`
`INSERTIONLos
`
`
`
`INSERTIONLOSS,dB
`
`——* KEMAR, 0° AZIMUTH
`——* re ANSI 83.19
`
`125 250 500
`
`1K 2K 4K 8k
`
`FREQUENCY IN HERTZ
`
`——s KEMAR.OAZIMUTH
`—s re ANSI $3.10
`
`125 250 500
`
`1K
`
`2K
`
`4K ax
`
`i4. Insertion loss characteristicsforaPickering OA-88supra-aural
`
`
`
`
`2K 4K 8K
`128 280 600 1K
`Frequency in Hertz
`
`Figure a Insertion loss characteristics ofpersonal radio headsets at 90°
`azimuth,
`
`Figure £ Insertion loss characteristics ofpersonal radio headsets at 0°
`azimuth,
`
`Sound andVibration * May 1985
`
`
`
`the supra-aural headsets (1.25 kHz) providinga greater mag-
`nitude ofattenuation through the frequency range of 1.25 to 5
`kHz than for the supra-aural headsets.
`Figure 6 also shows theinsertion loss characteristics of the
`two semi-aural headsetsat the 0° incidence angle. There is a
`very slight trend towards negative insertion loss beginningat
`approximately 500 Hz, reaching a maximum ofroughly -1.7 dB
`at 1.6 kHz. A crossoverto a positive insertion loss occurs at
`roughly 2 kHz, reaching a maximumpositive insertion loss of
`approximately 5 dB at 3.15 kHz.
`Figure 7 showsa graphicillustration 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 to the eardrum is observed overthe
`frequencies exhibiting amplification. This should be antici-
`pated since the sound wave can more effectively couple to the
`headsets at this angle.A similar increase in the eardrum to the
`free-field transformation ratio is observed.'!
`The average overall effect of the personal radio headsets on
`Figure 5. Insertion loss characteristicsfor a i 12-185 circumaural
`an individual's noise exposure was determined by assuming
`headset (Note: change in scale in comparison to Figures 3 and 4).
`an exposure foaflat (pink) noise spectrum. The reduction in
`this noise spectrum was calculated by subtracting the headset
`‘set variety at a 0° incidence angl.: are also presented for com-
`insertion loss values fromit to determine the interior (under-
`parison in Figure 6. Again,a negative insertion loss is observed
`the-headset) noise levels. The difference between the exterior
`through the frequency range of 500 Hz to 1 kHz. The magni-
`C-weighted andinterior A-weighted SPLs was then computed.
`tude of this amplification, reaching -6 dB at roughly 630 Hz, is
`These valuesare similar to Noise Reduction Ratings (NRR).'”
`greater than that of the supra-aural variety. A positive inser-
`They donotinclude a spectral uncertainty contribution and
`tion loss is evident begining at a lower frequency than that of
`are lacking a two standard deviation correction.
`
`128 260 600 1K 2K
`
`4K 6K
`
`FREQUENCY IN HERTZ
`
`

`

`
`
`6 7
`
`Conclusion
`The results of this research indicatethat the typical personal
`radio headsets studied (those which commonly accompany
`“Walkman” style radios) do notsignificantly alter the sound
`field reaching the eardrum,andthey do not provide anysignif-
`icant degree of hearing protection.
`
`Acknowledgements
`This research was supportedin part by a traineeship award
`in OccupationalSafety to the first author undertraining grant
`5-T-15-OH-07101from the NationalInstitute of Occupational
`Safety and Health, CDC, DHHS.
`
`Table 4. Modifed NRRs(see text), dB.
`Lights Flash for Earphone Users,” The
`2. Fantel, H. (1983), “Warning
`New York Times, July oa,hate. 19.
`f
`Numberof
`Modified NRR, dB
`ations, H. (1982), “Headphone Radios,” Professional Safety,
`Samples
`Headset Siyle
`0° Incidence 90° Incidence
`pril,
`12.
`4. Huber,L. J. (1984), “Headsets are Hi-Fi Hazards,” NationalSafety
`Supra-Aural yoo. ce ces cic 16
`0.3
`0.3
`News, Juz, 43-46.
`Semi-Aural vos. c cc scvccecces
`2
`0.6
`2.6
`an
`js oe=oc ——— H. L., SandersonBS: and Pucnanan, BR.
`Circumaural ..,... tela eelitens
`2
`1.9
`1.2
`1982),
`“Stereo
`ones and
`Hearing
`hig
`ew
`England
`Journal
`ine, Vol. 307, 1460-1461.
`Sd
`The predicted effect on an individual's noise exposure level
`. Kidder,
`M. (1982), “Banning
`the Walkman: What 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 the 0° and90° incidence
`. Lohr, S. (1982), “Headsets and Ear Damage," The New York Times,
`~~July 17, a a ;
`angles is presented in Table 4. The results of this analysis
`8. Anonymous (1984),
`“Warning
`of Irreparable oo toHearing,”
`Journal
`the Commonsseulit
`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-
`reviewing the data presented for the semi-aural and circumau-
`une, Aug, 8, Sec. 12, 3.
`ral headsets it must be rememberedthat these 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, Washington, D.C., Nov. 25, 1-2.
`change in magnitude would be expectedifadditional units had
`11, Skrainar,S. F. (1985),
`“The Effects on Hearing of Using a Personal
`beeninvestigated.
`Radio in an Environmentwhere the Daily Time-Weighted Average
`is 87 dB," Masters Thesis, Departmentof Industrial Engi
`North Carolina State University, Raleigh, North Carolina.
`12. Burkhard, M. D. (1978), “Non-hearing Aid Uses of the KEMAR
`Manikin,” in Manikin Measurements, edited
`Burkhard, M. D.,
`Knowles Electronics Inc., Elk Grove Village,
`Illinois.
`13. Burkhard, M. D. and Sachs, R. M. (1978), “Anthropometric Mani-
`kin for Acoustic Research,” in Manikin Measurements, edited by
`Burkhard, M. D., Knowles Electronics Inc., Elk Grove Village, Illi-
`nois.
`14. American National Standards Institute (1974), “Measurements of
`Real-earProtection ofHearingProtectors and PhysicalAttenuation
`Earmuffs,” Standard $3.19-1974, ANSI, New York, New York.
`15. Burkhard, M. D. (1978), “Anthropometric Manikin for Acoustical
`Research. Supplementary
`Design Information,” in Manikin Meas-
`urements, edited by Burkhard, M. D., Knowles Electronics Inc., Elk
`Grove V.
`, Illinois.
`16. Berger, E.
`H. (1985) “Methods of oe Alienuation of
`Hearing Protection Devices,” submitted for publication toj. Acous.
`Soc. Am.
`17, Berger, E. H. (1979), “E-A-R Log 2: Single Number Measures of
`HearingProtectorNoise Reduction,”SoundandVibration, 13:8,BE
`12-13.
`
`1. Bishop,J. E. (1982), “Researchers Say Portable Tape Players with
`Earphones can Cause Hearing Loss,” The Wall Street Journal,
`December2, 14.
`
`SESESSTgIeacre
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