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`THE Norse AND VIBRATION CONTROL MAGAZINE
`Noise and Vibration Control 0 Structural Analysis
`Dynamic Measurements I Dynamic Testing
`Hearing Conservation 0 Architectural Acoustics
`
`
`MAY 1985
`
`Editorial
`
`VOLUME taillUllBEl-i 5
`
`Should the Walkman Talia a Walk?
`Larry H. Royster
`
`Features.
`Do Personal Radio Headsets
`Provide Hearing Protection?
`8. F. Sluainar. L. H. Floyster. E. H. Berger and Ft. G. Pearson
`Alternatives for
`Hearing Loss Risk Assessment
`John Erdreich
`
`Audiometrlc Evaluations for
`Industrial Hearing Conservation
`Julia Boswell Floyster
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`5
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`24
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`Products and Literature - 30
`SJV News —- 1
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`Advertiser's index — 34
`Our Authors - 6
`-—~—————-—.-—..________.._.,__
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`Cover
`
`One method of assessing the attenuation of circumsurai hearing protection
`devices is the dummy head specified in the supplemental physical method of
`ANSI 83.194974. An B-kg version of that head. machined from cast alu‘
`mlnum and covered with an experimental artificial flesh, is shown here during
`the testing of the Insertion loss ofeset of lightweight plastic earmutfs. {Photo
`courtesy of E-A-R Division. Cabot Corporation, lndlanapolis, iN.)
`
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`Sound and Vibration I May 1985
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`

`

`
`I This material may be protected by Copyright law (Title 17 us. Code)
`'
`
`
`Do Personal Radio Headsets
`Provide Hearing Protection?
`
`Stem-n F. Strainer. North Carolina State University. Raleigh. North Carolina
`Larry it. Router. North Carolina State University. Raleigh. North Carolina
`E. H. Berger, E-A-R Division. Cabot Corporation. lndtanapolis.-lndiana
`Richard G. hereon. North Carolina State University. Raleigh. North Carolina
`Ahhorataryhvedigflimwueondadedtodeflmhethe
`acouflcmmofmperaonalradiaheadeetsmeen
`aaMtwoseni-mlandhvodrenmnnlhedaete
`wemmdadeiheerflonlouwaameumedforgnfingand
`
`00
`
` l
`
`outed by comparing the Malta to real-ear mounted at
`Mold values derivedvia theatethodology ofANSi 53.19-
`lWQI‘hereeulademustrahedarangeofNRR—lihuumhers
`mammammmm
`circumnaldeviceeproridedupto7d3aalplifleetlouatm
`Hzndaflofthedeflmdgnilicentblflededthesotmdlpec-
`hon-thequeaduahovezhflal'hensultsofthisiuwsfiga-
`finindiuUMingeneraLpersonalradloheadeetsdonot
`significantlymdifyextemal sound fieldsasperceivedatthe
`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 conuuercial market in 1979 by the Sony Corporation. these
`devices. commonly referred to as 'Wallrmans.“ have become
`exceedingly‘ popular.
`In the past two to three years several articles have been writ-
`ten on personal radios and their 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 perception ofincoming auditory
`information such as commtuticat ion and warningsignals; and
`3. they may cause noise-induced hearing loss.
`-
`In 1982 the town ofWoodbridge. New Jersey passed legisla-
`tion prohibiting the use of personal radios on the streets of
`their town. The township council President was quoted as say-
`ing ‘1 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
`individuan “contentration to traffic conditions can be com—
`promised by headphones.” and that “they {headsets} can also
`be a hazard when performing jobs where an auditory alarm or
`feedback is essential . . . "
`We. recently investigated“ the potential for personal radios
`to contribute to noise-induced hearing damage. The study
`concluded that. at lent for the one industrial noise environ-
`ment investigated. 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-
`mend certain 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 fab.
`When discussing the potential danger of personal radios
`interfering with incoming auditory informal ion. one consider-
`' alien is the attenuation characteristics of personal radio head-
`sets. iluber strongly advocates that “none of the units on the
`market can reduce sound. nor could any of these headsets be
`rated able to attenuate sound as supplemental hearing protec-
`tion." Unfortunately. Huber did not supply objective data to
`substantiate his claim.
`
`15
`
`in.
`
`
`
`figure 2. Supra-aural. semi-aural. and dreamers! headsets.
`
`The purpose of this study. therefore. was to provide objec—
`tive data concerning the insertion loss characteristics of per-
`sonal radio headsets to facilitate management decision-mak-
`ing policy regarding personal radio use in industrial settings.
`
`Methodology
`The insertion loss. defined as the difference between the
`eardrum sound pressure levels {SPLs} with and without the
`headphones in place. was measured using REM.“ ‘3
`KEMAR was specifically designed to simulate the acoustic
`characteristic: of the human ear. head. and upper torso. in-
`cluding a Zwistocki coupler to model eardrum impedance.
`KEMAR includes geometrically accurate pinnas but was not
`designed to reproduce the dynamic properties of aural and cir—
`cumaurai flesh. nor the bone conduction pathways to the inner
`ear. Therefore. it was deemed important to justify the insertion
`loss data obtained using KEMAB with the results of real-ear
`attenuation at threshold values derived via the methodology of
`ANSI 53.194974.”
`
`Measurements Using KEMAR. Measurements were taken in
`a semi-free field. KEMAR was exposed to white noise gene rat-
`ed by a Celt-ad mini cube air-suspension speaker powered by a
`Realistic SAIOOB amplifier driven by a Genftad 1382 random
`noise generator. Measurements were taken at 0° and 90° inci-
`dence angles. These incidence angles follow Burkhard's con-
`vention" {reference Figure l).
`Eighteen headsets which commonly accompany personal
`
`“—__H_ -
`
`Sound and Vibration I May 1985
`
`

`

` e
`
`
`stleiJoomparirm-fitlwnmrmn lossclsamcterirticsgt'o
`in! in ne-
`OA'IOIP {supra-ante!)
`resumed in a mess sound
`oordsnu MANSISSJOMMadMWWfiHf m;
`using REM.
`
`
`.
`
`_
`
`insertion Loss [d3]
`One-Third Octave
`ANSI m
`Band Centr-
`. Mesa Std. Dev. Mean
`Frequency {11:}
`125 ........................ 1.3
`2.4
`-0.2
`100 ........................
`-—
`-
`-0.4
`can ........................
`-
`. - ,
`.—o.s
`250 ........................ 0.?
`2.1
`-0.3
`-
`-0.3
`-
`-0.3
`2 7
`-0.4
`-
`-0.7
`-
`-l.0
`2 0
`-i.5
`-
`—2.4
`2.9
`-3.|1
`3.0
`-3.5
`2.7
`0.8
`3.0
`1.2
`3.!
`6.2
`3.4
`13 6
`3.4
`11 0
`3.8
`
`
`
`-l 5
`
`‘
`Table 2. A rumpus-tron qfthe insertion losseirmrerirtrics‘go
`-
`041-88 (supra-turret) headset treasured its edges: sound
`id in
`ones with ANSI83.19 and in o directionnl'sonndfiehi [0' incidence) using
`'KEMAB.
`
`
`One-Third Octevc
`Band Center
`Frequency (its)
`
`Insertion Lass [dB]
`ANSI
`man
`Hun Std. Ber. Mean
`
`125 ........................
`100 . .
`
`1.0
`-
`
`' -0.8
`3.1
`-0.6
`-
`0.0
`-
`—0.2
`2.4
`-0.5
`-
`~03
`-
`-0.8
`2.?
`-0.8
`..
`41.5
`—
`-1.0
`2.4
`-i.3
`-
`-l.ti
`2.2
`~2.0
`2.?
`0.2
`2k ........................
`1.2
`3.3
`2.51: ........................ 2.5
`15
`4.3
`3.151: ........................ 1.1
`0.5
`3.2
`4k ........................ 2.6
`3.5
`3.i
`5k ........................ 2.5
`?.0
`4.0
`6.311 ........................ 6.3
`7.5at: ........................ -a.o 3.4
`
`
`
`
`
`
`
`.
`
`Table 3. A comparison 0 the insertion tors characteristics qt’c Tandy 12
`185 frtrcnmouraij
`t unsound in o diflirsr sound g“ in accord
`mind}: M81333 nndr'nadirectr'onoisoundfltdffl'
`luring
`KEM .
`One-Third Octave
`Insertion Ines td'B}
`Band Center
`ANSI
`arms
`Frequency {Hz}
`Mean
`Std. Dev. Heart
`125 ........................
`1.2
`2.5
`0.0
`100 ........................
`-
`-
`0.0
`200 ........................
`-
`-
`~03!
`250 ........................
`1.1
`2.1
`0.0
`315 ........................
`-
`-
`- 1.0
`100 .........
`-
`-1.1
`
`500 ..........
`.
`l 8
`-3.3
`630 ........................
`—
`-
`-10.5
`800 ........................
`-
`-
`-0.2
`[it ........................ -0 l
`2.6
`-3 0
`1 25k ........................
`-
`—
`ti 2
`1.8k ........................
`-
`—
`22 0
`2i: ........................ 17.3
`3.6
`27.3
`2.511: ........................
`-
`-
`24.0
`3.1511 ........................ 17.5
`2.2
`15.0
`Ilit ........................ 11.7
`2.5
`18.0
`Slt ........................
`-
`-
`19.5
`6.31: ........................ 22.1
`2.8
`10.5
`Bk ........................ 19.0
`2.7
`-I.0
`—...._—......_—._____—_
`
`r
`
`I
`
`be established.
`The insertion loss characteristics of the circumaurel head-
`
`radio units were evaluated to determine their insertion loss
`characteristics. The labelling oi headset style generally l'ol—
`iows the'deiinitions set forth in ANSI 53.194974.“ In total.
`twentg| test recordings_ were completed. sixteen using supra-
`aural eadsets {having aheadband and foam pads fitting light-
`ly against the pineal. two using semi-aural headsets (earw
`phones supported in the certain: ofthe ear canal}. and two tests
`using circumaural headsets (the earphone encloses the entire
`pineal (reference Figure 2). Two of the headset units had
`removableheadbands allowingthe esrphonestoheusedinthe'
`concha (semi-aural). .0! as typical open air headsets (supra-
`aurai). For the purpose of this research the two dual~use heed-
`sets were tested as both supra-aural and semi-aural devices.
`A—weighted, C-wcighted. and one-third octave band SPLs at
`the center band frequencies front125 Hz to 8 kHz were mea-
`sured with and without the headphones in place. An initial
`recording of the “no headphones" condition was conducted.
`[ollowed by three repetitions of the “headphones on” proce'
`dure. A line] recording 01' the “no headphones” condition
`concluded the measurements. All headsets were evaluated at
`each of the turn incidence angles previously mentioned.
`The average SPL values for the two test conditions (“no
`headphones" and “headphones on”) at the two incidence
`angles for all the one-third octave band SP1. recordings were
`. determined. The
`value for the “headphones un'I con-
`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 tin dB) at one-third octave band center frequen-
`L'IBS.
`.
`
`comparison to Real-Ear Attenuation at Threshold Data.
`Although KEMAR has been utilized to measure the insertion
`loss of hearing protection devices. it was not intended for that
`purpose and results with certain types of devices have shown
`significant disagreement with real-ear data.”'.“ We did not
`expect such problems with devices of the type included in this
`study due to their presumed tow inherent attenuation and
`their method of interface to the ear. However. we decided to
`confirm the acceptability of using KEMAR {or our purpose by
`measuring a circumaural and two supra—aural devices by the
`standardized real-ear threshold method of 5N5! 53.19 and
`comparing the data to KEMiili measured insertion loss values.
`The KEMAR data for a 0° angle of incidence are compared to
`the ANSI 53.19 values in Tables 1-3 and Figures 3-5. The slight
`differences observed in the measured insertion 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 otKEMAIt for
`measuring the insertion loss for the style of personal radio
`headsets investigated. The $3.19 testing was conducted at the
`E-A-it Div.. Cabot 'Corp. acoustical labs. and the KEMAR stu»
`dies were conducted at North Carolina State University.
`
`Finding. of Study
`The predominant style of headphones accompanying per-
`sonal radios are the supra-aural variety. The insertion loss
`characteristics of the sixteen suprewaural 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 ii {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 beginning to drop offand
`show a poaitlve insertion loss iattenuation effect] throughout
`the range iromltto 6.3 kHz. At thetilriishand center lrequency,
`a shift from a maximum positive insertion loss level of roughly
`8 dB to a negative insertion loss level ofapproximately —5 dB' is
`observed. However. due to the significant differencea between
`the data obtained using KEMAB and the ANSI $3.19 test fin-
`dings tdispleyed in Figures 3-5}. the values at the 8 kHz test
`frequency should be questioned until further verification can
`
`Sound and Vleiattcc o my toes
`
`
`
`
`I?
`
`

`

`— emu. I'flml
`H II MI “I.
`
`3.43 0eh
`
`is
`ee-9
`
`Ea
`
`iflmmtkfldfifl
`
`WYflm
`
`Figure 3. insertion loss characteristics
`aurai headset.
`
`fin
`
`a Pickemg' Oat-1MP supra-
`
`-——n IEMQJ'AIHJTII
`o———. u Milt la.“
`
`0
`
`
`“Wilt-El"!
`
`INBEHTIONL085.dB 3t.
`
`o au
`
`«I II
`as
`rasasosoo Is
`FREQUENCYmtEfiTZ
`
`recession in it
`
`as It
`
`Figure 5. insertion toss musics a Tom? tit-185 cirrumaurai
`headset (Note: change in scale in comparison to igures 3 and 4).
`
`set variety at a 0" incidence angle are also presented for com-
`parison in Figure 6. Again. a negative insertion loss is observed
`through the frequency range oi 500 Hz to 1 kHz. The magni-
`tude of this amplification. reaching —6 dB at roughly 630 Hz. is
`greater than that of the supra-aural variety. A positive inser~
`tion loss is evident beginiug at a lower frequency than that of
`
`
`
`
`as
`rss season In
`time-rm
`
`as at
`
`Figure 3. insertion toss chmarterirticr ofpersonai radio headsets at 0°
`azimat .
`
`Figure 3'. insertion loss characteristics quersm'tat' md'l'o headsets at 90"
`azirnut .
`
`the supra-aural headsets (1.25 trite} providing a greater mag-
`nitude ot' attenuation through the frequency range of 1.25 to 5
`kHz than for the supra-aural headsets.
`Figure 6 also shows the insertion loss characteristics of the
`two send-aural headsets at the it“ incidence angle. There is a
`very slight trend towards negative insertion loss beginning at
`approximateiy 500 Hz. reaching a maximum ofroughly -1.7 dB
`at 1.8 kHz. A crossover to a positive insertion loss occurs at
`roughly 2 kHz. reaching a maximum positive insertion loss of
`approximately 5 dB at 3.15 kHz.
`Figure 7 shows a graphic illustration of the insertion loss
`characteristics for the supra-aural. circumaural. and semi-
`aursl headsets at a 90° angle of incidence from the noise
`source. At the 90“ orientation a slight increase in the magni-
`tude in sound transmitted to the eardrum is observed over the
`frequencies exhibiting amplification. This should be antici-
`pated since the sound wave can more effectively couple to the
`headsets at this angie. A similar increase in the eardrum to the
`free-field transformation ratio is observed."
`The average overall effect of the persona] radio headsets on
`an individual's noise exposure was determined by assuming
`an esposure to a flat {pink} noise spectrum. The reduction in
`this noise spectrum was calculated by subtracting the headset
`insertion loss values i’rorn it to determine the interior (under-
`the-headset] noise levels. The difference between the exterior
`C—weighted and interior A-weighled SPLs was then computed.
`These values are similar to Noise Reduction Ratings {NRRJ."
`They do not include a spectral uncertainty contribution and
`are lacking a two standard deviation correction.
`
`Sound and Vibration 0 May 1955
`
`

`

`