THEORY & APPLICATIONS

Balanced Attenuation Ear Protection

fflt hen exposed to extreme sound liA.I levels, we can and should use earplugs as often as possible, for any­thing we can do to protect our ears from intense sound is worthwhile. His­torically, anything from cotton, lambs­wool, (petrolatum-soaked or not), silicone-putty, foam, molded or store­purchased plugs, to sophisticated (and sometimes expensive ear-muffs) have been used. Properly fitted foam plugs and earmuffs offer the most attenua­tion. The key words here are properly fitted. Many people use these protec­tive devices on a regular basis, but if the plugs or earmuffs are not properly fitted, any potential benefit can be lost.

However, properly fitted or not, it is a well-known fact that virtually all com­mercially available earplugs, as well as "home-made" types, cut out more high frequency than low frequency. Figure one illustrates the various attenuation afforded by properly fitted ear protec­tion devices. The predominance of

high frequency attenuation is clearly noted.

This lack of balanced attenuation is one of the many reasons given by musicians, sound engineers, sound­mixers, et al, for not using ear protec­tion devices. They complain of a lack of clarity or an "untrue" sound re­

ceived when using ear-plugs; it is most difficult to do a good job as a musician, sound engineer, or sound mixer if the sounds you hear are not true to the ear.

Altshuler is Professor, Audiology, at Hahnemann University, and Chief, Audi­ology/Speech Pathology, Veterans Ad­ministration, Philadelphia, PA, and is a

member of the Sound & Communications Technical Council.

by Mort Altshuler

0

10

I 2

� �"l)

� ? .II()

1: .so

loo

,1-,;

Figure 1. Attenuation afforded by various ear protection devices (after E.H. Berger, High Fidelity, July 1988).

This indictment is indeed a valid one - or I might report now - has been a valid reason.

Etymotic is a "new ancient Greek" word meaning "true to the ear." Mead C. Killion, Ph.D., president of Etymotic Research, Elk Grove, IL, reports that his company expects to be in full pro­duction by the fall of this year with what he refers to as the "Musician's Earplug," the ER-15. This new ear pro­tector was developed several years ago by Elmer Carlson of Industrial Re­

search Products, a Knowles Company. Ed DeVilbiss, who is vice president of Etymotic Research, reported that about 150 of their ear-protectors are currently in use, most of them in the ears of jazz, rock, and symphony musi­cians. Almost all report great success regarding reduction or elimination of acoustic trauma and the return to sen­sitive, "true" hearing.

Reprinted with permission from

The reason for the success of these ear protectors over those earlier de­scribed is based on the fact that the ER-15 earplug attenuates a uniform 15dB, allowing the user to hear ac­curately in high SPL environments. In a recent article Killion, DeVilbiss and

Stewart stated the need for a "high fidelity" earplug with a uniform response. What good fidelity means, in

essence, is proper spectral balance. They report that, · 'The trick to produc­ing this high-fidelity response is to reproduce the shape of the natural fre­quency response of an open ear, but at a reduced level."

Figure 2 illustrates the open ear resonance with the usual peak at about 2700Hz and the ear with a well-made, properly fitted ER-15 earplug. The dif­ference between the two is the real-ear

attenuation of the earplug. One can clearly note the closely parallel curves.

The device is actually a small plastic acoustic sound chamber that is at­tached to a specially made earmold. Figure 3 is the cross section of the ER-15 earplug and the electrical analog equivalent circuit. Compliance is in the form of a flexible plastic diaphragm (C1) the sound channel (L1) is the acoustic mass. "... a Helmoltz reso­nator is formed between the inertance of the sound channel and the com­bined compliance of the flexible diaphragm and the ear-canal volume." The plastic sound chamber is affixed to a soft vinyl {or silicone) deep-canal ear mold fabricated from individual ear impressions of the users' ears. The material used and the insertion deep in the canal are necessary to avoid an occlusion effect (the hollow, in-a-barrel effect when we cup a hand over or ac-

Sound� Communications vol 35 no 3; 12-14 (1989)

-' a. Cl)

::,; 20 ::i a: 10 0 (Il �o 0 UJ �

OPEN EAR -.. V",.,. � .......... -�

, ----UJ -10 , ----.,.. __ ... WITH ER-15

-20 --- EARPLUG

UJ a:

20 50 100 200 500 1 kHz 2 kHz 5 kHz 10 kHz 20 kHz

FREQUENCY

Figure 2. Normal open ear canal resonance and attenuation curve with the ER-15 (after Killion, DeVilbiss and Stewart, The Hearing Journal, May 1988).

tually close our ear with a finger and listen to our own voice). The length of the canal portion (ideally 10mm) and the diameter of the sound channel (L1), 4mm, are critical to insure the bal­

anced attenuation that is sought. When worn, these devices sit well down in the concha (bowl) of the ear.

The author ordered a pair of these devices and had his own ear-canal plugs fabricated. I found the soft vinyl plugs easy to insert, comfortable to wear and easy to extract. Listening to very loud music pumped into one of my acoustic test booths at RMS 100 dB SPL was very comfortable, undistorted and it was immediately discernable

that there was an unloadinq of pres­sure in my ears. (I had listened to 3

minutes of the music without the devices about 20 minutes prior to wearing the

plugs.) It was clear that the high frequen­cies were coming through in a normal rela­

tionship with the lows.

Appropriate testing before and during use of the devices revealed, as claimed, a uniform attenuation.

L 1

Figure 3. The 15 dB Earplug (after Killion, DeVilbiss & Stewart, The Hearing Journal, May 1.988).

DeVilbiss informed me that there are about seven labs in this country and in Canada that are able to fabricate the ear canal plugs. It is further reported that local suppliers who are able to make ear im­pressions of the required (high) quality are

growing in numbers throughout North

America. DeVilbiss reported that a pair of

attenuators and plugs would retail for ap­

proximately $100.00 to $125.00. The devices would be a boon to others

who must attend a large number of loud concerts (journalists, reviewers, security personnel, and the like). Other loud/noise environment workers would appreciate these also, wherever the need for ''bal­anced" hearing exists.

I don't know about any of you out there, but I intend to wear mine the next time out. •

Reprinted with permission from

Car Audio and Electronics

Hearing protection products are rated by the Environmental Protection Agency with a Noise Reduction Rating (NRR). The NRR tells you how many decibels are allenuated by the device. Mos! earplugs you can buy over the counter have NRR ratings from 6 dB lo 40 dB. For instance, an earplug with a 20 NRR rating would reduce your exposure in an environ­ment with 110 dB of ambient noise lo a much safer 90 dB of exposure.

Earplug types range from rubber, wax, or foam inserts lo earmuff models typically used on shooting ranges. These over-the­counler ear protection devices are inexpen­sive and can be purchased al drugstores or sporting goods stores.

Audiologists say the most important factor for an earplug's effectiveness is how well ii conforms lo the inner ear canal to prevent sound from reaching your eardrum. They say foam plugs seem lo do the best job because they expand lo fit your ear canal ofter inser­tion and maintain a light seal even when your canal area changes during facial and jaw movements. For more information on obtain­ing high-quality foam inserts, contact Cabot Safely al (800) 225-9038 or Moldex of (800) 421-0668.

The main drawback of this type of protec­tion is that the higher frequencies are overly ollenuated so that music sounds "bossy." And the user's speaking voice sounds abnormally loud and muffled to the point of distraction. Known as the occlusion effect, earplugs cause the sound of your voice lo vibrate in the empty area of your ear canal.

Recently, a more advanced type of hear­ing protection called the ER-15 has been introduced. Referred to as "the musician's earplug," the ER-15 reportedly allenuales lo mirror the natural frequency response of the open ear, but al a reduced level of 10 to 15 dB.

Instead of gelling an unbalanced allen­ualion of the higher frequencies, the ER-15 provides a more natural sound by incorpo­rating a diaphragm similar lo a passive speaker cone. The occlusion effect is also lessened because the plug fits deeper info the ear canal.

The ER-15 can be purchased only al hear­ing aid dispensers where the user is custom filled by making molds of the inner ear canals. Cos! with custom fillling is around $120 lo $140. For more information on the ER-15, contact Westone Laboratories al (800) 525-5071.-A.J.

--

TECHNOLOGY

An Earplug With Uniform 15-dB Attenuation

By MEAD KILLION, ED DEVILBISS, &JONATHAN STEWART

C urrently available custom-earmold hearing protectors have one defect

in common: They muffle the sound. Technically speaking, they give more attenuation at high frequencies than at low frequencies. Figure 1 shows representative performance of a well­sealed and of a poorly sealed custom­earmold type of hearing protector with solid construction, based on data from E. H. Berger. 1

Another type of custom-earmold hear­ing protector includes a small vent chan­nel, often with a stepped diameter. If the vent channel is very small (0.5-mm diam­eter, for example), such devices give a real-ear attenuation that is generally sim­ilar to the curve labeled ''Leaky Earmold H.P." in Figure 1. If the vent channel is a little larger, an undesirable resonance peak is created, and the earplug actually provides amplification instead of atten­uation at the resonance frequency. A I-mm diameter vent, for example, gives a peak of about 5 dB near 250 Hz.

Mead Killion, PhD and Ed Devilbiss, MBA are President and Vice President, respectively of, and Jonathan Stewart, BSIEET is Engineer with, Etymotic Re­search, Inc. (manufacturer of the ER-15 earplug). Correspondence to: Etymotic Research, Inc., 61 Martin Lane, Elk Grove Village, IL 60007.

14 TIIE HEARING JOURNAL/MAY 1988

Regardless of their exact construction, a reasonable generalization is that exist­ing custom-earmold hearing protectors produce 10 dB to 20 dB of excessive high­frequency attenuation. A hearing protec­tor with more uniform response-a high­fidelity earplug, if you will-seems needed.

A NEW EARPLUG The curve labeled "15 dB Earplug" in Figure 1 shows the expected real-ear at­tenuation of the ER-15™ earplug, based on KEMAR measurements. The trick in producing this high-fidelity response is to reproduce the shape of the natural frequency response of the open ear, but at a reduced level. Figure 2 shows the response of the normal open ear, plotted as the eardrum SPL developed in a diffuse sound field, and the response of the ear with a properly constructed ER-15 ear­plug in place. The difference between these two curves represents the real-ear attenuation of the ER-15 earplug, which is a nearly uniform 15 dB as shown in the solid curve of Figure 1, based on KEMAR measurements.

The ER-15 earplug is a novel develop­ment by Elmer Carlson, who added acoustic elements into the sound chan­nel in order to accomplish this result. Figure 3 shows a cross-section drawing of the ER-15 earplug, along with the elec­trical analog equivalent circuit (included for those who enjoy reading schematics). A flexible plastic diaphragm acts as a compliance, and is labeled Cl in the

Reprinted with permission.

equivalent circuit. The sound channel (Ll in Figure 3) acts as an acoustic mass, so that a Helmholtz resonator is formed between the inertance of the sound chan­nel and the combined compliance of the flexible diaphragm and the ear-canal volume. With the proper combination of diameter and length for the sound channel, the Helmholtz resonator will resonate at 2. 7 kHz, providing the desired boost at that frequency as illus­trated in the lower response curve of Figure 2.

CONSTRUCTION VARIATIONS Figure 4 shows the medium depth ER-15 earmold with the ER-15 attenuator but­ton snapped in place. The "canal-aid" style construction should make for a nearly invisible earplug in most ears. The right and left earmolds must be color coded.

A version designed to produce less oc­clusion effect (i.e., fewer "my own voice sounds hollow'' complaints), shown in Figure 5, is suitable for persons with larger-diameter ear canals. The reduction of occlusion effect is a result of the deep seal of the plug. 2•

3 The standard 3.5-mm diameter sound channel can be drilled with the same .142" drill used for #13 super-thick tubing. Some ear canals will be so flattened that such a hole, extend­ing for 10 mm down the canal, will not be practical. A roughly oval hole may be used in these cases to obtain the desired acoustical results, as suggested years ago by H.S. Knowles. Figure 6 shows elon-

voi.41 (5); 14-17

EARPLUG ATTENUATION

- 0-----------------, m Q �-��-:

P

.:\ Z 10 ----o O 1...:.:15�0

:.:B

:_:EARPL.,;.:..:_uo_---....._.,-:�--""'..:,�---,..---. - ', --........._

!c:, 20 ', �

z ·--- ...... ----· .... , ... -0--0''

� -� EARMOLD H.P. /'' ',

� 30

'6,

,

a: '•- .... --•--� .a I

.J < w a: 50.l_--------------,---,--.,..-......,

0.125 0.25 0.5 2 4 8 FREQUENCY IN KHZ

... a. • :I 20

i 10 0 ID a:: 0 C 0 Ill z

... - -10 > 5 -20 .. a::

lO

OPEN EAR,lr-,..._ L.........- I I"---

,, ,--, --- ---· .__, ..... , '" 1:11-1:, EARPLUG

I I

eo IDD zoo IOO I- a- ·- IQ.. zo-

FREOUENCY

Figure 1. Performances of a well-sealed and of a poorly sealed custom-earmold-type hearing protector with solid construction.'

Figure 2. Expected eardrum SPL in diffuse (random incidence) sound field with ear open or occluded.

gated holes, equivalent to 3.5-mm and 4-mm diameter sound channels, with flat-side dimensions of 3 mm. In order to check the accuracy of the frequency response and/or the amount of occlusion effect on an individual ear, a 1-mm o.d.

L1

Figure 3. Construction of 15-dB earplug.

probe-tube hole can be ordered with the earmold. Figure 7 shows the preferred and alternate locations for the probe-tube channel, which should be sealed com­pletely after testing is completed.

Despite the best of intentions, ear­molds occasionally will be badly made. The effect of two likely errors, lack of seal and undersized sound channel, is il­lustrated below with specific examples. Figure 8 shows the effect of a leak or an undersized sound channel (2-mm diam­eter instead of 3.5-mm diameter) on the eardrum SPL generated in a diffuse sound field. Figure 9 shows the resulting real­ear attenuation expected for these errors.

EARMOLD MATERIAL From an acoustic standpoint, any ear­mold material can be used, but we recommend soft vinyl or silicone for two reasons: ( 1 J It eases the task of obtaining

a good seal; (2) It permits a deep seal with good comfort. The disadvantage of soft (30- to 40-durometer) materials is their reduced durability compared to acrylic.

APPLICATIONS Two potential applications for the ER-15 earmold stand out: First, for the musi­cian who wants some protection but needs good fidelity (proper spectral balance) in order to perform properly; and second, for the factory worker who has a high-frequency hearing loss and re­fuses to wear conventional hearing pro­tection because he needs to hear more clearly. Figure 10 shows the expected sound-field audiograms for a person with normal hearing, and for a typical 50-year­old man using either conventional custom-earmold hearing protectors or ER-15 custom-earmold hearing protec­tors. The audibility of important high­frequency speech sounds is clearly im-

Figure 4. Medium (First Bend) Depth. (Standard ER-15 earmold for ER-15 attenuator.)

Figure S. Long (Second Bend) Depth. (Low-occlusion-effect version of ER-15 earmold for larger ear canals.)

16 THE HEARING JOURNAL/MAY 1988

A)

-3.Smm ROUND

B)

4 mm

ROUND

- 3 mm

ELONGATED

3 mm

ELONGATED

Figure 6. Sound channels for round and flattened ear canals: IA) 3.5-mm equivalent diameter; !BJ 4-mm equivalent diameter. Figure 7. Preferred and alternate probe-tube channel locations.

I 20

� 10

I !

.., 0 "' .. -,o

-20 ..,

I I I i I I ..,

! i I ! !

i I I / I I

I I OPEN EAR -.../""""-.J I

I I './" I - i ... I .. . : POOR SEAL )·-.. ..J 1/:' '--',, I

.. , l �ZE

I tCORRECTI ! SOUND CHANNEL1

I ! I I I I I

10 IOD ZOO M)O I....,_ z_,., S- 10.. ZOIIMI FREQUENCY

i /

I I

I I !

zo

I I

I i . :

I

! i I I

I

I I I

! I so ""' zoo

I I I

i !

i I I - I I .. , I

! I '---� i I

I I I ! ! I I I I ' I

SOD I.., z- SIMI IO- zo-.

FREQUENCY

Figure 8. Expected eardrum SPL with ear open and with three con­structions of ER-15 earmold.

Figure 9. Calculated ER-15 performance vs. earmold construction: (- ) correct 13.5 mm) sound channel, well-sealed; I- . . ) poor seal, equiv­alent to 0.028" vent hole; (- - -) undersized sound channel (2-mm dia. ).

SOUND FIELD AUDIOGRAMS

NORMAL

HEARING

125 250 500 1K 2K 4K BK Ilic

"'� - ......._ . ........ sol--4--1--+---l-+--I

801-----l'-----+--+---it---l

1001--1--+--1--+----,t--t

ER-15

CUSTOM EARMOLD

TYPICAL

MALE AGE 50

125 250 500 1K 2K 4K BK

20 � t1s0w, ,- .m R:;2'i }iw0\". '%(

40 "'� ';,;;..· ;cc;;:, "'2 . ·:""t, ·;,;/

-..., -- .2 r

60 ' -' t IJ ER-15

80 t---t--+-+--+--•• •._ .. -4 1 CUSTOM

I--+-+-+--+-+......;

� EARMOLD 1001----1---------

Figure 10. Expected sound-field audiograms, using conventional or ER-15 hearing protectors, for a normal-hearing person (left) and for a typical SO-year-old man (right) .

proved with a flat attenuator. Note: this is a low-attenuation earplug with an es­timated noise reduction rating (NRR) of 5 dB to 8 dB,· and is not meant for pro­longed use in high levels of industrial noise or with gunfire.

Another potential application is for the person whose hearing probably is not really at risk, but who would prefer to hear without discomfort at amplified­music concerts. The authors also find that these attenuators make travel by both automobile and airplane more en­joyable. Production quantities will be available in the.third quarter of 1988�

• The NRR estimates the A-weighted noise expo­sure from a C-weighted sound level meter reading under worst-case ( - 2 sigma) conditions. The calcula­tion of NRR is laborious and not simply related to the actual attenuation of an earplug at any frequency.

REFERENCES l . Berger EH: Can hearing aids provide hearing pro­

tection? Hear Instr 1987; 38(3):12-14. 2. :Killion MC, Wilber LA, Gudmundsen GI:

Zwislocki was right . . . . Hear Instr 1988; 39(1 ) : 14-18.

3. Berger EH, Kerivan JE; Influence of physiologi­cal noise and the occlusion effect on the mea­surement of real ear attenuation at threshold. f Acous Soc Am 1983; 74:81-94.

THE HEARING JOURNAL/MAY 1988 17

EARPLUG PROTECTION LEVELS: To choose the appropriate model of earplug it is important

to know the sound pressure level of your environment. A sound level meter, such as the low cost Radio Shack model 33-2050, is a good tool for measuring environmental noise levels. It is also important to obtain a good seal in the ear, since a leak can reduce the attenuation by half or more,

especially below 1 kHz.

Noise induced hearing loss is a function of exposure time, the average noise level and the peak

level of very loud sounds. Some people are more susceptible to hearing loss than others, so that

protection on the basis of an average time and sound level exposure will only protect the "average"

person. Even under optimistic OSHA conditions (see table), regular listening for 2 hours without

protection, would be the safe limit at levels of 1 00 dB, and this assumes that for the rest of the day

the wearer is not exposed to sound levels exceeding 85 dB. In general, the ER- 1 5 attenuators are

designed for environments where the A-weighted sound pressure level is 1 05 dB or less. The

ER-25 attenuators are for use in environments above 1 05 dB and below 1 20 dB. The attenuation

shown in the graph on the first page is for an average ear; at least 1 O dB of protection for the

ER-1 5, at least 1 5dB of protection for the ER-20 and at least 20 dB of protection for the ER-25 are

achieved in almost any ear with these attenuators properly in place. The following table i ncludes

safety data of the U.S. OSHA standard as well as the more conservative 85 dB equal-energy (EE)

calculations.

AVERAGE SAFE HOURS PER DAY

Noise Level No Protection 1 0 dB Protection 1 5 dB Protection 20 dB Protection

in dB A EE OSHA EE OSHA EE OSHA EE OSHA

85 8

88 4

90 8

94 1

95 4 8

97 1 /2

100 1 /4 2 2-1/2 8 8

1 05 1 3/4 4 2-1/2 8 8

1 10 1 /2 1 /4 2 3/4 4 2-1 /2 8

1 1 5 1/4 1 1/4 2 3/4 4

120 1/2 1 1 /4 2

1 25 1

NOTE: The ER-1 5, ER-20 and ER-25 are not intended for maximum attenuation. For that application,

conventional foam or fully sealed premolded hearing protectors are recommended. For further information

about sound levels and ear protection a recommended reference is Noise � Hearing Conservation Manual by

Berger, Ward , Morrill & Royster, American Industrial Hygiene Assn.

ESTIMATED END USER COST

ER- 1 5 with Custom Earmold

ER-20 with Generic Eartip

ER-25 with Custom Earmold

$ 1 20 to $ 1 50

$20 to $30

$ 1 20 to $1 50

per pair

per pair

per pair DESIGNED

1 2/94

-

ETYMOTIC RESEARCH

PROBLEMS WITH CONVENTIONAL EARPLUGS:

ER-1 5 MUSICIANS™ EARPLUG

ER-20 HI-Fl™ EARPLUG

ER-25 MUSICIANS™ EARPLUG

EARPLUG ATTENUATION There are three basic problems with conventional

earplugs. Most important, they produce 1 0 to 20 dB

of extra high frequency attenuation; second, they

have a large occlusion effect, which makes the

users hear their own voice with a boomy quality;

and th ird, they attenuate more than necessary for

much of the noise in industry and the environment.

A frequent result of these problems is that some people will either wear no protection or they will

wear their earplugs loosely so that sounds such as

speech, machinery, noise or music can be heard

more clearly.

0-r-------------------,

:!:!. -10 z

:::, -20

� -30 a:

� -40 a:

ER-15 MUSICIANS PLUG

ER-25 MUSICIANS PLUG

(tentative)

FOAM E-A-R PLUG (DEEP)

-50-'---r-�-����-�����-�....,....., 0. 125 0.25 0.5 1 2 4 8

FREQUENCY IN KHZ

SOLUTIONS PROVIDED BY THE ETYMOTIC RESEARCH EARPLUGS: The ER-1 5 and ER-25 Musicians earplug and the ER-20 HI-Fl earplug provide nearly equal attenuation at all frequencies. The fidelity of the original sound is preserved, and the world doesn't sound muffled. Musical levels are attenuated with minimum change of tone qual ity.

To reduce the occlusion effect, a deep seal of the plug in the second bend of the ear canal is necessary. This is made possible by using a custom earmold. The ER-1 5 (black connector nipple) and ER-25 (white connector nipple) are interchangeable in a custom earmold -- they are snapped into place -- while the ER-20 is avai lable with a different but generic eartip.

THEORY AND DESIGN OF A FLAT-RESPONSE ATTENUATOR: A flat-response attenuator

must have a frequency response that fol lows the shape of the natural frequency response of the

open ear, but at a reduced level . Both

the ER-1 5 and ER-25 use a diaphragm,

similar to a passive speaker cone, to

achieve the desired response curve.

The ER-20 uses a tuned resonator and

acoustic resistor. r/

Musician's Earplug in Earmold

e ,,.. 1 Conn���or

� /., .... ,&��

ER-15 (�

White �\ 0 Connector ER-25

,<>;:/ �"' ;/ "i

ER-20 with Generic Eart1p

APPLICATIONS FOR FLAT-RESPONSE ATTENUATORS: There are two groups of people that

can benefit from the use of these plugs. Fi rst are people exposed to 90 - 1 20 dB sound levels,

who need to hear accurately. This group includes musicians, their sound crews, recording

engineers, night-club employees, certain industrial employees such as machinists and foremen,

racing pit crews, motorcycle riders, etc. Second are people whose hearing may not be at risk but who want to hear without discomfort, and who will not wear conventional hearing protection because they need to hear more clearly. This group includes regular airl ine or auto travelers and

individuals that occasionally attend loud concerts. Musicians wil l find the ER-1 5 and ER-25 attenuators useful in reducing discomfort and ear fatigue without sacrificing clarity. The greater attenuation of the ER-25 should prove useful to percussionists, rock musicians and individuals that

experience post-exposure tinnitus.

ETYMOTIC RESEARCH, 61 Martin Lane, Elk Grove Village, I l l inois 60007

Etymot,c !et- ,m OH t,k) ,s a · new anc,ent Greek word" which means true to the ear.

(708) 228-00013

Fax (708) 228-6835

THEORY AND DESIGN OF A

FLAT RESPONSE ATTENUATOR

A flat-response attenuator must have a frequency response that fol lows the shape of the natural frequency re­sponse of the open ear, but at a reduced level . Both the ER-15 and ER-25 use a diaphragm, simi lar to a passive speaker cone, to achieve the desi red response curve. The ER-20 uses a tuned resonator and acoustic resistor. To reduce the occlusion effect, a deep seal of the plug in the second bend of the ear canal is necessary.

EARPLUG ATTENUATION 0,--

-----------�

� -10 z

:3 -20 z w

..: -30 a:

..: -40 w

EA-15 MUSICIANS PLUG

FOAM E-A·A PLUG (OEEP)

-50-'-r--.--.--.--.--.--.--.--.--.--.--.-� 0.125 0.25 0.5 1 2 4 8

FREQUENCY IN KHZ

I n general , the ER-15 attenuators are designed for envi ronments where the A-weighted sound pressure level is 105 dB or less. The ER-25 attenuators are for use in environments above 105 dB and below 120 dB. The attenuation shown in the above graph is for an average ear; at least 10 dB of protection for the ER-15, at least 15 dB of protection for the ER-20 and at least 20 dB of protection for the ER-25 are achieved in almost any ear with these attenuators properly in place.

SAFE EXPOSURE LEVELS

Noise-induced hearing loss is a function of exposure time, the average noise level and the peak level of very loud sounds. Some people seem to be more susceptible to hearing loss than others, so that protection on the basis of an average time and sound level exposure wil l only protect the "average" person . The fol lowing table includes data for the more conservative 85 dB equal energy (EE) approach as wel l as the U.S. OSHA standard . We assume that at least 10 dB of protection for the ER-15, 15 dB of protection for the ER-20, and 20 dB of protection for the ER-25 is achieved in most ears with these attenuators in place.

Noise

Level

in dB

85

88

90 94

95

97

100

105

1 10

1 15

120

125

AVERAGE SAFE HOURS PER DAY

No

Protection

EE OSHA

8 4

8

4 ½

¼ 2

1

½

¼

10 dB

Protection

EE OSHA

8

2½ 8

¾ 4 ¼ 2

1

½

15 dB

Protection

EE OSHA

8

2½ 8

¾ 4 ¼ 2

1

20 dB

Protection

EE OSHA

8

2½ 8

¾ 4 ¼ 2

1

NOTE: The ER-15, ER-20 and ER-25 are not intended for maximum attenuation. For that application, conventional foam or fully sealed premolded hearing protectors are recommended. For further information about sound levels and ear protection a recommended reference is Noise &

Hearing Conservation Manual by Berger, Ward, Morrill & Royster, American Industrial Hygiene Association.

FOR MORE INFORMATION CONTACT:

DESIGNED Patented

High Fidelity

���00�00® �OO@IJ�©IJ�@OO

ER-1 5 MUSICIAN'S EARPLUGS

ER-25 MUSICIAN'S EARPLUGS

ER-20 HI-Fl EARPLUGS

• Sound Quality is Clearer and More Natural

• Fidelity of the Original Sound is Preserved

• Fatigue Associated with Noise Exposure is Reduced

• The World Doesn't Sound Muffled

Designed to provide moderate attenuation at all frequencies.

EFFECTIVE • PRACTICAL • COMFORTABLE

PROBLEMS WITH

CONVENTIONAL EARPLUGS

PROBLEM 1 :

Exist ing earplugs attenuate more than necessary for much of the noise in industry and the environment.

PROBLEM 2:

Regardless of their exact construction , exist ing earplugs produce 10 to 20 dB of high frequency attenuation and the resu lt is that people often reject them because they can't hear speech clearly.

PROBLEM 3:

Exist ing earplugs make the wearer's own voice sound hollow (known as the occlusion effect) .

PROBLEM 4:

Many people r isk their hearing by either wearing earplugs loosely or wearing no protection at all so they wil l be able to hear voices, machinery or music more clearly.

Avai lable with a custom earmold only. An accurate impression is critical to ensure a proper fit .

ER-20

Avai lable with a ready-fit eartip (as shown) or with a custom mold.

sealing damper ring

cpdr� eartip stem end cap

ER-20's patented acoustic damping network provides nearly uniform attenuation.

WHO CAN BENEFIT FROM

ER ,1 5 R ·2 ERK20'?'

Those who are exposed to 90-120 dB sound levels for various time periods and need to hear accurately:

• Musicians

• Dentists

• Traders

• Pi lots; airl ine personnel who do not require maximum attenuation

• Record ing engineers

• Sound crews

• Most industrial workers

• Mach inists

• Restaurant and dance club employees

• Rock music l isteners

Those whose hearing may not be at risk, but who prefer to hear without discomfort:

• Airplane and auto travelers

• Fl ight attendants

• Rock music l isteners

• Spectators at sporting events

• Persons with tinn itus

• Persons with h igh frequency hearing loss who reject conventional ear protection because they cannot hear speech clearly

• Persons with an abnormal sensitivity to loud sounds