History and Design of Flat Response Attenuators
20
OPEN EAR
10
0
15 dB
-10
-20
Ready-Fit Earplugs
ER-20 High Fidelity
Earplugs were developed
to provide low-cost, onesize-fits-most high fidelity
Diagram of the ER-20
earplugs that can be used in
a variety of noisy environments.
The goal of the ER-20 design was the same as for
the ER-15: to reduce noise but preserve sound quality;
in effect, to turn down the noise but not muffle voices,
environmental sounds or music.
ER-20s use a tuned resonator and acoustic resistor
to give essentially equal sound reduction at all frequencies which preserves the fidelity of the original sound.
-10
EARPLUG ATTENUATION
Real-Ear Atten
uation (dB)
Relative Eardrum SPL In dB
Musicians Earplugs
In the late 1970s Elmer
Carlson, an engineer at
Knowles Electronics, develSchematic side view
oped what we now call
of the ER-15
Musicians Earplugs. His
C = compliance
design replicated the natural L = inductance
response of the ear canal so R = resistance
that sound heard with these
earplugs would have the same quality as the original,
just quieter.
In 1985, while consulting with the Chicago Symphony
Orchestra, Mead Killion, Ph.D., president and founder
of Etymotic Research, concluded that there was a real
need for Carlson’s earplugs.
10
20
30
40
WITH ER-15 EARPLUG
Mean Attn.
0
ER-20 HI FI EARPLUGS
FOAM E-A-R PLUGS
SHALLOW INSERTION
(typical real world)
~12 dB of
muffling
FOAM E-A-R PLUGS
DEEPLY INSERTED
50
.125
20
50
100
200
500
1k
2k
5k
10 k
.250
20 k
.500
1
2
3.15 4
6.3 8
FREQUENCY IN kHz
FREQUENCY in Hz
Open ear response of the average ear measured in a
diffuse field or reverberant room. The response of
the ER-15 Musicians Earplug indicates a 15 dB reduction in eardrum sound pressure at each frequency.
Lost high frequencies with conventional earplugs,
compared to response of ER-20 High Fidelity Earplugs
ER-20 UltraTech™ Earplugs
ER-20 UT Earplugs have the same acoustic
The ER-15, the first Musicians Earplug, properties and the same construction as ER-20
was the standard from which all of the High Fidelity Earplugs. The only difference is their
other ER attenuators were designed.
color and a retaining cord for convenience.
ER-15-SP
The ER-15SP (Sports Plug) response is simular to
the ER-15, but the 6 kHz side branch resonance (which
smoothes the ER-15 response above 3 kHz) was
sacrificed in order to provide the smallest possible size.
ER-25
The ER-25 has an increased diaphragm stiffness
and an acoustic-mass channel molded into the button
for more attenuation.
Mean Attenuation Characteristics
of Musicians Earplugs
-10
EARPLUG ATTENUATION
Real-Ear Atten
uation (dB)
ER-9
The ER-9 has reduced diaphragm stiffness for
less attenuation.
Mean Attn.
0
ER-9
ER-15
10
ER-15SP
20
ER-25
30
40
50
.125
.250
.500
1
2
FREQUENCY IN kHz
3.15 4
6.3 8
ER-4 MicroPro™ Reference-Quality Earphones
ER-4 MicroPro Earphones are high fidelity
transducers developed specifically to combine flat
frequency response with isolation from external noise.
They deliver transparent, reference-quality sound and
provide at least 20-25 dB of external noise exclusion at
all frequencies, which allows listeners to hear the full
dynamic range of recorded or live music at safe levels.
ER-4 Earphones are popular among audiophiles for
personal listening (e.g. CD, cassette players).
Many stage performers and recording engineers use
ER-4 Earphones as in-ear monitors to monitor or
isolate their own and others’ instruments or voices
from the rest of the band or mix. Deep insertion
of the eartips is essential for good bass reproduction.
Custom earmolds can be made for these earphones.
Quick Reference
Earplug name
ER-9 Musicians Earplug
Description
Attenuation
ER-15 Musicians Earplug
ER-15SP Sports Plug
ER-25 Musicians Earplug
ER-20 HI-FI™ Earplugs
Attenuator buttons that attach to custom earmolds
9 dB
Available colors
15 dB
Earmold impression
Ready-fit earplugs
15 dB
25 dB
Brown
ER-20 UT Earplugs
Orange
Tan
20dB (NRR = 12)*
Yellow flanged tip/purple
stem and cord
White flanged tip/tan stem
Requires a deep earmold impression (past the second bend of ear canal)
—
Shape and size
Compact
Interchangeability
Compact
Original
Compact (smaller and thinner)
One size
—
—
Identical dimensions. Change buttons for different listening conditions.
Earmold styles**
—
Standard
Available from
Partially countersunk
Countersunk
Countersunk only
Music stores, catalogs
Etymotic Research
Hearing professionals
Catalogs, Etymotic Research,
Aearo Corp.
Cleaning
Remove button from mold. Use water and mild soap on the mold only.
Dry mold thoroughly before replacing button.
Remove eartip from endcap and stem. Use water
and mild soap on the eartip only. Dry thoroughly.
Insertion
Moisten the mold for ease of insertion.
Pull the ear outward and upward while easing the mold into the ear canal.
The right mold is usually designated with a red dot. Fit should be deep but comfortable.
Moistening the eartip eases insertion.
Pull the ear outward and upward while
easing the earplug into the ear canal.
May be needed due to deep insertion of custom molds.
Usually not needed.
Discoloration, shrinkage, cracking, hardening of earmold material, deterioration in performance
Torn or cracked eartip, deterioration in performance.
Wearing schedule
Reasons for
replacement
* NRR (NOISE REDUCTION RATING) is a laboratory-derived numerical estimate of attenuation. The Environmental Protection Agency (EPA) requires manufacturers to
print an NRR rating on the label of all non-custom hearing protectors sold in the U.S.
** Earmolds are made with silicone or vinyl materials (countersunk style uses silicone only). All custom molds are available with or without a removal filament.
ER
-9
ER
-15
ER
-25
ER
-4
ER
-20
Recommended Earplugs for Music Professionals
Musicians practice and perform in a variety of different
settings and they are exposed to high levels of sound,
sometimes for long periods. They require different amounts
of protection, depending on the sound levels they encounter
during rehearsals and performances.
As designated by the number classification, ER-25s and
ER-9s provide either more or less attenuation than ER-15s.
Some musicians use one type of attenuator in one ear and
one type in the other, depending on the source and location
of the sound.
For more in-depth information regarding the clinical assessment of
musicians, room acoustics, the physics of musical instruments, and
environmental strategies used to reduce noise exposure for musicians,
refer to: Chasin, M. Musicians and the Prevention of Hearing Loss.
Singular Publishing Group. 1996.
Harmful Sound Comes From:
Small strings
Own instrument
Large strings
Brass section
Woodwinds
Brass section
Brass
Own instrument, other brass
Flutes
Percussion
Percussion
Vocalists
Acoustic guitar
Own instruments, other percussion
Own voice, speakers, monitors
Drums, speakers, monitors
Amplified instruments
Speakers, monitors
Marching bands
Instruments behind
Music teachers
Multiple sources
Recording engineers
Speakers, monitors
Sound crews
Speakers, monitors
Frequently Asked Questions:
Effective
for anyone who needs to
hear accurately in a noisy
environment…
What’s wrong with
conventional earplugs?
How can the occlusion
effect be measured?
Conventional earplugs attenuate more
in the high frequencies than in the low and mid
frequencies, which makes music and voices unclear
and unnatural. Deeply inserted foam earplugs can
provide 30-40 dB of attenuation, although typically
only a small amount is needed.
1. Using probe measurement equipment,
disconnect the loudspeaker, place the probe in the
ear and measure the difference between the SPL
developed in the open ear and in the occluded ear
during vocalization of “oo” or “ee.” If the difference at
250 or 500 Hz exceeds 10-15 dB, consider a remake.
2. Using an inexpensive, hand-held, stand-alone
Occlusion Meter (Etymotic Research, 1999),
determine the difference in SPL as described above.
How much protection
do people need?
Hearing loss is a function of exposure time,
the average sound level, and the peak level of very
loud sounds. Some persons seem more susceptible
to hearing loss from high-level sound than others.
The table below contains data from the OSHA
standard, and the more conservative equal-energy
(EE) method. Many industrial workers can be
adequately protected with as little as 10 dB of
attenuation: the majority of eight-hour-equivalent
noise exposures fall between 85 and 95 dB.
Average Safe Hours Per Day
source level
in dB
85 88 90 92 94 95 97 100 105 110 115 120
OSHA
EE
16
8 4
8
6
1
4
3
⁄4
3
1
⁄2
2
1
⁄4
1
⁄2
1
⁄4
1
⁄8
1
Example: According to the OSHA standard, a person can
be exposed to a 95 dBA environment for 4 hours before
risking hearing damage; with 10 dB of protection, that
person can be exposed to 95 dB for 16 hours per day.
Conservatively, ER-15 and ER-20 earplugs provide at
east 10 dB of protection and ER-25s provide at least 20 dB of
protection. For maximum protection, foam earplugs, muffs
or other hearing protection devices are recommended.
What are the two greatest
sources of error with
Musicians Earplugs?
1) Earmold impressions that are not long enough
(past the second bend), and 2) earmolds received
from the earmold lab that are not long enough.
Why are special earmold
impressions required for
Musicians Earplugs?
Deep earmold impressions (past the second
bend of the ear canal) are required because when
earmolds do not seal deeply in the bony portion of
the ear canal, wearers experience the occlusion
effect. A shallow earmold can increase the occlusion
effect by as much as 15-20 dB at low frequencies.
Silicone impression material is recommended. Vented
otoblocks decrease the likelihood of discomfort or
damage to the ear during removal of deep
impressions. If a remake is necessary because of the
occlusion effect, it may be helpful for the person to
vocalize “oo” or “ee” while the impression is setting.
Aircraft
crew
flight instructors
passengers
pilots
Athletics
athletes
coaches
How can the attenuation
of Musician Earplugs be
verified clinically?
1. Using a probe microphone, measure
insertion loss: The difference between the open ear
response and the occluded response is the amount
of attenuation.
2. Under earphones, measure thresholds with
and without earplugs: The difference is the amount of
attenuation. A small correction—usually subtracting
< 2 dB from the measured attenuation value—will
compensate for the decrease in volume under the
earphone.
3. In the sound field, measure threshold
differences with and without earplugs. Plug or mask
the non-test ear if individual ear data are desired.
Construction
carpenters
equipment operators
road builders
steel workers
Emergency
Vehicles
EMTs
highway patrol
firefighters
Note: When hearing is normal, testing should be
done in a booth that is quiet to audiometric zero. 1
1
Most sound booths do not meet this standard.
Who makes earmolds
for Musicians Earplugs?
Authorized earmold laboratories make earmolds
for Musicians Earplugs. These labs use an acousticmass meter to verify that custom earmolds have the
correct volume of air in the sound bore to produce
flat attenuation when the buttons are in place.
Etymotic Research manufactures and tests each
attenuator button for proper resistance and
compliance values.
In what special cases are
Musicians Earplugs helpful?
Musicians Earplugs can prevent or significantly
reduce the debilitative symptoms for persons whose
tinnitus is induced by loud sounds. There are also
documented cases in which Musicians Earplugs
provide relief for those with hyperacusis.
Industrial
factory workers
shop teachers
students
supervisors
Leisure
concerts
night clubs
noisy restaurants
sporting events
Medical-Dental
dentists
dental hygienists
dental technicians
surgeons
Motor Sports
motorcyclists
pit crews
race car drivers
Others
®
ETYMOTIC RESEARCH
RESEARCH AND PRODUCT DEVELOPMENT FOR THE EAR
61 Martin Lane, Elk Grove Village, IL 60007
847-228-0006 www.etymotic.com
The ER family of earplugs is covered by three U.S. patents
(4,852,683; 5,113,967; 5,887,070).
The ER-20 is manufactured by AEARO Corporation under ER patents.
HI-FI and UltraTech are trademarks of AEARO Corporation.
MicroPro is a trademark of Etymotic Research.
ER-9-15-25/20FG-15-09/99 ©1999 ETYMOTIC RESEARCH
delivery drivers
market traders
night club staff
truck drivers