18, The SafEar (Fig. 18), also known as the
HALCO Safety Ear Piece and as the Noise
Braker, is a soft, factory-made, custom-fitted
earplug with “the No. 80 Acoustic filter inserted
in the sound passage.” The filter is a small vent
communicating between the enclosed canal and
the environment. When tested according to the
standard ANSI procedure, the device behaves
like an earplug with a hole in it: sound gets
through. Company literature indicates, however,
that this plug is intended for high-level-noise
service. We did not test it in such noise, but did
read two company-provided reports. Both show
average attenuation properties in noise that are
beyond those considered theoretically possible
(Zwislocki, 1957) ; test procedures seem to be at
fault. Still, the concept of a perforated earplug
that improves its attenuation as noise increases
is based in fact (Forrest, 1971), but the data
suggest that such effects are negligible until very
high sound pressures are reached; Forrest found
a 110-dB SPL threshold for this action, and an
increase in attenuation that stabilizes above 140
dB SPL at a rate of about 1 dB per 2-dB rise
in signal level. This result can hardly be squared
with the perfect compression advertised for
SafEar’s “Accelerated Resonance Decay Prin-
ciple.” They claim that, “ .. above 85 db
[sic], the noise is attenuated to 85 db. The
higher the noise the more efficient the attenuation.
Thus noises of 140 to 150 db are attenuated to

SOUND MASTER

‘T |
40} g
@ so}
€ % a
s y
$ 20
3
& vol | |

“TEP iy

' v6 +900 —t
Frequency in He

Ficvxe 19. Measured attenuation provided by Sound

Master, The line represents the mean attenuation ;

the shaded area represents the range.

1

85 db... .” This plug may well be useful in
situations in which the primary exposure is to
high-level impulse noise.

19, Sound Master earplugs (Fig. 19) are
custom-fitted-and do not require factory construc-
tion. They are stamped to identify which ear
each plug was made for. It is not necessary to
handle the material at all.

20. The Soundown earplug (Fig. 20) is a
custom-fitted, factory-made plug that is par-
ticularly light in weight and particularly com-
fortable to wear, according to subjects’ reports;
extraneous material has been removed. The plug is
formed from two types of acrylic—one hard and
one soft—with the soft part fitting into the canal.
However, the plug slips out of place with very
little head movement, and so requires frequent
adjustment if it is to offer much attenuation.
This looseness of fit may account for the good
comfort reports. In the tests, the ANSI require-
ment for head movements before measurement
generally led to an open channel into the ear
canal,

21. Johnson & Johnson cotton wool (Fig. 21)
was tested because people still use it for earplugs.
Domestic airlines in some countries even furnish
cotton wads to their passengers for that purpose.
Although wet cotton would be considerably more
effective an attenuator than dry, our tests were
run with dry cotton to simulate actual-use con-
ditions.

SOUNDOWN
Z
Z
8
€ y
$s 4
3 Z
2 Uy |
a +
Go|
Yt
1G
Sige PO ta

Frequency in Hz

Ficcre 20, Measured attenuation provided by Soundown.
‘The line represents the mean attenuation; the shaded
area represents the range.



Table 1

List of manufacturers, brands, and characteristics of the tested hearing protectors.

Manufacturer
Adcomold, Inc.
H. EB. Douglass
Engineering Sales
Company

Environmental
Acoustical Research

Flents Products
Company, Inc.

French Laboratory
Frontier Industrial
Products Company

General Electric
Company

Human Acoustics,
Ine.

Johnson & Johnson
Kimberly-Clark
Corporation

National Research
Corporation

Oto-cure, Inc.

Rockford I. C.
Webb, Inc.

Safety Ear Protec-
tor Company

Sigma Engineering
Company

Sonotone
Corporation

Sound Master
Products, Inc.

Stayrite, Inc.

Wade Products
Company

Wade Products
Company

Willson Products
Division

Brand Name

Adcomold

Sound Sentry
(50008)

EAR.

Flents

Soundown

Frontier

Peacekeeper

SafEar

Johnson &

Johnson

Kleenex

Oto~cure
Cus tom Ear
Protectors

Billesholm
Swedish Wool
SEPCO
Com-Fit
Sonotone

Sound Master

Stayrite
Shell-type
Earplug

Mark IL

Nods

Sound
Silencer

Manufacturer's
Description

of Material
Soft acrylic

Neoprene

Polyvinyl
Wax impregnated
cotton

Acrylic

Wax impregnated
cotton

Silicone

Vinyl

Cotton wool

Paper tissue

Polymer foam

Silicone
elastomer

001-002 mm
glass fibers

Neoprene}
latex foam

Silicone

Vinyl flex

Silicone

Polyvinyl
chloride

Silicone
elastomer

Foam latex,

wax impregnated

on one end

Vinyl

Dee

Formed in
place

Preformed

Factory
formed

Formed by
user

Factory
formed

Formed by
user

Formed in
place

Factory
formed

Formed by
user

Formed by
user

Formed by
user

Formed in
place
Formed by
user

Preformed
Pre formed
Factory

formed

Formed in
place

Preformed

Formed by
user

Formed by
user

Pre formed

Comments

Custom.

Canal cap with headband.

Custom.

Custom. Lightweight, "shadow" mold.

Custom. Two series tested.

Custom. Has vent.

Expands slowly after compression.

Custom.

Has two vents.

Cus tom,

Cus tom.

‘Three shapes; looks like a custom
plug.

Tested. both dry and lubricated
with water,


SOUND SENTRY

®
g
=

3 ih

3 |

* 7

me

re!

ae)

Frequency in Hz

Freure 6. Measured attenuation provided by Sound
Sentry (5000B). The line represents the mean atten-
uation; the shaded area represents the range.

6. The Sound Sentry (5000B) (Fig. 6) is an-
other unique item in this study. It is not, prop-
erly speaking, an insert earplug at all. Rather,
the attenuation results from covering the opening
to the canal with a neoprene cap that is held in
place by a headband. It is difficult to position
the cap accurately for the initial wearing, but
once it is adjusted, it is easy to put back on, No
subjects complained of the headband.

SOUND SILENCER (DRY)

7. For comments on the dry Sound Silencer
(Fig. 7), see paragraph number 3, above.

8. Flents (Fig. 8) are made of wax-impreg-
nated cotton fiber that is hand-formed by the
user. Some subjects complained that the wax
felt funny in the fingers. The expected life of
such plugs is, at most, a few wearings.

9. The Frontier earplug (Fig. 9) is similar to
Flents (see paragraph number 8) except that
less material is furnished.

FLENTS

s0 | |
@ 30
g
5 zof
3
$
= lor

oa

Frequency ie He

Fictre 8. Measured attenuation provided by Flents.

‘The line represents the mean attenuation; the shaded
area represents the range.

FRONTIER

"1 -~
i

Attenuation in 4B.

Frere 7.
cated Sound Silencer. ‘The line represents the mean
attenuation; the shaded area represents the range.

Measured attenuation provided by unlubri-

y Y
© _

,

y

@ 30- -y
8 aot ty Z
2 Z
E10 Z :
ony A - “pop
i
a a

Frequency in He’

Fievre 9, Measured attenuation provided by Frontier.
‘The line represents the mean attenuation; the shaded
area represents the range.



Table 2

Ratings of tested hearing protectors.
tion characteristics can be considered as similar.
include the best attenuators; Group VII includes the worst.

Within each group, attenua-
Groups I and IT
Within

each group, brands are listed alphabetically.

Brand Name

Group I
1, E*A-R
Group II
2. Com-Fit
3. Sound Silencer, wet
Group III
4. EAR.
5. Nods
6. Sound Sentry (5000B)
7. Sound Silencer, dry
Group IV
8. Flents
9. Frontier
10. Sonotone
Group V
11. Billesholm Swedish Wool
12. Mark IT
13. SEPCO
Group VI
14. Adcomold
15. Oto-cure Custom Ear Protectors
16. Peacekeeper, early instruction
manual
17. Peacekeeper, late instruction
manual
18. SafEar
19. Sound Master
20. Soundown
Group VII
21. Johnson & Johnson
22. Kleenex
23, Stayrite Shell-type Earplug

the plug won’t hurt (although the highest-rated
plugs are generally considered easy to wear).
Too, every sort tested shows a wide range of
attenuation patterns, so variations among people

Type

Wearer-molded

Pre-molded
Pre-molded

Custom-molded, factory
Wearer-molded
Pre-molded, canal cap
Pre~molded

Wearer-molded
Wearer-molded
Custom-molded, factory

Wearer-molded
Wearer-molded
Pre-molded, vented

Custom-molded,
Cus tom-molded,
Cus tom-molded,

in-place
in-place
in-place

Custom-molded, in-place

Custom-molded, factory, vented
Custom-molded, in-place

Custom-molded, factory, "shadow"

Wearer-molded
Wearer-molded
Pre-molded, "custom"=shaped

have to be expected and prepared for in a prac-
tical hearing-conservation program. Even more
important than the individual differences in
effectiveness and comfort is the fact that many


were randomly selected from a large pool of uni-
versity students, As the standard requires, each
plug was tested on ten listeners, with at least
three tests per plug performed on each person.

‘The ambient noise levels in the anechoic cham-
ber were determined to be low enough to meet,
the standard’s requirements both by measurement
with a Bruel and Kjaer model 2203 sound-level
meter that served to operate a remote Bruel and
Kjaer model 2111 octave-band analyzer, and by
psychoacoustic measurement of the minimum
audible field as detailed in the ANSI standard.
The noise was well within acceptable limits.

Open-ear threshold tests and earplug attenua-
tion tests were made using a Grason-Stadler
model E-800 automatic audiometer both as the
signal source and as the response recorder. The
audiometer’s signal was led to a loudspeaker in
the chamber through a power amplifier; the
motor-driven attenuator and the motor-driven
oscillator were both retained in the circuit in
order to produce, automatically, continuous-
frequency graphs of each subject’s thresholds.
The technique is identical to that used in Bekesy
audiometry.

One group of ten subjects was used in 11
series of measurements (one series of Com-Fit
tests, and ten others). Other groups of ten sub-
jects were used for series as small as two and as
large as six. Altogether, 60 subjects participated.
With each group, the procedure was the same:
the first threshold of the day was with open ears,
to provide a baseline; then, in random order,
earplugs (always including one series of Com-
Fits) were tested for two hours or until each
type had been measured three times, following
which another open-ear threshold was taken. If
two hours were not adequate to finish all the
necessary series, the next day’s tests also included
open-ear thresholds at the beginning and end of
the session. A 5-dB variation at any frequency
between the two baseline curves was chosen as
large enough to invalidate that day’s data. It
was not necessary to throw out any tests for this
Each attenuation test was compared to
the average of the two baseline curves that were
taken on the same day.

Where manufacturers or distributors furnished
instructions, earplugs were inserted accordingly.
Otherwise, subjects were told to put the plugs in
so that they fit comfortably and were tight.

reason,

Then they made the adjustments and performed
the jaw and head exercises prescribed in the
ANSI standard.

Some custom-made varieties use an impression
of the ear as a model from which to manufacture
a plug; others use the impression itself as the
earplug. For both types, the impressions were
made by a skilled technician who followed manu-
facturers’ recommendations precisely. The object
was to simulate the way that the earplugs would
be prepared in the field. In one case, detailed
in the Results section, a company chgnged its
published instructions after our tests were com-
plete; a second series was run with earplugs
made according to the new directions.

For units that were factory-molded from a
model, the ear impressions were shipped to the
company’s plant in time to permit the finished
earplugs to age in our laboratory for at least a
couple of weeks before testing was started. For
units that were manufactured in the subject's
ear, a similar aging period was also required,
just in case shrinkage might occur and change
the results.

As much as possible, the tested earplugs were
treated as they would be in the field. For ex-
ample, normal procurement procedures were fol-
lowed (although some manufacturers furnished
the plugs at no cost when they learned of our
intentions to test the products), as were normal
fitting and molding practices.

III. Results and Discussion.

Nearly any material inserted into nearly any
ear canal in nearly any way will attenuate high-
frequency sounds to some extent. In comparing
the effectiveness of earplugs, then, it is sensible
to use the low-frequency blockage as the measure
of effectiveness. Table 2 groups the tested ear-
plugs in descending order of average attenuation
(based on the area under the attenuation curve)
between 125 and 1000 Hz. Within a group, units
generally differ insignificantly. The last group
(numbers 21, 22, and 23) contains plugs that are
far worse than any of the others; none of them
can be recommended for any practical acoustic-
quieting function.

A high position in Table 2 cannot serve as an
adequate sole reason to purchase a particular
brand of earplug. The wearer’s comfort is essen-
tial, and a high rating does not guarantee that



of the very large number of subjects whose data
are included; Com-Fits served as the reference
for every person used throughout these experi-
ments, Individual groups of ten subjects show
ranges that are similar to those that they pro-
duced for the other earplugs.

SOUND SILENCER (WET)

y
50 T
eee
@ 307] ty Y 7
£ iY,
§ zol ag i
s G \%
i 4 "
£0 + 4 1
|
° --4
pS 0 TAR Se!

Frequency in Hz

Figure 3. Measured attenuation provided by lubricated
Sound Silencer. The line represents the mean attenua-
tion; the shaded area represents the range.

3. The Sound Silencer earplug (Figs. 3 and 7)
in the standard size fits most adults. Other sizes
are available. It feels like a rubber bubble be-
tween the fingers. This structural characteristic
made it very comfortable for all subjects who
used it, but also made it difficult for about half
of them to insert properly. The instructions call
for wet insertion (which is quite easy), but many
users may not have a ready source of water when
it is time to put on their plugs, and saliva is a
less than satisfactory substitute both because of
hygiene and because of the flavor of ceruminous
residues. Therefore, tests were run on this ear-
plug both lubricated with water and dry. As
might have been predicted, the lubricated (and
therefore well-seated) plug produced better at-
tenuation scores. A dark green plug is available,
as is a version that is strung on a cord.

4, The E.A.R. (Environmental Acoustical Re-
search) plug (Fig. 4) is a soft, factory-made,
custom-fitted device. Subjects found it comfort-
able and easy to insert, but, like all the custom-
made plugs we tried, users were less comfortable
with them than they were with most pre-formed
or wearer-formed varieties.

Z
Yj,
Y
yy
8
£
s Yj
3 Ui,
g
opt] |
if
Plidiilil
nies Too 7 + TOO * T 16 600

Frequency in He

Fioure 4, Measured attenuation provided by EB. A. R.
‘The line represents the mean attenuation; the shaded
area represents the range.

5. Nods (Fig. 5) are made of wax-filled foam,
and are manipulated by the wearer until they
seal the canals. They are comfortable in the ear.
We have no data on the expected life of Nods,
but would expect them to be reusable for many
days before they begin to lose their effectiveness.
It is not necessary to touch the waxed end with
the fingers in order to use these plugs. They soil
easily.

Nops
4%
Z
80 ZZ
40
Y
B30 y e
© By
£ Qyy Y
$20
3
8 Y
=
£10 is
Ae ae
7
Py i ll
r 55 +—7a6e—t a
Frequency in Hr
Fievre 5. Measured attenuation provided by Nods.

‘The line represents the mean attenuation; the shaded
area represents the range.


TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No.

FAA-AM-73- 20

2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

EAR-PROTECTOR RATINGS

‘5. Report Date

December 1973
©, Performing Organization Code

7. Author(s)

Jerry V. Tobias, Ph.D.,and F. Michael Irons, M.Ed.

8. Performing Organization Report No.

9. Performing Organization Name and Address

FAA Civil Aeromedical Institute
P. 0. Box 25082
Oklahoma City, Oklahoma 73125

10. Work Unit No.

11. Contract or Grant No.

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Addres+
Office of Aviation Medicine
Federal Aviation Administration
800 Independence Avenue, S. W.
Washington, D. C. 20591

QAM Report
14. Sponsoring Agency Code

15. Supplementary Notes

This research was performed under Tasks AM-A-71-PSY-8, AM-A-72-PSY-8,
AM-B-73-PSY-16 and AM-A-72-PSY-37.

16. Abstract

Twenty-one brands of ear protectors, including custom-molded, wearer-molded,
and pre-molded types, were evaluated according to American-standard procedures.

Earplugs are described and are listed in the order of their low-frequency

(below 1000 Hz) attenuation.

17. Key Words

Earplugs
Hearing
Hearing Conservation

18. Distribution Stotement
Availability is unlimited. Document may
be released to the National Technical
Information Service, Springfield, Virginia
22151, for sale to the public.

19. Security Classi. (of this report)

Unclassified

20. Security Classif. (of this page)

ZI. No. of Pages | 22. Price

13 $3.00

Unclassified

Form DOT F 1700.7 (8-69)



SePco TO - CURE
y
so so
| | yy | Y
40, Y 40h,
@ sof Y ly g so} 7
= YY £
£ 20h § eof + Hs
E10 : 2 0} y
Yj Y ]) |
' Y ui
° | ! A " Za ° | | Up an
| (|
Let ee ee Petal Pg EA eT
Frequency lo He Frequency in Hz
Proce 13, Measured attenuation provided by SEPCO. — pygcee 15, Measured attenuation provided by Oto-cure

‘The line represents the mean attenuation; the shaded
area represents the range.

manufacturer's instructions carefully and accu-
rately; there is no substitute for experience in
earmold construction. The Adcomold material
is slightly more difficult to work with than is
that furnished for others of the molded-in-place
type.

15. Oto-cure Custom Ear Protectors (Fig. 15)
are custom-molded and do not require factory
construction. The mold cures to become the final

ADCOMOLD

WS
NS

Attenuotion in 4B

7 7 Te08 + camer
Frequency in Hz
Frevre 14, Measured attenuation provided by Adcomold.

"The line represents the mean attenuation; the shaded
area represents the range.

Custom Ear Protectors. ‘The line represents the mean.
attenuation; the shaded area represents the range.

earplug. For Oto-cure, the process requires the
use of volatile chemicals whose fumes were
strongly disagreeable to the people who had to
work with them, The material is difficult to
handle properly.

16. The Peacekeeper (Figs. 16 and 17) is a
custom-made -earplug that does not require fac-
tory construction. The silicone mold cures to
become the final earplug. The Peacekeeper re-
quires that the material for both ears be mixed
simultaneously. As with all plugs, we obtained
the molding kits through normal procurement
procedures. Then we made the plugs strictly
according to the accompanying instructions, aged
them for a time, and tested them. The kits in-
clude a dip that helps to seal the surface of the
plugs and to smooth out irregularities, thus in-
creasing the size slightly. Plugs can be redipped
to improve the fit, although the need for such
improvement would not be obvious without a
laboratory test of effectiveness; such tests are
not likely to be performed in field use of the
devices because of lacks of time, money, and
facilities. In these studies, the dip was used pre-
cisely according to the instructions. Tests (Fig.
16) showed less attenuation than some of the
manufacturer’s reports showed, and General
Electric requested us to test plugs made by a
manufacturer’s representative. We asked instead
for better instruction manuals or for an indica-



SONOTONE Z
Z
Y
20 | | ZY,
40]
Y
Z
@ 30)
3
£ Wy
§ 20] %
7
2 Za
s
= oh |
ol | “A OG|
ee
‘ 7 7 +—aos camer
Freaency le Hz
Frere 10, Measured attenuation provided by Sonotone.

‘The line represents the mean attenuation; the shaded
avea represents the range.

10, Sonotone earplugs (Fig. 10) are rather
like the E.A.R. plugs (see paragraph number 4),
except that the segment that fits into the canal
is a little longer.

11. Billesholm Swedish Wool (Fig. 11) is a
fiber-glass material that is hand-formed and is
advertised to be effective “in 80% of all noise
situations.” It is meant to be thrown away after

BILLESHOLM

oo

Attenuation in dB
8
7:

Frequency in Hz

Fievre 11, Measured attenuation provided by Billes-
holm Swedish Wool. The line represents the mean
attenuation; the shaded area represents the range.

“TTI

40

ASS
\W&
\\\S

Attenuation in 4B
S_

Z
im sf
1 | / i
ot EE ET
rremaney 9H
Ficvre 12, Measured attenuation provided by Mark II.

The line represents the mean attenuation; the shaded
area represents the range.

one wearing, but can be reused several times if
necessary. It is generally considered comfortable,
and no subject who used it complained of any
itching that might have been caused by fiber
glass.

12, The Mark II (Fig. 12) is hand-formed by
the user, and it feels somewhat waxy, although
there is no wax to come off on the hands. It is
made of a silicone product that is advertised to
“last indefinitely.” It was generally considered
to be comfortable despite the waxy touch that
some subjects disliked.

13. SEPCO earplugs (Fig. 18) are formed
from a pink neoprene shell (with two pinhole
perforations in the tip) that is filled with a foam
cushion (with a single pinhole perforation show-
ing at the open end). The vents appear to be
associated with pressure equalization for ease of
insertion rather than with any acoustic function
(but see paragraph number 18).

14, Soft (they are also available in a hard
material) Adcomold earplugs (Fig. 14) are
custom-fitted and do not require factory con-
struction. It is necessary to work rapidly with
such material because it sets up very shortly
after the catalyst is mixed in, and can become
stiff so quickly that reforming it into the right
shape is impossible. It is critical with all custom-
molded plugs, and especially with those that do
not require factory construction, to follow the


people who ought rigorously to use hearing pro-
tection will not do so without external incentives.
Some industrial personnel might be motivated
by plugs of a brightly colored material (several
are available) that can be highly visible to a
distant foreman, if the foreman makes it a regu-
lar point to check to insure that the plugs are
properly in place. Other prospective users may
respond positively to an option such as the head-
band or cord that some brands offer, that makes
plugs easy to put aside temporarily without get-
ting lost. Some who get custom-molded plugs
may wear them because of a belief that an expen-
sive safety device strictly for their personal use
must be good.

The critical point is that the procurement of
earplugs will conserve no hearing if the plugs
are always worn in the pocket. Selection has to
be made with the idea of getting the plug to the
anatomical place where it will do some good.

A few additional details will help in the inter-
pretation of Table 2:

1. The E-A-R (National Research Corpora-
tion) earplug (Fig. 1) is a unique type in this
study. The material is soft and easily com-
pressed, but it returns to its original shape rather
slowly under normal circumstances, permitting
an insertion of the compressed, cone-shaped form,
which then expands to fill and seal the entrance

E-A-R W ;
Z
30
| | Z
sof, +—t
oy Z
Z
g 30h yy Z
$B 2ol| aA
2
& 1Ob)
°
pt ee ta
Frequency in He
Fiaure 1, Measured attenuation provided by E-A-R.

‘The line represents the mean attenuation; the’ shaded
area represents the range.

to the canal. All the subjects who used this plug
found it very comfortable. We have no data on
the expected life of the E-A-R earplug, but one
member of the laboratory staff used a pair for at
least one hour per day for one month, and there
was not much sign of deterioration in the ma-
terial. The plug does change compression prop-
erties when used in high summer temperatures,
so it may be more difficult to insert it effectively
jin environments hotter than 90° F or so; how-
ever, there are no numerical data to support this
contention as yet. The plugs are furnished in a
bright yellow. They soil rapidly, and must
therefore be handled carefully if they are to be

reused.
Wh

COMFIT

g 30
€
§ 20} |
3 ia
2 | y i:
s i
g “t
a
° — 4
| i
i]
3° 0 + ia00 T1888

Frequency in Hz

Ficure 2. Measured attenuation provided by Com-Fit.
‘The line represents the mean attenuation; the shaded
area represents the range.

2. Com-Fit earplugs (Fig. 2) have been tested
often before, both in this laboratory and in
others. In the standard size, they fit most adults.
Other sizes are available. Although most sub-
jects found Com-Fits comfortable, a few who
had slit-like (rather than rounded) canal open-
ings did not. Many subjects, long after their
tests, reported that they continued to use Com-
Fits when they had abandoned their more expen-
sive, custom-fitted plugs. The Figure for the
Com-Fit plug seems to show much more vari-
ability in attenuation than any of the others.
That range represents one aspect of the proce-
dure; it is not a measure of something special
about the earplug. Variability is large because



EAR-PROTECTOR RATINGS

I. Introduction.

Ears differ. They vary in shape, in the diam-
eter and circularity of the external canal, in the
position and sharpness of the canal’s bend, and
in the availability and strength of conchal folds
that might be used to anchor an earplug in place.
Thus, it seems reasonable to assume that a stand-
ard, off-the-shelf, pre-molded earplug ought not
to do as good a protecting job as a personalized,
custom-fitted plug can. It looks as if the custom-
made plug, with its accurately determined con-
tours, should provide a better and more precise
seal within the ear canal, should do so along most
of the length of the inserted segment, and there-
fore ought to offer better attenuation character-
jstics than can be found in a mass-produced
device. Additionally, a custom-molded earplug
ought to be more comfortable and ought to be
easier to insert. This family of assumptions has
a strong appeal for the casual reader’; intuitively,
it all seems correct.

For several years, this laboratory has con-
ducted a program to test various brands of read-
ily available earplugs, including custom-molded,
wearer-molded (such as wax-impregnated fiber),
and pre-molded types. In general, the wearer-
molded plugs are the least expensive, and the
custom-molded are the most. If all the assump-
tions about comfort, acoustic seal, and ease of use
are true, then personalized earplugs would be a
bargain despite their higher cost. The tests re-
ported here indicate that many of the specially
fitted plugs are not a great bargain at all.

In a comprehensive review, Gasaway (1971)
discussed dozens of studies of earplugs, earmuffs,
and similar hearing-protection devices, while in
a more recent paper, Flugrath and Turbeville
(1972) compared five pre-molded and one wearer-
molded plug using a non-standard measuring
technique. Except for a few experimental types,
the various pre-molded insert (earplug) protec-
tors have been reported to perform nearly alike
through much of the tested frequency range.

However, the tested varieties have not commonly
included custom-molded plugs; no nationally
distributed brands have been available until re-
cently. A major purpose of our study was to
make direct comparisons among many sorts of
plugs, with special emphasis on the personalized.

II. Method.

Twenty-one brands of canal-sealing appliances
wert tested. Of these, two brands were each
tested under two conditions. The list includes
most of the commonly used earplugs, except for
the V-51R, which has been tested repeatedly in
many laboratories. Although a “reference ear-
plug” was to be tested on every subject in order
to present a common point of comparison, the
V-51R was not chosen as the reference because
of the care required in selecting the correct size,
and because many wearers report that the plugs
lose their flexibility when skin oils lixiviate or
leach out the material’s plasticizers. Therefore,
the Com-Fit plug was chosen as the reference
because its attenuation characteristics are also
well known (and are similar to the V-51R’s),
because it stays soft, and because it is easy to fit.
The choice was not made from any bias favoring
the Com-Fit’s performance; the decision was
made only to insure that every subject would
provide a common attenuation curve, namely the
one for the reference earplug.

Table 1 lists, alphabetically by manufacturer,
the brand name of each tested appliance, the
manufacturer’s description of the material, and
the type of earplug (pre-formed, wearer-formed,
or custom-formed). Another column offers ad-
ditional information where necessary.

The basic test procedure is the one described
in the American National Standards Institute
(ANSI) method for the measurement of ear
protectors at threshold (Standard 22422-1957).
This standard calls for tests to be done in an
anechoic chamber on randomly selected listeners
with good hearing. The subjects for the tests



COTTON

STAYRITE

; | |
40 Z
9 20 es °
8 s
s : Oy £
s,! i y 5 i
8 20; Ly 2 —_
a 3
: z |
a '0 iF « Fy
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1 a ia
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i ee ee ee a ee ee
gE 77800 715800 7 F968

Frequency in Hz

Ficure 21. Measured attenuation provided by Johnson
& Johnson cotton wool. The line represents the mean
attenuation; the shaded area represents the range.

22, Kleenex tissue (Fig. 22) was tested because
people still use it for earplugs. Subjects who
were tested with it complained of itching and
irritation, This material is available in many
colors.

23. The Stayrite Shell-type Earplug (Fig. 23)
is soft and is pre-molded, but it is designed to
look like a custom-molded plug. It is furnished
in three shapes (listed as small, medium, and
large), all of which were reported as uncomfort-
able by all the subjects who tried them.

KLEENEX
50

Attenuation in 48
—

Frequency in Hz

Ficure 22, Measured attenuation provided by Kleenex.
‘The line represents the mean attenuation; the shaded
area represents the range.

Frequency in He

Measured attenuation provided by Stayrite
Sheil-type Karplug. The line represents the mean
attenuation ; the shaded area represents the range.

IV. Conclusions.

The data clearly show that good earplugs can
be found among all types: a good custom-molded
plug, a good wearer-molded plug, and a good
pre-molded plug may be nearly indistinguishable
in performance. However, the probability of
getting a less-than-good plug is increased if se-
lection is limited to custom-molded models, es-
pecially the ones that are not returned: to the
manufacturer for factory construction, or the
ones that incorporate such gimmicks as per-
forated or light-weight construction.

Problems of economy in earplug selection are
difficult to solve. The least expensive good plug
will not necessarily be the best-accepted one, and
an unworn plug is ultimately too expensive. It
can lead to permanent hearing loss for a worker
and to compensation claims against an employer.
A prospective wearer may select his earplugs on
the basis of looks, comfort, cost (sometimes be-
cause they cost a little, sometimes because they
cost a lot), or availability. He may not under-
stand that speech and emergency signals are
heard more clearly when he is wearing earplugs
(Kryter, 1946), and he may not recognize the
constant importance of protecting his hearing.*
Whatever leads him to his selection, though, if
his choice is a plug that will attenuate noise and
will be worn, it is economical. If that plug is
one of the costly, custom-molded types, the fact




ACKNOWLEDGMENT

This work could not have been completed without the assistance of Walter
E. Morris, Vincent Kidd, Sharon Swift, Debra Hutchinson, and Douglas Polk.





PEACEKEEPER

50,
aot
a.@
$ Y
rLdy
8 % j q
g yyy Ge q
= d We
Evol 4
‘ | | |
og a ee
Frequency in He
Fiavns 16, Measured attenuation provided by Peace-

keeper made according to early instruction manual.
‘The line represents the mean attenuation; the shaded
area represents the range.

tion that the plugs would always be sold with
the fitting service included. A revised manual
was published, and a second series of tests was
performed on plugs made according to the new
instructions (which called for more rapid mixing
of the substance and for a momentary reapplica-
tion of presstire on the earmolds after they had
rested in the canal for a short time). The second

PEACEKEEPER (SECOND RUN)

Z
so | |
y
aor Z
@ 30} q
o ed ;
- Yh
& 20h |
8 Y d
ae i
|_| .
° | | 7
F 7 T60 rr eT
Freeney io He
Ficcre 17. Measured attenuation provided by Peace-

keeper made according to late instruction manual.
The line represents the mean attenuation; the shaded
area represents the range.

10

series (Fig. 17) is almost indistinguishable from
the first, but on careful comparison proves to be
slightly better. Two of the subjects were later
refitted by a manufacturer’s representative with
yet another pair of Peacekeepers; on a retest, one
subject’s performance was similar to that in the
previous two tests; the other subject’s perform-
ance showed greatly improved attenuation. How-
ever, even ten months after our last Peacekeeper
studies (as this paper is being prepared), we
have met a private customer who was sold several
kits without an offer by the manufacturer to fit
them, and without either old or new instructions.
Potentially, this plug may be a good one, but
purchasers apparently must make do with the
printed instructions or must insist on General
Electric’s furnishing personnel to make the plugs.
For a facility with several thousand pairs of
plugs to be fitted, the manufacturer might be
requested to furnish a training course for the
technician who is to make them, but the expense
and time could be unreasonable for a small op-
eration, These plugs are available in a bright
color, and are furnished with small handles that
are color coded to identify which ear the plug
was made for. A hole in each handle permits
the optional use of a cord.

17. For comments on both series of Peace-

keeper tests (Figs. 16 and 17), see paragraph
number 16, above.

SAFEAR
. |
| | ZZ
@ 30 _ .
waY © wy
$2 " =» tty
i ? 7 nal
$ Y Z |
Fa a 4
g Me |
A i
.
Pllilildt
ae
Fievre 18. Measured attenuation provided by SafEar.

The line represents the mean attenuation; the shaded
area represents the range.


that it will be used makes it valuable and worth
the money.

In general, though, custom-molded earplugs
are judged to be less comfortable than others
(wearer-molded plugs are judged to be more
comfortable than others). Custom-molded ear-
plugs, on the average, give less attenuation than.
others, both at the low frequencies reported here
and at high frequencies as well (Bess and Town-
send, 1973). And, of course, the financial outlay
for custom-molded plugs is relatively high.
Most of these specially fitted plugs therefore
have to be considered too expensive for most
users. But where an over-the-counter type would
not be worn because of a user's ear-canal shape,
because of a comfort problem, or because of an
attenuation problem, the custom plug can be a
rational solution.

From our experience, we estimate that adults
with fitting problems constitute at least 5% of

the population and no more than 15%. A useful
hearing-conservation program needs to take those
percentages into account and to make available
at Jeast one kind of personalized device. The
plug might be a custom-molded or a wearer-
molded type; optimally, both ought to be offered
in order to insure that every noise-exposed person
receives the kind of protection that he needs in a
form that he will use.

*People understand and fear hazards to their eyes
because the effects are often sudden and dramatic; the
need for protection is obvious. These same people often
ignore hazards to their ears because the usual nolse-
induced hearing loss is of slow onset, permitting the
gradual deterioration to go unnoticed until the process
is far-advanced. Also, many people, not recognizing that
deafness is much more socially debilitating than blind-
ness, are terrified at the prospect of a loss of vision,
but give little serious thought to the consequences of a
loss of hearing.

REFERENCES

. American Standards Association: American Stand-
ard Method for the Measurement of the Real-Ear
‘Attenuation of Ear Protectors at Threshold. Ameri-
can National Standards Institute, 224.22; 1957.

2. Bess, F. H., and T. H, Townsend: High-Frequency

Attenuation Characteristics of Ear Protectors,

JOURNAL OF THE ACOUSTICAL SOCIETY OF

AMERICA, 53 :328, 1973.

Flugrath, J. M, and J. B. Turbeville, Jr.: ‘The

Effectiveness of Earplugs, SOUND AND VIBRA-

TION, 6: No. 5, 32-33, 1972.

Forrest, M. R.: Ear Protection and Hearing in High-
Intensity Impulsive Noise. In Robinson, D. W.

s

s

13

(Hd.), Occupational Hearing Loss, New York, Aca-
demic Press, 1971.

. Gasaway, D. C.: Personal Ear Protection, Aeromedi-
cal Review, 2-71, USAF School of Aerospace Medi-
eine, Brooks Air Force Base, Texas, 1971.

5, Kryter, K. D.: Effects of Har Protective Devices on
the Intelligibility of Speech in Noise, JOURNAL OF
HE ACOUSTICAL SOCIETY OF AMERICA,
18 :413-417, 1946.

7. Zwislocki, J.: In Search of the Bone-Conduction

Threshold in a Free Sound Field, JOURNAL OF

THE ACOUSTICAL SOCIETY OF AMERICA,

29:795-804, 1957.