4. The Decidamp earplug (Figure 5) is similar outside. Although it feels to have somewhat
to the E-A-R earplug (see paragraph 1) except —_ less body than the E-A-R, subjective reports of
that it is beige with one end surface tinted bright _its characteristics are quite similar. P-AR=322
yellow—presumably, that end is to go toward the

DECIDAMP

50
a
vo
=
z
2
ra
<z
D>
z
Ww
be
kK
 ¢

|

318 6s (26 250 800 1000 2000 4000 ‘e000 "6000
-10 1 n n Ll j } 4 4 4 1
2 8 100 2 5 1000 2 5 10000 2

Frequency in Hz

Ficure 5

16


24. The Hear-Saver earplug (Figure 26) is

made of wax-impregnated cotton that is pre-

IN dB

ATTENUATION

sO

40

30

20

-10

formed into hollow cones.

P-AR=344

37

HEAR-SAVER
i. ¥
L whe +
o
+
+ 4
128 250 500 1000 2000 4000, (000 16000
1 1 4 4 4 4 4 1
2 8 100 8 1000 2 5 10000 2
Frequency in Hz
Ficure 26



of the substance and a momentary reapplication
of pressure on the earmolds after they had rested
in the canal for a'short time). The second series
(Figure 22) is almost indistinguishable from the
first, but point-by-point comparison proves it to
be slightly better. Only the first series was in-
cluded in the computation of earplug mean and
standard deviation. Two subjects were later re-
fitted 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 and the other subject’s
performance showed greatly improved attenua-
tion. Potentially, this plug may be a good one,

but purchasers apparently must either make do
with the printed instructions or insist that the
manufacturer (the plug is now produced by
Marion Health and Safety, Inc.) furnish per-
sonnel to make the plugs. For a facility with
several thousand pairs of plugs to be fitted, a
training course might be requested for the tech-
nician who is to make them, but the expense and
time could be unreasonable for a small operation.
These plugs are available in bright colors 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. P-AR=443

PEACEKEEPER 2ND RUN
50 |
40 +
no]
30 7
z
z + 4
é T
< 4
> T + rT
Gi
EF 1OF NIA» _
F Tt +
& | |
° | +
ars 63 125 250 $00 1000 2000 4000 8000 16000
-10 1 1 L 1 4 4 4 4 4 4
5 100 2 5 1000 2 5 10000 2

Frequency in Hz

Ficure 22



29. The Hearite series B earplug (also known of which is also a soft-plastic bubble but is
as the Stayrite Type B) (Figure 31) is a soft- straight rather than bent. This plug is available
plastic bubble that fits fairly well compared to in three sizes, and the handle is perforated for
the other two plugs from the same company, one stringing. P-AR=234

HEARITE SERIES B

a
uv
z=
z
°
BK
.4
2
2
W
kK
Ll ~ +
< -
|
ok - 4
1 318 63 125 280 500 1000 2000 4000 8000 16000
=10 eda. + L in =_e 4 i i L
2 5 100 2 5 1000 2 5 10000 2

Frequency in Hz

Fievre 31

42


TABLE 3. Ratings for Earplugs in Order of Attenuation

Two Standard Deviations Below the Mean

Figure Mean Mean-c Mean-20
Number Earplug Attenuation Attenuation Attenuation P-AR

1 E-A-R 31.5 24,1 16.5 111i

2 Softseal 27.4 21.8 15.7 2 1 1

3 Sound Silencer wet 25.3 19.4 12.5 3 2 2

4 Sound Silencer dry 23.7 17.1 10.3 3 2 2

5 Decidamp 25.0 16.7 8.4 3 2 2

6 Bilsom 18.4 13.5 8.4 4 3 2

7 Sonic Ear-Valv 26.6 17.5 8.3 2 2 2

8 V-51R 28.7 18.6 8.2 2 2 3

9 Flexiplug 26.3 17.3 8.1 2 2 3
10 Sound-Ban 20 22.9 15.4 7.6 3 3 3
11 Insta-Mold 21.9 14.7 7.2 3 3 3
12 Dr. Frank 22.8 15.0 7.1 3.3 3
13 Healthways 22.1 14.1 6.0 3 3 3
14 E.A.R. 23.6 14.8 5.9 3 3 3
15 Sound Sentry 22.2 14.0 5.7 3 3 3
16 Frontier 21.3 13.1 4.9 3 3 3
17 Oto-Cure 15.4 10.0 4.4 4 4 3
18 Silaflex 23.6 13.8 4.0 3.3 3
19 Accu-fit 25.5 14.9 3.9 3 3 3
20 3M 24.1 14.0 3.7 3.3 3
21 Peacekeeper 15.0 9.5 3.4 4 & 3
22 Peacekeeper 2nd 15.2 9.6 3.6 4 4 3
23 SafEar 16.2 9.9 3.5 4 4 3
24 Com-Fit 21.9 12.7 3.2 3.3 #3
25 Genie 20.3 11.8 3.0 3 3 3
26 Hear-Saver 20.3 11.2 2.0 3 4 4
27 Flents 20.0 11.0 1.8 4 4 4
28 SEPCO 19.7 10.4 1.0 4 4 4
29 Nods 21.1 10.9 0.7 3 4 4
30 Soundown 14.7 7.7 0.6 5 4 4
31 Hearite B 25.8 13.2 0.3 2°93 4
32 Silent Partner 24.7 12.5 -0.1 3 93 = 4
33 Sonotone 20.4 10.3. -0.1 3 4 4
34 Auri-Seal 26.1 13.0 -0.2 2 3 = 4
35 Sound-Ban 10 20.0 9.9 -0.3 4 4°54
36 Hearite A 17.4 8.6 -0.4 4 4 4
37 Johnson & Johnson 7.3 3.4 -0.7 6 5 4
38 Sound Master 15.4 7.3 -0.8 4 4 4
39 Mark IT 19.6 9.0 1.4 4 4 4
40 SMR 22.8 10.5 -1.9 3.4 4

(continued)

10


39. Soft (they are also available in a hard difficult to work with than is that furnished for
material) Adcomold earplugs (Figure 41) are many others of the molded-in-place. type.
custom fitted and do not require factory construc- P-AR=554
tion. The Adcomold material is slightly more

ADCOMOLD

50

a
° +
z +
z
° +
a
<z
p=) > +
> +
W
be —_=-
bt
a g
250 800 1000 2000 4000, 9000 000,
4 4 4 4 4 1
2 8 1000 2 8 10000 2

Frequency in Hz

Ficure 41

52


37. The Mark II (Figure 39) is hand formed
Irregularly placed bubbles in the
silicone material seem to have no continuity with
each other and therefore probably do not permit

by the user.

ATTENUATION IN dB

leakage. The plug is advertised to “last. indefi-
nitely.” It is generally considered comfortable
despite the waxy touch that some subjects dislike.
P-AR=444

MARK IL
+
a a
a 4 4
cy 1000 2 8 10000 2
Frequency in Hz
Figure 39

50


48, Fitsrite Audiophone De Luxe Ear Drum jects nearly always found them uncomfortable,
Protectors (Figure 45) were designed for swim- primarily because of the cylinder. The earplug
mers. They are pink silicone formed around a —_ was sometimes difficult to remove. It is available
metal cylinder that is sealed on one end. Sub- under several trade names, P-AR=345

FITSRITE

@
3
z
2
2
FE
<z
5 L +
2 +
uJ
be
| od
<
2000 4000 8000 6000
4 4 4 4 4
000 z 3" "16600 2

Frequency in Hz

Fievure 45

56




35. Johnson & Johnson cotton wool (Figure erably more effective an attenuator than dry, it
37) was tested because people still use it for ear- is not commonly used, and anyway, wet plugs
plugs. Domestic airlines in some countries even can be expected to dry out eventually. Tests
furnish cotton wads to their passengers for that were run with dry cotton to simulate actual-use
purpose. Although wet cotton would be consid- conditions. P-AR=654

JOHNSON & JOHNSON

50

IN dB

ATTENUATION

4
2 8 100 2 5 1000 t 3 10 600 2
Frequency in Hz

Ficvre 37


8. The Flexiplug (Figure 9) is a soft silicone inserting them, and a few people who had slit-
plug with flanges of graduated diameter, de- like (rather than rounded) canal openings found
signed to fit a large portion of the population them extremely uncomfortable. The plugs are
with only one size. As with most flanged ear- orange and can be bought strung on a cord.
plugs tested, some subjects reported difficulty in P-AR=993

FLEXIPLUG
a > > er
aod
2
2 > +
6 + +
K
<x
D>
> + + 4
WW
KE
=
° | |
| |
us Lh) 128 250 500 1000 2000 4000, 8000 16000
=10 1 1 1 1 i n i fi n 1
2 8 100 2 3 1000 2 5 10000 2

Frequency in Hz

Figure 9


25. Flents (Figure 27) are made of wax- (see paragraph 15) except that more material is
impregnated cotton fiber that is hand formed by furnished. P-AR=444
the user. They are similar to the Frontier plugs

FLENTS

IN dB

ATTENUATION

-10

8 63 12s 230 500 1000 2000 4000 800C 16000
4
4

4 n
2 8 100 2 5 1000 2

Frequency in Hz

Ficune 27

38


EARPLUG RANKINGS BASED ON THE PROTECTOR-ATTENUATION
RATING (P-AR)

I. Introduction.

When a laboratory measures the effectiveness
of a hearing protector, it reports the mean at-
tenuation (and its standard deviation) at each
octave or third-octave frequency. These numbers
allow comparisons between devices at each fre-
quency, but they do not help with the direct
determination of the relative overall effectiveness
of two protectors.

The Department of Labor’s Occupational
Safety and Health Administration (OSHA)
Standards Advisory Committee on Noise’ recom-
mended three methods for calculating single-
number noise-reduction factors. These figures of
merit permit direct comparisons of earplugs or
earmuffs, All three procedures lead to estimates
of the A-weighted sound pressure level (SPL)
under each protector in the presence of a specific
noise. The best estimate is the one calculated
from the specific noise in which the device is to
be used, but simplifications and approximations
are offered too. A problem necessarily arises,
though, even when one knows the spectrum of
the noise in which a worker is expected to use
hearing protection: if he moves from one area to
another, the spectrum will likely shift and the
exactly calculated level at his eardrum will
change. Only rarely will an environment re-
main constant enough for the exact-calculation
procedure to work completely. However, the
OSHA. approaches are useful despite this imper-
fection, and they are instructive to the developer
of more refined measuring and reporting tech-
niques. They include two important ideas: first,
they recognize that the protection offered by a
wearable attenuator must be a function of the
noise spectrum in which it is used; and second,
they note that reporting the mean attenuation
of a device indicates only how much protection
is offered to the average-or-better user—but re-
porting the mean-minus-two-standard-deviations
indicates very nearly the least expected amount

of protection, a critically important piece of in-
formation to a purchaser who must consider the
compensation costs of underprotection.

Other approaches were developed from these
concepts. One train of thought suggested that
a general purpose noise-reduction number would
be the average attenuation a given device pro-
duced in a large number of industrial noise en-
vironments. The computational task would be
huge, of course, were one to use available com-
pilations of hundreds of spectra. Average at-
tenuation values for an earplug in 600 noises or
even in 100 would require a lot of arithmetic,
and J. H. Botsford? saw a way to simplify the
problem. He abstracted from large samples of
spectra a set of six that, although not “real” in
the sense that they belong to some particular
industry, represent the gamut of spectral types.
For an ear protector under test, the Botsford
method calculates an A-weighted noise-reaching-
the-ear for each of the six noises, subtracts that
number from the C-weighted level of that noise,
and then averages all six of the C-minus-A
figures to produce a single reduction factor de-
scribing that device.

Johnson and Nixon® tested Botsford’s method
against the OSHA reduction figure and also
against a far more complex method of their own
that involves 150 spectral calculations. The
surprising outcome is that Botsford’s value for a
given ear protector produces all the necessary
information available from the more complicated
procedures, and further that a simple 6-dB cor-
rection produces a figure of merit that represents
the minimum effectiveness of the tested device
in 99 percent of the 150 noises, Six calculations
can take the place of 150.

D. L. Johnson and I* further simplified the
process. We derived a single spectrum (see
Table 1) that serves the same function as Bots-
ford’s six; we called it The Typical Noise
(ITN). Calculating ear-protector effectiveness



19. The 3M earplug (Figure 20) is a soft,
white, synthetic-rubber device that is advertised
as disposable. Although it looks like many of
the other flanged plugs, its flimsiness in use does
require that it be replaced after a few days’
wear; its relatively low cost encourages such
replacement. Manufacturer’s instructions sug-
gest that users who find the plug uncomfortable
or insecure can remove one or more discs from

3M

the tip. Two of our subjects did so; their re-
sults are not distinguishable from those of sub-
jects who left the plugs whole. All subjects who
used this plug found it comfortable. This ear-
plug was tested after most other data had been
collected. It was not included in the computa-
tion of earplug mean and standard deviation;
its P-AR is derived from the distribution of the
other earplugs. P-AR=333

50

+
°

IN dB
o
°

z
iS 20
kK
xq
==)
z - -
ty 10 = iz
k
=
< fe)
us 63 125 250 500 1000, 2000 4000 000 16000
10, 7 00 z 3 To00 2 nar 16600 3

Frequency in Hz

Ficone 20

3L



5. The Bilsom earplug (Figure 6) is also
lmown as the Billesholm and as Swedish Wool.
The material is fiberglass that is hand formed
and is advertised to be effective “in 80% of all
noise situations.” It is meant to be thrown away

IN dB

ATTENUATION

40

30

20

-10

after one wearing, but it can be reused several
times if necessary. It is generally considered
comfortable, and no subject who used it com-
plained of any itching that might have been
caused by fiberglass. P-AR=432

17

BILSOM
H _—
* Ss °° “s 250 $00, 1000 2000 (6000 000
1 4 4 | | 4
2 8 700 3 tooo 2 3" ~10600 2
Frequency in Hz
Figure 6



Ji, Although the Dr. Frank earplug (Figure
12) is sold in sporting goods stores as much for
use in swimming as for hearing protection, when
properly fitted, it is a fairly effective sound at-

manufacturer’s simple instructions, if read, are
adequate to solve that problem. Earplugs were
sometimes hard to remove. The same plugs are
available under the name Voit; they may be

tenuator. It is made in many sizes, and fit is distributed under other names as well.
critical. Subjects had difficulty determining P-AR=333
which end should go into the ear canal, but the
DR FRANK
50 |
40}
a
7 3s0f = +,
z
z J +
2 20 [
b&b aa >
<z
=) > —
Fit +
a 10
=
<
°
as 63 128 250 500 1000, 2000 4000 €000 16000
-10 1 L nN 1 hi n ni n 4
2 5 100 2 5 1000 2 8 10000 2

Frequency in Hz

Figure 12



7. The V-51R (Figure 8), a plastic earplug
developed for use during World War II, remains
a good and versatile device. A few problems do
arise for its user, though. Foremost among these
is the need for accurate fitting: the plug is avail-
able in five sizes (although most buyers stock
only two or three), and many ear canals seem to
fall between sizes. Further, day-to-day varia-
tions in canal dimensions may require selection
of different sizes at different times for the main-
tenance of both attenuation and comfort. The
plug’s asymmetry also contributes to problems
of accurate fitting. Although usually soft and
pliable when first worn, the V-51R loses some of

its plasticizer within a few weeks. Wearers then
complain of discomfort from the “stiffness” or
“prittleness.” Despite these problems, it is still
a popular and effective earplug. Several manu-
facturers produce it. My stock includes V-51Rs
distributed by American Optical Corporation, by
Mine Safety Appliances Company, and by United
States Safety Service Company. It may be
available from others as well. The current data
were collected on plugs bought from Mine Safety
Appliances. The V-51R was not included in the
computation of earplug mean and standard
deviation. P-AR=223

V-5SIR
50
40 -— =
a
ao]
z
z
©
= +
<z
=)
z
a i +
F 10 “<= so
= +
<
fo)
318 63 125 250 500 2000 4000 000 6000
-10 Lb 4 Ll | in hi 1 h 1
2 8 100 2 8 1000 2 8 10000 2

Frequency in Hz

Figure 8

19



20. The Peacekeeper (Figures 21 and 22) is a
custom-made earplug that does not require fac-
tory construction. The silicone mold cures to
become the final earplug. The material for both
ears is mixed simultaneously. The molding kits
were obtained through normal procurement pro-
cedures—ours came from the former manufac-
turer, General Electric. We made the plugs
strictly according to the accompanying instruc-
tions, aged them for a time, and tested them.
The kits include a dip that helps to seal the
surface of the plugs and to smooth out irregu-
larities, thus increasing the size slightly. Plugs
can be redipped to improve the fit, although the
need for such improvement would not be ob-

PEACEKEEPER

vious without a laboratory test of effectiveness;
such tests are not likely to be performed in field
use of the devices because of lack of time, money,
and facilities. In these studies, the dip was used
precisely according to the instructions. Tests
showed less attenuation (Figure 21) than some
of the manufacturer’s reports showed, and Gen-
eral Electric requested that we test plugs made
by their representative. I asked instead for
better instruction manuals or an indication that
the plugs would always be sold with the fitting
service included. After the company published
a revised manual, we performed a second series
of tests on plugs made according to the new
instructions (which called for more rapid mixing

7

40

Ww

30 -

20 -

ATTENUATION IN dB

$00 1000

Frequency in Hz

3

Ficure 21

32

1000



3. The Sound Silencer earplug (Figures 3 and
4) in the standard size fits most adults. Other
sizes are available. The plug feels like a rubber
bubble between the fingers. This structural
characteristic made it very comfortable for all
subjects who used it, but also made it somewhat
difficult, for about half of them to insert prop-
erly. 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 because of cleanliness and

SOUND SILENCER

because of the flavor of ceruminous residues.
Therefore, tests were run on this earplug both
dry and lubricated with water (only the lubri-
cated test was included in the computation of
earplug mean and standard deviation). As
might have been predicted, the lubricated (and
therefore better seated) plug produced somewhat
better attenuation scores. However, P-ARs were
the same. A dark-green plug, a black plug, and
a flesh-colored plug are available, as is a version
that is strung on a cord. P-AR=822

WET

ATTENUATION IN dB

300
4

1000 2000

i 4
5 1000 5 10000 2

Frequency in Hz

Ficure 3

14


45. Crown earplugs (Figure 47) are aqua-
colored plastic plugs designed for swimmers and
available in dime stores. The central core is
extremely stiff and led to complaints of discom-

fort and irritation by most subjects. The ear-
plug was sometimes difficult to remove. P-AR=
555

CROWN
50 |
40h
a
a @ i
z
&
= 207 + —-—
<x + v7
2]
2
ry)
FIP —
= + T +
aq
o | — T
3s 63 125 250 $00, 1000 2000 4000, e000 000
-10 1. 1 1 1 4 4 4 n 4 1
2 3 700 z 3 1000 2 3" "16600 2
Frequency in Hz
Fieure 47
V. Conclusions, necessarily be the best-accepted one, and an un-

Good earplugs can be found among all types:
a good custom-molded plug, a good wearer-
molded plug, and a good premolded plug may
be nearly indistinguishable in performance.
Purchasers need to remember though that the
people who will wear the earplugs may decide
to use them or not on the basis of issues that do
not become apparent from a study of P-AR
values. The least expensive good plug will not

58

worn 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. A worker who balks
at using hearing protection may need counseling
on the fact that speech and emergency signals


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17. Silaflex (Figure 18) is a wearer-molded ease of use. The putty-like material is flesh
silicone plug. Users include both strong pro- colored. P-AR=333
ponents and strong opponents of its comfort and

SILAFLEX
50
| TT
40+ =
o
> 30
2 | 7 in on —_
o
 20f rT
<
BS)
> 4
rm
bE 1OF
f+
° | -
31s 63 128 250 500 1000 2000 4000 8000 46000,
-10 aL. _L L 1 1 4 1 1 1 1
2 8 100 2 5 1000 2 5 10000 2

Frequency in Hz

Ficure 18

29



14. The Sound Sentry (5000B) hearing pro-
tector (Figure 15) is another earcap on a head-
band, and not an insert earplug. Attenuation
results from covering the opening to the canal
with a neoprene cap. The cap is difficult to

SOUND SENTRY

position accurately for the initial wearing, but
once adjusted, it is easy to put back on. No
subjects complained of the headband, but several
found the caps themselves to be uncomfortable.
P-AR=333

50 |

+

o +

mo]

= ~

2 T T

° | +

@ tL

>

Zz + +

Ww

i —

bE +

<

, | |
31s 63 126 250 500 1000 2000 4000, (e000 16000
-10 1 L 1 L 4 4 i n 4 1
2 8 100 2 5 1000 2 8 10000 2

Frequency in Hz

Figure 15


to be optimally helpful, it needs to include num-
bers representing those two additional kinds of
ratings.

As used in this paper, P-AR values are three-
digit numbers. The first represents the earplug’s
rating (1, 2, 3, 4, 5, or 6) for an average member
of the population of users—it is calculated from
mean attenuations as described earlier. The
second digit represents the rating for a hypo-
thetical user whose benefit from that plug is
somewhat less—he is one standard deviation be-
low the mean and is compared to similar —1¢
people in the attenuation distributions of the
other earplugs. The third digit represents the
rating for a user who is two standard deviations
below the mean. One way to interpret the P-AR
values is to consider the first digit as indicating
the worst predicted performance of the plug for
50 percent of the population of wearers, the
second as indicating the worst predicted per-
formance for 84 percent, and the third for 98
percent. Quite likely either the second or the
third digit will ultimately be dropped as con-
tributing too little additional information, but I
am not ready yet to decide whether it should be
done, and, if so, which one should go.

Remember that the classifications used for the
plugs reported in this paper are not based on a
nationally accepted baseline. Only earplugs and
earcaps (not earmuffs) are included in the dis-
tribution, so the calculated means and standard
deviations for plugs might turn out to be derived
from an inadequate population of hearing-
protection devices. In a few cases, the plugs in-
cluded here have been superseded by new models
whose attenuation characteristics may be dif-
ferent. The test procedures and methods were
developed for purposes that may be different
from those that will lead to a generally used
distribution. However, the earplug means and
standard deviations at the user mean, at the
mean-minus-one-standard -deviation, and at the
mean-minus-two-standard-deviations as reported
here can serve as a start in the rating of ear-
plugs, at least. Also, devices whose attenuation
characteristics were not included in the baseline
calculations can be classed according to where
they fit into the original rating scheme,
just. as they would be in the situation where
baseline measurements were made by a group
like the. National Bureau of Standards. This

paper includes five extra inclusions of that sort:
one is an earplug (the 3M) that appeared on the
market too late to be part of the distribution,
one is a classic earplug (the V-51R) that was
inadvertently left out of the calculation, two
were second tests of earplugs whose first tests are
included in the distribution (the Sound Silencer
and the Peacekeeper), and one is an insert head-
set (the Genie). They are all noted in the
Results and Discussion section. Were they to be
incorporated into a new distribution, the effect
would be small: three earplugs rated near the
top and two rated near the bottom would shift
to a poorer rating in one of the three digits.

Il, Earplugs.

Earplugs and earcaps are devices that are in-
serted in or pressed against the external ear
canal to reduce the effect of ambient sound on
the auditory system. Because every ear is unique
in shape and size, several approaches to solving
the problem of designing adequate earplugs have
been taken. As a result, commercially available
earplugs may be premolded, moldable, or custom
molded. Each type has several subtypes. Pre-
molded plugs include varieties that are vented
and varieties that press a cap across the open
end of the canal as well as plugs that insert
more or less deeply to block the canal opening
completely. Moldable plugs include impregnated
and non-impregnated porous materials, expand-
able foams, and putty-like substances. Custom-
molded earplugs include those that are made by
the manufacturer from an ear impression and
those in which the ear impression itself becomes
the earplug. Since every ear is unique in shape
and size, one might assume that a standard, off-
the-shelf earplug would not protect as well as
a personalized or custom-fitted earplug. Intui-
tion says that a custom-fitted plug should provide
a better, more precise seal within the ear canal,
should do so through most of the length of the
inserted segment, and should be more comfort-
able and easier to insert. Although they are
generally the most expensive, 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
reported here, though, indicate that many of the
specially fitted plugs are not great bargains at
all.



TABLE 1,

Corrected Spectral Levels for The Typical Noise (TTN)

octave-band
center frequency 63 125 250
in Hz

79 84

A-weighted level
in 4B m

500 1000 2000 4000 8000

89 93 93 92 87

Uncorrected overall level = 99 dBC

with TTN gives a value that includes a 3-dB
correction; the result is the amount of protection
each device offers against 99 percent of noises.
OSHA’s recommendation requires a correction
of 18 dB, Botsford’s requires 6, and. Johnson and
Nixon’s requires 4.

Finally, working with TTN-calculated reduc-
tions, I considered the possibility of reporting
hearing-protector effectiveness in simpler terms
than the usual decibel numbers. Many potential
users of protectors (and of protector ratings)
are only peripherally acquainted with the pe-
culiarities of decibel notation. Not only might
they have trouble interpreting the meaning of
reported reduction factors, but they could easily
be led to emphasize the generally meaningless
fractional-decibel differences between devices
that really perform similarly. I felt that a
classification number would be preferable to an
attenuation value, so I computed mean attenua-
tions in TT'N for each of 42 types of earplugs,
found the standard deviation of that series of
attenuations, and classified the plugs by where
they fell in the series: Class 1 includes any ear-
plug whose mean attenuation is two or more
standard deviations (c) above the mean attenua-
tion of all the earplugs; Class 2 includes the ear-
plugs whose mean attenuation is one or more o
above the mean (but less than two); Class 3
includes those at the mean or higher (but less
than one «) ; Class 4 includes those from —1¢ up
to the mean; Class 5, those from —2¢ up to
—1o; and Class 6, those below —2c. All a per-
son needs to do to use this classification scheme
is to remember that first Class is better than
sixth,

This protector-attenuation rating (P-AR) of-
fers a simple way to rank hearing protectors.
Of course, if it is generally adopted, a basic

distribution of hearing-protector attenuations
needs to be developed and retained as the base-
line for judging all future protectors. Other-
wise, the P-AR values would have to be modified
every time a new device came onto the market.
I have suggested the National Bureau of Stand-
ards as the proper agency to gather and main-
tain this distribution of ratings. Once that has
been done, any new earplug or earmuff can be
classified according to its position in the pre-
viously determined distribution. Only one pre-
caution must be taken: high-Class hearing
protectors must be capable of protecting hearing
so that a prospective buyer can feel confident
that what he gets will work. Ultimately, one
might expect that most available ear protectors
would fall into Classes 1, 2, and 3.

Neat as this classification system is, as thus far
described it is inadequate. Remember OSHA’s
point that reporting only the average’ effective-
ness of a device may mislead as often as it in-
forms. Different kinds of users need different
kinds of information in order to make informed
purchasing decisions. An individual buyer gets
his best estimate of how a particular earplug
will work for him by studying the mean per-
formance, whereas a bulk buyer has greater con-
cern for the attenuation he can expect the plug
to give to the employee who uses it least well.
The bulk purchaser’s best information might be
found not in the mean effectiveness, but in a
mean-minus-one-standard-deviation or even a
mean-minus-two-standard-deviations _classifica-
tion.* Under the circumstances, for the P-AR

* Note that the standard deviations talked about here
are measures of the variability of a given device in a
population of wearers. The standard deviations used
to create the six Classes of protectors are measures of
the differences between protectors.


SOUND SILENCER

10000

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500
n
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t T

Ros

50
40

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Frequency in Hz

Ficure 4

15



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9. The Sound-Ban 20 (Figure 10) is an earcap
with a plastic-tubing headband (another version
of this cap is discussed in paragraph 33). The
earpiece is soft-textured, air-filled, blue vinyl.
Attenuation is the result of covering the opening
to the canal rather than inserting something into
the canal itself. Although it is necessary to po-

SOUND-BAN MODEL

sition the cap with the proper front-rear orien-
tation, subjects had no difficulty with the task.
The Sound-Ban 20 may be worn with the head-
band under the chin or behind the neck. Head-
set users sometimes complain about headband
discomfort, but no subject. complained about this

one. P-AR=333

20

50

IN dB

ATTENUATION

315 63 28 250 800 1000 2000, 4000
-190 LL 1 1 1 4 n 4 _
2 5 100 2 8 1000 2 10000 2
Frequency in Hz
Figure 10

21



Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM~75~ i /
‘4. Title ond Subtitle 5. Report Date

EARPLUG RANKINGS BASED ON THE PROTECTOR-ATTENUATION [@- Performing Organization Code
RAT ING : (P-AR)

8. Performing Organization Report No.

7. Author(s)
Jerry V. Tobias, Ph.D.

10. Work Unit No. (TRAIS)

>

Performing Orgonization Name and Address
FAA Civil Aeromedical Institute
P.O. Box 25082 Ti. Contract or Grant No.
Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address

Office of Aviation Medicine OAM Re
Federal Aviation Administration ast Report
800 Independence Avenue, S.W, 14. “Sponsoring Agency Code

Washington, D.C. 20591
15. Supplementary Notes

This reséarch was conducted under Tasks AM-B-74-PSY-51 and AM-D-75-PSY-55.

16. Abstract

Forty-five attenuation spectra for earplugs were classified according to a
simplified method designed to produce single-number ratings of noise reduction.
The rating procedure was applied to the mean attenuation scores, to mean-minus-~
one-standard-deviation scores, and to mean-minus-two-standard-deviations scores.
The reporting of all three numbers seems to give the fairest indication of an
earplug's value in controlling hearing damage in noise-exposed populations.

The tests are described and ranked, This report supersedes "Ear-Protector
Ratings" by J. V. Tobias and F, M. Irons, FAA Office of Aviation Medicine

Report FAA-AM-73-20 (1973).

18, Distribution Stotement

17. Key Words
Earplugs Document is available to the public through
Hearing the National Technical Information Service,

Springfield, Virginia 22151

Hearing Conservation
Hearing-Protector Measurement

19. Security Classif, (of this report) BH. Security Clossif. (of this page) BI. No, of Pages | 22. Price
3.00 PC
Unclassified Unclassified i °95 MP

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized



31. Sonotone earplugs (Figure 33) are soft,
factory made, and custom fitted. They are
rather like the E.A.R. plugs (see paragraph 13),

is a bit longer. P-AR=344

except that the segment that fits into the canal

SONOTONE
50/- | ~ —
4o- +t
o +
7 30h
z I —
4 +
&
ra 20+ -) ——— ae oe
< \
D
a
b 1OF - —
= + + i
< T + :
i
i
0 -fo — fe = 1
| | | :
; oats 6 125 250 500 1000 2000 4000 2000 ‘e000 |
-10 = Ley ke 1 1 a 4 4 4 | L
2 3 700 z 5 Tooo 2 3" "10600 2

Frequency in Hz

Ficure 33


In a comprehensive review in 1971, Gasaway*
discussed dozens of studies of earplugs, earmuffs,
and similar hearing-protection devices. In a
more recent paper, Botsford’ offered a thorough
description of the characteristics and uses of ear
protectors. The detailed writing in those two
reports is readily available to the interested
reader, so I will not repeat it here. Further,
Willson and Sims* published a fairly good ear-
protection bibliography. However, except for an
inadequate, single-subject test conducted by Con-
sumers Union’, and a previous report from this
Laboratory” on a preliminary approach to rat-
ing earplugs, only each manufacturer’s own test
results have been available to the public. Now
the results of a large series of tests can be pre-
sented.

Til. Method.

Forty-five brands of canal-sealing appliances
were tested. Of these, two brands were each
tested under two conditions. The list includes
many of the commonly used earplugs.

Table 2 is an alphabetical list of the brand
names of the tested appliances. For each one,
the manufacturer’s description of the material
is noted, as is the type of earplug (premolded,
moldable, or custom molded). Another column
offers additional 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.+ This standard calls
for tests to be done in an anechoic chamber on
randomly selected listeners with good hearing.
The subjects for the tests were randomly selected
from a large pool of university students. As
required, each plug was tested on at least 10
listeners with at least three tests per plug per-
formed 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 measure-
ment 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.
Ambient noise was well within acceptable limits.

Two liberties were taken with the standard
procedure, First, continuous-frequency (rather

than discrete-frequency) open-ear threshold tests
and earplug attenuation tests were used. A
Grason-Stadler model E-800 automatic audiom-
eter served both as signal source and as response
recorder. The audiometer’s signal was led to a
loudspeaker in the anechoic chamber through a
power amplifier; both the motor-driven atten-
uator and the motor-driven oscillator were re-
tained in the circuit in order to produce,
automatically, continuous-frequency graphs of
each subject’s threshold. Thresholds were al-
lowed to stabilize before the oscillator motor was
engaged. The technique is identical to that used
in Békésy audiometry.

The other liberty was a philosophical one.
Most laboratories, in testing particular brands
of earplugs, commonly strive for optimum test
conditions. Thus, if a manufacturer’s represen-
tative can be at the test site to ensure proper use
of his company’s device, his services are accepted
and welcomed. As a result, those tests give a
reasonably good estimate of the performance
that the plugs are capable of when they have
been optimally fitted.1? However, tests in this
laboratory were designed to test the effectiveness
of plugs that were fitted by an expert of the sort
available to most industrial plants or government
installations: fittings were made by carefully
following any instructions furnished with the
delivered materials. Had a manufacturer’s pub-
lished instructions indicated the need for a
factory-trained fitter for his earplugs, we would
have gotten one; no manufacturer printed that.
kind of instruction. Several manufacturers
guarantee replacement of unsatisfactory earplugs
(including those that might be unsatisfactory on
the basis of their attenuation characteristics)
and, indeed, in some instances our laboratory
tests suggested that such replacement was desir-
able. However, when we asked our subjects if
they were satisfied with the performance of such
earplugs, they always said that they were—
perhaps on the basis of comfort. So it is reason-
able to believe that a purchaser who does not
have appropriate laboratory facilities will judge
the efficacy of any particular device strictly by
his perception that it is or is not doing something
that he wants it to do. If it feels good, he will
not send it back for a plug that attenuates more.

As a result, some of the tests reported here
may show smaller values of mean attenuation or
larger standard deviations than will tests re-


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44. The Hearite series C (also known as the
Stayrite Type C) earplug (Figure 46) looks
something like the classic V-51R earplug al-
though the relation of length to diameter is
different. Many subjects complained of discom-

HEARITE SERIES C

fort with this earplug, especially when its flange
irritated the ear canal upon removal. The poor
attenuation reported may very well be a result
of the relatively short length of this plug.
P-AR=555

i
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Frequency in Hz

Figure 46

57



27. Nods (Figure 29) are made of wax-filled many days before they begin to lose their effec-
foam and are manipulated by the wearer until tiveness. It is not necessary to touch the waxed
they seal the canals. They are comfortable in end with the fingers in order to use these plugs.
the ear. I have no data on the expected life of | They soil easily. P-AR=344
Nods, but would expect them to be reusable for

NODS
50 |
40
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30-
z r Y
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Frequency in Hz

Fieure 29


16. Oto-Cure Custom Ear Protectors (Figure quires the use of volatile chemicals whose fumes
17) are custom molded and do not require fac- were strongly disagreeable to the people who
tory construction: the mold cures to become the had to work with them. The material is difficult
final earplug. For Oto-Cure, the process re- to handle properly. P-AR=443

OTO- CURE
50
| |

40F =
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Frequency in Hz

Fioure 17


32. The Auri-Seal (Figure 34) is made by the for most. subjects tested, the canal piece seemed
same company as the more popular Com-Fit, — too short and the plug felt as if it were slipping
but it has a large flange to rest in the pinna of out. ‘It is extremely easy to handle. P-AR=234
the ear. When it fits, it is very good. However,

AURI-SEAL

40}

30 fF

.
© iemmr
a | { [ t

-

ATTENUATION IN dB

318 es 128. 250 800; 100. 2000" 4900 ‘e000. 6000

-I L 1 n 1 4
° 2 5 100. 2 5 1000:

n L
s 10000 2

at

Frequency in Hz

Figure 34

45



15. The Frontier earplug (Figure 16) is made that the wax felt funny in their fingers. The
of wax-impregnated cotton fiber that is hand expected life of such plugs is, at most, a few
formed by the user. Some subjects complained —_ wearings. P-AR=333

FRONTIER
50 |
4o-
+
S
30 F =
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5 4
=)
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w 10} 4 ——
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aq
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2 5 100 2 s 1000 2 8 10000 2

Frequency in Hz

Fieure 16

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6. The Sonic Ear-Valv (Figure 7) is a rede-
signed version of the old Lee Sonic Ear-Valv
(see paragraph 42), The new model has a much
longer, flanged neck for insertion into the canal.
In both models, the soft plastic material is fitted
around a metal piston inside which a valve is
supposed to work to shut off incoming sound
when the intensity is high enough. At all other

SONIC EAR-VALV

times, according to the advertising, the earplug
is totally open down a long central perforation.
The new version with the long canal piece has
been sold with various pistons. The one tested
here is not now on the market; its piston seemed
to be in the closed position all the time, thus
accounting for the very good performance.
P-AR=222

50
40 }
@ L i + + {TM
30 F
z
z rT
fo} +
rE 20H +
=z +
=) -
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WwW
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e
<
|
318 Ld 26 280 600 1000 2000 4000 e000 16000,
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“2 5 100 2 8 1000 2 8 10000 z

Frequency in Hz

Ficoure 7

18


42, The Lee Sonic Ear-Valv (Figure 44) is ways open, and the attenuation is thus constantly
the earliest version of the Sonic Ear-Valv (see adversely affected (see paragraph 21). P-AR=
paragraph 6). Because the short ear-canal piece 445
js filled by a metal tube, the perforation is al-

LEE SONIC EAR-VALV

IN dB

ATTENUATION

Frequency in Hz

Fieure 44

55



attenuated to 85 db... .” This plug may pos-
sibly be useful in situations in which the primary
exposure is to high-level impulse noise.
P-AR=443

22. Com-Fit earplugs (Figure 24) have been
tested often before, both in this laboratory and
in others. In the standard size, they fit most
adults. Other sizes are available. As with all

COM-FIT

the flanged earplugs we tested, many subjects
found them fairly comfortable, but subjects with
Jess-than-round canal openings sometimes com-
plained. Military use of these earplugs has led
to their being manufactured by companies other
than Sigma Engineering, and some of these
alternate firms use stiffer, less satisfactory ma-
terials than one finds with plugs bought directly
from Sigma. P-AR=333

S50

4oF

20 -

ATTENUATION IN dB

Frequency

in Hz

Ficure 24



28, The Genie headset (Figure 25) is not,
properly speaking, an earplug at all. It was
designed for aviation-communication use and in-
cidentally for keeping noise out of the user’s
ears, The Genie is included here to illustrate
how the hearing protection offered by devices
other than earplugs and earmuffs can be classi-
fied with P-AR values. This insert headset uses

the perforated, flanged silicone tip of the old
Lee Sonic Ear-Valv (see paragraph 42) for
coupling to the wearer’s external ear. Unlike
the Lee Sonic, though, the Genie backs the tip
with solid material, thus making it into an effec-
tive acoustic barrier. This headset was not in-
cluded in the computation of earplug mean and
standard deviation. P-AR=333

GENIE
50
+
o +
o ~
z r ~
z +
° +
= - +
<
2
z
Ww >
Fr 10 =
EF +
a +
i)
318 63 125 250 500 1000 2000 4000 ‘000 Wooo
-10 1 n _L 1 1 n i 4 4 n
2 5 100 2 ry 1000 2 8 10000 2

Frequency in Hz

Fieure 25


38. The SMR (Surgical Mechanical Research) found it comfortable. However, also because it
earplug (Figure 40) is premolded in black vinyl. has no flanges, correct fit is critical—the SMR
Because it has no flanges, subjects generally comes in eight sizes. P-AR=344

SMR
50
aor a.
a ~~
mo}
30} +
z +
3
a
2 4
E TT
p=)
é
Ee tot =
kb +
i¢ +
°
{
sole eee
2 3 100 2 ry 1000 2 3 10 000 2

Frequency in Hz

Ficure 40

51



12. Healthways earplugs (Figure 13) are made _—volunteer comments on them at all. The manu-
of pink, preformed rubber, molded in a single, facturer specializes in gear for swimmers.
fairly thin layer. Apparently they are comfort- P-AR=333
able and easy to insert, since subjects did not

HEALTHWAYS
50
|
|
o Ty tL TT
mo] ot
z +
> to
3 +
b
< +
=)
z
Ww aa T
E TOT
<
| |
38s 25-250 800-000-2000 m0 wm (800
~10 1 n 1 1 rn | nt n | L
2 8 100 2 5 1000 2 3 10000 @

Frequency in Hz

Figure 13


41. The Stayrite Shell-type Earplug (Figure large), all of which were reported as uncomfort-
48) is soft and premolded, but it is designed to able by all the subjects who tried them.
look like a custom-molded plug. It is furnished P-AR=655
in three shapes (listed as small, medium, and

STAYRITE SHELL TYPE

50 -
o 4 i
ZU
z +
z \
° + !
rE $V
<q
D>
2
Ww
bt
b +
<q +
2000 4000, (8000 +6000
| 4 4 1
2 5" 10600. 2

Frequency in Hz

Ficure 43

54


NOTICE

The United States Government does not endorse products or manufac-
turers. Trade or manufacturers’ names appear herein solely because they
are considered essential to the object of this report.


30. The Silent Partner (Figure 82) isa putty- tion preformed/wearer-formed earplug. The
filled soft-plastic bubble. Although some sub- canal portion is bright blue, and the visible
jects found it difficult to wear, some found it handle is orange. P-AR=334
very easy. Its construction makes it a combina-

SILENT PARTNER

50
40+ +
-_ -

@
vu

sof 7 +
z=
z +
S 2o| GL. 7.
| ae
E +
p=)
2 —_—
Gig]
kK 4+
< +

°
31s
ero af eee
2 8 100 2 5 1000 a 5 10000 2

Frequency in Hz

Fioure 32

43



28. The Soundown (Figure 30) is a custom-
fitted, factory-made plug that is particularly
light in weight and, according to subjects’ re-
ports, is particularly comfortable to wear;
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 ear canal. However, the plug can slip out

of place with head movement and so requires
frequent adjustment if it is to offer much atten-
uation. This looseness of fit may account for
the good comfort reports. In the tests, the
ANSI requirement for head movements before
measurement often led to a partially open chan-
nel into the ear canal. P-AR=544

SOUNDOWN
50 _
+
a +
v +
z
2 +
4 4
e
<
> bo a >
2 +
WwW
EF
- tI +
< :
+
+ _ Ly
i
280 500 1000 2000 4000 ‘9000 16000
1 1 f f 4 fl fl
2 8 1000 2 3 10000 2

Frequency in Hz

Ficure 30

41



TABLE 3 (continued)

Figure Mean Mean-g Mean-25

Number Earplug Attenuation Attenuation Attenuation P-AR
Al Adcomold 13.9 6.0 -2.0 5 5 4
42 Kleenex 6.7 2.2 -2.4 6 5 4
43 Stayrite 8.9 2.3 -4.8 6 5 5
44 Lee Sonic 20.1 7.4 5.5 4 4 5
45 Fitsrite 21.1 7.6 -6.1 3 4 ~=5
46 Hearite C 14.2 2.8 8.7 5 5 5
47 Crown 12.3 1.9 -8.7 5 5 5
Mean* 20.1762 11.6047 2.5476
Standard Deviation* 5.4706 5.0719 5.6693

*Calculated excluding the dry Sound Silencer, the second test of the Peacekeeper,

the Genie headset, the 3M, and the V-51R.

Some who get custom-molded plugs may wear
them because they enjoy the idea that an expen-
sive safety device was made strictly for their
personal use.

The critical poimt is that procuring earplugs
will conserve no hearing and will make no change
in compensation payments if the plugs are al-

ways worn in the pocket. Selection has to be
made with the idea of getting the plug to the
part of the anatomy where it will do some good.
In general, I recommend that more than one type
be made available to workers.

A. few additional details will help in the in-
terpretation of Table 3:

iW



40. Kleenex tissue (Figure 42) was tested be- and irritation. This material is available in
cause people still use it for earplugs. Subjects many colors, P-AR=654
who were tested with it complained of itching

KLEENEX

IN dB

ATTENUATION

as 63 128 250 500 +000, 2000 4000 8000 00G +
-10 a bee ke 1 i i de n —- “ J
5 100 2 5 1000 @ 5 10000 2

Frequency in Hz

Frieune 42

53



are heard more clearly when he is wearing
earplugs.**1" He may not recognize the con-
stant importance of protecting his hearing :
hazards to the auditory system are not dramatic
like hazards to vision—onset is slow and de-
terioration is gradual. Often the process is far
advanced before it is noticed, and only then is
the extreme social debilitation of deafness recog-
nized—too late for either preventive or corrective
measures to help much.

Whatever leads a user to his selection, the
person who pays for the plug ought to recognize

that any plug that will attenuate noise and will
he worn is economical. If that plug is one of
the more costly custom-molded varieties, the fact,
that it will be used makes it valuable and worth
the money. The ultimate decision about wearing
or not wearing protection is the worker’s, and
for that reason, offering him a choice from sev-
eral types of plugs is useful. Having more than.
one kind on hand also decreases the number of
cases in which a potential wearer cannot be suc-
cessfully fitted. Then, every noise-exposed per-
son can be given the kind of protection he needs
in a form he will use.

References

. Botsford, J. H.: Revised OSHA Noise Regulations,
SOUND AND VIBRATION, 7:24-28, November
1978.

Botsford, J. H.: How to Estimate dB(A) Reduction
of Bar Protective Devices for Use in Noise Environ-
ments, SOUND AND VIBRATION, 7 :32-83, Novem-
ber 1973.

Johnson, D. L., and C. W. Nixon: Simplified Methods
for Estimating Hearing Protector Performance,
SOUND AND VIBRATION, 8:20-27, June 1974.

Tobias, J. V., and D. L. Johnson: The Typical Noise:
First Step in the Development of a Short Procedure
for Bstimating Performance of Hearing Protectors.
Manuseript prepared for submission to SOUND
AND VIBRATION, 1975.

. Tobias, J. V.: P-AR: Protector-Attenuation Rating
Procedure for Earplugs and Barmuffs. Manuscript
prepared for submission to NOISE CONTROL
ENGINEERING, 1975.”

Gasaway, D. ©.: Personal Ear Protection. Aero-
medical Review 2-71, USAF School of Aerospace
Medicine, Brooks Air Force Base, Texas, 1971.

Botsford, J. H.: Ear Protectors—Their Characteris-
tics and Uses, SOUND AND VIBRATION, 6:24-29,
November 1972.

Willson, A. H. G., and M. G. Sims: Bibliography on
Ear Protection. Royal Aircraft Establishment
Library Bibliography 335, 1973.

. Consumers Union: Hearing Protectors, CONSUMER
REPORTS, 40 :618-621, 1975.

nv

2

a

59

10. Tobias, J. V., and F. M. Irons: Ear-Protector Rat-
ings. FAA Office of Aviation Medicine Report No.
AM-73-20, 1973.

. American Standards Association: American Stand-

ard Method for the Measurement of the Real-Har

Attenuation of Ear Protectors at Threshold. Amer-

ican National Standards Institute 224.22, 1957.

Franzen, R. L., and L. Stein: Influence of the Fitter

on Earplug Performance, SOUND AND VIBRA-

TION, 8:28-29, January 1974.

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.

Forrest, M. R.: Ear Protection and Hearing in

High-Intensity Impulsive Noise. In Robinson, D. W.

(Ed.): Occupational Hearing Loss, New York, Aca-

demic Press, 1971.

Kryter, K. D.: Effects of Ear Protective Devices on

the Intelligibility of Speech in Noise, JOURNAL

OF THE ACOUSTICAL SOCIETY OF AMERICA,

18 :413-417, 1946.

Frélich, G.: The Effects of Ear Defenders on Speech

Perception in Military Transport Aircraft. In

Aeromedical Aspects of Radio Communication and

Plight Safety. AGARD Advisory Report 19, North

Atlantic ‘Treaty Organization, Neuilly-sur-Seine,

France, 1969.

Williams, ©. E., J. R. Forstall, and W. C. Parsons:

Effects of Earplugs on Passenger Speech Reception

in Rotary-Wing Aircraft, AEROSPACE MEDICINE,

42 :750-752, 1971.

12.

13.

14.

15.

16.

17.



2. Softseal Hearing Protectors (Figure 2) are
made of a silicone polymer that is tacky at body
temperature and behaves much like Silly Putty.
Enough material for two earplugs is packaged
in a sealed envelope or in a plastic box. It is
formed into two cones, pressed into the ears
where it is held for 10 seconds, and then left in
place. Most subjects found it comfortable and
easy to handle, but because of its tendency to

SOFTSEAL

collapse under the influence of gravity, a few
subjects considered it difficult to use. It was
sometimes hard to remove. It does pick up dirt,
which is then difficult to separate from the ear-
plug material. If left out anywhere except in a
small, enclosed container, the material puddles
out into a fairly thin layer; in hot environments,
the layer is very thin. P-AR=211

50

40h

30 F-

>
=

10

ATTENUATION IN dB

31. 128

1 1

|
| |

-10 1
2 ry TOO ry

ni
6 1000 2 5

Frequency in Hz

Ficure 2

18



ACKNOWLEDGMENT

This work could not have been completed without the assistance of F.
Michael Irons, Vincent Kidd, and Walter E. Morris. In addition, Lt. Col.
Daniel L. Johnson of the Biological Acoustics Branch, Biodynamics and
Bionics Division, Aerospace Medical Research Laboratory, Wright-Patterson
Air Force Base, by verifying the appropriateness of the simplified measure-
ment described in this paper, deserves particular gratitude.



21. The SafEar (Figure 23), 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. I did not test it in such noise, but did
read two company-provided reports. Both show
average attenuation properties in noise that are

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,
but the data suggest that such effects are neg-
ligible until very high sound pressures are
reached, Forrest! found a 110-dB SPL thresh-
old 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 Principle.” They claim that,
«. .. above 85 db, the noise is attenuated to 85 db.
The higher the noise the more efficient the at-

beyond those considered theoretically possible*;  tenuation. Thus noises of 140 to 150 db are
SAFEAR
50 |
40F
a
2 30h
Zz
z y
Qo 2oF
- +
a
=) +
Zz
WwW
bE 10F IN
‘=
< + +
+
° 7 - -—— —_ ~ —
ars 63 125 250 500 1000 2000 4000 8000 16000
-10 1 a n L i p n i n L
2 5 100 2 5 1000 2 3 10000 2
Frequency in Hz
Ficure 23

34


10. Insta-Mold earplugs (Figure 11) are. cus-
tom molded in place—that is, the user can wear
the molds as earplugs as soon as the material
has cured. Problems with the catalyst led us to
waste nearly half of the earmold material that
we purchased. One must learn to work rapidly
with this sort of material because it sets up very
shortly after the catalyst is mixed in and can
become stiff so quickly that reforming it into the

other such plugs. As with all custom-molded
plugs, and especially with those that do not re-
quire factory construction, the manufacturer’s
instructions must be followed carefully and ac-
curately; there is no substitute for experience in
earmold construction. Subjects found Insta-
Mold plugs comfortable and easy to insert, but,
like all the custom-made plugs we tried, they
were less comfortable than were most preformed

right shape is impossible. With Insta-Mold, this or wearer-formed varieties. P-AR=333
situation arose far more frequently than with
INSTA-MOLD
50
| T
40h
S
30 -
2 ~
z aa t + +
= 20 -
be —
aq
=)
z +
F tof -
ast +4 +
a f
|
| | | : | - |
3 125 250 500 1000 2000 4000 e000 46000,
-10 1 1 1 1 fi fi 1 1 _
2 100 2 8 1000 2 s 10000 2
Frequency in Hz
Freure 11

22




33. The Willson Sound-Ban 10 earcap (Figure adjustable metal headband that can be worn
85) is similar to the Sound-Ban 20 (see para- across the top of the head as well as behind the
graph 9), except that this one has a padded, neck or under the chin. P-AR=444

SOUND—- BAN MODEL 10

50 ae
+
{re}
3
z a =
2 T +
2
Pa _
q +
2
z ~_
WW
a |
bE +
9
i
250 800 1000 2000 4000 ‘8000 W000 |
L 1 4 4 4 t — -
2 8 ooo z I V6500

Frequency in Hz

Fieure 35

46


18. Accu-fit earplugs (Figure 19) are a soft, than other flanged plugs. Accu-fit plugs are
preformed type. They seem less easy to insert available strung on a cord. P-AR=833

ACCU- FIT
+
tot 4
(re)
nol +
ate
z
z
°
e _— >—
4 +
i)
2 +
uu —
b +
i
< |
|
i
250 $00, 1000 2000 4000, ‘8000 16000
L 4 ni n fot 4
2 5 1000 2 5 10000 z

Frequency in Hz

Figure 19

30


26. SEPCO earplugs (Figure 28) consist of a end). The vents appear to be associated with
pink neoprene shell (with two pinhole perfora- pressure equalization for ease of insertion rather
tions in the tip) filled with a foam cushion (with than with any acoustic function (but see para-
a single pinhole perforation showing at the open graph 21), P-AR=444

SEPCO

50 |

40o-

IN dB

20F

ATTENUATION

S 3 28 250 $00 1000
-10; 7 1 1 i 4
001

n 1
6 10000 2

000 4000, 8000, 000
100 2 5 1000 2 +
Frequency in Hz

Fiaurr 28

39



13. The E.A.R. (Environmental Acoustical the Insta-Mold carplug, it is custom made and
Research) plug (Figure 14) is a soft, factory- users find it somewhat less acceptable than many
made, custom-fitted device. Subjects found it of the preformed and wearer-formed plugs.
fairly comfortable and easy to insert, but, like P-AR=333

IN dB

ATTENUATION

50

-10

E.A.R.
T
+
4
+ >— 4
>
_ _—
it) 16 280 600 00 2000 4000 e000 woo
n 1 4 1 n n 1 14
2 100 2 8 1000 2 8 10000 2

Frequency in Hz

Fieure 14



ported elsewhere on the same brands. Neverthe-
Jess, these numbers are believed to be fair
representations of the effectiveness of the re-
ported earplugs as they would be used in the
field. Where manufacturers or distributors fur-
nished no instructions, subjects were told to put
the plugs in so that they fit comfortably and
were tight. When instructions were furnished,
they were followed exactly. For custom-molded
varieties that use an ear impression as a model
from which to manufacture the plug, and for
eustom-molded varieties where the impression
itself is the earplug, the impressions were made
by a skilled technician who followed manufac-
turers’ recommendations precisely. In one case,
detailed in the Results and Discussion section, a
company changed its published instructions after
our tests were completed; a second series was
run with earplugs made according to the new
directions.

Factory-made custom-molded earplugs were
permitted to age in our laboratory for at least 2
weeks before testing started. A similar aging
period was also required for units that were
formed in the subject’s ear. A still better pro-
cedure would have been to age all tested earplugs
during a month of actual use. To do so, though,
would not only have taken an exceedingly large
number of subjects and an exceedingly long time,
but in the case of most of the plugs tested, would
have led to too few trials being run; some sub-
jects in almost every group found some earplugs
too uncomfortable to keep on throughout a
breaking-in ‘period.

One group of 10 subjects was used in 11 series
of measurements. Other groups of 10 subjects
were used for series as small as two and as large
as six. Altogether, 110 subjects participated.
With each group, the procedure was the same:
the first threshold of the day was taken with
open ears to provide a baseline; then, in random
order, earplugs were tested for 2 hours or until
each type had been measured three times, follow-
ing which another open-ear threshold was taken.
If 2 hours were not adequate to finish all the
necessary series, the next day’s tests also included
open-ear thresholds at the beginning and at the
end of the session. A 5-dB variation between
the two baseline curves (at any standard fre-
quency) was chosen to be large enough to in-
validate that day’s data, but this criterion was

never exceeded. Each attenuation test was com-
pared to the average of the two baseline curves
taken on the same day as the test.

IV. Results and Discussion.

Nearly any material inserted into nearly any
ear canal in nearly any way will attenuate high-
frequency sounds to some extent. Under the
circumstances, it is not surprising that people
believe they are protecting themselves with ear-
plugs made of dry cotton wool or of cigarette
filters—a little attenuation at high frequencies
produces a little change in tone quality, and the
user believes that that change means he has
blocked out damaging noise. The series reported
here includes cotton-wool and facial-tissue ear-
plugs.t

Table 3, like the commentary below, groups
the tested earplugs in descending order of per-
formance in The Typical Noise of Table 1, less
two standard deviations (in order to make the
values indicate the minimum expected protection
for 98 percent of the population), less the Tobias
and Johnson 3-dB correction to make the values
represent the minimum expected protection in
99 percent of noises. A high position in Table 3
cannot serve as an adequate reason to purchase a
particular brand of plug. The wearer’s comfort
is essential,t and a rating of Class 2 or better
does not guarantee that people who ought rigor-
ously to use hearing protection will do so without
external incentives. Some industrial personnel
might be motivated by brightly colored ear-
plugs—not for the esthetic value, but because
they know the plugs are visible to a distant fore-
man. Of course, the foreman has to understand
his obligation to see that hearing protection is
used. Other prospective wearers may respond
positively to an option like a headband, a lace, or
a cord, that makes it easy to keep track of the
plugs when they are temporarily out of the ears.

+I was not brave enough to try testing the attenua-
tion characteristics of cigarette filters. Not only is the
variety of structures nearly inexaustible, but the pro-
cedures required for extraction after use seemed par-
ticularly treacherous.

}A few people have experienced mild cases of external
otitis attributable to the use of earplugs. They need to
be counseled that application of petroleum products or
alcohol can exacerbate such problems for some people.
If they continue to be troubled by otitis, earmuffs are
certainly an appropriate alternative.



34, The Hearite series A (also known as the attenuation is better, except that the A is straight
Stayrite Type A) earplug (Figure 36) is similar where the B is curved. P-AR=444
to the Hearite series B (see Figure 31) whose

HEARITE SERIES A

50 |
40 + +
ao
7 304 : +
2 +
z j + +4
z= 20 + = a
o-§
=) +
2 4
Lif
E | + +
° L
3s 63 125 250: $00 1000, 2000. 4000: (8000 16000
-10 1 1 1 4 4 = 4 4 4 4
2 ry 100 2 3 1000 2 Ey 10000 2

Frequency in Hz

Ficure 36

AT



36. Sound Master earplugs (Figure 38) are which ear each plug was made for. It is not
custom-fitted and do not require factory con- necessary to handle the material during construc-
struction. They can be stamped to identify tion. P-AR=444

SOUND MASTER

50

40

30

IN dB

20

ATTENUATION

315 6 (25 280 500 1000 2000 4000 ‘8000 16000

2 i L
5 100 2 5 1000 2 5 10000 2

Frequency in Hz

Frevre 38

49



1. The E-A-R (National Research Corpora-
tion) earplug (Figure 1) is made of a soft, easily
compressed material that. returns to its original
shape rather slowly under normal cireumstances,
permitting insertion of the compressed form,
which then expands to fill and seal the entrance
to the canal. All the subjects who used this plug
found it 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 1 hour a day for 1 month without the ma-
terial showing any signs of deterioration. Dur-

ing this period, the plugs were washed a few
times with mild seap and warm water. The
plug does change compression properties when
used in high summer temperatures, so it may be
more difficult to insert it effectively im environ-
ments hotter than 90° F. or so; however, I have
no numerical data to suppert this contention.
The plugs are furnished in bright yellow. They
soil rapidly, and must therefore be handled care-
fully if they are to be reused for any appreciable
length of time. P-AR=111

E-A-R
50 |
aol ay
+ > T -

a
mol

30h
2 a
z at
en) =
Lt +
=}
ai
- tO
be
<

° _

I t
as 6s 2 280 $0c 1000 2000 4000, 8000 16000.
HO be le L E 1 f i fi i 1
2 s 100 2 s 1000. 2 8 40000 2

Frequency in Hz

Frcusr t

12