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METHOD
Ten
Otolarngologically
normal subject were
selected for the
tests. The subject
was seated in a
chair in an anechoic
chamber with his
head positioned
on the chin rest.
The sound source
was located in front
at a distance of
30cms from each
ear. The subject's
open ears hold (without
any ear defender)
and closed threshold
(while wearing an
ear defender) were
then determined
using the ear defender
the under test.
The following pure
tone frequencies
were tested: 250Hz,
500Hz, 1000Hz, 2000Hz,
3000Hz, 4000Hz,
6000Hz, 8000Hz,
each subject was
given their test
in intervals of
'One Minute'.
RESULTS
The
hearing thresholds
shifts caused by
wearing of the ear
defenders, which
corresponds to the
attenuation values
for the frequencies
of 250Hz, 500Hz,
as the 'closed thresholds'
could not be determined
due to audio- matriclimitation
of maximum tone
intensity at these
frequencies. The
attenuation for
the 250Hz and 500Hz
exceeded 10dB and
15dB respectively.
It is seen that
the maximum attenuation
is provided at the
important frequencies
of 2000Hz, 3000Hz,
4000Hz to ranging
from 30 to 47dBs
with a mean of about
35dBs. The new design
earmuffs have shown
better attenuation
at frequencies of
1000Hz, 2000Hz,
3000Hz & 4000Hz.
The improvement
is satisfactory
has regards fitting,
adjustability and
comfort. None of
the subjects reported
any discomforts.
CONCLUSIONS
The
attenuation characteristics
of the new design
ear muff type ear
defender are superior
to those of ear
muffs which are
used currently specially
in frequencies 1000Hz
to 4000Hz although
not fully to the
specification.
THE
TEST RESULTS
The
ear protectors were
evaluated for their
sound attenuation
properties according
to IS : 6229 -1971
by measuring the
threshold shifts
due to the ear protectors
determined by 22
persons in an anechoic
room using a pure
tone signal incident
from the front.
The ambient noise
in the anechoic
room at the position
of the subjects
ear was then that
given in cause 3.1.1
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