Audibility Test Apparatus.
Audibility Test Apparatus -
When worn over the head, the helmet shall not absorb excessive volume
of sound so at to pose as an accident hazard against any vehicle
approaching from the back of the user. For ensuring this, the helmets
shall be tested for their sound attenuation properties. The sound
transmission loss shall not be more than 10 dB (A).
The Audibility Test Apparatus
for helmets consists of a rigid angle iron frame to keep a test
head-form with the helmet under test mounted over it one end and a horn
placed at the other end. The horn is held such that that the sound waves
from it strike the helmet at its back in the same horizontal plane.
the horn and the head-form are mounted at a level 1.2 m above the
ground. The horn is operated by a lead-acid storage battery supplied
with the apparatus.
A microphone and a digital sound
level meter are provided for measuring the sound level. The microphone
is mounted inside the wooden head-form at the normal ear level of the
user. Two microphones are mounted in each head-form, one on the left and
the other on the right. The selection between left and right
microphones is done with the help of a change-over switch.
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