GS-HL001
Headphone exposure meter and automatic level attenuator
The GS-HL001 is designed to provide an intelligent solution to the problem of broadcasters meeting their obligations under The Control of Noise at Work Regulations 2005 whilst allowing users some control to meet their day to day requirements.
SEE ALSO OUR GS-HL002 'BELTPACK' HEADPHONE EXPOSURE METER & AUTOMATIC ATTENUATOR.
There are 2 limits set by the control of noise at work regulations.
A daily limit:
A time weighted average of 80dB(A) over an 8 hour period. The 8 hour period is
assumed to be taken within a 24 hour period.
A weekly limit:
A time weighted average of the daily noise exposure levels for a nominal
week of 5 eight hour working days.
A copy of the control of noise at work regulations can be found at: http://www.opsi.gov.uk/si/si2005/20051643.htm#4
Our GS-HL001 deals with the daily exposure limit and assumes that the employee or employer will be aware of how many days exposure have been used per week.
Examples that the exposure/ time that the daily limit of a time weighted average of 80dB(A) equate to are:
80
dB(A) for 8 hours.
80 dB(A) for 4 hours, and 100 dB(A) for 3 minutes.
73 dB(A) for 7 ½ hours, and 91 dB(A) for 30 minutes.
85 dB(A) for 2 hours, and 74 dB(A) for 6 hours.
103 dB(A) for 2 minutes 30 seconds.
At 118 dB(A) your whole 8 hour exposure allowance will be
used in under 5 seconds!
Further information on noise exposure including noise exposure calculators can be found at http://www.tonywoolf.co.uk/noiseregs.htm
WHAT DOES THE GS-HL001 ACTUALLY DO?
The GS-HL001 is calibrated to match a particular brand/ model & impedance of headphones. (pictured above are Sennheisers HD25 (70 Ohm)). Once calibrated the GS-HL001 knows what input voltage equates to what audio level in the headphones.
The
GS-HL001 is set by the user to start a new day (the user cannot set a new day by
accident) from this point on it measures and saves the users exposure until
another new day is set.
At the start
of the day the exposure counter is loaded with 28800 seconds (8 hours). During
normal operation, the A-weighted RMS level applied to the ears is measured once
per second, and the ‘cost’ (in seconds) of listening at that level is calculated
and subtracted from the exposure counter. Listening at levels below 80dB(A)
costs 1 second – you can listen at 80dB(A) or below all day. However, listening
at 86dB(A) would incur a cost of 4 seconds per second and use your daily
exposure allowance in just two hours.
The GS-HL001 measures the users exposure and after the daily limit is reached the level is attenuated down so as the exposure never exceeds 80dB(A) until a new day is started.
EXPOSURE
USE
As the daily exposure is used, an audio message
announces to the user 'X PERCENT REMAINING'. This message is played at 10%
intervals and allows the user to keep track of the daily allowance. It is
possible for the user to turn off these announcements.
AUTOMATIC TURN OFF
To
prevent exposure being wasted when the headphones are not actually being used an
automatic device turns the audio off when the headphones are removed from the
head. When the user replaces the headphones they need to press a switch on the
side of the unit which recommences audio and the measuring of exposure.
INCREASE GAIN
It is possible to increase the input gain of the GS-HL001. This is done for
example to allow a user to listen for noise on the incoming audio circuit. The
gain can be increased by 6 or 12dB.
MAXIMUM OUTPUT VOLUME (HARD LIMIT/ COMPRESS)
Because the GS-HL001 measures exposure over an 8 hour period it would be
possible to a have a very high volume e.g. 118dB(A) for a very short length of
time. This may be very uncomfortable for the user so a hard limit is set that
will not allow levels to exceed 101dB. This actually compresses audio over
100dB.
POWER & AUDIO
The
audio input to the GS-HL001 is unbalanced stereo. Normally this will be the
output of a headphone amplifier. Pictured above is a 3.5mm stereo jack plug
fitted for the audio input (other options are of course available).
The GS-HL001 is an active device and requires power. A power inlet cable is run next to the audio input cable. A regulated +5 volt DC @ 50mA is required. The GS-HL001 was actually designed to be powered from the 'LANC' socket of digital video cameras. For a battery power pack and 'beltpack' version please see below.
TEMPERATURE
Headphones can of course be worn across a huge temperature range, users exposure
does not change depending upon the temperature but the characteristics of
electronics do. Therefore the GS-HL001 includes sensors that compensate for
different temperatures and keeps the correct exposure levels to users regardless
of temperature. The tested temperature range is -10 to +45 Degrees Celsius.
BATTERY POWER PACK (GS-HL003)
An
external battery power supply has been designed to power the GS-HL001. This is a
'beltpack' unit and from 1 x PP3 provides the correct power requirements for the
GS-HL001. The power pack also has an external power supply inlet for providing
power from a plug top PSU.
Panel views of the power pack GS-HL003.
BELTPACK VERSION (NOT FITTED TO HEADPHONES)
The
GS-HL002 is a version of the GS-HL001 that is not fitted to headphones and has
its own battery. Link to GS-HL002.