WORKING SAFELY WITH SOUND
Although your new console will not make any noise until you feed it signals, it has the capability to pro-
duce sounds which when monitored through a PA system or headphones can damage hearing over time.
The table below is taken from the Occupational Safety & Health Administration directive on Occupational
noise exposure (1926.52):
PERMISSABLE NOISE EXPOSURE
DURATION PER DAY, HOURS SOUND LEVEL dBA SLOW RESPONSE
8 90
6 92
4 95
3 97
2 100
1.5 102
1 105
0.5 110
<0.25 115
Conforming to this directive will minimise the risk of hearing damage caused by long listening periods. A
simple rule to follow is the longer you listen the lower the average volume should be.
Please take care when working with your audio - if you are manipulating controls which you don’t under-
stand (which we all do when we are learning), make sure your monitors are turned down. Remember that
your ears are the most important tool of your trade, look after them, and they will look after you.
Most importantly - don’t be afraid to experiment to nd out how each parameter affects the sound - this
will extend your creativity and help you to get the best results.
Recommended headphone impedance is 50-600 ohms.
Points to Remember
In all cases, use good quality twin screened audio cable. Check for instability at the output.
Always connect both conductors at both ends, and ensure that the screen is only connected at one end.
Do not disconnect the mains earth from each piece of equipment. This is needed to provide both safety
and screen returns to the system star point.
Equipment which has balanced inputs and outputs may need to be electrically isolated from the equip-
ment rack and/or other equipment, to avoid earth loops.
It is important to remember that all equipment which is connected to the mains is a potential source of
hum and interference and may radiate both electrostatic or electromagnetic radiation. In addition, the
mains will also act as a carrier for many forms of RF interference generated by electric motors, air-condi-
tioning units, thyristor light dimmers etc. Unless the earth system is clean, all attempts to improve hum
noise levels will be futile. In extreme cases there will be no alternative but to provide a completely sepa-
rate and independent `technical earth’ to replace the incoming ‘noisy earth’. However, always consult your
local electricity supply authority to ensure that safety regulations are not being infringed.
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