Working Safely With Sound - SoundCraft LIVE 8 User Manual

Capacitive coupling between the screen and signal wires.
To minimise the adverse affects of the unwanted coupling to the signal wires, it is important that the screen is connected at one end only,
i.e. the screen must not carry any signal current. Any signal on the wires within the screen will be capacitively coupled to the screen. This
current will ultimately be returned to the source of the signal, either directly, if the screen is connected at the signal source end, or
indirectly via the earthing system, if the screen is connected at the signal destination end. The indirect connection will cause an increase
in high frequency cross-talk, and should be avoided wherever possible.
Therefore, in general, always connect the shield only at the signal source end. In high RF areas, the screen can also be connected to
earth via a 0.01 mF capacitor. This will present a short circuit at RF frequencies, thus lowering the effective shield impedance to ground.
However, at low audio frequencies the reactance of the capacitor will be sufficiently high not to cause an earth loop problem.
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 equipment 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-conditioning 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 separate 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.

WORKING SAFELY WITH SOUND

Although your new console will not make any noise until you feed it signals, it has the capability to produce sounds which when monitored
through an amplifier 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):
PERMISSIBLE NOISE EXPOSURE
DURATION PER DAY, HOURS
8
6
4
3
2
1.5
1
0.5
<0.25
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 understand (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 find out how each parameter affects the sound - this will extend your creativity and
help you to get the best results.
Recommended Headphone Impedance 200-600 ohms.
10
SOUND LEVEL dBA SLOW RESPONSE
90
92
95
97
100
102
105
110
115