User Responsibility; Speaker Protection - Crest Audio PRO7200 Owner's Manual

Safety
6

User Responsibility

Your Pro 200 Series amplifier is very powerful and can be potentially dangerous to loud-
speakers and operators alike.It is your responsibility to read all precautions and make sure
that the amplifier is installed, wired, and operated properly as instructed in this manual.
Many loudspeakers can be easily damaged or destroyed by overpowering, especially with
the high power available from a bridged amplifier. Always be aware of the speaker's con-
tinuous and peak power capabilities. Crest Audio is not responsible for damage to loud-
speakers for any reason.

Speaker Protection

All loudspeakers have electrical, thermal and physical limits which must be observed to
prevent damage or failure. Too much power, severely clipped wave forms, low frequencies
applied to high frequency drivers and DC voltage can all be fatal to cone and compres-
sion drivers. Crest Audio Pro 200 Series amplifiers automatically protect speakers from
DC voltages and subsonic signals.
Be sure that the low and mid bands of an electronic crossover are connected to the cor-
rect amplifiers and drivers, and not accidentally connected to those for a higher frequen-
cy band. The amplifier's clipping point is its maximum peak output power, and some of
the higher-powered Pro 200 Series amplifiers can deliver more power than many speak-
ers can safely handle. Be sure the peak power capability of the amplifier is not excessive
for your speaker system.
To ensure the speakers never receive excessive power and that the amplifier never clips,
use a properly adjusted external limiter (or a compressor with a ratio of 10:1 or higher)
to control power output; in systems with active electronic crossovers, use one for each
frequency band. The clip limiter will automatically limit the duration of squared-off, con-
tinuous wave forms applied to the speakers. The amplifier will, however, allow normal
musical transient bursts to pass. When the amplifier does clip, it is at its maximum out-
put power. Some speaker systems are packaged with processors that have power limit-
ing circuits and should not require additional external limiting. Fuses may also be used to
limit power to speaker drivers, although as current-limiting rather than voltage limiting
devices. Some poor quality fuses have a significant series resistance that could degrade
the amplifier's damping of the speaker's motion and may even deteriorate the system's
sound quality. If you elect to use fuses, check with the speaker manufacturer to deter-
mine the proper current rating and time lag required.
Do not drive any low frequency speaker enclosure with frequencies lower than its own
tuned frequency; the reduced acoustical damping could cause a ported speaker to bot-
tom out even at moderate power. Consult the speaker system specifications to deter-
mine its frequency limits.
The wire gauge charts in Appendix C will assist you in determining the optimum copper
wire gauge for your speaker cables. Remember that the speaker cable resistance robs
amplifier power in two ways: through power lost directly to resistance (often referred to
as I2R loss), and through increased total load resistance, which decreases the amount of
power available from the amplifier. Appendix C gives cable length figures in feet/AWG
wire gauges and in metric values.
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