Installation manual

Community S-Series - Operation and Installation Manual - Page 31
Most waveforms that occur in music and speech are the complex conjugate of sine and
triangle waves. Such waveforms have a relative short duty cycle, cresting to maximum
voltage for only a small part of each cyclic repetition. When an amplifier clips, it’s because
it’s reached its maximum voltage potential, so it starts to square off the crest of the
waveforms. This more or less turns the waveform into a square wave. Why is this bad?
Because unlike a sine wave or a triangle wave, both of which crest for only a short duration,
a square wave crests for a much longer duration. It can be described in technical terms as
exhibiting a long duty cycle. In effect, a square wave is telling the loudspeaker to move
forward in an infinitely short period of time – then to dwell there for a while – then to move
backward in an infinitely short period of time - then to dwell there for a while - then to
repeat the process. Whenever a loudspeaker has current running through its voice coil but
is not actually moving, such as at the lengthy peaks of a square wave, all of the electrical
energy is turned into heat instead of sound. Square waves will create rapid heating in even
the most robust of drivers, leading to equally rapid driver failure. Therefore, it’s better to
choose an amplifier that’s overly large for your loudspeaker but will remain out of clipping
at high levels, than one that’s too small and prone to clip.
Other attributes to consider in making a selection of amplifier type are:
• Sound Quality
• Reliability
• Protection Circuitry
• Heat Dissipation Method
• Tolerance to Voltage Fluctuation
• Damping Factor
• Signal-to-Noise Ratio
• Controls and Features
These items are briefly discussed below:
Sound Quality: Listen and compare! An amplifier that performs well in bi-amp mode with
one manufacturer’s loudspeaker may not perform as well when faced with the more
complex load of a passive crossover in another manufacturer’s loudspeaker. Make sure to
listen!
Construction Quality: Usually, this is fairly evident by taking a good look at the product,
but not always. Don’t be fooled by excessively thick front panels that hide poorly built
assemblies inside. Look inside if possible, but first make sure that the amplifier is
powered down and disconnected from the AC Mains before disassembling! An
amplifier that’s powered down and disconnected from the AC line can still cause a
shock from the energy stored in its capacitors. Be cautious! Things to note are an
excessive number of internal connectors (hardwired terminations are typically more
reliable); the quality of the pots, fans, and switches; the presence of wire jumpers and/or
cut traces on PC boards (these indicate that the design wasn’t ready for production); sheet
metal screws versus machine screws (machine screws are stronger); and the method used
to mount heavy components such as transformers and large capacitors (large bolts and
steel brackets are typically better than small bolts and gobs of silicon).
Protection Circuitry: Most modern amplifiers can sustain a dead short to their output
without damage. This is a good feature in the event that a driver shorts out, or wiring
becomes faulty. Many designs have some protection scheme against DC on the output,
which usually happens if an output transistor fails. This is another important feature as DC
will almost instantly destroy LF and HF drivers. Many amplifiers offer some sort of ‘soft’
clipping protection, which again is usually a good feature if it’s properly implemented.
Review the specifications carefully.
Heat Dissipation: Does the amplifier use forced-air cooling (i.e. fans) or passive
convection cooling? If forced air, can the fan filters be easily accessed and changed when
they get blocked with dust? If convection, can the amplifier stand up to high ambient
temperatures? Will there be a problem when multiple amplifiers are installed adjacent to
each other in equipment racks? Some manufacturers recommend putting spaces between
multiple amplifiers, especially passively cooled designs, which uses up a lot of valuable rack
space. Investigate carefully.
Tolerance to AC Mains Voltage Fluctuation: Different designs of amplifiers exhibit
widely differing behavior under fluctuating voltages. Those that are built with linear power
supplies will typically exhibit a loss of power output capability when the AC mains voltage