Installation manual

Community S-Series - Operation and Installation Manual - Page 37
reducing the power that’s required to obtain a given sound pressure level. This will result
in more available power, more headroom and less demand on the drivers, all of which
lowers the potential for distortion and damage under high power conditions.
Now that you’ve chosen the final physical locations for your full-range loudspeakers and
subwoofers, established their optimum phase relationship, and brilliantly EQ’d any
crossover peaks, you’re almost ready to permanently wire the system. But first read the
section below on “Absolute Polarity.”
Absolute Polarity
Quite a bit has been written about absolute polarity, particularly in regard to studio
recording and hi-fi sound reproduction. The subject is, however, often ignored in the field
of sound reinforcement. Essentially, positive absolute polarity refers to configuring the
system so that upon the first cycle of excitation by the source material, the driver(s) moves
forward toward the listener, thereby producing a positive wavefront. For example, at the
instant of impact when the head of the kick drum moves outward towards the microphone,
the speaker cones will also move outward.
Obviously, the polarity integrity of the entire signal processing chain must be maintained
for this to occur. Is absolute polarity audible? Should you be concerned? Yes, it is audible
and though subtle, it makes a big enough difference to warrant taking the time needed to
insure that the signal chain is polarity-positive throughout. You’ll hear an improvement in
sonic impact, especially in the lower frequencies.
We recommend that absolute polarity be kept positive in all low-frequency devices
whenever possible. This can be checked with a small handheld style polarity response test
unit, available from numerous manufacturers.
Although it’s easy to simply reverse the polarity of the subwoofer to determine its best
polarity relationship to the full-range loudspeaker system, if the best position turns out to
be reversed we recommend that you instead reverse the full-range system(s) so that the
subwoofer(s) can remain in a state of positive absolute polarity.
SYSTEM EQUALIZATION
There are numerous schools of thought on proper equalization techniques. Some believe
that using anything more than a touch of equalization is wrong, often attributing their
concerns to ‘phase shift’ from the equalizer. Others believe the opposite. Some say
equalization can’t be performed correctly without advanced instrumentation, while others
say it must be done by listening; after all, the end product isn’t a graphic display, it’s an
audible event.
One engineer would never equalize a sound system with a parametric equalizer, while
another would not use a graphic equalizer. A well known sound designer once stated that
when the equalizer is switched in and out, if he couldn’t hear the difference, he considered
the system to be properly tuned. As these examples illustrate, there are widely varying
beliefs on the subject of equalization.
Instead of touting a particular philosophy, let’s approach the practice of equalization by
looking at the transfer function of the loudspeaker and room together. We can do this with
a two-port FFT analyzer.
For the sake of this short discussion, let’s assume that the loudspeaker we’re using exhibits
a perfectly flat frequency and phase response in a free field environment. We’re going to
assume this because it will help to illustrate the point of the discussion. The fact that few,
if any, loudspeakers are perfectly flat in a free field environment is not of paramount
importance, nor is the fact that many high quality loudspeakers can actually be equalized to
be almost perfectly flat, if one wants to go through the exercise of doing so. The point here
is to illustrate the principal of precisely correcting for room resonance.