Installation manual
Community S-Series - Operation and Installation Manual - Page 35
loudspeaker(s), such location may result in the subwoofer being drastically out of time
sync with one or more of the full-range speakers.
Sometimes the sound quality of a wall or corner placement is not desirable, simply due
to the room’s acoustical properties. Keep in mind that when wall and corner locations
are appropriate for use they’ll provide a tremendous increase in power output, but they
may not always be the best choice.
(2) Keeping the subwoofer(s) as close as possible to the mid and high loudspeaker(s) will
decrease phase irregularities and time smear. If the subwoofer(s) is placed too far
away from the mid/high loudspeaker(s), the listener will experience a disjointed
character to the program material, causing the musicality of the system to suffer.
(3) Although the subwoofer is not highly directional, still its acoustical output follows the
inverse square law. That is, every time the distance from the subwoofer to the listener
is doubled, the output level will decrease by 6dB. When covering a large space with
multiple subwoofers, it may be of benefit to space them some distance apart from one
another to even out the levels throughout the space. Typically, this would only be done
if the mid/high loudspeakers are also spaced apart from one another, such as in a
distributed system in a sports venue. Although this will help maintain an even level
throughout the listening space, there may be some areas that lie between two or more
subwoofers that experience a certain amount of power subtraction caused by
destructive interference. Destructive interference occurs when waveforms meet and
are partially or wholly out of phase with each other, due to unequal path lengths.
Conversely, if multiple subwoofers are located directly adjacent to one another, their power
output will add together almost seamlessly. This is known as constructive acoustic
addition. However, this may produce an undesirable hot-spot of low-frequency energy that
may be too close to a seating area.
Polarity
Unless the full-range loudspeaker(s) is stacked directly on top of the subwoofer(s) with its
cone drivers aligned with the subwoofer cone drivers, it’s likely that the phase relationship
of the two systems may not be optimal. This can be tested by reversing the polarity of one
system relative to the other, as described below.
First, however, it’s important to understand that the correct polarity of the full-range
system relative to the subwoofer is a function of their physical placement in relation to one
another. This is known as the Phase Relationship of the two systems, though Absolute
Polarity plays a role as well, which will be discussed later.
Depending on the placement of the subwoofer in relation to the full-range loudspeaker(s),
as well as the selected crossover point, the optimal response of the system might be
obtained by reversing the polarity of the full-range loudspeaker(s). The easiest way to
determine the proper polarity is to excite the system with a test signal (such as pink noise)
and to view the resultant response on an audio spectrum analyzer. If such equipment is
not available, it is also possible to determine the best polarity relationship by careful
listening.
One orientation of polarity, either normal or reversed, should result in a discernable dip
through the crossover region, due to acoustic cancellation. The opposite polarity should
result in either a flat response or a peak through the crossover region, due to acoustic
addition.
Note: When experimenting to determine the proper polarity, you can reverse the full-range
loudspeaker(s) or the subwoofer, but never both at the same time (reversing both at the
same time will not alter the phase relationship of the two systems). If there is one
subwoofer and several full-range enclosures in the same system, it will, of course, be easier
to reverse the subwoofer’s polarity to test the response. Ultimately, as we’ll see below, it’s
best to keep the subwoofer in a polarity-positive state.
If there is no discernable difference or only a very minimal difference in the measured or
audible response when the polarity is reversed, it indicates one of two things:
(1) The full-range system that the subwoofer is being used with does not reproduce
enough low-frequency output to cause either cancellation or addition with the