Placement; The Ins And Outs Of Polarity - Mackie SRM1550 Owner's Manual

Placement

SRM1550 subwoofers are designed to sit on the floor
or stage. They are not designed to be pole-mounted
or suspended.
When pole-mounting loudspeakers, be sure that
the subwoofers are stabilized and secured from falling
over or being accidentally pushed over.
SRM1550s have no rigging points and are
not suitable for rigging. NEVER attempt
to suspend an SRM1550 by its handles.
Polarity Waveforms
Figure 1: Normal [0˚]
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The Ins and Outs of Polarity

SRM1550 subwoofers include a switch that allows
you to quickly invert the polarity of the subwoofer's
output relative to the input signal it is receiving from
the mixer or other sound source. But what exactly does
that mean? A subwoofer works by literally pumping air
as the woofer cone moves in and out with respect to the
cabinet in which it is housed. It does so according to the
low-frequency portion of the signal it receives from the
sound source.
The woofer cone is simply following the waveform as
seen in the sine wave in Figure 1. As the sine wave rises,
the woofer cone pushes out. Likewise, as the sine wave
falls, the woofer cone pulls into the cabinet. A musical
signal is much more complex, of course, but the same
principle applies. Movement of the woofer cone causes
air pressure changes that we perceive as sound.
When the normal/invert [polarity] switch [4] is
engaged, the original waveform is simply reversed 180˚
[see Figure 2]. Again, the subwoofer cone follows the
waveform. However, this time the woofer cone starts
by pulling into the cabinet followed by the woofer cone
pushing out. If you have ever experimented with a
subwoofer polarity switch, you may not have noticed
any changes to the sound regardless of its position,
especially if you are listening to just the subwoofer.
This is normal, as our ears perceive them both at the
same time.
The normal/invert [polarity] switch comes into play
when the subwoofer is paired with a loudspeaker.
Ideally, the woofer cones of the subwoofer and full
range loudspeaker would work together by pushing
and pulling in unison. SRM1550 subwoofers are
designed to be used in a broad range of applications.
The flexibility provided by the polarity switch is
necessary to ensure that you are receiving the best
possible sound from your system, regardless of your
setup.
Figure 2: Invert [180˚]
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Owner's Manual
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