Placement; Care And Maintenance; The Ins And Outs Of Polarity - Mackie Thump 18S Owner's Manual

Placement

The Thump18S subwoofer is designed to sit on the
floor or stage. It is not designed to be pole-mounted
or suspended.
When pole-mounting loudspeakers, be sure that the
Thump18S subwoofers are stabilized and secured from
falling over or being accidentally pushed over. For
stacked scenarios, it is highly suggested that straps are
utilized. Failure to follow these precautions may result
in damage to the equipment, personal injury, or death.
The cabinet has no rigging points and is
not suitable for rigging. NEVER attempt
to suspend an Thump18S subwoofer by its
handles.
As with any powered components, protect them from
moisture and extreme cold and follow the other Care
and Maintenance suggestions below.

Care and Maintenance

Your Thump18S subwoofers will provide many years of
reliable service if you follow these guidelines:
• Avoid exposing the subwoofers to moisture.
If they are set up outdoors, be sure they are
under cover if rain is expected.
• Avoid exposure to extreme cold (below
freezing temperatures). If you must operate
the subwoofers in a cold environment, warm
up the voice coils slowly by sending a low-level
signal through them for about 15 minutes prior
to high-power operation.
• Use a dry cloth to clean the cabinets. Only do
this when the power is turned off. Avoid getting
moisture into any of the openings of the
cabinet, particularly where the drivers are
located.
Polarity Waveforms
Figure 1: Normal [0˚]
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Thump18S Powered Subwoofer

The Ins and Outs of Polarity

Thump18S 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 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 Thump18S 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. Thump18S 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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