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Protection Circuits
There are several protection mechanisms designed
into the TH-18s to safeguard the subwoofers and
amplifiers from inadvertent damage.
CAUTION: The protection circuits are
designed to protect the subwoofers under
reasonable and sensible conditions. Should
you choose to ignore the warning signs (i.e.,
frequent OL LED indications, excessive distortion), you
can still damage the speakers in the TH-18s by overdriving
them past the point of amplifier clipping. Such damage is
beyond the scope of the warranty.
Limiting
The driver has its own compression circuit, which
helps protect it from damaging transient peaks. The
compressor is designed to be transparent and is not
noticeable under normal operating conditions.
Overexcursion Protection
A 12 dB/octave high-pass filter at 40 Hz just prior
to the low-frequency amplifier prevents very low
frequencies from being amplified. Excessive low-
frequency energy below 40 Hz can damage the woofer by
causing it to "bottom out," also known as overexcursion,
which is equivalent to a mechanical form of clipping.
Thermal Protection
All amplifiers produce heat. The TH-18s is designed
to be efficient both electrically and thermally.
The amplifier module is mounted on a large
heatsink, which is cooled by convection where cool air
is drawn over the rear panel, carrying the heat away.
In order for this convection cooling to work efficiently,
it is important to provide adequate airspace behind
the subwoofer. When you position the TH-18s, we
recommend leaving at least six inches of air space
behind it.
If for some reason the internal temperature gets too
hot, a built-in thermal switch activates and turns down
the amplifier. When the amplifier cools down to a safe
temperature, the thermal switch resets and normal
operation resumes. If the internal temperature again
gets too hot, the output level reduction process repeats.
Should this happen, make sure that airflow to the rear
of the cabinet is not restricted.
12
Placement
The TH-18s 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
TH-18s 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.
WARNING: The cabinet has no rigging
points and is not suitable for rigging.
NEVER attempt to suspend the TH-18s 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 Mackie 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 cabi-
net, particularly where the driver is located.
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