Protection Circuits; Input Signal Wiring; Placement - Mackie TH-12A Owner's Manual

Protection Circuits

There are several protection mechanisms designed
into the TH-12A to safeguard the loudspeakers and
amplifiers from inadvertent damage.
CAUTION: The protection circuits are
designed to protect the loudspeakers 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-12A by
overdriving them past the point of amplifier clipping. Such
damage is beyond the scope of the warranty.
Overexcursion Protection
A 12 dB/octave high-pass filter at 60 Hz just prior
to the low-frequency amplifier prevents very low
frequencies from being amplified. Excessive low-
frequency energy below 60 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-12A 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 loudspeaker. When you position the TH-12A, 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 off the amplifier. This protection
operates independently for the low-frequency and
high-frequency amplifiers. Therefore, it is possible
for only the low frequency or high frequency
amplifier to shut down while the other remains on.
• When the amplifier cools down to a safe
temperature, the thermal switch resets
and normal operation resumes.
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• If the internal temperature again gets too hot,
the shutdown process repeats. Should this
happen, make sure that airflow to the rear of the
cabinet is not restricted. If the ambient air
temperature is very warm, try pointing a small
fan toward the rear panel to increase the airflow
across the rear panel.
Driver Protection
Each driver has its own compression circuit, which
helps protect them from damaging transient peaks. The
compressors are designed to be transparent and are not
noticeable under normal operating conditions.

Input Signal Wiring

You should use high-quality, shielded cable to
connect the signal source to the INPUT jack on the
TH-12A.
• High quality microphone cables work well.
• Foil shielded cables are commonly used for audio
wiring.
• The better the shield, the better the immunity
from externally induced noise (like EMI and
RFI). Route the cable away from AC power cords
and outlets. These are common sources for hum
in an audio signal. You can purchase quality
cables from your Mackie dealer.

Placement

The TH-12A loudspeaker is designed to sit on the
floor or stage. It may also be pole-mounted via the
built-in socket on the bottom of the cabinet. Be sure the
pole is capable of supporting the weight of the TH-12A.
WARNING: The cabinet has no rigging
points and is not suitable for rigging.
NEVER attempt to suspend the TH-12A by
its handles.
As with any powered components, protect them from
moisture. If you are setting them up outdoors, make
sure they are under cover if you expect rain.