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10
Protection Circuits
There are several protection mechanisms
designed into the TH-15A 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-15A 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 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-15A
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 through
it’s fins, 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-15A, we recommend leaving at least
six inches of air space behind it.
• If for some reason the heatsink 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 heatsink cools down to a safe
temperature, the thermal switch resets
and normal operation resumes.
• If the heatsink 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 heatsink to increase the
airflow through the fins.
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 IN
jack on the TH-15A.
• Foil shielded cables, such as Belden 8451,
8761, or 9501 are commonly used for
studio wiring.
• Microphone cables work well.
• 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-15A loudspeaker is designed to sit
on the floor or stage. It can 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-15A.
WARNING: The cabinet has
no rigging points and is not
suitable for rigging.
NEVER attempt to suspend
the TH-15A 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.