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10
Protection Circuits
There are several protection mechanisms designed
into the S•8 to safeguard the loudspeakers and
amplifi ers 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 Clip LED indications,
excessive distortion), you can still damage the
speakers in the S•8 by overdriving them past the point
of amplifi er clipping. Such damage is beyond the
scope of the warranty.
Overexcursion Protection
A 12 dB/octave high-pass fi lter at 40 Hz just prior
to the low-frequency amplifi er prevents very low
frequencies from being amplifi ed. 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 amplifi ers produce heat. The S•8 is designed to
be effi cient both electrically and thermally.
• If for some reason the heatsink gets too hot, a
thermal switch activates and turns off the amplifi er.
This protection operates independently for the
low-frequency and high-frequency amplifi ers.
Therefore, it is possible for only the low frequency
or high frequency amplifi er 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 airfl ow 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 airfl ow through the fi ns.
Integrated Magnetic Shielding
The S•8 contains drivers with large magnetic
structures. The drivers’ magnets are shielded to help
prevent the magnetic fi eld from radiating out into
the environment and playing havoc with computer
monitors or TV screens. Unshielded speakers can
cause distortion in both the shape and color of the
picture if placed too close to a CRT (cathode ray
tube). If you have a particularly sensitive computer
monitor or TV screen, it may be necessary to move
the speakers a few inches away.
Input Signal Wiring
You should use high-quality, shielded cable to
connect the signal source to the INPUT jack on the S•8.
• 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.
• In certain home theater applications, it may be
necessary to connect the speaker outputs from
a stereo receiver to the inputs of the S•8s, if the
receiver doesn’t have preamp outputs or other
line-level output connections.
CAUTION: Do not attempt to
connect a speaker output directly
to the input of the S•8! Speaker
levels are much higher than line
levels and can damage the input
circuitry in the S•8.
You can, however, insert a speaker-level-to-
line-level signal attenuator between the receiver’s
speaker output and the S•8’s input. Your Mackie
dealer may be able to help you fi nd one, or if you
enjoy do-it-yourself projects, you can build your own.
Contact our tech support department for more
information.