8
Protection
HF Protection
A protection circuit is built into the
6912, 6915, and 6925 to protect their high-
frequency compression drivers from excessive
power. When tripped, the protection circuit
substantially reduces the power to the
HF driver. After the driver cools to a safe
operating temperature, the protection
circuit resets and normal operation resumes.
However,
if the protection circuit senses
excessive power, it will trip again. In this case,
it is necessary to reduce the power to the
loudspeaker by either turning down the gain
controls on the power amplifier or turning
down the master volume control on the mixer
or other sound source.
CAUTION:
The protection
circuit is designed to
protect the HF driver under
reasonable and sensible
conditions. Should you
choose to ignore the warning
signs (i.e., frequent clip LED indications on
the mixer or power amplifier, excessive
distortion), you can still damage the drivers
in the Series 69 loudspeakers by overdriving
them past their recommended amplifier
power-handling ratings, or past the point of
amplifier clipping. Such damage is beyond
the scope of the warranty.
Amplifier Power
We give you two power-handling
numbers for the Series 69 loudspeakers:
continuous amd program. So how much
power do you really need to drive the Series
69 loudspeakers?
The answer to that question depends
on what type of program material you are
running through the system and how loud it
needs to be.
Some audio signals have lots of
momentary peaks whose amplitudes
extend far above the average overall level
of the program. Percussion instruments are a
good example of this. Other types of signals,
like highly compressed rock music, have
a higher average signal level with fewer
peaks. Speech reinforcement requires less
power overall, but involves large moment-
to-moment variations in level.
Assuming you want to use the full
capability of the loudspeaker, and the
program contains at least some momentary
peaks, we recommend that you use
an amplifier that is rated at twice the
continuous power rating of the loudspeaker
(into 8 ohms). For the 6912s, this would be
250 watts x 2 = 500 watts per channel into
8 ohms. This insures that the amplifier can
reproduce peaks that are 6 dB higher than
the continuous (rms) power-handling rating
before clipping occurs.
Recommended Power Ratings
6912
500 watts into 8 ohms (250 watts rms x 2)
6915
600 watts into 8 ohms (300 watts rms x 2)
6925
1200 watts into 8 ohms (600 watts rms x 2)
6918s 900 watts into 8 ohms (450 watts rms x 2)
Preventing Loudspeaker Damage
Speaking of clipping, this is likely
the number one cause of damage to
loudspeakers. Clipping occurs when the
signal at the output of any device in the
system (not just the amplifier) reaches its
maximum level. The input signal to the
device may continue to increase, but the
output simply stops, and is characterized by
a “flat-top” appearance to the waveform.
Normal Sine Wave Signal
☺
Clipped Sine Wave Signal
Clipping interrupts the motion of the
transducer, creating distortion and excessive
heat in the driver, which can damage it
over time.
