Owner
’s Manual
13
Owner’s Manual
Protection
A protection circuit is built into the DRM passive
loudspeakers to protect their high-frequency 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 DRM
passive 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
The DRM passive loudspeakers have three power-
handling numbers: continuous, program and peak.
So how much power do you really need to drive these
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
Ω
). For the DRM212-P
loudspeaker, this would be 800 watts × 2 = 1600 watts
per channel into 8
Ω
. This ensures that the amplifier
can reproduce peaks that are 6 dB higher than
the continuous (rms) power-handling rating
before clipping occurs.
Recommended Power Ratings
• DRM212-P: 1600W into 8
Ω
(800W rms × 2)
• DRM215-P: 2000W into 8
Ω
(1000W rms × 2)
• DRM315-P: 2300W into 8
Ω
1150W rms × 2)
• DRM12A-P: 2000W into 8
Ω
(1000W rms × 2)
• DRM18S-P: 2000W into 8
Ω
(1000W rms × 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 character-
ized by a “flat-top” appearance to the waveform.
Clipping interrupts the motion of the transducer,
creating distortion and excessive heat in the driver,
which can damage it over time.
Some folks think that if they use a power
amplifier whose power rating is below the maximum
power-handling rating of the loudspeaker, then
they can’t possibly damage the loudspeaker.
But if the amplifier is driven into clipping, even
a lower power amplifier can damage the loudspeaker.
The bottom line is that to prevent damage
to the loudspeakers, you must have a properly
operating sound system. Proper operation of a sound
system includes being aware of types of audio signals
being reproduced, controlling the output levels
accordingly, and operating all the devices in the system
so that no clipping occurs within the signal chain.
Care and Maintenance
Your DRM loudspeakers will provide many years
of reliable service if you follow these guidelines:
• Avoid exposing the loudspeakers 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 loudspeakers
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 cabinet,
particularly where the drivers are located.
Normal Sine Wave Signal
Clipped Sine Wave Signal
