Community R-Series Installation/Operation Manual for Models R.5 and R.25 — Page 20
Use of Limiters
Community recommends use of a limiter to help prevent loudspeaker damage due to sudden transients
(dropped microphones, etc.) or amplifier clipping. When used for this purpose, connect the limiter as the last
item in the signal chain before the power amplifier (at the input to the power amplifier). Set the limiter’s
“threshold” high enough so that no limiting occurs until the signal is in danger of clipping. Set the limiter’s
“compression ratio” to a high enough ratio to prevent clipping. For professional audio equipment, a typical
threshold setting would be +10 dBu and a typical compression ratio setting would be 10:1 or higher.
Use of Protection Capacitors
A properly chosen high-pass filter and limiter will provide all the protection needed for most systems. However,
a properly chosen capacitor, inserted in the speaker line between the amplifier and loudspeaker, acts as an
additional high-pass filter providing an additional level of protection when needed.
Use a non-polarized capacitor with a voltage rating exceeding the peak-to-peak voltage output of the power
amplifier. A “motor start” capacitor will usually meet these specifications. Install the capacitor in the equipment
rack or in a weather-tight electrical box near the loudspeaker. Choose the capacitance value from the following
equation:
Where C is in microfarads,
π
= 3.14, z is the actual impedance seen by the power amplifier and f is the desired -
3dB frequency. A good choice of f is the same frequency as the recommended high-pass filter for the chosen R-
Series model. The impedance seen by the power amplifier will be 8-ohms for a single R-Series model, 4-ohms
for a pair of loudspeakers in parallel and 2-ohms for four loudspeakers in parallel.
For a 70-volt system, a single protection capacitor can be installed for all of the distributed loudspeakers
connected to a single amplifier channel. Use the same equation to calculate the capacitor size. Remember that
the amplifier peak-to-peak output voltage will be very high (at least 200 volts) so choose a non-polarized
capacitor with an adequate voltage rating. To calculate the impedance presented to the amplifier, use this
equation:
Where z is the impedance presented to the amplifier and P is the total power drawn by all of the distributed
loudspeakers connected to that amplifier channel. That power is simply the sum of all of the 70-volt taps chosen
for the individual loudspeakers. For a 100-volt system, substitute the constant 10,000 in place of the constant
5,000 in the equation.
INSTALLATION
z
f
C
*
*
000
,
500
Figure 2:
Protection Capacitor
Equation
P
z
000
,
5
Figure 3:
70-Volt Impedance
Equation
