Community R-Series Installation/Operation Manual for Models R.5 and R.25 — Page 21
Loudspeaker Grounding
In a low-impedance (8-ohm) system (not 70/100-volt), the minus (-) output terminal of the power amplifier is
usually grounded. This provides a ground reference for the loudspeaker.
In a 70/100-volt system, it is necessary for the amplifier output terminals to be ungrounded. Thus, there is no
ground reference for the loudspeaker. In most cases, this is acceptable. However, in outdoor installations in
areas prone to lightning, it is possible for static electricity to build up on an ungrounded loudspeaker line. In an
extreme case, the static electricity can reach a high enough voltage to arc to ground, either at the loudspeaker or
at the power amplifier, causing damage to the loudspeaker or amplifier.
If this is a concern, it is possible to bleed static charge away from the loudspeaker line by connecting a resistor
from each side of the line to ground either at the power amplifier or at the loudspeaker (in a weather-tight
electrical box). Typically, a pair of 5,000-ohm resistors with 2-watt (or higher) ratings is used for this purpose for
70-volt lines. For 100-volt lines, use a pair of 10,000-ohm resistors.
Bi-amplification
R.5 and R.25 products include an internal passive crossover network. They are not designed for biamplification.
70-Volt, 100-Volt Autoformer
Transformer versions (“T” suffix) include an internal 200W, 70/100V autoformer or transformer. For 70V lines
the input taps are 200W, 100W, 50W and 25W. For 100V lines the taps are 200W, 100W and 50W.
Some models have a multi-wire input cable to select the tap (R.5SUBT, R.5HPT). In this case, termination is
usually best made inside an appropriate electrical box (weatherized as needed) using standard wire splicing
methods. Other versions have a screwdriver-selectable switch accessible through a plug screw (R.5COAXxxT,
R.25-94TZ & R.5xxTZ) which is accessed by removing the plug. Rotate the switch to the appropriate stop
(“click”) for the desired tap using a flat-head #1 screwdriver.
Re-insert the plug screw after adjusting the tap to maintain weather-resistance. Use caution not to over tighten
the plastic plug screw to avoid stripping the delicate plastic threads. For the R.25-94TZ, re-install the plug so
that is flush with the exterior of the cabinet to avoid undue pressure on the switch mechanism. See the charts
on pages 8-10 or the Specifications Section near the end of this manual for details about a specific model.
For additional information, Community’s web site includes a technical note on the design of 70-volt/100-volt
distributed systems.
Connecting Multiple Loudspeakers to a Single Amplifier
The best way to connect multiple loudspeakers to a single power amplifier is to design a 70-volt or 100-volt
distributed system. However, it is acceptable to connect as many as four 8-ohm loudspeakers in parallel and
connect this combination to a single amplifier channel provided that amplifier is rated for the resulting 2-ohm
impedance load.
INSTALLATION
