Installation manual

Community S-Series - Operation and Installation Manual - Page 27
Impedance and Paralleling Loudspeakers
Loudspeakers of identical type may be connected together on the same amplifier. This
forms a parallel circuit. When two loudspeakers are connected in parallel, the nominal
impedance of the circuit will divide in half. For example, if two 8 ohm loudspeakers are
wired in parallel, the result will be a 4 ohm load and the power from the amplifier (voltage x
current) will be divided equally between both. If four 8 ohm (or two 4 ohm) loudspeakers
are wired in parallel, the result will be a 2 ohm load. Again, the power will be divided
equally among the loudspeakers.
If an uneven number of loudspeakers are to be connected in parallel, you can use the
following formula to calculate the resultant impedance, where Z is the impedance in ohms:
(1/Z1) + (1/Z2) + (1/Z3) +… = (1/Zt) = Z.
In the above formula Z1 is the impedance of the first loudspeaker, Z2 is the impedance of
the second loudspeaker, Z3 is the impedance of the third loudspeaker, etc., and Zt is the
sum total of the loudspeaker impedances.
Here is an example using 3 loudspeakers, each with an 8 ohm impedance:
(1/8) + (1/8) + (1/8) = (1/0.375) = 2.6666 ohms.
Unequal Impedances
It’s important to note that when wiring loudspeakers of unequal impedances in a parallel
circuit, the power will not be divided equally among each loudspeaker. For example, if an
8 ohm and a 4 ohm loudspeaker are wired together in parallel, the resultant load will be 2.6
ohms. The 4 ohm loudspeaker will draw twice as much current from the amplifier as the 8
ohm loudspeaker. In this example, if the amplifier is capable of producing 1800 watts into
the 2.6 ohm load of the combined loudspeakers, the 4 ohm loudspeaker will receive 1183
watts while the 8 ohm loudspeaker receives only 591 watts.
Know Your Amplifier
Not all amplifiers can safely drive low-impedance loads, though usually 4 ohms and higher
is not a problem. Very low impedance loads may cause the amplifier to clip prematurely,
overheat, shutdown, or fail altogether due to internal device damage.
Even when an amplifier is quite stable driving a low impedance load, cable loss will be
greater than with moderate impedance loads, damping factor will be reduced, and if the
amplifier were to fail, a larger portion of the sound system is likely to be taken off-line due
to the fact that a low impedance load implies a larger number of loudspeakers being
powered from a common amplifier.
C-TIP: Keeping the loads at 4 ohms or higher will lengthen the life of your amplifier(s) and
improve the reliability and overall sound quality of the system.
Choosing Loudspeaker Wire
Wire and cable is used to transfer power between the amplifier and the loudspeaker. Wire
and cable can be purchased with copper and aluminum conductors; for loudspeakers only
copper conductors should be utilized.
The construction, conductor type, and insulation material of wire and cable vary widely.
Wire can be purchased with solid core construction, stranded core construction, and densely
stranded construction. Cables are typically available only as stranded or densely stranded.
Speakers may be driven through individual conductors bundled together and pulled through
conduit, or through a cable made up of a number of conductors covered with an overall
jacket, which then may or may not necessarily be installed in a conduit. Wire and cable
manufacturers offer multi-conductor cables with 30 or more high current conductors