Community Veris Series Spécifications télécharger pdf (Page 19)

VERIS 2 – Operation Manual - Page 19

WARNING: After wiring the amplifier(s) to the loudspeaker(s), first power up all

devices that are upstream of the amplifier, such as mixers, equalizers,

compressor/limiters, etc., before powering-up the amplifier. This avoids passing any

transient ‘clicks’ or ‘pops’ that may originate in the upstream devices to the

loudspeakers. The amplifier should initially be powered-up with its gain controls turned

all the way down. After making sure that a continuous signal is present, such as a CD

playing, slowly raise the level of the gain controls to establish that the wiring has been

installed correctly. Only then should the loudspeaker be operated at normal output

levels.

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.

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 covered

with a variety of jacket types. Jackets may be made of PVC, rubber, neoprene, and other

materials, depending on the intended conditions of use.

Generally speaking, the wires and cables that power loudspeakers do not need to be twisted

into pairs, though there is some benefit to doing so. A twisted pair of conductors has the effect

of cancelling electro-magnetic radiation, thereby reducing mutual induction among circuits

that share the same physical space (such as a cable tray or conduit), along with canceling the

crosstalk that might otherwise result.

Twisted pairs are commonly used for balanced line signal and microphone cables, in which the

nominal voltages are very low and the input impedance of the load is typically quite high

(>10K ohms). Under such conditions, the use of a twisted pair is essential to reduce crosstalk

among adjacent cables. The twisting insures that the differential amplifier in a balanced line

receiver will see identical phase and amplitude of any extraneous Electro Magnetic

Interference (EMI) induced in the cable on both polarities, thereby allowing the EMI to be

differentially cancelled.

In contrast, however, loudspeakers have input impedances that are quite low and operate on

much higher voltages. The potential of inducing an audible signal from adjacent wiring is close

to zero. The installer may, however, choose to use twisted pair loudspeaker cable for other

reasons. Certain amplifiers may exhibit instability when driving long lengths of wire installed in

conduit. A twisted pair will insure that the reactance of the loudspeaker cable is identical on

both the plus and minus wires, thereby presenting a more stable load to the amplifier.

Note that when specifying multiple twisted pairs of speaker cables intended to share the same

conduit, the conduit will need to be sized much larger than with loose or bundled conductors.

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Community Veris Series Spécifications Page 19

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