running more speakers off amps

[duro]

hi folks, i wonder if anyone can help

i currently work at a small theatre as a monitor engineer. we have four sends, each split into linked pairs. these are powered by two amplifiers with each send corresponding to one output of an amplifier.

what i would like to know is: what would be the outcome of linking more than two speakers together from the one output? would it simply result in a lower output volume or would the higher impedance put undue pressure on the amplifier?

ie would it melt!

any insight would be much appreciated

duro

[John Bell]

Hi Duro, adding more monitors to the same amp channels will reduce the impedance. If the amp can handle the lower impedance, the output will actually increase and pull more power. However, if the total impedance falls below what the amp can safely handle, it will either blow fuses, or go into a self protection mode. (overheating shut down/ short circuit protection).
My first monitor amp was a 350w RMS mono amp. It could handle 4x 8ohm monitors, with a total impedance of 2ohm.
It only produced it's full 350w RMS output with a 2 ohm load. With only 1x 8ohm monitor connected, it only produced just over 100w RMS. As my first monitors were only 125W RMS, this was an ideal amp to use. As I connected more monitors, more power was available. John.

[duro]

cheers john, am with you to a point.

but doesn't decreased impedance depend on the speakers being wired in parallel? i would be linking three or more wedges together via twin core, unbalanced, xlr leads between output and link sockets - which i presume would place them in series. this would then increase the overall impedance presented to the amplifier wouldn't it?

(i know very little about the internal wiring of the wedges - or impedance ratings off the top of my head)

also, while we're at it could you tell me why it is ok to use unbalanced cabling for monitor speakers, and is it ok to use balanced mic leads as a substitute?

its a bloody minefield!

many thanks

duro

[John Bell]

Hi Duro, link sockets are always in parallel, otherwise they would need a break-jack socket, similar to an insert point, to break into the circuit.
XLR link and input sockets are normally used on powered monitors for the mic/line internal amp connections and not the external speaker connections, which are normally Speakon.

Balanced mic leads, only carry very small currents at very low voltage, 10mV. A big wedge monitor's speaker connections will pull a large current at voltages around 100V. It would be better to use flexible mains cable than a mic lead. Always use the correct cables, as it will prevent failures and safety hazards, like fires & electric shocks.

As for the balanced leads, due to the large amount of gain used to boost the low mic level signals, any induced noise signals would also be amplified as well, so the balanced leads and circuits, cancel out any induced voltages. With speaker cables, this induced voltage is so small compared to the signal, it wouldn't be noticed, as there is no further amplification in that part of the chain. There are also capacitance issues.