pwr amps input question

[anthillrich]

hi all. i have a question on using two separate amps, with two separate speaker pairs, driven from a stereo eq, and stereo board.

i have a QSC Mx 2000a, connected to a pair of JBL's. the amp is set for parallel operation, so one input(chan A) drives both channels. thats for the right side of the sound system.

i have a CREST audio CA9 connected to another pair of speakers, and i want that to be driven the same way for the left side of the sound system(parallel).
and finally my question,

the inputs for the QSC is Tip negative, ring positive, sleeve gnd.
the inputs for the Crest is TIP positive, ring negative, sleeve gnd.

i am using unbalanced input cables( the boards outs are unbalanced), if i hook it all up with no wiring mods, my left and right speakers will be out of phase, right?

could i simply reverse the "Banana" plugs of the speaker cables of one amp to match the polarity of the other? should i do that at the input instead? is there any benefit to do it one way over the other?
lastly, why do manufacturers do this kind of stuff anyway?
thanks for any advice.

[Albert Kreuzer]

the inputs for the QSC is Tip negative, ring positive, sleeve gnd.
the inputs for the Crest is TIP positive, ring negative, sleeve gnd.

i am using unbalanced input cables( the boards outs are unbalanced), if i hook it all up with no wiring mods, my left and right speakers will be out of phase, right?

Right.

could i simply reverse the "Banana" plugs of the speaker cables of one amp to match the polarity of the other?

Yes.

should i do that at the input instead? is there any benefit to do it one way over the other?

Technically, it doesn't matter.
If you reverse the banana plugs, you don't have to make a special cable.

lastly, why do manufacturers do this kind of stuff anyway?
thanks for any advice.

QSC says it helps with unwanted feedback - well, why doesn't everybody do it? How can other brands survive being in phase?

Cheers,
Albert

[anthillrich]

thank you. i appriciate the help.

[Enzo]

QSC says that because it is something their amps do, so they trumpet it as if it matters. And as if they have the slightest idea what the phasal relation might be between someone's microphone and the speakers, through the mixer, through all the processing, and through the power amp.

Other than very basic systems, the average PA system has at least one phase reversal switch in the path.

it really only matters when used in the fashion you are using it in - with other amps.