Ohms HELP!!


2016-02-03 12:04 pm
Hi all,

Have just bought a Peavey XR684 powered mixer and am slightly (only slightly!) confused over the speaker ohmage limitations.

Heres the manual:


SO....taking into account I'll NEVER use the bridge output....can I have 4 speakers ( 2 either side ) @ 4 ohms each to get max power?? ....

OR...4 speakers ( 2 either side) @ 8 ohms each?

Slightly confusing...or is it just me?

Ta in advance, Si
It is rated down to 4 ohms, not 2 ohms.

The number of speaker cabs is not important, only the total impedance matters.

A 4 ohm cab or an 8 ohm cab presents exactly that to the amp - 4 or 8 ohms. Two cabs of an impedance, when connected together cuts the total in half. Two 8 ohm speakers in parallel makes a 4 ohm total. Two 4 ohm speakers makes a 2 ohm total.

item 37 in the manual states a 4 ohm lowest impedance on each channel. it even spells it out with examples of two 8 ohm speakers or four 16 ohm speakers. Both those combinations make 4 ohms.

Each channel has two jacks. The manual explains they are parallel wired. That means the two jacks for a channel are wired together. Just like the two outlets on a wall outlet for AC power. Just like a wall outlet, if ther is a 30 amp circuit breaker behind it, you can plug a 30 amp load into either outlet, but not a 30 amp load into each outlet. That would make a 60 amp load.

So if that is your confusion, you can plug two 8 ohm cabs into the two jacks of one channel, for a 4 ohm load on the amp. NOT a 4 ohm into each jack. Remember, it is the CHANNEL that has a 4 ohm limit, not each jack.

Daisy chaining speakers is still parallel wiring. That means running a speaker cord from the amp to one speaker, and another cord from that speaker to a second speaker, is exactly the same to the amp as running a cord from each jack of a channel to each speaker directly.
Bill, we can discuss impedance curves and resonant peaks and stuff, sure, but in this context that would be over the OPs level.

I did not mean to say that a 4 ohm nominal speaker would present exactly 4 ohms at all frequencies, I meant it to say if you connect a 4 ohm speaker to the amp, consider it is 4 ohms, not something else. The amps are made to drive real world speakers, impedance curves and all.
Let me simplify it:
can I have 4 speakers ( 2 either side ) @ 4 ohms each to get max power?? ....
No, this will damage the amp. Also, don't worry about max power. The difference is negligible when it comes to perceived loudness. eg: 200 watts is not twice as loud as 100 watts. It's a logarithmic scale so in order to get twice the perceived loudness you require 10x the power.
OR...4 speakers ( 2 either side) @ 8 ohms each?