OT - pa question

[protein]

Hello. Can you help me with a question re: pa systems? This is a long-winded question, sorry...

In my band's rehearsal room we have a pa system and one of the speakers died. I have managed to locate two new speakers. The PA is 4 ohm and has two jack outputs. The two new speakers are 8 ohm and have two "parallel" jack inputs.

The one remaining old speaker (which would make a handy monitor for the drummer) has speakon inputs (I have the necessary cables to link it to wherever).

I'm a bit backward on pa system terms "parallel" and "ohms" and so on. Firstly, is it ok to use the two 8 ohm speakers with the 4 ohm pa? and is there any way I can safely link up the third speaker? Do parallel inputs on the back of speakers mean you can daisy-chain another speaker from the spare jack input? ie. could I plug the two new speakers into the two outputs on the pa and then tack on the third speaker as a kind of "speaker thru" from one of the new speakers?

[CME]

Hooking up speakers in parallel halves the ohm load if both speakers are the same. For example two 8 ohm speakers would equal 4 ohm. The actual formula (where R equals resistance in ohms) for parallel is something like:

1/R(total)= 1/R + 1/R + 1/R ect.

The formula for series is much simpler, less common, harder to implement for multiple boxes, and is simply

R(total)= R + R + R + R ect.

So you basically add up the loads.

That is how you figure series and parallel ohm loads. The next thing to learn is do not subject an amp to less resistance than it is capable of handling (4 ohms in most cases). Most amps will burn up pretty quck if you do from what I've heard. Luckily I've yet to fry an amp, but have blown a speaker or two. So as far as your question it depends on whether or not it's a stereo PA? From your description I wouldn't try it unless you knew for sure you had two different amps. If it was two different amps I would probably hook the new speakers to one channel and the old speaker to the other.

[protein]

I only understood the bit at the end. I really am quite stupid I'm afraid.

It's a mono amp but it has two outs. What would be best?

[albee1952]

A mono amp has a single output which has 2 jacks wired in parrallel so its a single output for all intents. Your 2 speakers of 8 ohms each will net a 4 ohm load on your amp. Adding a third speaker may work, but it also may overheat the amp and it will shutdown (if it has thermal protection) or burn out.

[bb_aus]

if you want to run all 3 go buy a quest amp (dirt cheap and perform great) and put your 2 new speakers on one channel and the old speaker on the other channel. whis will load both channels are loaded at 4ohms and the amp will be happy, although you can runs quests down to 2ohms! but unless you need to dont as they will get hot.

to confuse you more 4/8ohm are just a theoretical rating and the actual loading will vary speaker to speaker and change as the speaker warms up.

[Chris Cavell]

I only understood the bit at the end. I really am quite stupid I'm afraid.

It's a mono amp but it has two outs. What would be best?

The 2 8-ohm speakers in parallel = 4 ohms. You'd be fine. But, don't run the third drummer monitor, as that would most likely drop down below the 4 ohm minimum rating for that amplifier. BTW, if it's a mono amp with 2 outs on the back, those outs are parallel.

The only thing you've got to worry about is blowing those 2 new speakers if they aren't rated for as much power (watts) as the amplifer.

[protein]

Thankyou very much everyone. The third little speaker can now be the drummer's beer holder instead.

[bb_aus]

The third little speaker can now be the drummer's beer holder instead.

sell it and buy more beer

[astrorock]

how powerfull is the amp? you can run all 3 if you run them in series..
when you run spks in series you doubble the resistance. so for example if you
have 3 8ohm speakers you'd have 24ohms in series. if your amp has some power
you be able to do that, it's actually safer.. you won't blow an amp at 24ohms.
you'll lose some output but if the amp is powerfull it should still be adequate
for rehersal.. unless you rehearse at ear bleeding volumes!!

[protein]

I'm confused now. The amp is a cheap hunk of junk we bought from ebay.

http://cgi.ebay.co.uk/Meridian-HA-10...QQcmdZViewItem

It's not very powerful I don't think.

The new speakers are Wharfedale Pro PT-12.

So, you are saying I should hook up the old speaker too?