speaker / amp ohms and watts!

[fordmandj 0]

hi all, i have just been offered 4x peavey st 15 speakers for a very low price http://www.dj-forum.co.uk/html//emoticons/biggrin.gif and i am just wondering how i could amp them up to run either 2x speakers or 4x speakers at once.

 

the speaker specs are

 

150w RMS @ 8 ohms per cab ( i know this is not great but i will be using them mailny for vocal reinforecment in a large hall only)

 

So i understand that i will need at 150w x 2 rms @ 8 ohms amp to run 1 pair but

if i want to run all 4 (2 per channel) what will happen to the ohms and wattage.

 

Someone told me that of i connect 2 of them in series (so the power actually goes through 1 speaker then through the other) then the ohms will drop to 4 ohms and the watts will double to 300W for the 2 speakers. IS this Correct??? or not??

 

and i think by what the guy told me, if you connect them in parrallell (<spelling!) then the watts and ohms will stay the same, is this right?? http://www.dj-forum.co.uk/html//emoticons/533.gif

 

O have been looking around at amp specs and have found the peavey pv - 900 which has the following spec:

 

2x450w rms at 2 Ohms

2x300w rms at 4 Ohms

 

how will this run my speaker system??

 

As you can see this is really confusing me, any help with the ohms / watts or reccommendations for amps for this lot would be great (bearing in mind that i want to try and run the same amp for either 2 or 4 speakers!

 

I know this is a long drawn out question, but i am really really stuck with this, HELP! http://www.dj-forum.co.uk/html//emoticons/wacko.gif http://www.dj-forum.co.uk/html//emoticons/wacko.gif

 

Cheers, james

[Gary 0]

Putting the wattages aside for a moment and just looking at the impedence (ohms).

 

If you attach 2 x 8 ohm speakers to one output channel of an amp using the double sockets on the rear of the speakers (parallel), the amp will see a 4 Ohm load on that output channel.

 

As for the wattage...2 x 150w 8 ohm speakers would normally be 300watts of course, but running at 4 ohms, instead of 8 ohms, then you've effectively got 600 watts.

 

Amp'ing the above...IF you want to get 600watts at 4 ohms out of your 600watt speakers (at 4 ohms per side) you should look at amps capable of delivering about 1000 to 1200+ watts at 4 ohms per side. Nice places will advertise such an amp at its 8 ohm ratings eg: 500 to 600 watts per channel @ 8 ohms... be wary of adverts of "A 2000watt amp for only...£..." they're probably quoting 4 or even 2 ohms...

 

As 2 ohm loads.... few amps can safely and reliably deliver 2 ohms at our sort of demand, all night. Sure, a few makes/models can eg: Amcron/Crown/QSC to name a few, but its safer to stick to 4 ohms and simply run more amps.

 

Personally, on the above set-up, I'd run the amps with their input settings at a little over halfway to 3/4s, with a compressor/limiter in-line between the mixer and amps in case of the mixer having any accidental operator issues eg: mixers master volume control getting nudged up to max instead of the intended channel 4 etc...

[jeffwall 0]

buy powered speakers!! http://www.dj-forum.co.uk/html//emoticons/biggrin.gif and forget ohms watts and amps http://www.dj-forum.co.uk/html//emoticons/beer.gif

[superstardeejay 0]

That PV amp will handle the load easily.

[norty303 0]

QUOTE

Amp'ing the above...IF you want to get 600watts at 4 ohms out of your 600watt speakers (at 4 ohms per side) you should look at amps capable of delivering about 1000 to 1200+ watts at 4 ohms per side.

 

Just checking this Gary - is this a U-turn by you on your opinion of NOT running amps of 2 x the rms rating of the speaker or is it a mis-type and it should have read '600watt speakers (at 8 ohms per side)' or where you still meaning there'd be 2 of these 600 watt 8ohm speakers in parallel per side?

[Gary 0]

Not a U-turn, as I've used the "Driving a car at 90mph when it can only do 90mph" analogy in previous threads, but I would add my usual comments that a compressor/limiter would be a worthwhile safety device, and that the amps should have their attentuation (volume as some my call em) controls turned down.

 

If a speaker is rated at 500w RMS then by all means fire 500w RMS into it, from an amp capable of delivering 500w easily. A 500watt amp would delivery 500watts (ish) but it would be thrashing itself and just waiting to send some nasty DC bits into your speakers. Safer therefore to use say a 900watts rms amp, which will simply be "doing just nicely thanks" when being asked to deliver 500watts rms. (again, attentuators down, and compressor/limiter in-line too).

 

What I think is crazy is when someone slaps a 1000watt amp, UNattenuated, onto a 500watt speaker, with their mixer outputing off into the red and wondering why their speaker cones ended up 40ft away, sunny-side down in the blue cheese dip on the buffet table:D then doing the Monday morning phone'round for re-coning services.

[norty303 0]

QUOTE

Not a U-turn, as I've used the "Driving a car at 90mph when it can only do 90mph" analogy in previous threads, but I would add my usual comments that a compressor/limiter would be a worthwhile safety device, and that the amps should have their attentuation (volume as some my call em) controls turned down.

 

LOL

 

Didn't think you had!

 

But if you re-read back what you wrote, you clearly stated that they wanted an amp capable of giving 1000 - 1200w/ch @ 4ohms to run their 600wrms 4ohm speakers.

[superstardeejay 0]

Most cheap and cheerful amps rated at a given wattage will actually be thrashing themselves at the stated output as Gary suggests.

 

Premium grade amps will generally have headroom built into the spec (remember the HH V series, Citronic PPX etc). They sounded much more solid, Watt-for-Watt than your modern Chinese units mentioning no names. A cheap amp will clip more readily after you've lit up all your VU leds!

 

If buying cheapies then add a few more watts on the figures they quote.