PA SPEAKERS

[GRAHAM SG1]

A question for you knowledgeable people out there

I use a Yamaha EMX88S powered mixer with two 400 Watt/8ohm 12" Peavey speakers in my band, the mixer has two 400 Watt amps (one per side), my guitarist has just bought a pair of Marshall 15" 125 Watt/8ohm speakers and insists that we can use these speakers with the mixer safely, I have always believed that the speakers ratings should be equal to or exceed the amps rating, now is he right or will the speakers get damaged by overloading if we use them with this mixer ?

Thanks

[allexcosta]

400W@4ohm, a lot less @8ohm per side...

You should be alright if you don't go crazy with the volume or bass frequencies... Your PV's will probably sound better and I don't see a reason to replace them with these Marshalls...

[juajuara]

Great question. You can use them safely, but as you point out, it places the burden of making sure you don't overdrive them on the sound engineer. I am not going to make a cohesive argument, or a complete statement, I'm just going to throw out a few thoughts:

- Twice as loud, in terms of energy, is 3dB. Twice as loud, in terms of audible perception, is 10dB. The difference in "loudness" between the speakers may depend more on their sensitivity than their power ratings: I recommend an A/B test at relatively low power levels to get used to the difference.

- Because of the logarithmic relationship between loudness and power, many amplifiers use logarithmic volume knobs. Be aware of this as you increase power levels: if 400W is a "10" on the logarithmic volume knob, 125W is about "8". On a linear knob, 400W would be 10, and 125W would be about 3.

- Many speaker failures are due to square-wave clipping and not total power input. It's equally important to have good program material as well as maintain proper power levels.

- Another large factor in figuring out how wide to open the throttle, is the power content of your program material. Amp/Speaker killers are keyboards/synths and bass. Use an RTA to help unlock this mystery.

- I would not use the Marshall's personally, as I don't see them as an improvement over the Peavey's. However the EMX88S say's it's maximum power rating is 400W/4 Ohm, with an 80W/4 Ohm nominal rating. I think either speaker would be fine.

Hope this helps,
Emil

[steveksux]

Yamaha EMX68S, EMX88S powered mixer.pdfMAIN L, R: 400 W+400 W/4Ω @0.5% THD at 1 kHz, 270 W+270 W/8Ω @0.5% THD at 1 kHz

So its only 270W at the impedence of the speakers you have, not 400.

Why replace the Peavy speakers you're currently using?

They're rated at 400w, driven by a 270W amp, you'd have a bit of trouble blowing them, and could actually give them much more power than have available.

The marshalls rated at 125w @ 8ohms can most likely be safely driven with a 270 W amp, but if you try to push them you could probably blow them.

If it was your amp, I wouldn't worry, you'd be listening to your amp, any signs of distortion you could turn down.

However:
How will you tell if those speakers are distorting from being pushed too hard if you are behind them since they're being used for PA?

Still don't understand why he bought those speakers when you already had the Peavey speakers. Are they monitor speakers and you're going to run them both off one channel of the powered mixer, and the mains off the other? That board can be configured to run that way.

In that case, you have 400W@4 ohms, divided by 2 8 ohm speakers, so each 125 W marshall speaker would be only seeing 200W, less likely to be too much, plus you'd be listening to them (they're monitors) and be able to hear when they start distorting and can turn down to protect them.

Randy

[GRAHAM SG1]

Thanks for the help guys .
I should add that I am the sound engineer as well as bassist and singer, yes I know I have an easy life
We only play relatively small venues, the guitarist bought the Marshalls at a steal and thought they would sound better being 15" as opposed to my Peaveys ?, he has more GAS than a donkey in an indian restaurant
For rehearsals I use a Carlsbro 100 Watt PA with two 10" speakers which is always flat out so we tried the Marshalls with that PA and they were good, the Carlsbro was on half instead of full so we will only use them for that, I agree with you guys so the answer to gigging the 15s is no-thanks