PA Setup...

[St.James]

A friend of mine is looking to buy a new PA. My suggestion to him was to match the Ohms with the power amp and speakers, but go with more wattage on the speakers than the amp, at least 20% more wattage.

I've always been told to do it that way and have always followed that rule. Like 100 watt Marshall heads through 300 watt cabs. A bit more than 20%, but works like a champ!

Today he goes to Guitar Center and starts asking questions there. One guy told him he wanted more power on the amp than the speakers, someone at Musicians Friend told him to match the wattage.

One of these dudes even told him that underpowering the speakers would burn them up. That's the first time I've ever heard anything like that.

I have a 500 Watt power amp running 250 watts to each stereo side to 2 500 Watt cabs and it sounds great. I'm by no means a pro sound engineer, but matching wattage doesn't sound like a good long term idea and over powering speakers sounds way off to me.

What do you guys think about tall of this?

[Jester700]

Here's the deal. "Matching" means less than you think it does. To a certain degree, manufacturers pull speaker wattage ratings out of their...hats. There are more variables involved in cooking a speaker than just wattage. Also, power amps vary in their output over time - that 500W amp is rarely putting out 500W - and speakers are rated a few ways - peak, rms, music, etc.

There are two common mechanisms for cooking a speaker - amp clipping and over powering. If you crank an amp so far that it clips (or even clip at an earlier stage and amplify that signal) it's full of LOTS of HF distortion. This is often what cooks a tweeter, though the woofer remains OK. This is what the "underpowering" guy meant - lower POWER doesn't hurt (after all, a 500w amp puts out less than a watt as your sound fades between songs) but a lower powered amp will *clip* sooner if you try to coax more volume from it.

You can over power a speaker as well, but you always have the option to lower the volume on a higher powered amp.

I get gear that's *fairly* well matched. Wattage ratings shouldn't be more than TWICE or less than HALF of the other. That's a wide range, but it allows flexibility in what's really important - how does the gear sound? If it sounds good, THEN crank 'er up and LISTEN. You'll hear the onset of distortion - at that point, turn it down. If that isn't enough SPL, trade up.

[nor]

How big is 'da rig? If this for club-size gigging, use powered speakers and forgetabutit.