Proper PA power?

Drive them with more power than they're rated?

Um, keep reading bro.

 

Are you just looking for mains? Do you have subs? Monitors?

 

There really is no hard fast rule. Most guys have enough power to blow their speakers apart, but you have to use your ears. Don't pump 300 watts into 150 watt speakers full on and expect them to survive.

If I were you I would get a whole different PA set up, but the simplest answer I can give you to your question is to just buy a used pair of Yamaha club series. Using the 808 you ain't going to do much better than that IMO.

 

If you want to play loud, get the speakers that can do it. Size the amps according to what the speakers can handle, using whichever multiplier "rule" you happen to believe in.

What you don't want is anything to be working too hard. That's when stuff starts breaking.

 

Hi.

First of all, the idea behind having more power output on the amps than the speakers can handle, originates from the same fact as the almost always misunderstood/mis-quoted underpowering "myth".

An amp, especially SS, can have a lot more distortion content in the upper region of the frequency spectrum than in the mids/lows when pushed to their limits. Badly/cheaply designed amps are worse than pro level amps.
On high SPL systems, that high frequency distortion can go un-noticed because the mids do not distort yet, or the driver distortion is masked by intentionally generated distortion. The result is a blown high-frequency driver by OVER-POWERING the driver.
Low cross-over point on 2 way systems increases that possibility drastically.

In the past, the amplifiers cost a lot more clamshells/watt than the speakers did, and that obviously led to using small amps with a lot of speakers. That also led to using horn loaded cabs, and since the horn shape design reduces audible distortion, the problems were actually worse than with direct radiator designs.

Pros obviously knew these things just as well (or even better ) than they do now, but the weekend warriors and clueless engineers were buying high frequency drivers and repair kits on a weekly basis.

USE YOUR EARS, and use quality gear and You'll be golden no matter what combination you choose to use.

Regards
Sam

 

The rule you’re referring to is "more power than speaker", so the amps don’t have to run cranked to push the speakers - reasoning that the amps last longer because they idle along (don’t have to work as hard).

The volume will only be as loud as what the speakers are capable of delivering. Start with speakers that cover your needs and have enough power to damage the drivers - but, never push the speakers to failure.

Overhead - You can never have to much extra power!!!

 

There's 3 ratings on most speakers.

Continuous RMS (1Khz sine wave at steady amplitude

Program RMS (music/varying freq's and amplitudes)

Peak (momentary transients)

A JBL prx415m speaker specs
300 cont (1/4 of peak)
600 prog (1/2 of peak)
1200 peak

You'll notice that if you only have the peak rating of a speaker, you can figure the cont rating will be 1/4 of peak, prog rating is 1/2 of peak.

1.5 x 300= 450
2 x 300= 600
4 x 300= 1200

A 300w cont rated amp will work but have no headroom for peaks without going into unacceptable levels of harmonic distortion if amplifier input is overdriven.

A 600w cont rated amp will allow 3 db of headroom before unacceptable harmonic distortion. (2x cont rating)

A 1200w cont rated amp will allow 6 db headroom (4x cont rating). It gives the best headroom but would require using a limiter to protect the speaker(s).

Live music has greater dynamic range than recorded music that's compressed and limited during production. A system used for a DJ can get away with less headroom. A band system you would want more headroom.

 

^^^ This is what I use as a guide. Case in point: we're using (2) daisy-chained Carvin 1503's (400 / 800 / 1600) powered by a single XLS2500 (2400 watts / 4 ohm bridged mono). Simple case of overkill, right? Not really. Each enclosure has the potential to "see" 1200 watts which equates to 1.5 X program RMS of 800 watts. Plenty of headroom and the amp doesn't even break a sweat. Add some judicious limiting and common sense and we're good to go.

This blurb was thrown at me several years ago by a builder several years ago: "...stupid behavior results in damaged speakers." IOW, pushing any driver / enclosure configuration beyond its design specs & limitations may result in component failure.

Riis

 

^ The 1.5 to 2x guide is based on continuous rating not the program rating. The program rating IS 2x the continuous rating.

 

Even just a couple of days ago we had a post from the Tech21 company representative claiming that most pro audio guys run double the power that their speakers can handle, and his own guy runs THREE times the power. He made this statement with total sincerity, intending to show how real professional guys do it.

Who am I to say they are all mistaken--especially the 3x power guy--after all, I'm not a professional soundman, nor do I represent a major brand!

 

The problem is that "3 times the power the speaker can handle" means nothing without stating if your basing the 3x on the continuous or peak.

A speaker can handle 300 cont and 1200 peak. 900w would be fine.
3x peak would not.

 

...but they don't get much work because they've blown up all their enclosures!

Just kidding. The extra power does allow for expansion / adaptation to meet the needs of the venue. I found this to be handy in more than a couple of situations.

Riis

 

You never want the amp to be the limiting factor.

The amount of power a speaker can make use of is a complicated thing, depending on crest factor, total power, frequency distribution, thermal power compression, and a bunch of other stuff. You can blow up a speaker box with much less power than the number on the box indicates and you can safely run it with much more. You just have to know what you are doing.

Amps are much more straightforward, once you hit the rail voltage or current capability of the power supply you are done. That's all you get and it sounds terrible. This is also a good way to pop all your compression drivers with almost no warning.

If you are using an amplifier rated at or below the thermal power handling rating of a speaker box you are leaving a lot of available SPL on the table. and you still have all the power you need to damage the box.

Power is cheap, get a bunch of it.

 

I'm w/ uhdinator and zooberwax in the general school of thought about system headroom. That's a different question, though, than the way the OP is thinking about system design (essentially: "how do I match components to get a foolproof loud with *no chance* of blowing speakers?").

The only rule of thumb there is that you have to listen to your system until you begin to know its safe operating range. If your speakers are chuffing or distorting, you need to back off the volume or adjust the eq, no matter what the component ratings.

Give the OP's genre preference, hearing system distortion can be harder, but cueing on the the elements of the band's mix that aren't intentionally distorted can help—as will listening to a variety of source material when setting up the system.

 

Ha-ha.....$14.95 at Pep Boys. I'll be a zillionaire!

Riis

 

It's complicated. Yes, you can blow up some speakers/crossovers by driving them with a relatively small amp pushed far into clipping. I have done that and it was expensive. You certainly can blow up speakers by overpowering them as well. Done that, too.

A better answer than saying speakers should be 2X the amp rating or amp 2X the speaker rating IMO is that they should both be capable of producing 2X to 4X the volume you will ever need. If you never push speaker or amp even close to its limit, it doesn't really make all that much difference which is rated higher and your sound will be much cleaner. Headroom is where it's at.

 

I've worked as a sound engineer for the past 3 years,

From my experience its always good to have much more power than you actually need, I've almost always only ever run my amps at half power (gains say about 12 o clock)

Get a decent set of speakers than can handle the power
Also, watch for your ohm ratings, if they don't match your output will be more of less what you expect!