Matching speakers to powered mixer

Powerslave

Hi

Our singer has an Allen & Heath PA12-CP desk:

http://www.allen-heath.com/media/PA12-CP_PA20-CP_User_Guide.pdf

Typically, we run a single speaker assembly either side (one per output channel). Currently, these are old-school 400w speaker enclosures picked-up from e-bay.

He's looking to purchase new speakers, and I'm unable to properly guide him as to what he should be looking for in terms of power rating. The PA12 manual indicates that the desk outputs 2x 500W RMS.

Speakers seem to be described by 3 ratings: continuous, program and peak on the web pages of manufacturers and stores.

I had an electronics guy at work try to describe some of this to me (it proved to be purely from a sine wave perspective, so he lost me). Can someone please provide an idiots guide to what he / we should be looking for?

We rarely run our PA with anything other than 3 vocal mics - on one occasion we mic'd the instruments, and we might do that once or twice again this year. We play small pubs, so don't really push the equipment. But, if the guy is spending proper money, I'd really like him to get something that is long-term fit for purpose. Given the space constraints of the places we play, I don't really see us being able to run additional enclosures (bass units, or second general-purpose speaker enclosures) either side.

He's looking at purchasing 2x Electrovoice EV SX300 which are rated at 300 / 600 / 1200. I'm happy to be proven wrong in this regard, but the numbers tell me that they're not a good match for his desk.

Thanks in advance . . .

Danny1969

The only thing your interested in is RMS in terms of watts but make sure you choose speakers that match the load your desk is designed for ............ a desk designed to drive 500 watts into 4 Ohms won't drive that power into 8 Ohms, and you can't choose another transformer tap like you can on a valve amp. Are the SX300 4 Ohms ?

I generally use amps that can provide more clean power than the speaker is rated for. You can kill a speakers with too much clean power but you can also kill a speaker by feeding it clipping signal from an underated amp. 

I like the active EV stuff but I've only ever used them complete with bins so no idea how they will be on their own 

Powerslave

Thanks for the response . . .

The SX300s are rated at 8 Ohms.

I've just realised that I've linked to the wrong desk (correct link below, also fixed in the opening post). Ours is the powered version (PA12-CP):

http://www.allen-heath.com/media/PA12-CP_PA20-CP_User_Guide.pdf

Thus, we are looking at passive speakers.

I understand that it has a switch for constant power into 4 Ohms or 8 Ohms.

Danny1969

I've just had a quick read, yeah can drive all 500 watts into 4 or 8 Ohms  per side so you can ignore my comment about that. That's a good design considering it's a class AB amp. 

I think you could do a lot worse than the EV's for the money but if it was me I would either want a bigger budget to include one or more bins or I would buy a pair of JBL SRX125's  or similar, basically something that handles some low end as well 

Powerslave

Thanks, Danny - really do appreciate your input.

Low-end handling aside, are the SX300's simply under-powered for what our desk "could" put out?

I'll take a look at the JBL's which you refer to . . .

Danny1969

Taken from the manual of the SX300 and kind of reinforces the point I touched on earlier regarding power handling :

To use the Sx300 to full capacity, skilled

experts in sound-system installation and

operation will obtain the best results if

the power amplifier is 2.0 to 4.0 times

the long-term average noise power rating

of the speaker system. For the Sx300,

this is 600 to 1,200 watts.

A more conservative, “normal” amplifier

size, which will produce audible results

nearly equal to those of the “expert”

recommendation, is 1.0 to 1.4 times

the long-term average noise power rating

of the speaker. For the Sx300, this

is 300 to 420 watts.

So yes I would say the speakers are a good match in terms of RMS power handing for normal use 

ICBM

Those EVs are as tough as anything, I wouldn't worry about running them with a 500W amp. I can't remember ever seeing more than one or two blown despite them being very widely and sometimes quite roughly used.

As with all PA (as opposed to guitar or bass) it's better to use more amp power than speaker rating, since the real enemy is distortion - it's much easier to blow a speaker with a slightly-underpowered amp that goes into clipping than a slightly-overpowered one that you make sure stays clean - although you *must* make sure it does stay clean.

Under these conditions it's the program to peak rating that really matters as Danny said - so 500W into a speaker rated at 600W program/1200W peak is fine.

maltingsaudio

Justa thought but if you are considering new speakers why not consider getting a pair of actives such as these Red5's which are a bit of a bargain http://www.red5audio.com/acatalog/Powered_Speakers.html not exactly subtle but loud and using your existing speakers as monitors you can do this easily on your desk

PS EVSX300 are a great speaker a s said but also have a look at HZ HE300 or Z500 British built to compete with EVSX's just as good and a lot cheaper on the 2nd hnd market  

Powerslave

Thanks for all your input.

Singer went ahead and bought the SX300s pretty much off his own back. Which is "ok" as it's his cash.

I still don't quite fully understand the idea of matching a 300w speaker to a 500w channel, but much respect contributions above tell me that's ok so let's see how it goes . . .

Thanks again

ICBM

Powerslave said:

I still don't quite fully understand the idea of matching a 300w speaker to a 500w channel

The reason is that music is not a continuous signal, but has an average level well below the maximum power - usually between half and a quarter, for mixed modern music. The power rating of a speaker is based on an average electrical power input, so it's that which is important to the cabinet.

But an amplifier needs to be powerful enough to deliver the peaks cleanly without distorting, so it must have a maximum power output of two to four times the average in order to do that. A 500W amp will actually only be putting out an average of roughly between 125W and 250W at the point the peaks start to distort… so is safe driving a 300W cabinet *provided* you don't let it distort.

The half to quarter range corresponds to the 300/600/1200W figures of course - the better and cleaner the mix, the larger the difference between peak and average which is why amps of up to four times the power are recommended for expert use. 'Normal' use assumes occasional slight distortion or use of compression to get the volume up higher.

The counter-intuitive bit is that an *underpowered* amp can blow a higher-rated speaker if you try to turn it up too loud to make up for the lack of power and it goes into distortion. A clipped power stage signal will try to approximate a square wave to some degree, and square waves contain much higher energy in both the very low frequencies and especially the very highs, than a smooth music signal - so there is a greater risk of blowing the tweeter in particular, or crossover components. (Although the bass driver will usually survive.)

For guitar or bass the opposite is true - distortion is likely and usually intentional, and the cabinets rarely (apart from some bass ones) have tweeters, so you need a speaker which can handle more than the maximum power the amp can put out even distorted. Blown tweeters are common in bass cabs too...

Powerslave

@ICBM

Thanks, matey - very much appreciate the detail response.

It certainly works against the grain in comparison to how I would match a guitar speaker to an amp, and your explanation clears this up for me.

Thanks again