Hi Folks

I keep hearing terms like “5kw rig”, “10kw rig” etc. bandied about by sound guys, but how does one measure the size of a particular system? What actually constitutes such a “5K, 10K, 30K etc. rig”?

Having heard the difference in volume between some 100w transistor guitar amps and other much louder 50w valves amps, I’m left confused. Why are PA systems and amps described in terms of how much power they use (watts) rather than by overall decibel level? Sure, it’s important to know how much power your system is consuming, so that you don’t overload everything, but I would have thought that the key factor when choosing a system for a particular venue would be whether it would be load enough (or whether the environmental health officers would be interested – and they talk in terms of Decibels when there is talk of closing down venues for excessive noise, don't they?).

WAL

A 5kw rig basically means the total output of all the amplifiers used is 5,000 watts.

The problem with the 'watt' measurement is that there are so many ways of measuring it. For example, you could measure it's 'peak' output, meaning an amplifier which can really only produce 100watts is actually capable of producing very short bursts in the power of thousands of watts.

Generally though, this is reserved for low-end hifis and a lot of snobby audiophiles. In the pro-audio arena, the ratings all seem to be pretty accurate.

A cynical person might suggest that it's because it's easier to exagerate power ratings to make systems sound more impressice on paper and also because it's a much easier figure to arrive at. In an (my) ideal world, all rigs would be expressed in terms of their maximum continuous SPL.

..and often completely meaningless. Power ratings on their own mean very little - they certainly have no direct correlation to "loudness" or "quality". Loudspeaker efficiency and dispersion etc must be taken into account.

While the figures are useful in comparing systems which are similar in other ways it's not an absolute reference.

I'm similarly cynical! Some "professional" kit specs are suspiciously like car audio ones!

Maximum continuous SPL is part of it (I assume you'll specify whether you're measuring at 1 metre, at the mix position or the back of hall) but even coverage is important on many applications as well. The biggest local receiving house in my city actually specifies "The FOH system as installed has been tested at, and is capable of, 120 dbSPL +/- 3db across the listening area, with a frequency response of +/- 4db from 37hz – 16khz.". This comes pretty close to being a REAL spec, though I tease that head of sound that he forgot to include the weighting. (It's "A" weighted by the way.)

Taking this back to the original query, the system that generates this spec could realistically be described as about a "40 kilowatt" system--or two or three times that if we lie and talk about peak power!

Bob

We Want Real Spec (well I do anyway)

Lets get a petition going and send it to all the big name pa companies, "we want our PA's loudness in MAX SPL @ 1W/1M, not in false 300w RMS/CONTIN/PEAK/PROGRAM

(Excuse the bad spelling)

No you don't. If you spec at 1W then you ignore power compression.

What Brian said..

...plus to add that the 1W @ 1 metre spec is a useful way of comparing speaker sensitivity but, even without the power compression issue doesn't tell you much about a full system unless you know both the power handling of the cabs in question and the available amplification...which brings you right back to all the various different ways of specifying this.

Bob

Sure, as it doesn't take things like an amplifier's damping factor into consideration which in some ways will directly affect the sound.

However, I have found (in my extremely limited experience) that *good* amplifiers with a high power rating tend to outperform *good* amplifiers with a lower power rating.

Although a *good* low power amp will outperform a *poor* high power amp of course, and this is where watts mean nothing.

1 vote here to change it all!

The likes of "PMPO" "PROGRAM" and "PEAK POWER HANDLING" does not relate in any way to quality, frequency response, SPL or even WRMS.

Yes, peak power is maximum handling but who is going to push a P.A to max then back down to nominal again?

Answer: NO ONE! ( sorry but I AM shouting!,.... to myself)

John Denim.

The term "5k Rig" has very little value but unfortunately there are many people booking PA systems who view it as a usefull guide to what they need. It's easy to find the term being massively abused, but I think all you can do is if asked have a reasonably accurate figure available (I'd use the power my amps would be delivering taking into account any limiting) and try and spec/quote for what the job actually needs.

IMO, talking of specs other than frequency response (based on a stated ±dB figure) and linearity is a waste of time and the only guide you should use is your own ears and actually trying the kit out.

For example, a speaker can state it could handle 1kW, but that may only be at a specific frequency/with limited or no harmonics. A 500 Hz sine wave is far easier to reproduce than a mixture of harmonics with a fundamental frequency starting at say, 25 Hz.

This I believe is how most amplifier manufacturers determine to power output of their amps.

Maybe " 1kw " is the output of each side, but not throughout the whole frequency range, everthing else is filtered out apart from 1khz.

John Denim.

It's the most common way of specifying something about the PA the client thinks they need as a temp install in a place. The SPL +-% spec is only appropraite for an installed system. though you might want a spl + tolerance spec that can only come by installation and test with certifies instrumentation. There is no knowing how much of the power performers will actually use! Some will spec a 5K rig for an intimate 100 guests - so it will never be turned up much, or try the same thing with 300w and thrash it.

It's a rare band that can say what they want to sound like in words, so just sending a rider for a 2K or 10K PA will sometimes indicate the scale that they expect.

Also a 1K or 100K PA tend to have different levels of side chain ad-ons and processing, and different crew levels!

I often find that most riders specify a watts per number of people ratio and whilst still not an acurate way at least takes some consideration to audience size/area. The same riders nearly always state that there must be an even coverage throughout the venue.

I have a tech rider in front of me now that specifies a 6kw rig minimum , shall I give them 6kw of Sound Lab or 6kw of JBL Hmm......

Nah, I'd give 'em 10k of Behringer!

You'll need more than that in a big tent

As others have mentioned, SPL is an almost useless rating in many ways too, as different venues will have completely different acoustics.

For example, in your own house, your average good-quality hifi can probably produce sound levels over 100 dB at 3-4m, but take it outside and you'll struggle to get even 90 dB.

Well, it depends how you specify the SPL. If you simply give a raw number then I agree it's useless. However, if you go into detail of the maximum SPL you want +/- a certain amount across the whole venue over a certain frequency response, then you're covering both the actual level and also how even the coverage is. Done this way it's probably the best way to spec something--but only decent engineers (probably using computer modelling) will be able to put together the right package to meet the spec.

Of course then we start talking about monitor world and that's a whole other can of worms!

Bob