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Is there any basic formula for calculating how many WATTS you would need to ADEQUATELY FILL a room with sound? Seems to be a crazy question but figured I'd ask? Probably too many variables but I'm sure some sound engineers have some basic formula?

I don't try to calculate & use systems that are tailored for any specific room. Plus the fact that you already mentioned, too many variables in components to really figure it out.

...if you are running subs.
...if the bar is an oddball shape,
...if the bar is an echo chamber,
...on the efficiency of your speakers - this is a biggy,
...on volume levels you wish to achieve,
...on the type of music you play,
...etc.

When doing live sound I look at the cap of the audience & try to push about 10 watts per person. I take this to karaoke as well. Now if your speakers are very efficient - say 100 db/1 W/1 M vs a speaker that's efficiency is only 90 db/1 W/1M then you could get away with a little less per person. In the first speaker 2 1/2 watts per person would achieve the same SPL as the second speaker with 10 watts per person.

No real formula to calculate.

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More important is sound acoustics. A heavy carpet will attenuate bass in a heart beat. Heavy milling SRO crowds will attenuate sound.

Outside I go more with the number of people. For 2-300 I run 2 Eon G's and 2 of the older non eons. I can entertain neighbors who are 1/2 mile away. For those listening they sit in front of the speakers For those socializing they sit behind or off to the side.

I think 10 watts/person is a good average.

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Using the 10watts person --- For a crowd of 100 --would be 1,000 watts
I assume that's total ? So a system pushing 2 x 500 watts @8ohms ?

(keep in mind this is just curiosity)
Never know I might land a big gig and want to be prepared

My outside setup is 1200 watts with a pair of 400's and a pair of 200's. With the G's 800 watts I do bars that seat 100-150 no problems. I prefer to add speakers and place for audio dispersion rather than mega watts on the stage.

I doubt if I ever do a large club again but if so will use inhouse PA system but wish I had another pair of G2's at times.

I sometimes remind folks that Woodstock 69 had about 3500 watts. Woodstock 99 had over a million. Go figure.

69
In 69 I was singing with maraiachi bands getting ready for discharge out of Navy. I sure wish I could have made that party..

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There is no way to derive an equation using watts/sq. footage, here's why. Take several speakers of different sizes and from different manufacturers. Hook each one up and see what comes out. A speaker rated at 200 watts @ 8 ohms from one company might have a high sensitivity and high SPL compared to another speaker with the same 200 watts @ 8 ohms from another company. I doubt any knowledgeable audio engineer would have a rule of thumb using watts per sq. footage because of this.

There are other ways to think about this, but because of the wide variation between different speakers, you end up with a crude generality or range.

A pair of 2 way speakers with 12" woofers and SPL of ??? would generally cover xyz square feet. You could possibly infer from that the watts based on the typical average wattage of several popular 2 way speakers with 12" woofers. This would give you a crude range.

I can tell you that you can generally achieve better sound quality in larger rooms using more speakers operating at a lower sound level than with a pair of speakers blasting at a high volume level.

It depends on the size of the room, how many people are there, the wall surfaces, the ceiling height, the shape of the room etc. It also depends on the kind of music you're playing, if you are using a sub or subs, what kind of sound level the crowd is expecting or wants.

I went to a bar recently and when I walked in I nearly fell over. The band was so loud and the bass was pounding so hard I considered turning around and leaving. I decided to stay and later I went up to the stage area to see what was making so much sound. They had 2 EV Eliminators and 2 EV Eliminator subs. They also had a couple of small Behringer monitors, but I doubt they contributed much to the overall sound and volume level. I only saw one Q66amp, but I'm sure there was another amp somewhere. One amp to power the tops and one for the subs. Could any 2 way speakers with 15" woofers and any pair of subs rated at the same watts put out that amount of sound? I seriously doubt it.

My experience is that EV speakers are quite efficient and can put out a lot of sound with much less power than for example a pair of Peaveys. This means you can use a less powerful amp because the speakers require less power, hence a less expensive amp. This I like.

A pair of 12"2 way speakers can generally cover x amount of people on average, a pair of 15s can cover z amount of people on average and so on. Big room and small amount of people? Different circumstances again . . .

Total watts. 2x500 would be fine for that scenerio. You can always plan for the biggest gig you might anticipate & get a system (at least power wise) to compensate. You can always turn a larger system down, but you can't always turn a small system up. Outside shows you typically want to go even higher.

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This looks like one of those questions that could have numerous answers. As I don't see a cut and dry way of knowing all the intangibles for every application then it all gets down to the "You can never have to much power theory" which is what I have lived by for thirty-five years. It hasn't failed me yet.

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Quickness of mind will deceive the eye

Wattage per sq foot or wattage per person or even the combine of both does not make much sense. If a simple guide line is needed, I would go for SPL (x db) at x ft from FOH speakers.

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I can neither confirm nor deny ever having or knowing anything about nothing.... mrscott

I thought about this in a roundabout way this past saturday night in a karaoke bar. The KJs equipment consisted of this: A 200 watt yorkville powered mixer and two older Yamaha 15 inch club speakers. At 9:30 when I walked into the place, their were maybe 30 people there and the sound wasn't to bad for what he was working with, ( he also had a Shure Beta -58 microphone that had a nice sound). By 11:30 their were at least 150 people packed into the place and crowding the dance floor while people sang and you could hear his equipment being pushed to its limit and sounding lousy. There just wasn't enough HEADROOM in the Amp to power the speakers properly!

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Man Must Know His Limitations -Clint Eastwood

That's why you hear live sound pros not talk about so much the square footage, but the number of people. People are like walking sound absorbers.

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[color=#ffff55]Mickey J.[/color]
Alas for those who never sing, but die with all their music in them.
-- Oliver Wendell Holmes, Sr.

The kind of people also. I've seen nice quiet crouds, almost entirely made up of karaoke people. They listen, and keep their conversations low and minimal. Then I've experienced the loud croud, where people are hooten and a-holerin', like kids out on a play ground. A small group there for the karaoke, and several other groups there for pool, sports, darts, and other things. The power needed can vary quite a bit, even for the same number of people......best to be very flexible.....

I already run 4,800 watts and I'm going to be doing a room in about three weeks that has me concerned. I expect roughly four hundred people and at this point I don't know the room lay out (I plan to investigate in the very near future). I'm seriously considering bringing in an additional 1,800 watt's for this gig (2 Yorkville U15P's). Power is the key to good sound, without power you could have the best of everything else and you are still going to be doomed to a night of frustration. Nothing sounds worse than a system that is trying to do more than it is capable of doing and nothing sounds better or is easier to run than a system with headroom to spare.

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Quickness of mind will deceive the eye

So..... Fat People (caloricaly challenged) absorb more sound than thin people... Stands to reason doesn't it? Just another reason to by decent equipment!

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Man Must Know His Limitations -Clint Eastwood

So your saying that I don't need more power, I just need them to be selective on who may enter the room. Perhaps a feasibility study is in order.

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Quickness of mind will deceive the eye

One thing to keep in mind with larger venues. Hopefully the ceilings are higher but power can be doubled by placing the speaker against a wall and more yet in a corner. It is best at ceiling height and angled down towards the opposite end. Multiple speakers are used for proper sound coverage. I have lit many bars where one could walk from end to the other with a constant volume throughout.


It is natural to think more and more watts but in large venues there are many more options with speaker placement. JBL Pro has many white papers on everything from small venues to churches. library.

I have installed old jukeboxes in fair sized bars with the old tube amps and 50 Watts per channel, often using the 70 volt system to disperse over larger areas.

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They all look good at closing time!

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Man Must Know His Limitations -Clint Eastwood

If I had to start over from scratch, I would invest in some really good powered speakers, like two Mackie SRM450 V2s (~$700 EACH), two lightweight powered subs, like the dB Sub 12 (~$650 each), and a heavy-duty powered sub like the Yorkville LS800P (~$1200).

I would use the powered speakers with one of the small subs for small venues, the powered speakers with both of the smaller subs for medium venues, and the powered speakers with the single giant sub for large venues.

It sounds like alot of cash to spend, but I guarantee if I add up all of the configurations I have gone through over the past 5 years, I have spent triple that for lower quality stuff.

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C Mc
KJ, FL

they also fart loud and often......stiff competition for even the best sub woofers.....

So what you are saying is the better brands of amps and speakers will be able to cut thru the fat people better ...than a lesser brand ?