Audio Systems: Decibels or watss range in closed and open areas, 100 square meters, professional loudspeakers

Question
Hello my question is the next:

Is the a value or a guide to choose the watts a speaker must have to be listened in open areas?'
I mean i I have 10 square meters, how many watts must my speaker should have??
And so on, for 100 square meters, 1000 squear meters, and so on ??
where can I get  this  info ??  

Answer
Hello,

Unfortunately, there is no mutually-agreed-upon standard for these measurements. I have heard of several different formulas, but they all boil down to one thing -- whether or not you can hear your sound where you need to hear it. Most professional loudspeakers have an "effective range" which is the range (usually in feet) extending from the front of the speaker, where the sound is "thrown to." Most speakers are what we call "unidirectional"; that is, they project the sound in one direction only. Generally, they are designed so that the audio is fairly uniform in volume up to a certain range (the effective range). Standing 5 feet away vs. standing 50 feet away should sound about the same, if you have good speakers. The speakers I use when I DJ, for example, (Yamaha S-122V) can be turned down really low, but you can still hear them across a crowded room as if you were right next to them.

For your outdoor situation, assuming that you have good speakers, and that you are using only two speakers, I would say that for 10 square meters, you would probably need at least 100 watts per channel. For 100 square meters, probably at least 250 watts per channel. For 1000 square meters, probably 750 watts per channel.

If you use more speakers, and place them in the correct spots, you can get away with using less power.

There really is no value or guide... it's just a matter of what sounds good.