posaune

Very rough rule of thumb: Assume your sound source is putting out maximum voltage without overdriving the amplifier, which is cranked to deliver its maximum rated power. Multiply the rated power of your amplifier by the acoustic efficiency of your speakers to get the maximum possible acoustic power generated thereby. Convert this power to dB, reference 1 picowatt. If your room is totally reverberant, (maybe it is...the dimensions sound more like a gym than a room in a house), then subtract 10 dB from the number you got from the watts-to-dB conversion. This will be roughly the maximum sound pressure level you could realize in that measurement environment. Of course, if the room is not very reverberant, then you have to subtract more than 10 dB.