How Much Power is Enough?

With 87dB with one watt at one meter sensitivity, you will need a little more than one watt if 87dB is the loudest sound you want, or a four watt amp for a maximum of 93dB, or a 16 watt amp for a maximum of 99dB, or a 64 watt amp for a maximum of 105dB, or a 256 watt amp for a maximum of 111dB. The formula for this is quadrupling the power will double the loudness (which is the same as adding 6dB). To be more precise, use a Radio Shack dB meter to measure the loudness of your speaker at three feet. Increase the volume until it is at a steady 80dB. Then step back to your listening distance and see how much it drops. You will have to compensate for that in your final calculation. The level probably won't drop too much.

Personally I have Klipschorn speakers with a sensitivity of 104dB/watt/meter. My 125 watt amp will produce about 125dB which is twice the threshold of pain. I have to attenuate the preamp 20dB so a quarter turn on the volume knob won't drive me out of the room.

Warrenh said "Elvick, you're a little mistaken with your calculations. you mean 3db not 10db. 10db= twice the loudness."

Warrenh, an increase in wattage by a multiple of four will double the loudness which is an increase of 6dB not 10dB. An increase of 3dB is a 50% increase in volume. Therefore, an increase from 30 watts to 60 watts will double the power, but only provide a 50% increase in volume. An increase from 30 watts to 120 watts will quadruple the power, but only double the volume by adding 6dB.

I bet this makes things as clear as mud.