Efficiency with multiple drivers

[buyerchoice]

Do I have this right? When going from one driver to two, with the same amplifier input, the output goes up 6 db?

Is this also true? A woofer that plays at 86 DB with one watt input will play at 92 db when using two?

So that the efficiency goes like this. 1 driver to two = 6 db
Two to four, another 6 db
Four to eight = another 6 db.

So the end result is that 8 woofers rated at 86 DB at one watt will play at 104 db at one watt input?

Can this be right?

[ThomasW]

Due to what's called 'acoustical coupling', when the drivers are close together there's a +3dB increase for every doubling of the number of drivers.

When the amp powering the drivers 'doubles down' for each doubling of drivers, there's an additional +3dB in output

[buyerchoice]

Thomas,

Thank you for that answer. I have done a bit of reading here and you seem very knowledgeable. Perhaps you could clarify a bit.

Is the amp "doubling down" caused by the drop in impedance of the drivers when wiring them or do you mean to say an actual increase with the volume control?

[ThomasW]

doubling of amplifier power for each halving of impedance

[cowanaudio]

Unfortunately very few amplifiers will even come close to doubling their maximum output power with a halving of load impedance. Doubling up on drivers does increase the voltage sensitivity of the system by 6dB, though. (This assumes all drivers are within 1/4 of a wavelength at all frequencies in their passband) You can get a 6dB increase in maximum output for each doubling of drivers if you also double up on amplifiers, or buy one with enough power to start with.

Cheers

William Cowan