J

#### Jokari

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I asked this question at the KVR forums, but no one had enough knowledge of acoustics or speaker design to answer. So here it is: say you have a passive speaker or subwoofer playing a low-frequency sound. Its acoustic output is 90 dB SPL at 1 m. Now add an identical speaker powered by a second identical amp right next to it. The acoustic level will be 96 dB SPL at 1 m, which is +6 dB higher, or in other words 4 times as much power. Obviously something special is happening, since you would expect two speakers to yield only twice as much power. Especially remarkable is that each speaker is now twice as efficient, since it is fed the same electric power as when it was alone (assuming its impedance didn't change) but it now outputs twice as much acoustic power. Because you could repeat this process with as many speakers as you'd like (you could stick 100 speakers together) and because the efficiency cannot be greater than 1, there has to be a limit to this phenomenon ; so speaker designers would have to pick an optimal number of speakers, above which there will be distortion no matter the sound level (!), and under which the efficiency will be reduced.

Is this correct? Do you have further reading related to this issue?

(PS: I wasn't sure what section to post this in. I first thought of "Home audio acoustics", but I settled for this section instead since the question is much more related to speaker design than to bass traps or acoustic treatment.)