Stated output of amps compared to actual

[Bob Dore]

But if they are powered by the same amp, each speaker will receive only half of the electrical power, so no 3dB gain...

Ah, but two speakers in parallel will draw more power from the amp albeit not twice the power.

The resultant dispersion (and resultant increase in level) is, of course, dependent on speaker and cabinet design. The 3dB increase is theoretical, based on an equal output from both speakers and assumes they are trap arrayed.

We could start a thread on the relative merits of different arrays, traps, line arrays and point source (I'm a fan of point source arrays, unfortunately my bank manager isn't ) but this isn't really within the scope of a discussion on guitar amps. Or perhaps guitar amp manufacturers could consider building line arrays into their cabs which would make for some interesting guitar sounds

Bob.

[Didier]

But if they are powered by the same amp, each speaker will receive only half of the electrical power, so no 3dB gain...

Ah, but two speakers in parallel will draw more power from the amp albeit not twice the power.

In most case they won't, except with transistor amps which generally deliver more power with lower impedance (resulting of speakers in parallel), but going too far this way may destroy output transistors...

Didier