Really clever idea from guy on irc

[bigwill]

I was chatting on IRC to some guy, he doesn't really know a great deal about speakers however despite this I think he had a genuinely good idea. He was talking about subwoofers and how some had a passive radiator on the back. He then wondered what would happen if you had two active woofers instead. He is technically inclined enough to realise that in phase it would just act as a normal subwoofer, but he wondered what would happen if you altered the phase of one of them somehow. I suggested that if you had them 180deg out of phase they would act like a dipole, and the box would essentially have no effect. He then went on to suggest that maybe you could alter the phase response of one of the woofers so the system acts as a dipole at some frequencies, and a bipole at others, and even in between! I thought this was pretty clever! Has anyone tried this? There must be some advantages from doing this, such as having a nice fast dipole woofer that automatically turns into a monopole for the very bottom end! How cool would that be?

[sdclc126]

With a push-pull arrangement there is a serious possibility of cancellation, so room placement would be critical. I believe in dipole bass the two woofers remain in phase electrically for just this reason.

I don't see the utility or practicality of trying to change phase within a dual woofer system dependent upon frequency - it makes more sense to me to have dipole where it works best and a separate monopole/sealed unit for the very bottom frequencies.