"Jim Lesurf" wrote

If we ignore all the above complications and assume two speakers, each
radiating *in phase* at the same level then the result at a listening
location equidistant from both is a *6dB* rise. Not 3dB.

I thought that was only if they were reproducing the same signal.

"In phase" may imply that - how can they be in phase if they are reproducing
different signals - but I think some people take "in phase" to simply mean
wired correctly.

Tim