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Old 22nd March 2010
Gear Guru
Two Speakers

Hi Tonio, thanks. Chris has good reasons why he didn't include two speaker drive in FM. You can live without it just fine. Two speakers should excite the modes in the room a bit more evenly. One could be in a null, but two is less likely. More even mode stimulation should give better Waterfalls.
Two drive is not exactly the same thing as two individual responses averaged. Two speakers driven will fight somewhat, just like in real life with music!
I harbour the opinion that Room Measurements should ideally be done with two speakers running BUT with a Dummy Head Binaural Microphone recording in Stereo. FM can do this. This should give results more relevant to how and what we hear. I currently simulate this by moving the mic about half a head distance to the Left and Right of my measure spot, and repointing it directly at each tweeter. Ears.

Finally to answer your question :-) I use the Mono switch on my speaker controller to drive both speakers. If you don't have that facility, make a Y cable. For ETC drive one speaker. Full range sweep. For all measurements it can be worth trying longer sweeps, say 10 Seconds or/and synchronous averaging. Better S/N ratio, important for EDT.