Does Dr. Toole have a preference for mono setups when he wants to assess speakers by inquiring individuals about their perceptions?
If yes, why mono instead of stereo?
That's off-topic so I will answer quickly and if there is interest, it should go into its own thread.
At the start, Harman didn't believe in mono testing. So they set up a room that hydraulically switched full surround system speakers. Here is a picture of it:
Through testing, they realized that listeners were less critical to artifacts when presented in stereo vs mono. Indeed moving up to full surround made them even less picky.
They conducted full testing on them and published the results in the AES paper,
Comparison of Loudspeaker-Room Equalization Preferences for Multichannel, Stereo, and Mono Reproductions: Are Listeners More Discriminating in Mono?
The answer turned out to be "yes" to that question.
In controlled listening tests of Room EQ systems, here were the scores as they went from mono to stereo and then surround:
I have circled the NO EQ as an example. Notice that listeners gave very low scores in mono listening (blue). In exact same test, when the number of channels was increased to full surround, they almost became deaf to those artifacts!
Explanation is simple: the feeling of envelopment we get from stereo to full surround is so positive that we forget and forgive what can be wrong in the presentation.
Same thing exists in video by the way. Professional monitors have a button on them to turn off color so that we can see the artifacts in luminance channel (black and white). While those artifacts are there all the time, color makes the picture "too pretty" and harder to fault.
So while Harman still has the ability to perform multi-channel AB testing, they are focused on mono testing due to how conclusive this research has been.
BTW, the authors of the above paper were two of my colleagues, Allan Devantier and Sean Olive and Sean Hess. Not Dr. Toole.
The top worry about any speaker (or room) is the tonality. Mono is revealing of that just the same. After all, there is nothing the other speakers can do to change the timbre of another speaker in the room.
I have taken the "mono" test a couple of times and I can attest to it personally on how revealing it is of differences in speakers. Here is a picture of one of the times I took the test:
You can see the moving platform underneath each speaker. Of course there is a curtain there normally so you can't see which speaker is which. It is the best reality show in town when the curtains open.
