n80 wrote: I don't see how measuring a speaker against what a live guitar or live piano sounds like is practical. Even in a live situation a mic'd acoustic guitar will sound different from an un-mic'd guitar.
Agreed there are problems involved in comparing live to reproduced sound.
Yet I have to say I've found such comparisons quite useful and enlightening.
I've been obsessed with live vs reproduced sound as long as I can remember. So when I became more fervent about trying many different speakers and systems, in the field but especially in my own home, I made decent quality recordings of familiar acoustic sounds - my wife's voice, sons, my acoustic guitar, my sons playing their school instruments - trombone, sax, etc.
Being extremely familiar with those sounds, they really illuminate how closely a speaker in question can reproduce them. And sometimes I would do direct live vs reproduced comparisons (typically with speakers in my home).
Lots of speakers fail the comparisons, but some are surprising.
My Thiel 3.7 speakers, for instance, reproduced the sound of my playing my acoustic guitar with fairly astonishing accuracy - timbre accuracy, clarity, etc.
My MBL 121 omnis can reproduce the sound of my son playing sax with amazing verisimilitude.
But I don't always need those recordings on hand. When I go to audio shows, or high end stores listening to systems, it's often the case there are real voices nearby (obviously at audio shows, and often at a high end store the salesman may be talking to me or chatting with someone else).
So I often stop and take stock: if I'm playing, say, a good recording of Johnny Cash or some other simply mic'd male voice, I close my eyes and listen to the real voices present in the room and compare it to the reproduced voice. What IS IT that the real voices have that distinguish them from the voice coming through a sound system? It's always very telling, and the systems that actually have the least obvious departure from the real voices are the ones that I inevitably find the most mesmerizing and satisfying for long listening sessions. (Naturally the more complex and demanding the music source may be, the less able a modest system will be able to keep up. But, in general, a system that captures certain essences of live sound, to my ears, tends to predict longer satisfaction FOR ME).