How does solo piano help you evaluate audio gear?

I will add this observation, it takes many instrument and especially voices to evaluate the S.Q. of new speakers ... Piano was always a favorite of mine but cannot reveal all there is by itself alone for sure... Think for example like someone rightfully observed about cymbal decay...But by itself i think piano is a good "thermometer" of the room and not only a way to evaluate speakers...

But one this is said, remember that NO speaker can beat the room...

No speakers at any cost will beat by his upgrading power acoustic control,

Here are these 6 aspects of acoustic control parameters in a room i experimented with :

1 -Balance between absorbing surfaces,

2 -Reflecting one,

3 -Diffusive one....

This was "classical" passive material treatment of a room, now these 3 new other factors are related to my concept of the  mechanical active control of a room ( what i called a mechanical equalizer):

4-control over reverberation time and timing of the wavefronts

5- control over the distribution of the pressure zones

6- fine layering and tuning of the laminar flow

These 3 last aspects could be controlled with Helmhotz mechanical method NOT by electronical equalization...

Then the piano will not sound the same from the same pair of speakers in a non controlled room and in a controlled one...Not even close...
 

Dont upgrade good speakers with costly one BEFORE studying and experimenting with acoustic...

My acoustic devices and experiments were all homemade and cost me nothing...

I can then claim that great hi-Fi experience is possible at low cost contrary to what is claimed or supposed almost everywhere by almost everyone...

People dont know acoustic and never seriously try experimenting with it in a dedicated small room.

@mahgister,  I've agreed with pretty much everything you have said in this thread.   I will add a few comments/commentary.

When I am auditioning in a Brick and Mortar setting, time is limited and the variables are complex and not always controllable.   A speaker audition is a complex problem that is best solved by simplification.  Piano is a single, more or less full range instrument, whose harmonics are well known to most of us.  You can get to issues like tonal correctness across the audible spectrum and coherence/integration of drivers within a minute or two.  If a speaker fails this, you move on and haven't wasted 2 hrs on a speaker that might seem ok with other types of music, but 6 months and 20K later you want to get rid of.  I've personally not auditioned a speaker that passed the piano test and failed the voice test. My guess is there are none.   But piano won't tell you a lot that you need to know. Generally speaking, issues with imaging, soundstage width and depth, and dynamics, where many speakers can get very congested with a high volume complex orchestral work, may not be best discerned using solo piano.  So one certainly can't make a purchase decision based on piano alone, and I don't think anyone is really advocating that approach. 

 Piano is for me the first hurdle a speaker must pass.  I can reject a lot of speakers quickly using one or two well recorded and well known piano sonatas.  

What you say about the room is critical for anyone to understand.  But I won't take a pair of speakers home that don't sound right hoping the vendor had a lousy room.  Also, the caution you issue suggesting that people not go chasing expensive speakers until they are sure they have their room set up properly is extremely important.  Better speakers won't necessarily sound better in a room that is poorly treated and set up.  Relatively inexpensive speakers can sound mighty good in a room that is well set up. 

Along with absorbing  and diffusing surfaces, you mention reflective surfaces.  In my opinion, reflective surfaces and woefully underutilized.  Reflective surfaces that can convert early reflections into late reflections  is a trick I stumbled into by accident.  Proper use of reflective surfaces, in my experience, are an order of magnitude more effective in improving imaging and stage than absorbing surfaces. 

I concur with your post...

Especially this part..

Along with absorbing and diffusing surfaces, you mention reflective surfaces. In my opinion, reflective surfaces and woefully underutilized. Reflective surfaces that can convert early reflections into late reflections is a trick I stumbled into by accident. Proper use of reflective surfaces, in my experience, are an order of magnitude more effective in improving imaging and stage than absorbing surfaces

But also remember that all these qualities you mentionned here are easily improved to a huge extent by passive material treatment and active mechanical acoustic control, if we have realtively good speakers commensurate to the room dimensions to begin with...

Generally speaking, issues with imaging, soundstage width and depth, and dynamics, where many speakers can get very congested with a high volume complex orchestral work, may not be best discerned using solo piano.

There has always been a bit of uncertainty for me about which piano manufacturer I prefer. No, I am not a pianist, but my father was. He also tuned pianos. I only accompanied him while tuning a few times. Most of them by my taste were a fair example of a great instrument. Since we lived in a small town, there were few people that owned much above a spinet model so that tells a lot right there. I do remember being present to hear him for a part of the tuning of a Kawai. He would test his ability by a short performance. It was Better. The attack was not exaggerated or diminished and the tone was not too soft. The body that it developed was SO much better than what I was used to hearing.

 So recording a Good instrument has to be the starting point. Then the pianist. Don't forget the composition and of course the recording venue. I only own a few recordings of this fine instrument that truly move me, either owed to the recording, or maybe just an exceptional performance that transcends the ability of that time when recording instruments in general was enough of a challenge. 

 I tried only once to record my father playing. I just had to accept the fact that it was the best that I could do to have a remembrance of him.