How does solo piano help you evaluate audio gear?

reproducing piano is the toughest test for any music equipment.

it has to sound clean throughout all dynamic passages and throughout the entire keyboard. 

why it's the toughest test, because piano has all instruments combined. when you hit the string, you literally play drum and note together.

I've owned and played my share of pianos over the years, but I also play the fiddle and I have to say that massed strings is the true litmus test for determining the ultimate veracity of a system. And when you're judging a system by a piano recording, don't get too crazy! Many fine pianos sport a fuzzy tone in the midrange upwards, so you got to take what can sound like a mistracking cartridge or a gently clipping amplifier section in stride. And of course, as mentioned above, reproduction of the human voice shouldn't be given short shrift, either. I mean, how often do we hear a live, un-amplified human voice? A zillion times a day? True, it's not often enough that a vocal is recorded with true, convincing accuracy, but believable vocal rendition is still a worthy audio goal. In any event, true, dynamic range is important but I'll take a slight dynamic hit every time to preserve tonal quality and lack of distortion.

@hilde45

Maybe because pianos are the foundation of musical instruments in general. The rich tonality of the piano evokes incomparable pleasure for both musicians and listener alike. So what does piano reveals exceptionally well to my ears?

- musical scale, unlike any other instruments offering an incredible, unparalleled range.

- higher and lower scale in frequency range than any other instrument.

- both treble and bass clef while most other instruments reveals only one or the other.

Good luck and hope you find your forever speakers, I know I have :-)

@hilde45  I have found that solo piano recordings that I know well will reveal speaker aberrations pretty quickly.  I also use solo voice, hopefully, SATB, because I want nothing to do with a speaker that does not do voice right.  Not sure why, but I've also found  that good recordings of french horns can reveal aberrations that might otherwise go unnoticed.  If speakers pass these tests, then I go on to other speaker attributes.   I assume you are doing your evaluations at home in your own system with your own music.  Now that you are adept at optimizing speaker/room interactions, you are in a really good place to find a speaker that is going to do well for you. 

I also listen to the hammer strike, the initial overtones, and their decay. Instructive in terms of how the system handles the whole sonic envelope, not just wide frequency range. I’ve had a couple very good pianos, including a vintage Bosendorfer. You can make easy comparisons by ear with the live instrument and a recording. (Every piano, even the same brand/model, tends to sound different. Someone who restores these instruments knows how to voice them to achieve different tone and attack).

The trick is finding good recordings. Either the piano is too closely mic’d or is presented in miniature compared to a full sized grand.