How do you know what a good speaker is?

I think my speakers are good. They are largish tower speakers. They pass Tomcarr's smile test every time. And are a joy to listen to all evening long.

I don't know enough to explain why they are 'good'. But the two things you notice most when you examine them is that they are dense. Knock on them with your hand and it feels like they are made of a solid block of wood. Seriously. And the second thing you will notice is that they are heavy. Even heavier than their density and appearance would suggest. So heavy they are difficult to move around and re-position with just one person.

I have no idea if these are critical speaker features or not. But they are definitely noticeable and apparently very intentional.

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. If we're hearing it on a speaker then that sound has been recorded by someone. And all the manipulation that involves.  A recording is not the real thing. So it seems to me the gold standard would have to be that what you are hearing is being heard the way the engineer/producer intended you to hear it.

@bdp24 Agree completely. I probably should not have said how the engineer/producer "intended" it to sound. As you say, I think there are many legendary engineers who do have a very specific intent but even they don’t know when, where or how we will be listening to the music. I suspect most of the rest of the producers/engineers out there are just getting product out the door and/or dealing with budget and time limitations.

"I guarantee you most commercial recordings are NOT made to sound "accurate", but rather "good".

Agreed. That’s why I don’t think looking for accuracy is the best way to evaluate a speaker. There are usually too many variables and too much variance in production. I guess is all you listened to was classical piano and you knew which producers tried hardest for accuracy then that might be something to seek after but that would be a very narrow measure of a speaker intended for broader use.

And maybe what makes a good speaker should be defined as a speaker one likes.

But I will say this, the more I listen and the more I think about SQ the more I realize that for me it comes down to two big things. And oddly, sound stage isn’t one of them. The first is what I’d call separation or distinction between instruments, voices, etc and the second is sharp, tight, distinct, well defined bass. And then it comes to what I don’t like and that is overly bright high frequencies. Maybe fourth comes soundstage and as long as it isn’t one dimensional I’m happy with that.

@rbstehno Its funny how different we all are. I study car specs very closely. They actually tell you an awful lot if you are using the vehicle to its maximum potential. Not saying everyone should, but if you do then the specs are critical and you have to know how to evaluate them. 

I have high expectations for my traveling car (comfort, handling, hp/torque curve, etc. My truck has to pull 9000 pounds strongly and safely and my track car has to keep me safe and keep up with the Miatas (which can be harder than you might imagine.)

My analogy probably does not carry over to speakers, just saying that in some areas specs can be important.

But the 'true' sound of an instrument does not translate well with electric instruments. Once saw Andy Summers on a TV documentary make synthesized piano notes with his guitar demonstrating that with the available tech, he could generate any sound he wanted to with his guitar.