How do you know when a stereo sounds good?

To me it sounds good when the music can have a deep effect on me. When it sounds exceptional, then you will have shivers when you hear the song next time coming up even on TV or on your phone - even a low quality playback will be enough to recall the experience and bring you back to when you heard the song "for the first time for real".

Of course, this cannot be true for every music we play, as let's be frank - most live music is quite mediocre. Recordings take a notch (or several notches) down from there.

Yet, when you have a life changing live performance or song that talks to your soul, even taking that notch down is still a much more fulfilling experience than a whole bunch of mediocre live shows. That's how I know when a stereo system sounds good. Just forget about mesurberating. You will instantly know when the system sounds good. People will look as if they got an adrenaline shot or are just back from a trip to a different universe. When you need to reason the qualities, then there's always room to improve.

In short, when you get a Life Changing Experience, then it sounds good.

The sound waves travel my small room at a speed of sound, 343 meters per second or 1125 feet per second......

My room is 13 feet square... More than 80 crossing through my room each second...

This means my room atmosphere is like a tense violin cord....So sensible to any small change that is is easy to hear any new elements introduced in a room we already know...

My brain#ears decipher sound waves differently each one of them and make decision in SOMETIMES ONE MILLISECOND... ( Hass effect)

Then anything in the room, any acoustic material content, his geometry and the topology of the room, will deteriorate sound or improve its recognition in a way far greater than upgrading a good amplifier for a so called better one...

It is acoustic who dictate sound quality AT THE END...Not measurements of electronical piece of gear nor our own satisfaction after an upgrade...

Not the branded name of speakers or amplifiers...

Buy good gear FIRST and forget them after that , and read about acoustic....

And no acoustic tweaks will replace acoustic control...On the opposite we may replicate any tweak effect in a room by using acoustic treatment and acoustic Helmholtz mechanical control....

For example using angles in my speakers position and an acoustic screen i mimic an headphone effect ( the sound floating not in my head but around my head with some recording)...

But it is more easy to buy ready made costlier product than making our own acoustic listening experiment for sure...I dont negate the usefulness and practicality of products at all.. Few people use an audio dedicated room like i did...

I just want to make my point known....Acoustic reign supreme in audio...

Objectivism or subjectivism about the gear is a deceptive marketing effect RESULTING from years of customers publicity conditioning...

In short, when you get a Life Changing Experience, then it sounds good.

This is called a circular reasoning... This is a publicity motto... Sorry....

This is even used for decades to sell new upgrading product...

i always liked myself all my pieces of gear, one after the other all my life....But was never satisfied really... Guess why?

The only way to know if your system sound at his potential working peak, nevermind the gear, is by acoustic control...

After that all your albums sound interesting, all of them reveal the acoustical choices made at the recording time...

My worst album acoustically are now revealing and interesting...

If you look ONLY for very good audiophile recording it is a sign that your system dont worked at his potential working peak YET...WHY?

When your audio system is under control, all albums are suddenly musical in their own way, with specific acoustical choices and trade-off made by the recording engineer and even the bad one are interesting to know...

Music through sound and sound through music....Not one without the other....

“the amount of hatred and absurdity is stunning here.”

Agreed. There is a stunning amount of absurd hatred afoot.

Hatred is a strong word that shouldn't be misused. I would say strong disagreement.