How do you know what a good speaker is?

The sound must be as pure,like the (good,professional) recordings. There are a lot of bat recording and that is sad, because you pay for a good cd,or lp.
Every speaker is different ,but the most important thing is that you have a good harmony between high-mid and low. The most of the speakers (and amps ) have too deep low, throughout wich the “mid” is supplanted.
A Nice explane of a good speaker is the Ilumnia Magister.: a driver with a “floating” conus. In a while, he will be available in the States and Canada. I never heard such a natural speaker before.

Doug Sax at the Mastering Lab used Tannoy SRM-B 10” monitors in the early years with his own ML crossover. In later years, he used ATC 150ASL monitors similar to Pink Floyd and Telarc. At one time he was so busy that he was mastering 20% of the top 100 billboard albums. His work always sounded great. The secret sauce was the tube preamp designed by his brother, combined with great ears and great monitors.

Large ATC are rated at 120 dB SPL continuous at less than 0.3% THD. Of course at lower SPL the distortion is less. If you listen to ATC then on countless classic albums you will be hearing close to how Doug Sax heard it when the mastering was done (room, source, preamp excepted).

There is a selected list of albums on wiki. He did 1000’s of albums. Go to guy for all the top studios.

https://en.wikipedia.org/wiki/Doug_Sax

Doug’s original reference was live sound, as bdp24 indicated. He pioneered direct to disc. However he became so popular that eventually he had a busy business simply doing the final mastering of everyone’s mixes - hence the Mastering Lab. He was revered by legendary engineers with golden ears - a king of kings.

You can’t expect to have ears like Doug Sax. He is probably unique in the history of audio engineering. However, the ATC’s he used were out of the box unmodified and you can buy them as they are still in production. I believe that Manley issued a commercial production of a clone of Doug’s Tannoys but with heavier cabinets - the Tannoy ML10 - you can find these used (the driver is no longer in production). You can be confident that these are both good speakers, as the greatest ears of all time depended on them.

https://www.manley.com/pro/manls/

Wrong. This is an awkward effort to please the crowd and renounce objectivity. Really good speakers will be acknowledged as such by everyone with hearing regardless of sound preferences.