Classical concerts, either by professionals or amateurs.

I just like classical performances.

I know Sangdee Gallery has a weekly musical event, but besides this...

Or do I need to go to BKK?

Sangdee Gallery?

Who, What, Where, When?

and if BKK , where to hear really good performances?

Some really good ones can be heard for free at the Payap University Kaew Narawat campus next to Prince Royals College. You'll have to go to the campus (Music Department right in front) and look at the posters to see when the performances are.

Kad Suan Kaew has classical concerts in their theater but I recall tickets being 500 Baht on up. I've never been there for a concert. Don't even know where in KSK it is.

Elektrified, good one, thanks.

OneZero: it's googlable.

"Classical music

Payap University puts on regular classical music concerts at their Mae Khao Campus. The Chiang Mai Symphony Orchestra holds regular concerts at Kad Suan Kaew’s theater. Additionally, a group called Friends of Chiang Mai Music regularly brings in classical musicians from Bangkok for small shows. Both of these run their announcements in the community happenings page of the Chiang Mai Mail online and CityNow online."

I found this on Thaivisa.

http://www.chiangmaimusicfestival.com/2011/friends.php