most advanced speaker in a rectangular wooden box?

JBL 43 series are ultimate classic rectangles.

Agree with all of the above and will add Ryan Audio.

Lawrence audio double bass.

British brands : Spendor, Harbeth, Graham, Stirling Broadcast, Audio Note. These manufacturers realized long ago that there’s nothing wrong with wide-baffle monkey coffins if implemented correctly. IMO, many of them can go toe-to-toe with the exotic stuff from Magico, Vivid Audio and the like. This is especially the case when it comes to recreating the natural timbre of stringed instruments. They also tend to be less fatiguing.

Some can’t comprehend how this is possible because they focus on measurements and marketing jargon. Instead they should rely on their ears. The proof is in the listening.

Oops you said “Rectangular”.

British brands especially Harbeth and big Tannoy’s.

Kenny.