What would your "perfect speaker" sound like.

I had symphony seats perhaps 12th row. Not very loud there. It is nice to hear a violin sound the way you know it does. Ditto for chelo's I love the sound of a rich full bodied chili. For violins I want them to make me cry. 

An interesting exercise, and confusing when the adjectives start flying with no description of the meaning of the words.  First, a speaker should do no harm. In other words, it shouldn't change the sound (especially instruments), in any way, that was captured on the recording. 1) A flat frequency response is the first requirement (and easier said than done for most speaker designers). 2) Near zero relative phase response (how the drivers relate to one another in terms of phase). This will permit a proper leading-edge dynamic. It will allow a speaker to disappear as a source of the sound. 3) With those two goals intact, the speaker must be able to faithfully track the dynamics of the recording – both micro and macro dynamics (don't underestimate the importance of faithfully resolving micro dynamics).  4) Details: the elimination of anything that veils the sound on the recording. And the ability to represent all of the ambience (reverb) the recording has on offer. If all done well, the speaker will enlist your attention and draw you into the music's beauty and intent.

I like a speaker that provides a full range sound whether playing fairly loud or quietly. My Salon 2’s manage this now that I’ve added two very high quality subwoofers crossed over around 70hz. 

I want my speaker sounds natural and live. This video shows how the natural sound should sound. Alex/Wavetouch

Killing me softly - (Natural vs. Un-natural sound), PA speaker comparison.

Probably not a good space to design a speaker here. Once you have perfected it.....what does it sound like. Every one wants more bass. I don't I like it very fast and it doesn't have to be flat to 20 hz. That can rattle the walls. They would have to work in my listening room. Disclaimer  here I am not paying anyone to build a custom listening room.