Quietest air conditioners for a listening room for the upcoming hot summer?

The man needs a sleeve unit.  The side vents on the AC shown will NOT work.  It has to vent from the back.  The sleeve installed is made for a certain brand of AC, it's best you get the same brand to be compatible, otherwise you will severely shorten the lifespan of the units and they won't fit properly.  The best would be the AC with a small front and everything else is outside the window, but they won't work in the sleeve..  

Yeah , stereo5 is right if it has a sleeve you need a thru the wall A/C because regualr window units have side vents that the sleeve will cover so they don't work at all. The thru the wall units are not as efficient and more expensive too.

I went with a Mitsubishi  heatpump Mini Split. The Main unit is outside and I have a small air handler in the ceiling.On the lowest fan setting, I can barely hear it.  you can also get them set up like an all-in-one unit, like you'd see at Best Western or a Super 8. 

All the best.

@curiousjim 

I think OP has rules, perhaps he is in an apt, condo: one unit, in an existing sleeve the max size he gave us.

So, what fits? what is the quietest?

I forgot that when I saw that clever window unit design with the lowest sound rating.

@elliottbnewcombjr 

Good catch Elliott!

Sorry OP. I missed the whole apartment part.  They made me quit real coffee and I’m having troubles keeping focused.