Tweaks when building a listening room?

The flexible conduit mentioned above is a must. You always want the chance to pull wires. also, run an empty conduit with a string inside. you will be amazed how soon you will be using it.

On the walls, I would use two layers of sheetrock, but of different widths. I would probably put 3/8 against the studs and then use that newer fiberglass-based mold resistant sheetrock as the outer layer. This stuff also does not vibrate like regular sheetrock. I stumbled on this fact when I mounted some in-wall speakers in both kinds of sheetrock and the fiberglass stuff did not vibrate as much when I touched it while playing music. One other thing you might do is tack a layer of accoustic rubber between each layer of sheetrock. This stuff stops soundwaves really well.

If you want the room to sound entirely neutral, avoid drywall entirely. Sound bounces off drywall, distorting the music as it reaches your listening position.

There are sound-absorbing wall materials that can render the room anechoic, and this will enable you to hear your system without participation by the room. You can turn your system up as loud as it will go, and you will be amazed at what it sounds like without echo in the room.

However, these wall materials can be difficult to work with, and may not be aesthetically pleasing, so you will also need to figure out some means of covering them that does not then bring back the phenomenon of sound bouncing off walls. If fabric wall covering can work for you, that might be best.

Merely putting the sound absorption material inside the walls, and covering them with drywall, will not do much good.

Whatever you do, don't try to make the room anechoic. Anechoic rooms are not intended as music listening rooms.

lots of good advice and ideas.

i would recommend getting some professional advice on the effect of the shape of your ceiling on the sound. not all 'cathedral ceilings' are the same.....the solidity of the structure and the surface materials will have an influence as well as the exact shape. with a 15' width and height it might be a problem in terms of room nodes.

fixing it later will be expensive and a pain.

the room has the potential to sound very good. a purpose built 2-channel listening room is a joy.