Tweaks when building a listening room?

The number one rule is "broadband absorption' - keep the acoustic treatments even. If you have floor to floor carpet then you may already be ok in the mids and treble from the get go. Then all you need is large thick bass broadband absorbers and plenty of plush furniture. See my virtual system example for what you can do with a fireplace. There is such as thing as too much mid and treble absorption - so keeping the room lively may actually make it sound better. It is pretty much impossible to overdo treatments in the bass - so do as much as you can aesthetically handle...

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.

Building the room with the ideal dimensions will make the biggest difference. In your case installing a drop ceiling to the right height would be more ideal. Check out this web site http://www.decware.com/paper36.htm for the golden ratios for room dimensions.

My experience with building to Fibonacci (Golden Mean)ratios is very similar to Sarcher above. I ended up at 8ft H x 13ft W x 21ft L. The room response is remarkable.

Now is the time to consider the AC dedicated circuits and conditioning as well. Consider a dedicated circuit to each component and a large iso transformer on a subpanel just outside the room.

See details in my system.