Double-rock the drywall and use the very best sound insulation you can afford between the studs. There's a very dense specialized batting for sound, or blown-in is excellent as well. If you plan on running any systems in other rooms you may consider running some wires before the walls are buttoned up. Cat-5, speaker wire, and a set of coaxial wires would all be useful in running an extension system. I also did two dedicated 20 amp circuits and kind of wish I'd done a third.
I know its not cheap, but have you considered using the spray foam insulation ?
We did the whole house ( outside walls / attic ) last year with this to save money and it also did a good job of I guess you could say soundproofing the house.
If interested, contact me and I can send a link and it will show a video of the work that was done.
I recently finished a dedicated 2 channel room and used double 1/2 inch drywall and all walls were double insulated before the drywall went up. I too brought in two 20 amp circuits and two 15 amp circuits for power.
The best tweaks you'll make will be after the room is finished using room acoustic panels.
If you are considering a dedicated circuit: Use(as least) two runs(keep 12" separation between the two) of 10-2 Romex(equiv of 4Ga), and(minimum) hospital grade outlets(ie:http://cgi.ebay.com/Leviton-Ivory-HOSPITAL-Receptacle-Outlet-20A-8300-I_W0QQitemZ250202544990QQihZ015QQcategoryZ41985QQcmdZViewItem). Also- Consider Auralex, or some of the substitutes available on eBay, to deal with the reflections inevitable in a listening room. Click on topics: (http://www.asc-hifi.com/acoustic_basics.htm) (http://shop.ebay.com/items/__acoustic-foam_W0QQ_nkwZacousticQ20foamQ20QQ_cqrZtrueQQ_nkwuscZcousticQQ_nkwuscZfoamQQ_trksidZm38)
Thick carpet, bookcases, thick drapes over windows, sliding doors, and upholstered furniture will all contribute to improved bass extension, soundstage, and overall fidelity. Avoid openings to other rooms without doors. Keep the doors closed to keep the sound in. Enjoy !!
Prior to my listening room remodel, I contacted Cryo-Nebraska who in turn locally purchased 500' of 12 gauge and 14 gauge romex at their local Home Depot, double-cryo-treated it and shipped to me which was then installed for my 4 dedicated lines.
A few other tidbits include premium wall-to-wall carpet with premium pad, few windows, no hard-surfaced furniture including tables and leather, and recessed lighting.
These few basics, good room dimensions, and proper speaker placement should be all you need for a superior room.
For everybody else in the house and neighborhood I suggest insulating all walls.
Is this all new construction?
You can 'stagger' the studs. This, with proper insulation will help decouple this room from the one next to it. In this way, the sheetrock in each room will NOT be back-to-back on the same stud.
You can also weave some Very Heavy, acoustically dense materials between the studs to help reduce sound transmission.
Built ins? Book shelves work and are a good design element, too. Stuff 'em with your paperback collection!
I would also use an EXTERIOR=solid core, 36" door as an Interior door.
Is it possible to install a barrier in the attic to prevent sound from going 'over the top'?
Prewire for as many speakers as you think you'll ever need.
Use 'econotube' flexible conduit so you can later pull or replace wire.
Double sheet rock? Not all 4 walls. Maybe, the wall next to the existing construction and 1 adjoining wall.
Make SURE you get Low-E thermopane glass, too.
Some bass problems can be predicted from the room's dimensions; or, if you have not started the building process, the dimensions could be changed to those that minimize bass problems. Built-in bass traps designed by an acoustics engineer can be more effective and aesthetically more acceptable than after market units.
Thanks everyone for the input. I used every one's suggestions in some way or another. I'll give an update when the room is complete.
Instead of 2 x 1/2 inch drywall, I suggest 2 x 5/8 inch. I also strongly suggest gluing the drywall to the studs & between the layers,in addition to screwing. Tape and mud the 1st layer before applying the second on an offset of course. The difference is not subtle and the cost is not prohibitive. Install soundproofing, tape and a trim piece along the gap where the drywall does not touch the floor. I would want a spare 20 amp line as well as normal 15 amp outlets per code.
I envy you-have fun.
If you need isolation of the sound from adjoining rooms, I suggest you read the information on the Green Glue web site.http://www.greengluecompany.com/
Their testing indicates that two layers of drywall are essentially no better than one when trying to reduce sound transmission through a wall. The articles on this site are very informative.
Very...like its not the thickness or fastening,but the pliability.I wonder if 3/8" would nt be the best as it would bend easier and thus absorb more than any other???
A drywall surface on studs resonates with acoustic energy just like a drum head. You need something to damp that resonance, or the whole wall vibrates and transfers sound into the adjacent room. Adding another layer of drywall adds mass, which lowers the resonant frequency, but doesn't lower the sound transmission much. According to Green Glue, adding this product between the two layers of drywall provides the needed damping and the test results show a dramatic improvment. I tried this on the ceiling of my dedicated room and it worked extremenly well.
The green glue is very worthwhile but there are other types of permamently resilient glue that are also similarly effective.
The reason for the 5/8 drywall is that the added mass with the resilient glue helps the low frequency isolation which has always been most problematic in my experience.
Don't allow any 90 degree corners. Use dry wall to enclose all the corners to make bass traping. Use the new sheet rock called Quiet Rock I believe. You won't have to double it probably. Use rock wool as insulation. Wire at least one home run per component and then add more. Install a separate electric panel for your room where all audio/video circuits are located.
Build in the design a wood floor. If concrete, build a wood floor over it with 2 by 4 laid flat, then plywood, then carpet.
Use Cardas Golden Ratio Data to determine the best size room for your needs.
Hire Rives Audio for overall room design. As for book cases being diffusors and Traps, go to Real Traps.com and watch the video on diffusion. In fact it would really help you to view all their videos. While you're at it go to the ASC site, readytrap site, and rsc. sites.
I could add more.
I built my room about 3 years ago. If I could build it again, I'd include the ideas I've outlined here. I've learned so much since I built my room originally.
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.
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.