[Lissnr]

Hello gentlemen,
I've been following the very helpful threads here for quite awhile and have learned quite a bit so far: Thanks!  ...as my new dedicated sound room is under construction. I am converting a detached garage and need a few bits of advice for another step. I've replaced the main garage door with a "dummy door" by removing all the old tracks and through-screwing a new replacement door to some [vertical] 2" x 4" studs I secured along the sides (the door is a brand called "Coplay" I picked up at Home D.) below:

Two Layer Insulated Steel Garage Doors

   
•      2-Layer bonded construction provides quiet operation plus added security and dent resistance
•      7/8"  Insulation for energy efficiency and comfort
•      Weather-tight section joint helps seal out the elements
•      Prepainted white end stiles and interior steel backing provides a clean and finished appearance

My question is this: as I'm about to build the 'real' interior inner shell stud wall next to this door which will support all the sheetrock, romex, etc and I was wondering whether I was better off with 16" on center studs or 24"? The rest of the garage is already 24" on center so I'm inclined to keep it consistent but this is only a 7' high x 8' wide door section and obviously I can do it either way. I plan on using 5/8" sheetrock on the OUTSIDE of the framing (between the studs and the interior of the dummy door) as extra sound proofing by building it all on the floor first and then lifting it up and securing it completed. After all the wiring is done I will then insulate between the studs with standard R-13 fiberglass insulation and finish with 2 layers of 5/8 sheetrock  on the inside wall, possibly treated with green glue or at least a few tubes of a silicone based caulk/adhesive. The garage is about 50 yrs old, built with a 3/4" hardwood -of -sorts shell which was recently covered with vinyl siding, and all with 2"x4" studs on a concrete foundation. It has a pitched/ cathedral ceiling roof which is 6'8" at the top of the side walls and rises to a 9' center. The interior concrete foundation area is 13'5" x 18'8" but by the time I'm done with the additional inner walls (behind the garage door as described and the one at the opposite end which I've also already done (24" on center)) and the double layers of 5/8" sheetrock I'm planning (w/ Green glue on the left and right walls) the final interior dimensions will be about 13' 1.5" x 17'8" x 8'10" [on centerline] height.   Your advice on this and any other overall input is much appreciated. Thanks in advance. Grant

[MaxCast]

I just finished doing A/C, double 5/8 with green glue.  It was advised to me to do walls at 16 oc and 24 oc.  The reason being it changes the resonant frequency of the different sized cavities.  You do have a small area, but why not.  Do you have access to the other walls?  You could always toe in a few 2x4's and get other walls different as well.

[Lissnr]

Hi and thanks for the quick response. Yes, I still have access to all 4 walls (only the ceiling has already been sheetrocked = 1 layer of 5/8" on furring strips with R-13 between). You recommend adding additional studs to space alternating sections of 16" x 8" x8" x 16", etc??? instead of the 24" now? Thanks

[TomW16]

To add to what MaxCast mentioned, I believe that the opposite walls should have different spacing so one of the two walls facing each other should be 16" OC spacing and the other should be 24" OC spacing.  That way the sound bouncing off of those walls will excite different resonances rather than the same resonance.

Cheers,
Tom

[MaxCast]

Yea, what Tom said.  But I guess it would come out to be 24" on one side and 12" on the other.  I suppose you could just mix both sides up willy nilly.  6", 10", 20".  It would only cost a few extra 2x4's but make adding the insulation a bitch.

May I ask, why the furring strips and isolation?  Being detached, I guess you're trying to keep sound out?
What are you doing for heat and AC?

[Lissnr]

Thanks again for the input guys. Differentiating the studs behind the drywall to change the size of the cavities and therefore change the resonant frequencies of each cavity makes sense to me... the more varied they are the less one particular one will dominate. Check. In practical applications it does make for a bit more work when cutting insulation... that is, by requiring the insulation to be cut vertically to match the varying widths. I happen to have a few rolls of both 15" W R-13 and 23" wide R-13 for use as needed and I'll have to be buying more anyway so maybe I'll mix it up somewhat by adding a few extra studs and varying 16", the resultant 7" or so remaining, and then some at the standard 24"... and have them mismatch the opposite wall's version, this wouldn't require a tremendous amount of cutting (and it'll only be done for this one time obviously). I could do this with both of the 'fake' interior walls which are simply straight 2"x4" studs (as I said before, 1 wall is done and the other is the topic of this post).
 OTOH, technically the left and right pre-existing original walls are already of varying cavity sizes due to the presence of a diagonal (/)  bracing stud running from top left, down to the center, and then back up to top right, actually connecting the studs and making each cavity (both top and bottom) different volumes. This would also tend to make adding the additional studs just mentioned onto these walls, quite a bit more involved as they'd have to be cut to proper angles to meet with these cross braces... All in all, a lot more work. {They already require the insulation to be angle cut/ not full length with different sizes for each top and bottom piece} 
I used the furring strips on the ceiling to give the additional breathing room which is required for insulation that is used on ceilings, to improve airflow and reduce sweat from summer's rising heat. Understand the ceiling studs are only 2" x  4" and the insulation is 3 1/2" to almost 4" deep... the additional 3/4" of furring strip supposedly will make that airflow difference... so I'm told.
I also just had a new roof put on (tar-paper and roof shingles).
Yes, I do want to keep sound out but my primary concern is keeping my music sound away from the neighbors.
As for HVAC I'm at a crossroads right now. I live on Long Island NY and we get our fair share of both hot/muggy summers and below freezing winters so I 'm still investigating answers. Thought I'd try the ductless A/C  and heat pump system (quiet and efficient) but supposedly they're very good at cooling  yet no so good at heating. May just try a couple of the new portable space heaters that look like base boards and see how they'll do, possibly with a moderate sized wall mounted ac unit for the summer? Don't know yet...
For the record I ran a 2pole 70 amp breaker from my main house's 200amp panel into the garage to its own separate 100A sub panel (I dug a 20" underground trench partially under a concrete patio for 35' to run the cables inside 1 1/2" PVC conduit, then back filled it all) This was quite a job... My electrician pulled the cables through and rigged the sub panel. I will have several 20A dedicated lines running to my amps, my analog, my digital... the HVAC lines, lighting... everything I need out there, all separate and designated, so I'm excited about that. The actual Romex and outlets will follow after the wall is built this weekend (the subject of this post).
I know the room is a bit small (I'd love another 2 or 3 feet in width) but it will be totally dedicated so I can acoustivally treat it as extensively as needed with no WAF or any visual concerns,,, the sky's the limit where function is first, looks are secondary (though still important for me...) Input welcomed/ encouraged Thanks guys. Grant