[Russ L]

Hi guys- joined a few years ago but this is my first Acoustics Circle post.  I’ve given up the battle with my wife to turn the den into the A/V room so I'm going to finish the basement and make that my SACD multichannel listening room home theater viewing room.  My reluctance to do so earlier had to do with the size of the room; 12-feet 8-inches wide x 21-feet 2 inches long and 7 feet-three inches high to the bottom of the floor joists above (approximately 7 x 14 x 21; not exactly the golden ratio). 

Anyway, I’m off the next two weeks and started the construction yesterday with the hardest part; emptying out the room.    My current plan for the finished basement is five three-way monitors and an infinite baffle subwoofer.  The sub will be part of the construction of the front wall.  The preliminary design for the sub is 27-inches square by approximately 22-feet long (10-feet would be in the adjoining storage room) using four 15-inch drivers.  I’m not so much interested in loud but going very low with little or no distortion. 

The basement had been previously finished but the beat up paneling and the drop ceiling were removed quite some time ago.  The studs are mostly in-place other than where I’m extending a wall.  So, that leads me to my first acoustic question.  In order to eliminate any low frequency “boominess” from the walls resonating, would it be an advantage to implement either or both of the following ideas:

1.   Use 5/8-inch sheetrock in lieu of 1/2-inch?
2.   Add 2 x 4 cross members between the 16-inch on center wall studs, alternating, say rows of cross members at 1/3 and 2/3 down from the ceiling, with rows having a cross member 1/2 down from the ceiling?

My guess is the heavier sheetrock will provide more damping, and the addition of the cross members between the studs will also provide more damping and raise any resonances up in frequency due to the “virtually” smaller panels.

Any advice would be appreciated; might as well get it right before anything goes up.  BIG ceiling question coming up next after I nail this one down.  Thanks in advance.

Russ

[MaxCast]

I can't answer your question for certain but I recently did my basement.  If you want to change the resonant frequency of multiple similar cavities I would think you would want to vary the cavities with a full partition between the joists.  Mixing them up as you go along.  I suppose the more mass the wall has the more energy it would take to excite it.

I floated my walls and ceiling and have similar shitty ratios as you.  I did a frequency test and it wasn't that bad.  I have since added GIK absorption panels but I have not retaken the measurements.

[Bob in St. Louis]

Welcome Russ,
I'm no expert, but I would imagine the smart folks might suggest you have two layers of drywall (1/2"?) making for a very solid wall. Trust me, an infinite baffle like you're talking about has the ability to make things creak, rattle, pop, and buzz. I HIGHLY recommend you use a construction adhesive in addition to screwing the drywall to the studs. One step further would be to trowel on adhesive between the two layers of drywall. If you have the finances, a layer of "GreenGlue" between the drywall would be ideal. I can't answer #2, but mainly wanted to chime in to say that if your room's not SOLID, you will find out after it's too late to do anything about it.
Trust me on that one.

A case of 24 tubes of "GAP Liquid Nail" will cost you about $50. Don't cheap out. 

Use glue. And LOTS of it. Everywhere.

Bob --- Fellow quad 15" IB user

[Big Red Machine]

You really need a heavy, isolated room structure to keep noise from coming and going.  Heavy walls and ceiling isolated form the house itself.  It is well worth it.  You need to watch the flanking noise - noise which will naturally sneek past one heavy wall and out through a vent or weak spot.  With that low of a ceiling you could use rubber isolating hangers inbetween the florr joists above to get the drywall as close as possible to the bottom of the joists w/o touching them.  2 layers of 5/8 is recommended but 1/2 is cheaper and easier to handle.  The GreenGlue is the shiznits and worth it.  None of this advice helps you get much done in the next 2 weeks though.

[bpape]

When doing a room, you're always working somewhat at cross purposes.  Doubling drywall will help with isolation but also reduces the efficiency of the cavities (insulated) behind to help absorb bass in the room and prevent boominess.

Raising the resonances of the structure is exactly the opposite of what you want to do.  You want to lower it so that less and less of the content will actually excite it. 

If you want real isolation, you'll also need to watch all holes in the room (switches, lights, HVAC, etc.)  Any of those left undone will undo everything else you do.  Also, remember that sound also travels through the structure as much or more (in the bottom end) as it does through the air so any physical decoupling will help a lot. 

If you're doing an IB sub, the cavity for that will by definition help with the overlapping of dimensions.  10x VAS takes up a lot of space in a hurry.

Bryan

[youngho]

If you want sound isolation, that's one thing. Unfortunately, more massive walls can lead to more problems with bass. Floyd Toole, in his book "Sound Reproduction," discusses one instance where a well-meaning contractor put in a double layer of drywall, leading to significant problems with standing waves. Earl Geddes argues for "wall internal damping" with walls mounted in such a way that they flex, and I believe that he offers very specific construction advice in his book "Home Theater." However, Dennis Erskine made a case against relying on drywall bass absorption recently on AVS Forum. A better approach for sound isolation would be the "room inside a room" construction. But I didn't see you asking for tips on sound isolation.

Dimensions and calculations are one thing, but you may find that reality is different than predicted, especially when it comes to bass.

[MaxCast]

And...double check, triple check your lighting locations.  I thought I had it, but just now I bit the bullet and took out two lights as that is where my first reflection points turned out to be. 

If you need isolation listen to Bryan's advise.  I used Green Glue, double layer 5/8" and floated the walls.  I can pretty much listen at what I want without concerns about up stairs.

[JLM]

To isolate the room from the rest of the house on the cheap use insulated staggered stud walls, insulated weather stripped exterior fiberglass door, lined/insulated flexible ductwork, and suspended ceiling (via lightweight gauge metal "Z"s or channels).  Use wall sounces, not ceiling mounted lights.

To increase wall/ceiling mass and stiffness (to lower their resonant frequencies) vary randomly the stud/ceiling channel spacing and add a 2nd layer of drywall (thicker the better) with Green Glue in between. 

These ideas should be applied even more so to the back chamber of the I.B. sub as the pressures there will be much higher.

Go to the Cardias site and follow their ratios as closely as possible for the room dimensions.  Another option is to put the back wall on a slant.

I did most of the above with my basement man cave and it was weirdly isolated and has almost no need for treatments.

[warnerwh]

On my ceiling in the basement I put sheetrock, resilient channel, soundboard and acoustic tiles.  The need to isolate my listening room from the living room directly above had been my objective. This does an excellent job except in the bass.  However the bass that gets through isn't too bad. 

It's a big job just for the ceiling but was worth it. Doing that ceiling that way wasn't as much trouble as I anticipated. The resilient channel is a necessity but fortunately cheap to buy.

Mass is your friend so 5/8" drywall will be better. Stuff is pretty heavy too, you'll notice carrying it down to the basement.  Making cuts upstairs is a good idea when possible.

You certainly want at least 4 or 6 large bass traps.  Plenty of diy recipes or if you have the money you can get commercial ones.  You'll be glad you did.  If you treat it acoustically and hadn't had that kind of treatment before be prepared for your present system to sound like someone else's system. The improvement has to be heard to be believed.   Best wishes on your new room.