Axiom Home Page Forums General Discussion Home Theater Advice on New HT construction

I’m a newbie. I’ve tried to do a lot of research ahead of this posting, but I’m sure I’ve probably missed something –information overload. I'm building a new HT as part of a basement build-out and need some advice. I have reserved a rectangular space in the basement that is 19'(l) x 13.5'(w) x 9'(h) - unfinished. The walls on two sides of the space (the front screen wall and a side wall) will sit in front of cement foundation walls. About 9' of the 13.5' back wall sit in front of another concrete foundation wall and the balance separates the HT from the mechanical room. The remaining side wall (19’) separates the HT from the remaining basement, which when finished will be a rec. room with bar and pool table. This space is directly under the kitchen, which has wood flooring.

I want to make sure that I'm planning the sound isolation and acoustics properly. I’d rather spend the money up front then spend it on a divorce attorney later. I’ve already been down that road once. For sound isolation, I'm planning on the following:

1) The walls the sit in front of foundation walls will be 2x4 construction with RC, fiberglass insulation and double dry wall (1/2 and 5/8) screwed and green glued. They will sit approx 1 inch off the foundation wall, which is wrapped with insulation. There are two small (1'x2') basement windows along the top of the side wall which I plan to wall off. I plan on keeping a small gap (to be chalked with sound chalk) where the wall meets the ceiling and the floor in order to isolate it more.

2) The side wall adjoining the living space will be double 2x4 construction (1" gap), RC on the wall inside the HT, both walls insulated and double dry wall on both sides (different thicknesses, gap at top and bottom, same as above). This wall will have an exterior grade metal door with a weather seal in it. (Unfortunately, it will be located in the front half of the HT, just ahead of the first row of chairs.)

3) The ceiling will be heavily insulated (6"+), 1#/ft mass loaded vinyl, RC double dry wall (similar to walls). I plan on building a 1’ soffit around the outer 3” perimeter so that the recessed lights will not penetrate the ceiling.

4) For the floor, I’m considering either using 2#/ft mass loaded vinyl under the carpet and mat or a floating floor using the pads and two layers of sub-flooring. (I’m strongly leaning toward the mass loaded vinyl route.)

If I’m careful to plug all the cracks, I’m hoping to get a STC over 60. Do you think this will be adequate to keep the noise from reaching the kitchen and/or rec. room? I’m planning on running a Denon AVR-4306 with 7.1 Axiom Epic 80/600 speaker system. I like a true cinema experience (i.e., I tend to crank it up). What am I missing in terms of isolation?

For acoustics, I saw a HT where the four side walls were lined floor to ceiling with 2” mineral wool fiber covered with fabric (for absorption). I probably need to put a panel on the door to stop any first reflections that will occur at that point.

The front of the HT will be a 6” high stage, 3’ deep in front of a 100” screen. I would like to find some way to hide the front speakers and sub. I have seen HTs where the LR front speakers are placed behind black fabric walls that are build at a 30-45 degree angle both sides of the screen. As long as I frame the wall so that the 2x4s are well clear of the speaker fronts (i.e., put by cross support 2x4 at least two feet above the top of my LR speakers) does this create a problem? I would have the speakers in direct contact with the back of the fabric and could even remove the speaker grills. I would also put base traps in the front corners of the HT behind the speakers and fabric walls (any suggestions?). For the center and the sub, I was planning to build a framed-in cabinet (open across the front along the back of the stage just below the screen. It would be covered with black fabric like the fake side walls. Again, I would keep the framing material away from the speaker fronts. I know most hard core audiophiles cringe at the thought of anything being between he speaker and the listener. But would this set-up appreciably reduce the sound quality by any noticeable amount?

Will the mineral wool on all four walls be too much? Should I do something different for the back half of the HT (for diffusion) vs. the front (for absorption)? If so, what would work and keep with my general design?

Thanks for all your comments. Happy Turkey Day!

Bob

Bob, welcome. Some of our members have been personally involved in constructing their rooms with soundproofing in mind and/or treating room modes, so hopefully they'll be able to comment if they're not getting an early start on that turkey. I'll comment a bit on STC theory. A typical room at home has a background noise level on the order of 40dB. So, an STC of say 65 would prevent a sound at a 105dB level in an adjoining area from being actually heard in that room. Listening at about an 80dB average level is considered to be "comfortably loud" and no one who values their ears will listen at above a 90dB average. Very brief peaks, especially in material that has a wide dynamic range(i.e. much more likely with classical rather than pop music, and sometimes occurring in movies)might hit about 110dB. So in a kitchen, which tends to have an above average background noise level, there should be no problem with sound transmission if a STC in the mid 60s can be achieved.

>> The walls the sit in front of foundation walls will be 2x4 construction with RC, fiberglass insulation and double dry wall (1/2 and 5/8) screwed and green glued.

I am not sure if it is completly necessary (money wise) to use RC with GG on the concrete foundation walls. The only way sound will travel from the walls to upstairs is through the TOP of the wall that is attached to the ceiling joists.

I would say that Double drywall with GG would be enough for the concrete foundation walls.

All in all, you have an AWSOME idea of what is needed to attain the STCs you want.

>>The side wall adjoining the living space will be double 2x4 construction (1" gap), RC on the wall inside the HT, both walls insulated and double dry wall on both sides (different thicknesses, gap at top and bottom, same as above). This wall will have an exterior grade metal door with a weather seal in it. (Unfortunately, it will be located in the front half of the HT, just ahead of the first row of chairs.)

The double studded wall system ALONE with double drywall on each side and NO green glue yields an STC of 63. Adding GG will probably get you over 70 STC. I tried looking on the GG website, but could not find a test with double studded and GG.

I don't think you need to do RC on this wall if you are doing double studding. It would probably be a waste of money because your studs are not touching the other wall, RC is designed to stop sound transfer through the studs, and since you have a completly separate wall on the other side, RC will do little to nothing.

What you could do aswell is double drywall and GG the other side of the double studded wall (on the rec room side). That would make that wall literally commercial theatre quality sound proofing.

3) The ceiling will be heavily insulated (6"+), 1#/ft mass loaded vinyl, RC double dry wall (similar to walls). I plan on building a 1’ soffit around the outer 3” perimeter so that the recessed lights will not penetrate the ceiling.

Are you going to Green glue the ceiling between the double drywall? I would suggest this.

Mass loaded vinyl will not outperform double drywall and Green glue (MLV is around 45 STC, Double Drywall and Green glue is 54 STC). If you also add RC to the ceiling combined with double drywall and GG, you will get really good results. (I think around 60 STC)

4) For the floor, I’m considering either using 2#/ft mass loaded vinyl under the carpet and mat or a floating floor using the pads and two layers of sub-flooring. (I’m strongly leaning toward the mass loaded vinyl route.)

Since you are on concrete foundation, I don't think you need anything special on the floor unless you have ducts that are traveling through the cement floor to other areas of the house. In which case the mass loaded vinyl would probably be enough.

I would say, all in all, you will have an AWSOME theatre. Do alot of research on greengluecompany.com for construction tips, they know ALOT about sound isolation and can guide you through everything.

Thanks Robb,

Sorry I haven't responded earlier, I've been out of town. I think I will drop the RC on the walls and use RCIS-1 on the ceiling, cover all walls and ceiling with 2 layers of sheetrook and GG. I've seen some people suggest that 1/2 + 5/8 is superior to 2 layers of 5/8, any opinions. If I understand the argument, 1/2+5/8 will minimize the potental for ressonance between the rock. Doesn't the GG deal with this issue? ALso does anyone see any benefit in putting MLV on the ceiling before I install the RCIS-1 brackets (in addition to using GG)?

I'm a little troubles by the door. I'm planning on using a solid core (steel covered) exterior grade door with a threshold and seal. Do I just install it in one wall (e.g., the interior wall)? What should I do about the door jam between the two walls to avoid creating a hard connection? I realize that two communicating doors is a better option, but I think this is an impossible sale to the wife.

Bob

Bob,

I am not sure about the 1/2" and 5/8" argument.

And concerning the double doors...you should really take your wife on a nice romantic dinner, set up some candles for her to take a bath, and after 15 mins in the bath mention to her the double doors because this will complete your soundproof room. If you don't have double doors it will be the weak link in your room.

Regarding the MLV in the ceiling. Go here and read up on the tripple leaf effect. It may have an effect with MLV, then RC, then Drywall. Read that page anyway because it has alot of info on double studded walls.