[TomW16]

I am in the planning stage of a dedicated home theater / 2-channel listening room that will be constructed in our basement.  The room is pretty much an L shape, however, for acoustical purposes, I will build a wall so that it will be a rectangle and the other part of the "L" will be another room.  Unfortunately, I had to concede pocket doors that have the capability of opening up the L shape, which killed any hopes I had about sound proofing the room.  Since I do not know how to attach a screen shot from Excel, the room is approximately 25' long, 15' wide and 92" high (unfinished).  Below is a rough sketch:

                                                   14' concrete wall
                |<---11'  concrete wall ==============                
======================                               |
                                      X                                         |
Stairs                                                                X       |
    |                                                                            |  16'
    |          |X                                                               | concrete wall
    |          |                                                                 |
    V         |                         Me                                 X |
               |                                                                 |
               |X                                                               |
               |                                                                 |
               |                                                        X       |
               _____****___X_____                                  |
                        Door                |                                 |
                                               _____***********___ |  
                                                        Pocket doors       |

The "X"s are approximate speaker locations and I will be listening at the "Me" location.

So here are my questions:

1. How does an approximately 25' x 15' x 7.5' room look acoustically?  I realize that the 25' and 15' are both multiples of 5 but note that the widest portion of the room will be approximately 16.5' and the narrowest portion of the room will be 11'.

2. Rather than build a standard room with sheet rock and then add accoustical treatment afterward, I was wondering if I could integrate the accoustical treatment into the wall.  My thought is to put OC 703 fiberglass in "windows" in the wall so that it would be flush with the surrounding sheet rock.  I would then put some acoustically transparent material over it with a frame to look something like a colonial panels on the wall.   What do you think?

Thanks.

Tom

[TomW16]

OK, so the Audio Circle software removed the spaces from my "sketch" and it was uncomprehensible.  I have, therefore, taken a screen shot from Excel and posted it in the Gallery.  Below is the link so that you can see my basement plans in all its glory.

http://www.audiocircle.com/circles/galleryimage.php/albuv39/Basement_Plan.sized.jpg

Thanks.

Tom

[MaxCast]

If you tell us how you did that with excel we'll tell you how to treat your room

I think intigrating absorption into the room is a gret idea.  YOu can read a bunch at www.realtraps.com.  
Find a room mode calculater to get a rough idea of peaks.
The jist of it is: the more the better for bass traping.  
exposed surface area of an accoustical absorber is key.  
High density for low frequencies.  
Lower densities for first reflection points.  
Tri-corners and corners are best place to trap bass.

YOu could build bass absorbers in the two front corners and the corners behind the chairs.
You could do the first reflection points for each seat on the side walls and cieling.  Don't use a coffee table in front of the couch.

You can also use an absorber or difuser behind the speakers.

[TomW16]

The jist of it is: the more the better for bass traping.
exposed surface area of an accoustical absorber is key.
High density for low frequencies.
Lower densities for first reflection points.
Tri-corners and corners are best place to trap bass

Thanks MaxCast.  My thought process is to put bass traps in the 4 corners of the room and potentially behind the chairs as you mentioned.  Potentially also all along where the walls meets the ceiling.  I have heard that you cannot provide too much bass trapping.

You could do the first reflection points for each seat on the side walls and cieling.

What I am planning to do at the first reflection points is to stuff acoustical absorber between the studs on the wall and the joists on the ceiling and then cover with acoustically transparent fabric so that it is flush with the surrounding wall and ceiling.  I am hoping that this would provide some architectural interest without looking like traditional acoustical treatment.

Tom

P.S.  All I did with Excel was reduce the row width and column height to obtain "squares" and then drew lines where walls were or were to be built.  The chairs, TV and "speakers" were simply clip art.  It was a simple way for me to get a scale drawing of the basement.

I just hit the "print screen" button on my keyboard to copy the Excel screen shot and copied it to a photo editing software (Arcsoft) and resaved the "picture" as a jpg file.

[avahifi]

Walls  - - - double layer sheet rock for additional stiffness.  Cover with Acoustic Fabric, available at any high quality wallpaper store, goes on like wallpaper.

Ceiling, thinnest grade Sonex, goes on like ceiling tile, use their own adhesive to avoid damage.

Floors, thick soft carpet.

That is all you need.

Frank Van Alstine

[TomW16]

Walls - - - double layer sheet rock for additional stiffness. Cover with Acoustic Fabric, available at any high quality wallpaper store, goes on like wallpaper.

Thanks for the advice Frank.  I was going to do away with the double thickness of sheet rock as I assumed that was to contain sound (sound proofing) and since I will have so many "holes" in the room (pocket doors), there was little point in the addtional expense of trying to contain the sound within the room.  Does the double sheet rock also provide some additional bass traping capability?

I will have to check out accoustical fabric.  I am a little sceptical that it would be as effective as thick high density fiberglass since I am assuming that it is very thin (like wall paper).  Does it work like a diffuser?

Thanks.

Tom

[samplesj]

A layer of acoustically transparent cloth on top of sheetrock wouldn't really be much help, but you do often see that same cloth used to cover the treatment.   A common theme in DE style theaters over on AVS is rigid fiberglass up to ear level and then polyfill above.  You could either drywall the inside and add "fake" studs and/or furring strips or you could just use the treatment/fabric as the inside wall.

As far as ceiling goes I'd stay away from foam just because of price/flamability when you can get rigid fiberglass.  I want to say that Ethan has even said that 12+ inches of fluffy stuff in a joist is as good as the rigid.  Again you could just cover that with fabric or you could use a ceiling tile.

[TomW16]

A common theme in DE style theaters over on AVS is rigid fiberglass up to ear level and then polyfill above.

Thank for the advice Jeremy.  Any particular reason the ridid fiberglass would not be extended to the ceiling?

Just to clarify about the "holes" in the room, I plan to listen with the pocket doors closed so that there is symetry around the speakers but my understanding of sound proofing is that all air gaps must be sealed to contain sound within the room.  Since I have 3 doors in the room, there was little point to go through the expense of double sheet rocking the walls and ceiling.  

My goal is to treat the acoustics within the room and not worry about sound proofing.

Tom

[bpape]

I'd also consider some bass control.  With the thin Sonex on the ceiling and carpet on the floor, you have a ton of HF only absorbtion and basically nothing on the bottom.

[TomW16]

Thanks bpape.

I looked at your link to the sensible sound solutions web page.  Any experience with stuffing the wall flush with OC 703 and then covering it with acoustically transperent material so that the treatment is not proud of the sheet rock?  I am looking to combine some wife acceptace factor but not lose too much performance  

Thanks.

Tom

[avahifi]

Bass control -- the double layer paneling for stiffness to keep the room from talking at LF.  The acoustic fabric wallpaper is not "acoustically transparent", it is a very good acoustical hi and mid absorber, and a lot better looking than Sonex.

This is exactly what I have done to turn a mundale 24 x 16 x 9 surburan "family room" into a quiet dead and acoustically pleasing listening room. I did not even do the double paneling but lived with what was already there.
Fortunately two walls were below ground level mostly anyway and the floor was concrete so they were plenty stiff as is.

The process costs a lot less than far out audiotweek things and looks very nice when finished.

Frank Van Alstine

[TomW16]

Thanks for the clarification on the purpose for the double sheet rock Frank.  I do not have a walk out basement and am, therefore,
completely underground so not much point in double sheet rocking the concrete walls.  I will, however, double sheet rock the outside of the separating wall and the stairwell wall with a single sheet of sheet rock on the inside.  I have heard that this is a somewhat effective bass absorber when the studs are stuffed with high density fiberglass.  The bass frequencies travel through the single sheet rock, become somewhat attenuated travelling through the high density fiberglass hit the double sheet rock on the outside, reflect back towards the room, become further attenuated in the high density fiberglass and then out into the room again.

Tom

[samplesj]

Any particular reason the ridid fiberglass would not be extended to the ceiling?

I think the normal reason they don't go all the way to the ceiling is that it would be too much absorption.  You'd end up with the bass vs mids/highs way out of whack.

[JLM]

I believe what Frank is trying to say is that the drywall itself isn't as stiff as you might think.  Cheaper yet that double layering the drywall is to reduce the stud spacing (from 16 to 12 or 8 inches).  And make sure to use wooden, not metal studs as the metal studs have far less stiffness than wood.

Use a suspended ceiling to keep sound from going back and forth from basement to first floor.  An alternative would be using gauge metal channels between the structure and drywall (but my contractor refused as he claimed it might crack).

Use insulated flexible duct for the supply air runs.  I can barely hear the furnace run on any projects I've used it on.

Run a dedicated circuit to the system, preferably one per receptacle.  Tie all the system receptacles/circuits to a separate ground.  While you're at it you might try audiophile receptacles or at least a hospital grade (fit tighter) from a home improvement store.

To bad about the pocket doors.  I insulated/weather-sealed exterior fiberglass works great.

[samplesj]

The acoustic fabric wallpaper is not "acoustically transparent", it is a very good acoustical hi and mid absorber, and a lot better looking than Sonex.

I was really hoping you just meant acoustically transparent.  Do you have any measurements (even from the vendor) about how well this fabric works?  A lot of those style treatments are generally considered snake oil which makes that recommendation coming from you somewhat ironic.  Unless the stuff is way thick then simple physics will rule out much benefit for balanced treatment.

The process costs a lot less than far out audiotweek things and looks very nice when finished.

You do realize that you don't need to be on the attack over here.  Most of the stuff people will suggest here actually has real science behind them.  While you may not agree with the pricing, that doesn't mean it isn't a valid technique.

Rigid fiberglass is actually pretty cheap.  I only have ~$30 in my 2x4 4" panels.  Raw 2" sheets themselves were only ~$10.  Foam seems to run in that same price range.  Rigid fiberglass has measureably better performance than foam for equivalent thicknesses.

[TomW16]

Thanks for the clarification Jeremy.  I am planning on using Owen Corning 703 6 inch thickness fiberglass, assuming I can find it locally.  It is suppossed to be fairly broadband for absorption from bass to highs.  Below are some measurements taken from the following thread:

http://johnlsayers.com/phpBB2/viewtopic.php?t=562&postdays=0&postorder=asc&start=0

All Measurements mounting direct to reflective background (no cavity).

Freq: 125, 250, 500, 1000, 2000, 4000 Hz

6 inch
OC 703 · 6.0" · 1.19 · 1.21 · 1.13 · 1.05 · 1.04 · 1.04

JLM, good advice about the additional studs to stiffen the sheet rock.  I will likely do that and will also go the poor mans isolation route and put isolation tape on the studs to help dampen the sheet rock.  I don't have any false hopes of isolating the sound in the room but any taming of sheet rock resonances would be beneficial.  My original plans had a completely isolated room but I had to make some concessions when obtaining authorization from management (aka wife)     I'm not too concerned about containing sound within the room since the bedrooms are on the second floor and I don't listen terribly loud as I would like to retain my hearing as long as possible.

Thanks.

Tom

[JLM]

Don't forget to consider what sounds transmit into the room.  With only an insulated ceiling I hear the dishwasher, washing machine, dryer, and vacuum very easily from the floor directly above.  

Folks I show my room to make the same assumption, that I play loud.  I don't.  The insulation and isolation is more to keep the outside sounds out than to keep the inside sounds in.

[bpape]

Actually, if you want to vary and broaden the frequency range that the walls will absorb (even stiff they still act as somewhat inefficient bass absorbers), alter the stud pattern to be a mix of 16 and 24" on center.

[avahifi]

After turning two separate lower level rooms into outstanding listening areas, I kind of resent the "snakeoil" comments regarding my suggestion about using acoustic fabric wallpaper.  It is of course designed to kill mid and hi frequency reflections.  I do not know the numbers, but if you would make a trip to the wallpaper store and look at the data in the design books for it there rather than calling names you would have a much better use of your rather (useless it seems to me) time.

In other words p--- off.

Frank Van Alstine

[2bigears]

is a solid wall of bookcases in the rear o.k. to do?? just starting to do my room as the sound is real bad.          the room is 13 by 18ft