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54 Posts
Discussion Starter · #1 ·
I will apologize in advance, as I know that somewhere in the vast archives of this wonderful site these questions have surely been asked. I can only hope I don't get a bunch of responses saying, "Try Google", "Did you search the forums". I'm knew to this site and haven't seen much of that going on but my experience with forums is more automotive related and the people on there can be a little rough to "noobs" asking "silly" questions.

I've been reading almost non-stop for the last several days (well for several years actually, just more intense as of late) and have gathered a ton of information on the forum here and a few other sites. Too much information actually and my head is spinning.

A little background on the project:

I just finished building my speakers, which are GR Research AV-3 Towers, an AV-3S and 4 AV-1RS's. Here are a few pics.

I've also added a second layer of sheetrock to my walls and applied Green Glue between the layers.

I am getting ready to build my sub/sub(s), not sure if I will do 1 or 2 but someone can chime in if there is an advantage to have a pair vs. one.

The room is 20'x17' with a 9' ceiling. There is an area that protrudes (closet of master bedroom behind there) that makes the front stage area 15' wide. Also of importance, it's on the second floor above my garage.

I'll be using an Optoma HD70 (It's what I have) and was planning on doing a DIY screen (Painted with http://www.liquiscreen.com/ ).

I am on a tight budget so everything will be done by myself and as cheap as possible. I can build anything, which helps of course.

1) I want to build a stage up front even if it's just cosmetic but need to know what I should do about filling the cavities. I know why sand is so valuable and that decoupling is as well. I've read a lot on this but still can't find out what to do if you are building a stage on a second floor joist system room. Do I fill the areas with sand where the speakers will rest? Do I isolate these sections from the rest of the stage so that there is a, let's say 1/4" or so gap between them? Do I use a product like http://www.roxul.com/residential/whe...e+theatre+room in the cavities? I'm pretty confident that some sand will not be a problem as the wall where the stage is directly over an enormous weight-bearing joist and is a sheer wall to boot. I do NOT feel comfortable filling the entire stage with sand though, not without talking to a structural engineer. Lastly should I decouple the stage with these? http://www.soundisolationstore.com/j...rs.html#topic1

2) Riser- I am planning on building a riser at the back of the room that will be approx 14" high and 20' wide with a depth of approx 7'. Is it necessary to decouple the riser? Can I get away without decoupling it? Fill it with what material? Safe'n sound or regular fiberglass insulation? Does it need to be vented/ported in the front for acoustic purposes? Any advantage to putting a few layers of OSB/Plywood with green glue between the sheets?

3) Subwoofer placement- It seems like most suggest a more center stage position due to the troubles of corner placement. I could set the sub to the left or right of the center speaker since I am building it myself and can design the enclosure to meet my needs.

4) Seats- I was originally planning to place the rear row very close to the wall since the depth for viewing is only 17'3" and being that I thought 7' for riser depth would be =necessary for the recliners to work correctly it only allows about 9-10 feet of viewing distance for the front row (never plan to sit there, will be more for kids) but I'm wondering if I need to rethink the riser depth or make any adjustments. The room orientation is such that if I have the room rotated 90 degrees so that the viewing distance is in the 20' dimension it either puts the doorway on the rear seating area and greatly reduces the width of the rear seating since it's the area where the closet protrusion is and makes the rear riser a mere 11' in width or the screen ends up on the wall where the doorway is.

5) Acoustic treatments- I am really struggling here. What should I be doing with my walls? I understand where to place some of the acoustic panels (mirror trick) but the front stage area I assume needs some sound absorbing properties on the entire wall? What if the screen is painted on like I plan to do, does this cause any issues with sound bouncing back off the back wall from the front speakers? What materials should I be considering if they are needed to treat this wall (I'm cheap remember
) Should I be covering the walls with carpet part way up, fabric, etc? Can I just texture the walls and add acoustic panels where needed?

This is enough. I feel like it might be too many questions to start with but if I can get a few answers I would be very very grateful to you experts. Thanks in advance!!!!!

· Registered
278 Posts
No, probably not. It seems best if you have some history on the site to get some active response. Or perhaps put the questions in respective forums where they apply more. I dunno.

I'm a newb too and have had limited response in my own theater build thread so all I can do is urge patience.

I'm definitely not the right guy to answer your questions either so will point you here to see if any of the answers can be found there .

cheers and welcome

· Registered
5,128 Posts
Not a pro, but I'll chime in anyway. Try posting a layout, may help getting more responses - people here like pictures - nice speakers btw.

1) I would just fill with insulation if its on a 2nd floor. Ordinary fluffy pink insulation, nothing fancier needed.

2) Decoupling the riser is recommended, but there are lots of folks that don't, and seem happy with the result. Also fill with standard fluffy fiberglass insulation. It doesn't need to be vented unless you intend to port it and use it as a helmholz resonator (in which case the size of the port needs to be sized according to the frequency you're tuning it to). Most people use at least a couple layers of plywood or OSB, with roofing felt in between, or liquid nails - not sure if Green Glue would be advised there, since it would damp, for the stage to transmit tactile feel, you might not want that - not sure though.

3) Best placement is really trial and error - one approach is to place the subwoofer in the primary listening position, and then crawl around the room to determine where the bass sounds best - that location is where you'd put your sub.

4) 7' sounds about right for riser depth if using recliners.

5) Even after having read the entire Acoustic Treatment master thread end to end - *twice* - I'm still not sure lol. I believe if your screen wall is acoustically reflective, then you'd want some absorption / diffusion on the back wall (especially if the seats are close to the back wall). For materials, rigid fiberglass panels are preferred - OC703 or similar - cover with fabric - definitely not carpet.

· Registered
54 Posts
Discussion Starter · #5 ·
Thanks for the replies. "The Dark Knight" thread looks well organized and a good resource. I will start reading (AGAIN!)
I'm sure like so many passions that you just keep learning and learning and never stop.

I will post a few screenshots and see what people think. I have no desire to draw anything fancy but might make a sketch of the plans for the room as I see them now.

Thanks again!

· Registered
162 Posts
I'll respond, but here's a disclaimer: I'm certainly not an expert... In fact, you're further ahead in your build than I am in mine. So take my comments with a grain of salt.

Originally Posted by clarkb6 /forum/post/19523257

Also of importance, it's on the second floor above my garage.

Depending on what your goals are for soundproofing, that could be either good or bad news. Because it's on the same floor as a bedroom, you have to worry about sound traveling to and from the theater through walls, floor, and ceiling. You should probably think about adding GG & another layer of drywall to the ceiling, as well as GG and another layer of subfloor.

Here are some more comments.

#1: I've seen builds where stages above the ground floor are just filled with fiberglass insulation. If you're placing a sub on the stage, you could just fill under the sub with sand. But do what you feel comfortable with. Remember that a cast iron bathtub filled with water and a person can weigh well over 1000 lbs, and it distributes that weight on four rather small legs: a much smaller area than your stage.

#2: Riser. I would at least fill it with fiberglass batts. I wouldn't bother with anything more expensive than that. Apparently, there's little or no additional value to more expensive products from an acoustical perspective. I'm sure others with more experience can provide advice on additional layers, decoupling, porting, etc.

#3: Subwoofer. Take a look at the THX and Dolby recommendations. If you'll only have one subwoofer, center front is probably the most common. If you have more than one, I believe the best bet will probably be trial and error, but I've seen multiple subs on the stage, and on opposing side walls.

#4: I've only got 12' of width, and 13' of depth in my room. I'm putting my seating row as far back as I can, so it will probably be ~11 feet to the screen. I'm using a 104" 2.35 screen, so I think I'll be alright. As far as your room goes, I'm sure you'll get more comments if you add plans/pictures of the room.

#5: I can only comment on my plans. Bass traps in the corners with floor-to-ceiling 17x17x24" OC 703. 1" Linacoustic or OC 703 covering the screen wall. OC 703 to ear height on the side and back walls, polyester batting above that to the ceiling, all faced with acoustically transparent fabric. I'll also fill soffits with fiberglass and face with AT fabric. I plan to build a DIY screen with AT material, so I can't comment on a DIY painted screen.

So now that another newbie has responded, maybe the experts will chime in to give you the right answers
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