Need help with riser construction and height and sub layout - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 15 Old 01-26-2017, 11:30 AM - Thread Starter
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Need help with riser construction and height and sub layout

I am building my second dedicated theater although this one is much less expensive and much less "intensive" than my last theater that was a room stripped to the studs with DD/GG, hatchannel, a baffle wall, etc (in the avatar picture).

Here are some details of the room and plans:

This new room in my new house is an upstairs room above a 2 car garage and it current has no "rear" wall. I will be building a wall there. The room comes off of the game room which is seen in the picture below. The dimensions are 17'10"W x 22'L x 9'H but the ceiling slopes to the sides and intersects the side walls at 6 ft height. The middle of the room is 9 ft high and that flat section is 10 feet wide on the ceiling before it starts to slope down to 6 ft.

I LOVED my old screen size (160" wide 2:40) and seating distance (about 13.5' from screen to the back of the front row chairs, so I want to keep that again in this theater.

Bryan Pape at Gik has been helping me select acoustic treatments (not finalized) which I believe will consists of 3" of 3lb Ecose or OC703 covering the front wall and a pile of cut oc703 24"x24" panels 6ft high in the four corners. That would be a 2'x2'x6'H bass trap in each of the four corners, which I "think" will absorb quite low. The first and second side reflection points will get GIK 244 panels, more 244 panels on the first row ceiling first reflection points, and the GIK Polyfusors on the back wall and maybe back side walls.


My questions are these:

1. Since my screen is so wide, and the room starts sloping after a 10ft section, the screen obviously will have to be mounted low enough to not hit the side walls. I will put it as high as I can, but it will be a bit lower than my last theater, I believe. How do I calculate how high to make the riser behind the front seats? I plan on Fusion seating for the front row, and "real" fold down, bolted down theater seats for the second row (good value suggestions for those are appreciated). I don't know how high to plan that riser so the rear seats easily see over. I also plan on probably only a small area big enough to walk normally between the front and rear rows, to maximize the distance from the rear wall and the diffusors for the second row guests.

2. In constructing that riser, is a layer of OSB, then GG, then another OSB the "standard, but not overkill" construction, or something else? Do I need to fill the riser with pink fluffy? Some other material? Does it need the nailor grates like my last theater, or how beneficial to making the riser a bass trap are those?

3. I have four subs for this room (DIY 15" Ultimax sealed subs from Parts express with iNuke rack amps). They will be at the front, side, and rear wall midpoints. The front will be hidden in the screen wall, the sides recessed into the knee walls (I can get to the area behind), but the rear sub will have to be IN the room. Since I am building it myself, I can put the input (it is rack amplified so no onboard amp) on the side of it, and face that sub UPWARDS, so it could be surrounded by the back of the room riser with a grate over it (sub touching the riser of course). Does that sound like a good idea?

4. It is useful to build the back wall with two layers of drywall and GG if none of the other walls are built that way? Would it help sound transmission at all?

Thanks for reading and any and all help! The picture is VERY crude but hopefully conveys my ideas. The real picture is from the previous sellers pictures but shows the angle of the ceiling. The camera lens makes the room look long and narrow but the dimensions are as I specified.
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Last edited by hifiaudio2; 01-26-2017 at 11:35 AM.
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post #2 of 15 Old 01-26-2017, 12:45 PM
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Your diagram shows a pathway around the riser that is close to the wall. Make sure that you have sufficient width and ceiling height so that you don't bump your head on the sloped ceiling as you walk there, especially in the dark.


1: Graph paper is your friend. Although there are online calculators, I find it easiest just to take some measurements, draw it out to scale on the graph paper and use a straightedge to visualize the sight lines.


2: If the top layer of your riser is not thick enough, it will vibrate like a drum head and sound as well as feel hollow when you walk on it. Green glue between layers is great if you have some left over, but roofing felt also works. Filling the space with fluffy insulation helps eliminate resonances. The bigger that you can make the vents on top, the more it will work like a bass trap.


3: I like that idea of putting the subs behind the knee walls. I generally avoid placing subs pointing up for several reasons. Unless you put some sort of cover on it, objects might fall on or get placed on the speaker, causing damage. Dust and small objects can fall on the speaker and stay there, causing rattles and buzzing. Dust won't be a huge problem, anything like the size of a grain of sand or bigger might.


4: It certainly can't hurt. While the other walls will allow flanking paths to the rest of the house that can be unpredictable, the back wall is in a position to be a direct sound radiation path. The cost of the extra drywall and Green Glue for such a small wall would be so minimal that you might as well give it a shot.


EDIT: Others may disagree, but thinking about this further, I'd actually be inclined to build the back wall as a double stud wall with two layers of drywall and Green Glue on the theater side. Certainly some of the benefit will be "short circuited" by flanking through other walls, but given that this wall is in common with the rest of the house, it would act like a drum head to transmit sounds to the other side. Partially decoupling it could offer improvement for a very minimal cost. The extra cost of some studs would be in inconsequential and the labor is minimal. If you build it with 2x3s instead of 2x4s it will minimize the wall thickness. You can make good 2x3 substitutes by ripping 2x6s down the middle. They will be slightly thinner than normal 2x3s, but the difference won't matter. You can usually find good, straight 2x6s to work with.



Last edited by DaveClement; 01-26-2017 at 02:30 PM. Reason: Added additional comments about back wall.
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post #3 of 15 Old 01-27-2017, 09:47 AM - Thread Starter
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post #4 of 15 Old 01-30-2017, 08:51 AM - Thread Starter
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Thanks for the help so far... now for a bit of talk about "mounting" my speakers.

1. On the front wall of the theater, where I will be putting a covering of 3" of OC703, I was thinking about also covering that wall first with green glue and a single layer of OSB to give that wall some mass and a little bit of isolation from the outside world (that is an exterior wall). Then I was thinking of putting three L brackets and shelves for my LCR speakers, which will be Emotiva Stealth 8 powered speakers. These can play loud and reliably down to around 35hz, although I plan to cross them over around 55hz. Is mounting these on shelves like that advisable? Am I asking for vibration or transmission of a lot of sound into the structure that another method would eliminate? I can put the speakers on a rubber pad on the shelf as well if that helps.

2. Similarly, I plan on recessing the side surrounds into the knee walls so that only the face of the speaker is in a plan with the in room drywall, and plan to make a shelf between the studs in a similar way. Any advice on this as well to keep resonance or vibration down? These surrounds are active Emotiva Airmotiv 6s speakers.

3. On the topic of surround placement, I want to get as many front row seats in the theater as possible, but dont want the side listeners to have their ears right in the side surrounds. Should I place the side surrounds about a foot back from being in line with the front row? Or just have less seats? If the space is almost 18' wide. Three seats are 8.25 wide, four are almost 11' wide, and five are 13.5' wide. How many can I get away with before the sitting angle or the small distance to the side surrounds becomes an issue? I had only three front row seats in my last theater. I also always *want* a middle seat so four is less desirable but I could be convinced.
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post #5 of 15 Old 01-30-2017, 09:44 AM
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Green Glue and OSB on the wall certainly can't hurt with sound isolation transmitting through this outside wall, but don't count on a lot of improvement. Vibration and sound will find their way in through the weakest link, and if you don't treat all of the walls that way, the walls without this treatment will let the sound in or out. Think about it like a room with an air conditioner and leaving the door wide open. It might get somewhat cooler than with no A/C, but it may never really work well enough to properly cool the room.


If you are trying to prevent vibration from transmitting through the walls, mounting the speakers on the walls will likely transmit more vibration through them. Rubber pads will help, but you can achieve better isolation by putting speakers on stands that stand on the floor, rather than mounting to the wall. This may not always be possible, especially with surround speakers mounted in columns.


Dolby and THX recommend that the side speakers be placed between 90 - 110 degrees to each side. With one set of side speakers and two rows, the compromise is usually to put the speakers to either side of the rear row, perhaps slightly in front of it, and behind the front row in approximately the 110 degree position from the center seat. The layout of your space will influence how you end up compromising. A lot depends on how many of the seats will be occupied. Your priorities may be different if the side and back row seats are used for less critical viewers like the neighborhood kids.


Keep in mind that having a certain number of seats in a row does not mean that people have to sit in them. Having more seats allows you to fit in more people, even if the experience is not as good for the outer seats. Eliminating those seats entirely means that people won't be able to sit there at all.


Finally, think about what you are doing about aisles. Given your measurements, it sounds like you can have an aisle on either side that is a little over 2' wide. That's workable, but a little on the narrow side. If you are planning on only one aisle, you seating will be shifted to one side, and four seats may work better at providing a "middle seat".
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post #6 of 15 Old 01-30-2017, 09:58 AM
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Thinking about your layout a bit more, I realized that my answer was rather generic and would fit most rooms with walls that are of similar construction. I got to thinking about how your theater is in the attic above the garage and that the side walls do have additional isolation between the theater and the outside world. On the other side of your knee walls, there is air space and the roof structure with the roofing material. This may mean that you already have somewhat better sound isolation on the side walls than the front wall. Therefore, putting some additional isolation on your front wall may help it to "catch up with" the side walls. Given that the front wall is rather small in terms of square footage, I am thinking that maybe it would be worthwhile to put up the OSB and Green Glue after all.
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post #7 of 15 Old 02-02-2017, 11:43 AM - Thread Starter
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I will do that, then. Thanks!

Any suggestions on the layout of the Atmos speakers? Locations? I plan on getting Goldenear HTR7000s for those.
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post #8 of 15 Old 02-02-2017, 04:16 PM
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Quote:
Originally Posted by hifiaudio2 View Post
I will do that, then. Thanks!

Any suggestions on the layout of the Atmos speakers? Locations? I plan on getting Goldenear HTR7000s for those.

Here is what i used for setting up my Dolby Atmos System. It is based on the number of speakers you are planning.


https://www.dolby.com/us/en/guide/sp...tup/index.html

Marantz AV7703 : MM8077 : MM7055 : (2) MiniDSP DDRC-88A
Radiance Pro 4242 : JVC DLA-X750R
Klipsch (2) RP-280F : RP-450C : (2) R-115SW : (2) RP-250S : (2) RP150M : (4) CDT-5800-C II
OPPO UPD-203 : Panasonic UB900 : XBOX ONE X
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post #9 of 15 Old 02-03-2017, 11:33 AM - Thread Starter
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Looks like the overhead speakers are closer to the MLP than I would have thought....

So on this 9.1.4 setup....

https://www.dolby.com/us/en/guide/sp...tup-guide.html


Have any of you successfully implemented wide speakers as shown here? I could do them, but want to make sure they are actually used by my surround processing (Right now an Emotiva XMC-1 which is to get the Atmos upgrade at some future date... could be a future Emotiva RMC-1 with additional channels later).
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post #10 of 15 Old 03-03-2017, 12:22 PM - Thread Starter
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I think I want to build one of @BIGmouthinDC 's minimalist screen walls for my forthcoming 160" wide scope screen. I am tentatively planning on just putting up the support posts and a cross member at the top to put the Falcon screen mounting bracket on. I would also like the rest of the front of the room to be black fabric, though. Any suggestions on a simple buildout for the rest of that front? It would be nice if one of the sides were removable to get behind the screen to the speakers.

Any material cheaper than GOM that I should look at for black fabric?
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post #11 of 15 Old 03-03-2017, 03:46 PM
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For black fabric, can you use speaker cloth?
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post #12 of 15 Old 03-07-2017, 08:06 AM - Thread Starter
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I suppose I could use anything... Just needs to have a finished look and be able to be stapled around framing members or, if I feel like paying for it, fabric channel...

Speaking of which, is there a cheaper fabric channel than the name brands?
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post #13 of 15 Old 04-30-2017, 09:38 AM
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Just found your thread on AVS. What's the status of your build?

If you want some ideas, you may wish to check out my build thread. My home also has a 2nd story media room above the garage that I'm converting into a dedicated HT room.

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post #14 of 15 Old 05-09-2017, 09:24 AM - Thread Starter
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Cool thanks I will check it out, Screen went up this week and working on fabric and final touches before getting the rack back in its recessed area and then starting calibration. I have not built the riser for the second row yet.. basically I will have the theater up and running and the first row only for a bit....
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post #15 of 15 Old 08-31-2017, 01:02 PM
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Have you completed the room?
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