In Wall Sub Placement advice - AVS Forum
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post #1 of 9 Old 01-28-2013, 06:09 PM - Thread Starter
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Long time lurker...reader...student of your expertise. I am building a theater/demo room in my basement based on several theaters I have seen here but heavily on Cinemar. The space is 23 by 13 with open stair case in left rear, fireplace on back wall, two awning windows high on two walls and a pocket door to the equipment room.


I have two in wall dual 8" subwoofers to place in the room. I have read all that I can find and it appears there are several schools of thought. One is two in the middle of the walls. Front and back won't work due ot the fire place. side to side won't work either due to the proximity to the seating. There are some that recommend opposing walls 1/3 or 1/4 wall length. The first pillars are centered at 7 1/2 feet or close to 1/3, I could do opposing there. In this pic you can see that I have room to do them opposing in the from of the room between 2-3 feet as well behind corner on stage.


So I see it as I have these options.
1. Opposing side walls at 7 feet
2. Opposing walls at 2.5 feet
3. Front wall near wall both sides
4. Front wall left side, right wall at 7 feet

Thoughts would be appreciated.
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post #2 of 9 Old 01-28-2013, 06:22 PM
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How far into construction are you? The best way to figure this out is to actually hook them up and start playing around with placement. Are these your main subs or balancing subs.

Are you going to be able to put them into the front corners behind the angled pieces? Just because they are "in-wall" doesn't mean you have to put them in the walls.

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Is it solipsistic in here, or is it just me?
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post #3 of 9 Old 01-28-2013, 06:49 PM - Thread Starter
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I only had to tear out the front wall and about 4 feet back on both sides and for the pocket door. I reframed the front wall to accomodate the LRCs behind AT screen. I thought about buiding a frame to mount the subs in and do what you are suggesting for placement, but with walls out, no stage, no soffits, no furnature/sound treatments, I thought it might be a waste of time. I thought about mounting behind the angled enclosures at any angle once built out. here is what it looks like right now...







I have finsihed up all electrical to include a home run circuit for the equipment rack. I need to finish purring in supports on fron wall then I am going to run speaker wires. I have marked the soffit 2x2 lines and will srat to hang that soon.
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post #4 of 9 Old 01-28-2013, 07:20 PM
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Hopefully someone with more knowledge chimes in here but from what I have read I would guess that the low frequency response will be similar enough to place the sub in various locations and expect to get useful information about what your room does with low frequency sound.

Meaning that probably the same room modes will be excited now as when the room is finished.

Are you putting a door to the stairwell?

I am not sure how much you like your bass but most likely your dual 8'' in walls times two will not be sufficient for your room. Those subs are probably more suited for use as balancing subs as Blldo sort of alluded to. You might want to consider placing a very powerful sub behind your false wall (make sure you give yourself at least 2 to 2.5 ft). Then experiment with the placement of your in wall subs as balancing subs to smooth the frequency response and help to keep the response even through multiple rows of seating. You would need a way to EQ the subs differently with this method. So if your AVR does not have a way to do this you would need to buy a separate dsp unit.

If you are going to stick with just those two subs then there are many theories as to what gives the best response. Best could mean most powerful (how to take full advantage of room gain to make it go really loud) or best meaning most even frequency response. The oft cited resource is the paper by Welti and Devantier. Here is a link.

http://www.aes.org/tmpFiles/elib/20130128/13680.pdf

There is a cliff notes version with slides somewhere that gives a rundown of best placement scenarios. Basically 2 subs is almost as good as 4. Front and back is a good option. So is midpoints. This strategy is assuming that they will be EQ'd the same.

If you have the time or expertise to fiddle with it a potentially superior solution is to do what I described before. I think one of the people to implement this strategy was Earl Geddes. You can google it.

Here is a link to BG radia in wall subs installation manual. There are some tips on placement. Check out page 3-6 especially.
http://www.bgcorp.com/PDFs/Support/BGX-manual%2004302010.pdf

Now if you are only EQing for one seat it is my understanding that this is far simpler and does not require all of this black art stuff.

Anyway there are tons of resources here. I am not really one of them.

Good luck.
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post #5 of 9 Old 01-28-2013, 08:09 PM - Thread Starter
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I had found your first reference, but all the reading I have done is in a closed space. i am assuming that leaaving the stairs open with cause all kinds of problems. I looked into acustic room diviers...curtians that could be pulled across the opening. The wife wants it open. In any case thanks for the pointers and comments. i will reconsider hooking one up and moving it around since the shape of the room is so ...black magic proof.
Any more ideas or perspective would be appreciated.
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post #6 of 9 Old 01-28-2013, 08:22 PM
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Oh, I don't know that it would necessarily cause any problems. It looks like you still have locations along that wall to place surround speakers so no big deal there. It will affect how the surround speakers interact with the room back there and what kinds of reflections you get. How? I have no idea.

I was actually thinking along the lines of soundproofing. It looks like you are not planning to do that though. It would be a significant cost so I understand.
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post #7 of 9 Old 01-29-2013, 02:40 AM - Thread Starter
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Soundproofing this narrow low ceiling location is a non-starter. I am however trying to acoustically treat where feasible. Bass corner traps, denim in the soffits, Linacoustic dead front wall and back, top half of side walls are panels with 1" behind them. Surrounds are in aft columns. A couple more questions about elevation. It appears closer to the floor is better. If I mounted them higher they lose punch? Thanks for the assistance.
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post #8 of 9 Old 01-29-2013, 07:26 AM
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I really should not be speaking to this so please ask someone else too but I believe that the closer to a boundary you are the more boundary gain can be achieved. And if you are close to even more boundaries such as in a corner you will get even more boundary gain.

Here is a good resource for boundary gain among other things. It goes into more detail than I care to in a post.

http://www.audioholics.com/education/loudspeaker-basics/subwoofer-measurement-data
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post #9 of 9 Old 01-29-2013, 06:07 PM - Thread Starter
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I did more reading today and I think I will go with one in front wall left and one right side wall 7 feet back in column. I will run RG-6U to both sides front so I can add a regular sub if need be at completion.

One more question. I have planned for a stage top to ceiling base trap in the front corners. If I put the in-wall sub in the front corner, should I raise the bass trap up and put it in the very corner or have it one foot off the wall next to the bass trap? Traps are made of OC703 cut into 1’ wedges.
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