2 In-Wall Subs, Short Back Wall: Which Sub?

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

So installing it without the back box would mean using the wall cavity as the enclosure and sheetrock as the enclosure walls? If yes, that is not a good idea. A properly built enclosure should be resonant free. You can't get that with sheetrock.

With your multi-sub setup, what equipment are you going to use to tune them? Does each amp have a fully adjustable phase setting? Have you tested each location with a standard sub to see what the response will be?

-Robert

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

Besides, a sub should never be in the center of a wall. I didn't read the paper you linked, but if it says to put subs in the middle of a wall, with only sheetrock as enclosures, it isn't worth the paper it is printed on. Pun intended.

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

I don't know about the in-wall part, but after reading the same research paper (by Harman, a very reputable speaker manufacturer JBL, Infinity, etc.), I did follow the front and rear center placement in my old theater. I had about 12' in front of the seats to the front wall and about 5' from the back seats to the back wall. I adjusted the phase on one sub and also used a BFD EQ. Spent a few hours setting it up. In my new theater I upgraded to one SVS in the front right corner. Here are some of the differences:

• In my new theater I can localize the bass. If there is an explosion I have to force myself not to look at the sub. In the old theater, that was not an issue.
• The new theater the bass is stronger in the front right seat than the back rear left seat. In the old theater the bass was equal in all 8 seats.

I don't know how much of the differences listed above was caused by the smaller new theater or the better SVS. I am considering putting another sub in the back left corner if I get a day to waste.

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

What's your crossover set to? 80hz should be very difficult to locate unless there's a lot of higher harmonic distortion or you have great ears.

As for the localization and unbalanced sound, I solved that with dual subs. I was running a pair of sealed 15's on each side of my center channel until my amp decided to crap out on me. Now I'm running a little 12" sub under my center channel. I'll be making three IB manifolds this weekend. One will be placed over each main and one over the center. Each will contain a pair of 18's.

-Robert

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

I still stand by my opinion that placing a sub in the middle of a wall is ill advised. The problem with the arguments in favor of it is they are approached with tunnel vision, focused only on the balance of sub level across the sitting area and completely ignore the acoustic problems created by having a sub equadistant from two surfaces. In my opinion, since you are talking two subs anyway, a far better solution is to put them both at or near the front corners. This not only eliminates the imbalance of level from side to side, it considerably reduces the room interaction problems as well as eliminating bass from the rear, which I find incredibly annoying. Also, with subs in thhe middle, there is still a fluctuation in volume from side to side. It's just focused on the center.

I find a lot of tunnel vision regarding sub placement. Nearfield placement and the center placement being discussed are just two of them. There are a lot of variables and factors to consider, and those arguments completely ignore many of them in favor of limiting only one or two.

I know I haven't read all these white papers. My experience unfortunately only comes from years of personal experimenting, observation and understanding of the laws of physics.

It also strikes me as ironic that having a sub in the front corner is distracting, but having one in the back of the room isn't.

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

FWIW Dave, of your choices I would install the two subs in the front, preferably a bit outside the L&R speakers.

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

I think they are great, but then again I have never tried any others.

I didn't go into detail earlier because my lunch was over. My crossover is set at 80hz. In my first theater I had a 12" front firing Sony up front. In the back I had a down firing 10" JBL. The room was about 14 x 22 and the seats were centered. My new theater I am using a SVS PB12-NSD front firing sub and the room is about 15 x 19 with the back row up against the wall.

John, I have been reading your posts for some time now and you give sound advice. As I said "I don't know how much of the differences listed above was caused by the smaller new theater or the better SVS." But I can tell where the sub is. Because it is a better sub, maybe I feel the sound coming from that direction. It definitely has more oomph than the other 2 together. I also have issues looking at my center speaker during some dialogue. My last theater I ended up with one center below the screen and a small one above. I know that is a no-no but it sounded ok and I wasn't distracted by the speaker location. In the new theater I started out with the center below the screen and moved it above. It sounds better, but the voices do not come from the actors mouth. They come from the ceiling. I am considering trying the phantom center to see what that sounds like.

Getting back to the two subs. I didn't sit in each seat with the SPL meter and record the levels. I did sit in each seat many times during many movies and the location and quantity of bass never distracted me from the movie. In my new theater with one sub, I do notice the bass coming from the front right corner. I was thinking of putting the Sony in the back left just because I have another RCA wire run there. The front left would probably be a better location sound wise I agree, but there is no RCA there and we would trip over it getting to my equipment.

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

BTW Dave, looking back I can see that part of the previous post probably sounded more sour than I intended.

First, is it possible to move the sub more toward the middle, just not exactly in the middle? Maybe around the right speaker? Also, it is always worthwhile to experiment with settings. Often when the sub is that localizable it is because it is running too loud, the phase needs adjustment or it just needs to be moved slightly. The thing about subs is moving them only a couple inches can make a big change. Also, you may actually want to raise the crossover frequency (I know, I sound like a broken record on that one) rather than having it so low. Why do I say that when it seems to fly in the face of what most people recommend? Because if the crossover is too low, it creates a gap between the response of the sub and mains and exaggerates the difference in their locations. You need to give the mains enough room to blend into the output of the sub.

Beyond that, it often comes down to just getting used to the new setup and environment. You are (possibly too) aware of the placement of everything, thinking of possible changes to make, analyzing every little detail and so on because you have taken time to set it all up. Try to do your best, then just see how it works and give the criticism a rest for a while. Invite someone over for a movie who has absolutely no idea about how the stuff is set up and ask them if the sub was distracting. It will never be absolutely perfect and you will find problems if you look for them.

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

If you can't find an appropriate in-wall sub, then build one - DIY in-wall subs.

-Robert

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

Big mistake.

FWIW, and just to show I practice what I preach, I recently did some changing around. The RPTV in my main system died and I just can't do anything about it right now, and probably not for the forseeable future. So, I moved my "good" sub up from the main HT to the little system in another room. For functionality reasons, the sub has to be about 45 degrees off the line to the TV. Still, after some tweaking over the last couple of days I was able to virtually eliminate any noticeable directionality from the sub. This is with the crossover at 150 Hz, since the speakers are fairly small bookshelf models. I'm here to tell you, it can work. It's not ideal, but we all have to live in the real world.

Re: 2 In-Wall Subs, Short Back Wall: Which Sub?

I don’t know much about them, except that you might need a brighter projector. I order to let the sound through; there are small holes in the screen. These holes do not reflect the projectors light back. Have you looked into Stealth Speakers? I don’t know much about them, except I saw them demo-ed in a showroom 2 years ago. With proper installation, you can’t tell they are there.


I didn’t pick up any sour notes. You did get me thinking though. When I moved in my new house last April, I set up the theater and calibrated in a day. I have been busy since with everything else move related and my Mother-in Law had hip replacement surgery. After she moves out in February, I need to spend some time tinkering with the sound.