Complete In-Wall surround sound setup

**ThomasW** · 20 February 2006, 16:53 Monday

There is no real theory, it's just the crossover must be custom designed with no baffle step compensation. It would be best to not limit the speaker to just the depth of a stud bay. Deeper is better for any speaker and using drywall as the rearwall of a speaker cabinet isn't the best idea.

**cobbpa** · 20 February 2006, 19:25 Monday

What about using a paint on deadening behind the speakers? Or mat deadening could be used I suppose. And I've read that solid excursion is needed for IB subs, so I'm assuming the same for this. Does this mean the Extremis is automatically best? There aren't a lot of other woofers that can play to 1.5 khz or so and have 8+ mm xmax. Or would making each speaker a 3 way and using drivers more suited to the lower octaves be a worthwhile task?

**ThomasW** · 20 February 2006, 20:24 Monday

You need to clarify what we're taking about. You started out referencing 7.1 speakers and now you're talking about a IB sub and the Extremis?

So one thing at a time. Either the mains or the sub?

FWIW damping material on drywall doesn't make it stiffer, it just lowers the frequency were it vibrates.

**Dennis H** · 20 February 2006, 20:59 Monday

Time to define terms a bit. If you cut a hole clear through the wall so the backwave goes into another room or a very large space, it's an IB, and that's a good thing. If you just cut a hole in the front sheetrock of a stud wall and mount the driver, it's a box speaker, with a really crummy box made out of studs and sheetrock, and that's not so good. IB implies a very large space behind the driver.

**cobbpa** · 20 February 2006, 22:29 Monday

Holes in the beams could allow full airflow, making it IB, since sheetrock or mdf (for mounting the speakers on) would seperate the front & back waves, correct?

ThomasW: It is a 7.1 setup with 1 IB sub (not discussed in this thread) and 7 speakers made up of probalby an IB Extremis and a tweet. This will be mains, cc, surround, all speakers.

What if the damping material was put onto the concrete wall? Since the waves would be sealed off, would it be ok?

**ThomasW** · 20 February 2006, 23:07 Monday

Holes in the beams could allow full airflow

What beams?

What if the damping material was put onto the concrete wall?

What concrete wall?

If you want help with this you need to provide precise details as to the construction, not introduce a little bit of new information in each post.

Also please refer to the 2-ways as 'in-walls' not IB's.

**cobbpa** · 21 February 2006, 04:12 Tuesday

ThomasW, sorry, it's all in my head and I switched a couple terms earlier. Let's try this again, I apologize for my previous vague descriptions. The beams = studs that the drywall is on. Also, the concrete wall is referring to the basement wall as it currently is. Basically, picture an unfinished basement, no framing, all concrete. We are going to finish it. As I picture it, MDF could be attached to the studs in cutout portions of the drywall. These MDF cutouts would have drivers mounted on them (and xovers on the back) to create the in-wall speakers. This could make the opportunity to use IB mids for the in-walls, correct?
Someone mentioned airflow...I wouldn't think that 2x4 studs up against a concrete wall create anything air tight...as in, I'm certain (maybe even if they are air tight) the mids could have > 4 times their Vas in air. But I mentioned maybe drilling holes in the beams to ensure that there is enough air to really make it a good IB environment for the mids.
A question was raised about backwaves. First, I didn't know backwaves mattered when contemplating IB as long as they don't cross into the hemisphere of the front waves. But if so, would a damping material behind the woofers help?
I think that covers a lot. Now, the Extremis is something I mentioned because it is a very high xmax mid, another pre-requisite for a good IB speaker. Another forum someone said it would take about 50-75 watts to drive it to xmax in an IB environment, any comments on that estimate? Also, I'm wondering how higher response (1.5khz probably) is affected by a speaker being in an infinitely baffled configuration playing that wide of a range.

Okay. That's a lot of questions and I think some clarification. 7 in wall speakers for a surround setup in which all the mids are infinitely baffled. Advantages? Disadvantages? Comments? Questions?

**Dennis H** · 21 February 2006, 11:44 Tuesday

Cobbpa, it sounds like that could work well. As Thomas said, placing the cones too close to the concrete wall can be a problem. The sound wants to bounce off the wall and back out through the cone. The more space you can allow between the stud wall and the concrete, the better. Some damping material -- fiberglass, polyfill, Whispermat, etc -- behind the cone would also be good.

**ThomasW** · 21 February 2006, 12:28 Tuesday

Okay you continue to confuse the terms and the concepts. You're not building an 'IB' when you're putting an Extremis in a stud bay, you're building an in-wall.

The 4 times Vas rule is for IB subwoofers not in-wall midwoofers.

If you can use 2"X6" construction instead of 2"X4", life will be easier with the increased depth.

Whether you can get away using a single Extremis per channel depends on the size of the room, and the size is something you haven't told us.......

**J-Dub** · 21 February 2006, 13:34 Tuesday

Cobbpa,
What you need is what we call a Texas Attic. Basically it would be your basement with a horseshoe shaped wall wrapped parallel to 3 of your basement walls. Usually each new wall is about 3 to 4' away from the existing wall creating a 3 to 4' hallway around the back of your new theater. You should close off the ends of the "hallway" and add a door to at least one side so that you can access this area when needed.

This will give you the space needed for your IB setup, give you very easy access to all of you speakers, make any wiring new components a sinch and give you a place to hide all of your equipment, movies, CD's etc...

Ohh, and instead of drywalling it all in you can use insulation covered with an attractive cloth to dampen the theater. Look up DIY bass traps for an idea.

**cobbpa** · 21 February 2006, 14:45 Tuesday

The room is going to be pretty large, I'm estimating around 15,000 ft^3. The actual theatre area will probably be less than a third of that, but the back will be open to the rest of the room. The size of the room is what got me thinking about this originially, as it seems the Extremis could move the most air to be effective in this big of space. The room isn't an all-out home theater setup; yes there will be a projector, surround sound, a sub, etc., but very much it will be a family gathering place to watch football games & such. As in, people won't always be sitting, definitely not in any kind of 'sweet spot' either.
ThomasW, I must be missing something, can't midwoofers be infintely baffled also? I don't see why not as long as the front & back waves are sealed off. Or is the term for this type of setup simply "in-wall" and not referred to as IB, even though it really is? The 2"x6" studs sounds like a good idea, then probably damping material also behind the woofer.
J-Dub..sounds like an interesting idea. I'll try looking up some things on those concepts..

**ThomasW** · 21 February 2006, 18:51 Tuesday

No you won't be running the midwoofers as infinite baffles. Using a sub you're going to have a crossover point around 80Hz. So you might as well take advantage of an enclosure and use the thermal rating of the VC as opposed to the limits of the suspension.

Without knowing the distance from the speakers to the listening postition, it's bit difficult to know if a single Extremis in each location will have adequate output.

And without a specific floorplan all this is pure speculation.

**J-Dub** · 21 February 2006, 18:59 Tuesday

Speaking of speculation...

I just figured a picture is worth a thousand words so I drew this for you on my super sophisticated state of the art software :B

Just for ideas sake thats all. I was thinking that if you were already planning to put studs up against you existing wall, this shouldn't be too much trouble. Actually it would take less material except for the door/doors.

Oh yeah! don't forget to use wolmanised wood for your toe plates.

EDIT: Couldn't get the picture to work. Sorry :roll:

**Dennis H** · 21 February 2006, 20:15 Tuesday

I think they could be considered IB as long as there is a space between the studs and the concrete wall, letting the backwave expand along the whole wall. That would give a pretty large cavity for the drivers to play into. A 20' long by 8' high wall would give you about 80 cu.ft. if you spaced 2x4 studs 2" from the concrete. More spacing would be better yet.

**cobbpa** · 24 February 2006, 20:35 Friday

Ok, I'm hoping to still get some replies and change the idea of this thread...to forget the IB thoughts but make in-wall boxes. The fronts & center channel could have boxes of full-depth, but the surround speakers will be built to the depth of studs (possibly 6 inches). From what I understand, this could be fairly easy to do, right? Mostly because I won't have to compensate any for baffle step. I'm thinking real boxes could be made for the fronts & mids, then cut holes in drywall to put the baffles flush with the wall, thus keeping any sound from 'leaking' off the edges. Right? Just pick drivers & tweeters that match up well? (I know, it's not that simple..tell me why)
And finally, a very very rough sketch of what the room will be like:

It isn't really great proportions; total room is probably 65' x 35', theater area about 20' x 30'. The thin black lines are a staircase that will end up probably closed. The red line is where the screen will be (a sort of utility room is behind it) and blue lines indicate the walls the in-wall surround speakers will go. We are considering the 2 rear channels in-ceiling; is this a bad idea? (7.1 or 7.2 total speakers) We're not sure how else to space them correctly from the other surround speakers.