Theater in unfinished basement space

[patchesj]

Current unfinished basement has a "room" that is 14'x19.5'. No windows, opening in side wall for double doors. Floor is concrete. 1 and a half walls are poured concrete. Room is below the dining room and in the middle of the house, away from bedrooms. We would still like to keep it as tight as possible. The downside to this room is the HVAC trunk lines are running across the ceiling, taking up half of the room width. They are 92" at the lowest point, but I think for acoustics we should make the ceiling the same level the whole way across. This "low" ceiling height is a bit of a drawback, but I think it can be a workable space.

Equipment:
Integra 9.9 (pre/pro not decided yet, but leaning this way)
Sony 55ES*2 + 220ES amps
Thiel MCS1 L/C/R + SCS3 surrounds (could go di-pole here if it made sense on the sides)
Panasonic PT-AE2000
Not sure on sub choice yet

Based on my quick calculations I think a 110" wide 2.35:1 screen is appropriate. Looking into SMX 1.1 gain AT, but open to opinions on screen. I would like to have the L/C/Rs behind an AT screen for placement purposes, I don't think I can get proper alignment with that screen taking up so much of the front wall.

For construction: New North wall in front of concrete will be isolated from the joists above and be used to carry the load for the new ceiling joists below the HVAC work. Front theater wall (with screen) will likely be a false wall with plenty of absorption material behind it. All walls/ceiling will be double 5/8 drywall with green glue in the middle filled with insulation. Solid core or exterior type door. Platform will be 2x6 with MDF and insulation. Equipment rack will be under the stairwell on the front wall. Projector will be ceiling mounted (probably near the rear wall of the theater).


I'm looking for suggestions and ways to improve the plan. I like to have all options explored and the best choice made prior to picking up a hammer... I'll try to get some pictures of the raw space posted soon.

Thanks

[patchesj]

Note that the "room" dimensions listed there are for the space in front of the false wall and the new 2x4 wall on top. Speaker placement, seating arrangement, is all still up in the air. This was just my first stab at it.

Thanks!

[tonyvdb]

Placement of the surround speakers is wrong, The rear ones need to have more space between them (about 4') and you should move the rear seating forward about two feet to allow for better coverage of the rear channel speakers.
Your side surround speakers should be moved up farther so they are closer to the sides of the front row seating. See here for more details.

[patchesj]

tonyvdb wrote:

Placement of the surround speakers is wrong, The rear ones need to have more space between them (about 4') and you should move the rear seating forward about two feet to allow for better coverage of the rear channel speakers.
Your side surround speakers should be moved up farther so they are closer to the sides of the front row seating. See here for more details.

I remember seeing that the THX recommendation for rear surrounds was 1-3' apart on the middle of the back wall. I guess a lot of the surround speaker placement depends on my "primary" viewing location, right? I've been going back and forth on middle back row vs front row. I think my rear seating would be just within the max THX recommended distance for that size screen, but the front row is close to optimal. I'm not sure in this situation if di-pole sides would help with the dispersion issue and give a better sound for both rows?

This is my first venture into a decent theater, I'm more of a 2 channel audio guy. I'd like to make sure that I end up with a great music listening room as well, 2 channel or DVD-Audio/BR Audio/etc.

[bpape]

I would agree. In a 7.1 setup, you want a bit more space between them.

For the side surrounds, it's a tradeoff. IF they're dipole/bipole, and you're mostly concerned with the front row, then they should be directly to the sides of the front row. IF you want a better balance for both rows, then leave them as is.

From an isolation standpoint, using double doors is going to make that pretty unlikely. 1 large, solid core door is a much better isolation candidate.

Bryan

[patchesj]

bpape wrote:

I would agree. In a 7.1 setup, you want a bit more space between them.

For the side surrounds, it's a tradeoff. IF they're dipole/bipole, and you're mostly concerned with the front row, then they should be directly to the sides of the front row. IF you want a better balance for both rows, then leave them as is.

From an isolation standpoint, using double doors is going to make that pretty unlikely. 1 large, solid core door is a much better isolation candidate.

Bryan

Moving them seems to be the thing to do, not very difficult at this stage..

Right now the door opening is roughed in at 74x90. I can fit anything in there. For the walls that are existing, does it make sense to use isolation clips/channels of some type or would the double drywall sandwich be fine? I'm not as worried about sound migrating out to the other areas of the basement, but that 2x6 wall connects to the floor joists above. I have hardwood upstairs and my fear is that the wall will couple to the 1st floor and create a giant transmission path for the sound.


Thanks

[patchesj]

Is there a way to take advantage of the volume of unused space under the stairs, under the platform or at the back in the equipment room for use as a big bass trap?

[bpape]

Sound is going to move both ways through all of the structure. If the room outside isn't addressed, any sound going out the doors will get upstairs via that method.

For the structure, if the walls are already hard tied to the structure above, you have a couple of options.

- You can just do Green Glue and double drywall.

- You can use RSIC-1 and hat channel to decouple the drywall and them do the double.

- You can add a 2x2 frame around the perimeter of the room (have to remove drywall) and do your own set of staggered studs. This will not require clips but you still do double drywall. This has the effect of making your bottom and top plates 2x6 instead of 2x4. That way, the room side studs won't be connected to the drywall outside and you also have a deeper cavity for lower resonant frequency.

If you're going to the lengths of your own new joists, I'd probably select option 3.

Bryan

[patchesj]

bpape wrote:

Sound is going to move both ways through all of the structure. If the room outside isn't addressed, any sound going out the doors will get upstairs via that method.

For the structure, if the walls are already hard tied to the structure above, you have a couple of options.

- You can just do Green Glue and double drywall.

- You can use RSIC-1 and hat channel to decouple the drywall and them do the double.

- You can add a 2x2 frame around the perimeter of the room (have to remove drywall) and do your own set of staggered studs. This will not require clips but you still do double drywall. This has the effect of making your bottom and top plates 2x6 instead of 2x4. That way, the room side studs won't be connected to the drywall outside and you also have a deeper cavity for lower resonant frequency.

If you're going to the lengths of your own new joists, I'd probably select option 3.

Bryan

Given that one of the existing walls is already 2x6, can I just stagger 2x4s using the same top/sill plates? Basically have them stick out 1/2 inch past the existing studs? Is there an effective way to decouple the "new" ceiling joists from that wall? Maybe just connect them only to the new studs?

[tonyvdb]

patchesj wrote:

Given that one of the existing walls is already 2x6, can I just stagger 2x4s using the same top/sill plates? Basically have them stick out 1/2 inch past the existing studs? Is there an effective way to decouple the "new" ceiling joists from that wall? Maybe just connect them only to the new studs?

That 2x6 wall is likely a structural wall so I would be very careful what you change about that wall.

[bpape]

You can probably add some studs to the existing 2x6 and have them stick out but they're still going to be tied to the top plate, which is tied to the floor above. Another option is to just use firring perpendicular to the existing studs as a poor-mans type of hat channel decoupling. Not outstanding but much better than direct contact.

If you're doing your own joists lower than the existing ones, then it's all decoupled pretty much anyway.

Bryan

[patchesj]

tonyvdb wrote:

That 2x6 wall is likely a structural wall so I would be very careful what you change about that wall.

It is structural, but I think adding additional studs would be OK?

[patchesj]

bpape wrote:

You can probably add some studs to the existing 2x6 and have them stick out but they're still going to be tied to the top plate, which is tied to the floor above. Another option is to just use firring perpendicular to the existing studs as a poor-mans type of hat channel decoupling. Not outstanding but much better than direct contact.

If you're doing your own joists lower than the existing ones, then it's all decoupled pretty much anyway.

Bryan

My other concern with a wall in front of a wall would be the door jamb depth. We would be looking at a minimum of 8", probably closer to 10". Of course that gives me plenty of room to add some absorbtion material on the back of the door.

Any thoughts on wall treatments? I was thinking about using a heavy folded drape type material for at least the 1st 1/3rd of the side walls, maybe the whole way around the room. The thought being that if the appropriate material could be found it might negate the need for absorption panels in those locations.

Thanks

[tonyvdb]

As Bryan suggested above yes, adding to the wall will be alright.

[patchesj]

So here is a sketch of room/screen dimensions using a "room in room" approach to isolation.

[bpape]

I assume those are just supplies (HVAC) in the front. The returns should be in the rear. This is not just for airflow but also to draw any dirt/dust away from the screen instead of toward it.

For treatment, curtains all around is a bad idea. You'll have WAY too much high frequency absorption and not nearly enough in the low end. The rear of the room should be a bit more lively for good surround presentation. The front wall should be dead through the dialog range (200Hz or so). Corners are trapped with very thick absorption. The rear wall can be 2-3" material full coverage with a facing to reflect upper mids and highs.

Bryan

[patchesj]

bpape wrote:

I assume those are just supplies (HVAC) in the front. The returns should be in the rear. This is not just for airflow but also to draw any dirt/dust away from the screen instead of toward it.

For treatment, curtains all around is a bad idea. You'll have WAY too much high frequency absorption and not nearly enough in the low end. The rear of the room should be a bit more lively for good surround presentation. The front wall should be dead through the dialog range (200Hz or so). Corners are trapped with very thick absorption. The rear wall can be 2-3" material full coverage with a facing to reflect upper mids and highs.

Bryan

Those HVAC supplies are actually trunk lines that run the distance of the room from front to back. (i.e. duct work hanging from the existing ceiling.). There is currently a single HVAC supply duct located about midway along the concrete wall, with flex duct.

[bpape]

OK. You'll absolutely, positively need to bring a return into the room somehow or it will be unbearably hot in there very quickly. Pay very close attention to any HVAC or all of your isolation work is for nothing. A duct directly in the room in a trunk will allow sound into and out of the entire rest of the house. Bass will go through flex like it's not even there so that duct is essentially just a large hole in the ceiling in terms of bass transmission.

Bryan

[patchesj]

bpape wrote:

OK. You'll absolutely, positively need to bring a return into the room somehow or it will be unbearably hot in there very quickly. Pay very close attention to any HVAC or all of your isolation work is for nothing. A duct directly in the room in a trunk will allow sound into and out of the entire rest of the house. Bass will go through flex like it's not even there so that duct is essentially just a large hole in the ceiling in terms of bass transmission.

Bryan

I was planning on running the supply into a diffuser box of some type in the front of the room (I can't stand fiberglass duct board, there has to be a better way to supply air and block noise) and then try to pull the air out at the rear (near the projector...). The entire basement is on an independent HVAC zone (with pneumatic dampers in all of the trunk lines). So even if some sound gets in there it won't have any place to go unless the basement damper and another damper are open at the same time (possible), and the sound would need to travel all the way down the trunk into the plenum, turn around, and travel all the way down the next trunk/duct to a register.

The projector will be the only non-human heat generation in the room. All amps/processor/player/etc will be next door in a closet (with ventilation to the open basement).


Thanks

[bpape]

Plan on making your ducts encased in an MDF enclosure. Try for at least 3 bends in it and at least 5' between bends for best results. Even duct board won't do diddly to stop bass. Inside the MDF, use flex.

Even with nothing else, in an airtight room, 3-4 people and a PJ will heat it up in a hurry without sufficient ventilation. General rule of thumb if possible is twice as much return as supply so you're creating a vacuum and helping the air flow out of the room.

Bryan

[patchesj]

bpape wrote:

Plan on making your ducts encased in an MDF enclosure. Try for at least 3 bends in it and at least 5' between bends for best results. Even duct board won't do diddly to stop bass. Inside the MDF, use flex.

Even with nothing else, in an airtight room, 3-4 people and a PJ will heat it up in a hurry without sufficient ventilation. General rule of thumb if possible is twice as much return as supply so you're creating a vacuum and helping the air flow out of the room.

Bryan

What does the MDF do for the sound, if the flex duct is all going to be on the other side of the double drywall? I can understand the bends in the flex trying to absorb some of the sound as it travels inside the duct.

[bpape]

Ah, yes, BUT, the flex itself (where it's coming into the ceiling) is NOT behind double drywall. It's simply a hole. There is no drywall mass at the opening. That hole will allow the bass to go right through the flex and up through the floor above.

The MDF provides mass to stop sound transmission and acts as a labyrinth to help the sound dissipate and cancel itself before leaving the massive area.

The bends in the flex will be OK from say 1kHz up but do little to nothing below that without the mass. We want the waves to hit a flat surface and bounce back and cancel. Do this 3 times over 15 feet and it's down quite a few DB.

Bryan

[patchesj]

Got it. So the pressure waves are basically just "ignoring" the boundaries of the flex since it lacks mass...

[bpape]

Correct. The flex is great as opposed to tin as it absorbs mids and highs and doesn't ring and actually amplify sound but it doesn't have nearly enough mass to do anything for bass.

Bryan

[patchesj]

So what type of material/facing do you recommend for bass traps in the corners and to apply along the rear wall? I would purchase ready made traps/panels, but I'm going for more of a built in/hidden look for the treatments.