How would you treat this room?

[KnightRT]

I'm building a home theater in a 13'x25' basement room. Here's what it looks like so far:



I'll eventually place two cloth couches on the far side of the room, one on a wooden riser. I may also remove the far light fixture and replace the door on the left with a curtain. The subwoofer will be in the far left corner of the room.

The acoustics in the room are quite bad. My plan to improve them is to place 2'x4'x4" panels, three per wall and two on the ceiling suspended by wires where the circles are in the picture. They'd be made of 4lb or 6lb density mineral wool, or solid panels if they exist. Thicker bass traps are another possibility, but I'm unsure where I'd put them. The distance from the long walls to the wooden screen border is about 5". To the screen edges, perhaps 8". There's a curtained door opening just behind the camera vantage point, and the ceiling corner above the opening only has about 8" of clearance on one side. I wasn't planning to place anything on the back wall on the assumption the couches would provide enough diffusion and absorption.

Is this the right path? What would you change or add?

Per the tiles themselves, I'd rather just glue cloth to solid fiberglass than build frames. I've calculated a cost of around $17 for framing material per panel, and it adds a lot of bulk, weight, and complication I'd like to avoid. A local company gave me sample panels of the frameless concept. They used "6.0-7.0 PFC Fiberglass, 16-20 PFC Fiberglass, Mineral Fiber Core," all apparently glued together. Is there a single product suitable for a stiff panel, or must it be a composite?

Thanks in advance for your thoughts.

[Pier]

Originally Posted by KnightRT

The subwoofer will be in the far left corner of the room.

It would be better if you moved it around first to see where it sounds better.

As for the panels they won't do much in the sub 80Hz area. You will need serious bass trapping considering you have a sub, and you will watch movies at high levels.

I think you will need more of those panels to absorb mid high frequencies and reduce echoes, flutter, reverb and such. But just try and see for yourself if 8 panels are enough.

[Glenn Kuras]

. Thicker bass traps are another possibility, but I'm unsure where I'd put them.

You can straddle any corner in the room. See the following for layout of acoustics.
GIK Acoustics: Room Setup

[johndykstra]

superchunk bass traps above and below the screen in a black fabric... would look super pro.

straddle the side wall/ceiling corners with taller panels, ones that would bridge over the soffit on the left, to maintain a symmetrical look. Whole back wall can be a bass trap if you wish to go gung ho. Being the floor is carpeted, you may get more bang for the buck out of your original 8 panels on walls only, as they are hard, parallel, and fluttery.

couch at back of the room, make the sides and front of the platform breathable, and make a bass trap out of it.

[jdg]

if you could trap the entire ceiling, then do the standard corners and first reflection points on the walls, u'd be totally happy

[KnightRT]

Some interesting suggestions. It hadn't occurred to me to make the riser into a bass trap.

For ceiling trapping, that would be, say, a series of open-backed 4x2x6" panels, lower-density mineral wool, with a few inches of gap to the ceiling?

If I did a bass trap above the screen, it'd go in a triangular shape from the screen border to the ceiling to the light fixture.

There's also a large area behind the screen with windows, about 4'x10'. Is there any benefit to putting anything there? The screen is a countertop laminate, I don't think it's acoustically transparent to any of the higher frequencies, but what about trapping? No one can see that area, I could easily pile it with a bunch of fiberglass.

Does this room merit diffusers? Any thoughts on rigid fiberglass panels that wouldn't require frames?

[ciro]

Originally Posted by KnightRT

For ceiling trapping, that would be, say, a series of open-backed 4x2x6" panels, lower-density mineral wool, with a few inches of gap to the ceiling?

6" clouds spread in the room - Great!

Ciro

[Glenn Kuras]

There's also a large area behind the screen with windows, about 4'x10'. Is there any benefit to putting anything there?

Not really as most of the low end would pass through the window.

Does this room merit diffusers?

In a room this size?? Sure it would be great!! Back wall (with thick panels) and side walls behind the seating area.

[johndykstra]

the only benefit of frames on panels is looks. if you can make them look ok without frames, there's no reason they won't sound good.

[KnightRT]

Here's an updated view of the room:





I'm not happy with vocals or bass response yet. There's a massive null right behind the couch where it basically sounds like the subwoofer isn't on. Vocals from the center channel (or even the two mains with the center disconnected) sound decent if they're high-pitched, but anyone with a baritone voice provokes a lot of blurry room resonance. Only the surrounds sound about right.

Based on your suggestions, my next plan is to put six 2x4x2" panels on the ceiling, suspended down two inches. Eventually I'd like to add six additional 2x4x4" traps straddling the ceiling/wall borders on the left and right walls, and perhaps one in the back-rear of the room near the left surround.

And I may reposition the subwoofer, I haven't done the crawling test to see where it should be yet.

Is this the right route to follow? Put another way:

1) Can I get away with just absorption to treat this room, or must I have diffusors as well? The DIY diffusor plans I've seen are extraordinarily labor-intensive.

2) What percentage of the available wall and ceiling surface should be covered with absorption? This room has 13%, which surely isn't enough. What number should I shoot for that won't sound overdamped? On the same token, should any of these 4" traps be covered in reflective material to keep them from killing the highs?

The riser behind the couch is another question mark. It's 8' x 4' x 12" and similar in design to the one here:

http://www.bobgolds.com/HelmholzRiser.GIF

The surrounding frame is made from 2 x 12's. Internally, I've created one large partition of 4' x 4' and two smaller ones of 4' x 2'. The base is 1/2" plywood and top is 3/4" hardwood plywood. All inside compartments are sealed with Liquid Nails.

The room is 13' x 23' x 8' ceilings, with the riser positioned with the long side parallel to a short wall about 2" away.

Some questions about this arrangement:

1) Does it make any sense to turn this riser into a Hemholtz resonator? If so, what size holes should I make to the front of each partition? Is tubing required, or will the holes alone be sufficient? I'm not as versed in acoustic theory as I'd like to be, I just want to verify I'm looking in the right direction before I dive in too far.

2) What sort of insulation is appropriate for filler? The 8-pound Rockwool I used for my bass traps would be very expensive for this volume. Will pink R-13 or similar suffice?

3) How else might I use this riser as a bass trap if the Helmholtz idea is not appropriate?

I've also asked the riser questions at AVS forum, but I'd very much appreciate your perspectives as well.

[johndykstra]

Need bass traps.


Based on your observations, this is your next step. Forget about ceiling for now, and in fact, if the wall panels can come down easily, use them to determine where and how many you need.

I'd forego attempting a helmholtz bass trap for the riser. You'd need to know the frequency you want to trap with it, and it's likely not in an ideal location for a resonator trap regardless. Not to mention that an empty couch will provide less resonance restriction than a couch full of people, and playing with that type of math makes my head hurt all the way over here. Simply remove the front sides and back, and fill it with fiber. Replace the edge covering with fabric and trim.

Traps look great though, great start!

[KnightRT]

Thanks, it's getting there. What sort of traps do you mean? Would a superchunks-style trap along the ceiling/wall borders be appreciably better than my existing 4" design placed at angles to the same borders?

The flat ceiling trapping was supposed to clean up reflections from the mains and center and, maybe, help with bass response above 100 hz. Are you suggesting not to do this at all, or just to do it later?

As for the riser, the best I can do is to jigsaw out 10" x 10" holes across the front and sides. The design requires the outside pieces for lateral support. There's no going back if I do this though, is there anything else I should consider beforehand?

EDIT: Any thoughts on the fiberglass as well? I'd like to buy that today.

[johndykstra]

No, ceiling traps are certainly a good idea. It's just based on your observations, bass traps will yield more results on your chief complaint.

Super chunks up there would be a bit better, but given your soffit, straddle traps are probably a better return on investment due to time involved sculpting around that soffit. I still would do some above and below your screen as I posted earlier.

Perforating the sides of the riser is fine, and will probably hold up better to accidental kicks.

[Pier]

Originally Posted by KnightRT

Here's an updated view of the room:

Wow...

[ciro]

Originally Posted by KnightRT

For ceiling trapping, that would be, say, a series of open-backed 4x2x6" panels, lower-density mineral wool, with a few inches of gap to the ceiling

I´ll repeat what I said some days ago- "yes", again, do it - 6", not only 2".

Ciro

[KnightRT]

Would panels that thick not be more effective on the wall/ceiling joins?

[PaulP]

I can't tell from the photos but the panels on the walls should not be placed
across from each other but staggered so that each faces blank wall. Your
speakers are awfully close to the sidewalls which can't help. Just for fun
move them away from the walls and the screen to see what difference it
makes to the sound.

Paul P

[YRLK]

Cool room!

[KnightRT]

The panels are symmetrical, you're right. They're lined up on the studs in the wall. Each panel is 20 lbs, I'm unsure if drywall anchors will support than kind of load. At least two of them need to be symmetrical to deal with first-order reflections from the mains.

The studs are also why the rear surrounds are so far back.

I've decided just now that further treatment without measuring the room is throwing darts in the dark. I like the ideas here, I'll keep you updated on how I implement them after I buy an SPL meter.

One last question: is the effectiveness of the riser as an absorption bass trap determined by the size of the holes in it? Or will the bass frequencies travel through the 2" pine to reach the fiberglass inside? Drilling 2" holes all around won't be hard. Jigsawing the larger holes will be more involved.