Bass Trap and Diffusor Question

[MatrixDweller]

I'm planning on building a few room treatments including some QRD diffusors for the rear wall and chunk type bass traps in the corners. I don't want to sacrafice too much room space so I was considering making the corner bass traps 12x12x17. Most of the other posts I've read recommended 17x17x24 so would smaller ones be pointless?

I'm also wondering what frequency should I design the QRDs to diffuse down to? Are QRDs the way to go? They seem the simplest to make. I've considered skylines, but making them out of wood would make them pretty heavy.

For panel traps on the walls should I use 2" or 4" OC703 (or rockboard)?

[bpape]

How big is the room and where are the seats in relation to the length of the room. Diffusion isn't usually used on the rear wall of a home theater as you need the additional bass control there to control nulls off the rear - especially if you're going to halve the corner absorbers. Rear half of the side walls would IMO be a better option.

QRD's of 'reasonable' size will go down to around 500Hz if properly implemented. Even then, they'll be between 6 and 7" thick. Going lower not only requires more depth but also wider cavities.

The smaller bass absorbers will do OK - they just won't reach as deep and you have only 2/3 of the surface area.

What do you mean by panel traps?

Bryan

[eugovector]

1) One of our acoustics gurus can answer for sure, but I'd wager 12x12x17 will still do some good. Still, why are you going so small, instead of the popular 17x17x24?

2) I'll pass on this one, though I'm anxious to hear folks opinions. I want to try styrofoam skylines in my next place.

3) 4" for bass trapping, 2" for treating 1st reflection points (both spaced a little off the wall if you can).

[MatrixDweller]

I should have wrote panel absorber instead of trap. I'll probably make a few 2x2 or 2x4 panels for the first reflection points. The reason why I thinking smaller bass traps is that I have limited room and super chunk traps will protrude out from the wall quite a bit. I plan on putting up some curtains and a valance around the screen so the super chunk type trap will mean the curtains would be a foot and a half out from the wall. I suppose I could angle the curtains over the face of the trap. I'm not sure how good that will look though.

I also can't place a trap in the rear right corner due to the doors in that area. I could place a 7'7" x 1'6" x 4" panel absorber there though.

I have some floor plans on my construction thread. The room is basically 10x20 with the first row of seating about 10 ft back from the front wall. There is roughly 20" of space to either side of the screen and about 24" to the lip of the stage at the sides.

If you take a look at some of the other recent pictures on that thread you'll see the big bulkhead running across the width of the room. Should I put a corner trap along it or would a 4" panel absorber be better?

So looking at my room plans and pics of it furnished, what would you recommend for room treatments?

[bpape]

Gotcha. 2" will be fine for the reflection points.

In the rear, I was talking more about the middle of the wall for thicker bass absrobtion. As for the chunks, your call. If you can only do 2 corners, I'd want them to do as much as possible.

How about doing maybe a 2' wide x 1' thick absorber that's more rectangular so the curtains look like the come out from behind it (but don't)?

Bryan

[eugovector]

You might consider moving your seating back or forward 2-3 feet. Sitting with your head at the halfway point of the room length is going to give you less then ideal reproduction at the spot due to peaks/nulls.

Also, could you re-hang those doors to open outward, instead of into your theater. That would allow you to center your seating, and get more folks near the audio/video sweetspots. Maybe you've already done this (I'm reading through your thread now).

[MatrixDweller]

I will be reversing the existing door, but I have no choice about the middle door as it is to the furnace and there isn't enough space inside that room. I can't really move the seating forwards or back though because the seating platform is fixed in place. I've also sized the screen to be optimal width for that viewing distance.

Moving the couches laterally is not really much of an option. I could probably get them out about a foot, but any more would leave no room to walk. 10 feet wide is a lot narrower than I thought (an extra 2' would have been nice). Next house is going to be bought with building the ultimate HT in mind. That will be quite a bit in the future though so right now I'll have to work with what I've got.

I like the idea of the rectangular traps and will investigate. I have the curtains so I'll tack them up to see what they'll look like with corner chunks or squared ones. I will be able to put traps in 3 corners and have a tiny one in the fourth which will most likely just be a thicker panel.