Good cheap "test" treatment materials?

I would like to experiment with absorption, diffusion etc... but don't want to spend a bunch of money on anything until I decide what sounds best.

Any thoughts on cheap ways/materials for test purposes?

Any treatment recommendations for a 19x24 dedicated theater room with a coved ceiling where the rear wall is not square, but shaped a half an octagon?



One imaging problem I have is the entrance is open and sits 3 feet behind the screen wall.



The other side has an unused equipment closet. I have my rack on the side wall right about where the old owner is sitting in this pic. Can't hide my stuff, messy as it right now





The room now has four berklines in the front row and two against the center of the "octagonal" back wall.

Speakers three feet from the screen wall about 11 ft apart, listening position about 12 ft.

I need to get some current pics up, these are from our first visit before we bought.

EDIT: Sorry can't figure out why the pics aren't showing up

Caspyr said:

I would like to experiment with absorption, diffusion etc... but don't want to spend a bunch of money on anything until I decide what sounds best.

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Take some large bath towels and fold them over once or twice to be thicker. Then you can tape them to the wall (and ceiling if you want) at reflection points. That's not as good as real panels that absorb to a lower frequency, but soft towels are definitely good enough to be able to hear an improvement.

There's no easy/cheap way I know of to try diffusion in your room, but this video lets you hear what diffusors sound like:

All About Diffusion

Any treatment recommendations for a 19x24 dedicated theater room with a coved ceiling where the rear wall is not square, but shaped a half an octagon?

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The shape of your room is not much of a factor, and my standard advice (under my name below) applies to your room too.

One imaging problem I have is the entrance is open and sits 3 feet behind the screen wall.

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Openings in the front wall do not usually affect imaging, and certainly not as much as untreated reflection points.

The room now has four berklines in the front row and two against the center of the "octagonal" back wall.

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Reflective seat backs that are higher than your ears affect imaging in a bad way. More on reflections here:

Early Reflections

--Ethan

-----------------------------------------------------

All rooms need:

* Broadband (not tuned) bass traps straddling as many corners as you can manage, including the wall-ceiling corners. More bass traps on the rear wall behind helps even further. You simply cannot have too much bass trapping. Real bass trapping, that is - thin foam and thin fiberglass don't work to a low enough frequency.

* Mid/high frequency absorption at the first reflection points on the side walls and ceiling.

* Some additional amount of mid/high absorption and/or diffusion on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective. Diffusion on the rear wall behind you is also useful in larger rooms.

For the complete story see my Acoustics FAQ.

There's a lot of additional non-sales technical information on my company's web site - articles, videos, test tones and other downloads, and much more.

Hi Ethan,

I just watched your diffuser video via a good quality tube amp and some small B&W driver based speakers.

As a guitar player myself, I was really impressed with the diffuser sound - easily the best of all the surfaces sonically. The absortion panel sounded pretty lifeless and dead by comparison. Pretty much as I'd expect, I guess, but great to confirm it.

Playing an acoustic in the different rooms of my house, it is surprising how different each room actually sounds. Bizarrely, maybe, my favourite is the kitchen, which has the most reflective surfaces and very little damping of any kind. It probably has the most irregular wall surfaces, though.

Interesting stuff, and very well done.

Thank you for drawing my attention to it.

Justin

Let me second Justin's kudos for Ethan's web site. It's very informative!

Great information, thank you very much.

Would I be overdamping the room if I did acoustic panels on all the walls?

The theater was built with that intent, (all the moldings have 3/4 inch grooves to drop the panels in) but the old owner never finished.

User211 said:

my favourite is the kitchen, which has the most reflective surfaces and very little damping of any kind. It probably has the most irregular wall surfaces, though.

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A room where musicians play sounds better with some amount of non-resonant ambience. But when that is recorded and played back through loudspeakers, you don't want the playback room to add its own ambient sound on top.

--Ethan

Caspyr said:

Would I be overdamping the room if I did acoustic panels on all the walls?

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It's good to put some amount of treatment on each wall, but you don't want or need to cover the entire surfaces.

--Ethan

User211 said:

I just watched your diffuser video via a good quality tube amp and some small B&W driver based speakers.

Click to expand...

hey Justin, where is the diffuser vid? i moved from absorbative to diffuser treatments for my current room, and much prefer the sound.

my wife (bless her) also likes the look of multi surface diffusers so i'm going to put those between the front speakers and at the 1st reflection point.

actually, i might use a bit of absorbsion between the fronts with the diffuser.

Ethan - is there any way to employ crown molding around the ceiling as corner treatment? perhaps by stuffing it with insulation or mounting it so that it doesn't actually touch the wall/ceiling along the edges but only at a few points along the molding?

i'm thinking of your cutaway Figure 7. if i have a roll of fiberglass in the very corner, and then the crown molding suspended on brackets, would the crown not vibrate like the plywood in Figure 7, only to have the vibrations absorbed by the fiber behind?

zaphod said:

hey Justin, where is the diffuser vid? i moved from absorbative to diffuser treatments for my current room, and much prefer the sound.

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Ckick on "All About Diffusion" in Ethan's post above - it is underlined.

Ethan - yeah - I agree - but mics are weird. They don't hear like I do, and they really seriously pick up room acoustics.

User211 said:

Ckick on "All About Diffusion" in Ethan's post above - it is underlined.

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duh.... for some reason i just thought that was an underlined title. sigh.

I was able to put together a pretty cheap panel project:

http://www.martinloganowners.com/forum/showthread.php?t=6758

You can pick up some mineral wood panels online. Others on here have stacked rolls of insulation from the hardware store that can be returned after experimentation is done.

zaphod said:

Ethan - is there any way to employ crown molding around the ceiling as corner treatment? perhaps by stuffing it with insulation or mounting it so that it doesn't actually touch the wall/ceiling along the edges but only at a few points along the molding?

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Corner bass traps need to be large to be effective. So while wall-ceiling corners are a fine place for bass trapping, they'll need to be larger than anything I'd consider "molding."

--Ethan

Ethan Winer said:

Corner bass traps need to be large to be effective. So while wall-ceiling corners are a fine place for bass trapping, they'll need to be larger than anything I'd consider "molding."

--Ethan

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if you define "larger" i'll define molding

i'm thinking about 7" crown molding, not the small stuff. and would it be better than nothing? i have WAF to consider...

zaphod said:

if you define "larger"

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Corner bass traps are typically two feet across. Anything substantially less won't absorb to a low enough frequency. Maybe you could build a soffit? Then you can make large bass traps for those ceiling corners, but frame them (only) with wood and cover with fabric to look good. Or make the soffits from cardboard and paint them to match the walls. Cardboard used for shipping boxes is reasonably sturdy, and still lets bass through to be absorbed by fiberglass inside.

--Ethan

Ethan Winer said:

Corner bass traps are typically two feet across. Anything substantially less won't absorb to a low enough frequency. Maybe you could build a soffit? Then you can make large bass traps for those ceiling corners, but frame them (only) with wood and cover with fabric to look good. Or make the soffits from cardboard and paint them to match the walls. Cardboard used for shipping boxes is reasonably sturdy, and still lets bass through to be absorbed by fiberglass inside.

--Ethan

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ah.

well, the new place has a classic line of duct plenum down the right hand side of the theater, which i will have to frame in, but the left hand side is prime for a matching soffit that could be a bass trap.

thanks Ethan