Acoustical Treatments Master Thread - Page 57

pepar,

> Does not a room with "decay issues" have a "reverb" problem? <<br />
It depends on the size of the room. Smaller rooms have only modal ringing, where the extended decays are highly frequency selective. A large space, like a gymnasium or auditorium, has true reverb, where you can play 100 Hz or 101 Hz or 97 Hz and have similar decay times at all those frequencies. Medium size rooms fall somewhere in between. As I understand it, to be considered true reverb the sound must first swell over time, during which more and more reflections combine to create a coherent "haaah" sound. As opposed to the modal ringing and discrete "ping" and "boing" echoes you get in smaller spaces.

--Ethan

OK, my preference is to use monopoles for the rears in a 7.1. If your's are not adjustable, I would suggest moving them a wee bit closer together. As there are no discrete rear channels (yet) you will not be losing any separation. And you'll probably generate a more enveloping rear soundfield by hetting them away from your traps.

Just my $.01, $.02 or $.03.

Thanks.

Those reflections apply to frequencies above the schroeder/transition frequency where the drywall would be more or less uniformly reflective. Below the transition frequency, drywall flex actually aids modal issues. Any texturing of the typical wall would only affect frequencies way above 20KHz. Rest assured, there is absolutely no need to be looking into a smooth as glass concrete wall. As for vertical off axis problems, you're on top of things. Hence the operative word "lateral" when speaking of the beneficial early reflection in question.
Tumara Baap

Well, thanks for sharing Tumara. If nothing else I'll be sure to keep an open mind and A/B with and without treatments on my first reflection points.

The first absorber - 2" OC Selectsound Black - I placed at a first reflection point was the REAR wall, a surface that sometimes gets overlooked by us layman. The difference was ASTONISHING - improvements in clarity, main/surround integration and somewhat tightened bottom. The next surfaces I treated were left and right front walls. This produced an incremental improvement in clarity and main/surround integration. The final surface treated was the front ceiling. This made a larger improvement in the aforementioned areas than the side wall treatment, but not as great as the rear wall did.

Just my $.01, $.02 or $.03.

So on my back wall, which will be about 14-15 feet away from my Front speakers, should I use some sort of diffusion panels? if I keep it away from my rears (like above or below)?

I used absorption. Others recommend diffusion, and I might give that a try myself - just to see the effect. If you used diffusion, you would (probably) not need to worry about it's proximity to your surrounds.

For item (a) I don't understand what is being implied by the "polyester batting above". Where and how is the polyester batting used?

Ron Jones

Wow, thanks for the tip. I was thinking to target the sides first and go from there but this is interesting food for thought. In my case the main LP will be a home theatre recliner at front-center, and behind that will be a leather sofa on a 12" riser. I expect the reflection point to be the lower portion of the back of the sofa. So hopefully the sofa behaves better than a wall in terms of absorbtion and reflection. It will probably reflect high frequencies a fair amount; I guess I'll play around to see if buying a cloth sofa would make a substantial difference in SQ...

I had the same results, but did the sides first. Based on my temp placement so far, I'd say you should do sides, back, and ceiling.

Instead of buying a cloth sofa, how about just putting a think blanket over the back of the leather one?

Im getting ready to put the 1" Linacoustic RC on my walls....is there a front and back to this stuff?
What part do I put agents the wall?
And what is the best thing to use for your 1" Furring strips?

Thanks
Chillinintheoc

Ron.

The batting is used on the upper half of the walls to fill in behind the GOM to the same level as the Linacoustic below. If you don't want the extra HF absorbtion you can use something inert like styrofoam that will not absorb anything but will provide a more solid backing.

Chillin,

Use the side with the coating on it out toward the room. You'll have to rip the 1" strips yourself - or spend a lot of money buying craft lumber.

Bryan

Damn it...had a nice thought out response as to why I hate my batting...and then I hit the wrong button and it all disappeared.

So, long story short....I hate my batting above my OC701 so much so I actually considered tearing down all my GOM and wood work to replace the batting with wood, drywall or even Styrofoam as Bryan suggests. I found it impossible to get the batting to lay perfectly smooth as it does over the fiberglass. The fiberglass fibers hold the GOM nice and smooth while the batting causes it to "poof" out.

Anyway, do what you want...but the very very small amount of high freq. absorption afforded by the batting is FAR outweighed by the PITA poofy factor. (IMHO)

I went a different route than the above suggestions:

I looked around my local Home Depot and of course didn't find any wood that was perfect for 1" tall firring strips. However, I DID find some .75" tall pine and some .25" tall pine that stacked up to be the perfect height. Now, while I could have bought the exact same length for each material...I went the even MORE economical route of cutting the .25" stripes into 2" long "spacers". I simply nailed\\screwed the .75" strips to the wall every foot or so with a spacer between it and the wall. I found I had to pre-drill holes in the spacers to keep them from cracking, but it worked very well. I pretty much only air-nailed\\screwed at the wall studs. If I had a piece of firring that didn't line up on a stud, I used cheap drywall hangers (the plastic butterfly things that expand when you screw into them). This took a little extra time to put in the hangers, but I probably saved 50$ in wood. In either case, I would have had to use drywall hangers for some short firring pieces around outlets and at the riser steps.

To get a better idea here are a few pics of my room. Every where you see brown trim, there is firring strips behind the trim. This allowed my to make a pattern with my GOM and NOT have ANY visible seams. The GOM on each wall is a single continuous piece. FYI: I used outlet covers to hide the staples around the outlets along with small pieces of window molding under my soffits to hide staples and generic floor board molding at the floor. (It was all generic pine I stained.)

Front:


Back:

Stima, do you not find you get a lot of light reflecting off of the light surfaces, especially the ceiling, that washes out the projected image on the screen?

I do see some light reflecting off the ceiling and walls, but it does not deter the picture any that I can see.

I will take a picture of a paused movie with a wide angle lens and post it back.

edit: added pictures and modified above sentence regarding reflected light.

Didn't level tripod well, but you'll get the idea. Also, chromatic distortion by unicorns head is only seen on camera, not on screen.

Sony DSC-H5 F3.5, 1/2 sec, ISO-125


Sony DSC-H5 F3.5 1/6 sec, ISO-125
Zoomed to show lack of "wash out"

I agree with some of the posts from last week. We need a sticky for "where to buy" DIY materials for acoustic treatments. I, like many others, called high and low and spent hours drvingin around trying to find OC 703 or Johns Manville stuff at the Do It Best stores, HD, Lowes, etc. I finally found it by going to the spi website after reading one thread from someone building a theater in my neck of the woods. Once I found them, I made one call and went to pick up as much as I needed. It was all in-stock, 15 miles away, but SOOO hard to find them. I ended up getting a 1.5" thick, Johns-Mansville equivalent to OC 703 for about .80 per square foot near Cincinnati.

There's one here: Ethan's Forum

These materials can be purchased most economically at an HVAC (Heating Ventilation and Air Conditioning) supplier, but you must find a smaller one unless you need a lot of material or find one who'll accomodate you. I purchased two rolls of J-M Linacoustic at a distributor in the Philly area and three packs of four 4x8 sheets of OC SelectSound Black at a distributor close to MD. When I wanted to buy OC 703, I again priced it at the Balto place, but also found SPI. Coincidentally, their headquarters is 20 miles from my home. Their price was SO much better than the Balto one that I was insulted! The link is to their service center directory and shows locations all over the country with the highest concentration east of the Mississippi. They carry many brands, have favorable pricing and are the best resource I've run across for acoustical materials.

I guess it's a matter of preference - and how easily one is distracted. Personally, the light reflecting off the ceiling and the side walls would distract me too much. I prefer flat black so there is NO light coming at me from anywhere other than the screen.

The light reflection would probably be more noticeable if the viewing distance to screen diag ratio wasn't so close to 1. (10' wide screen with seating at 12" and 16") The picture is just so huge, my eyes just don't ever notice the extra light on the walls and ceiling.

I'm assuming you meant 12' and 16'. What's your source, don' t you find that too large/close for viewing?

Watching DVDs at a little less than 2 times the screen diagonal, I start to see some softness in the picture.

Yeah, 12' and 16'. I currently am running a InFocus SP4805 with a Panamorph Horizontal Expansion Lens to achieve 2.35:1. Source material is DVD and an old HD OTA receiver for Monday Night Football. I have a media server with DVD rips just itching to be used, but I don't have the cash to purchase a Media Extender that can handle ISO's.

Once I save some more pennies, the FIRST thing I will do is replace the source, projector and lens. I decided to first focus my money on the building of the room and it's audio properties. I can easily upgrade a projector...redoing acoustical treatments on the other hand ain't so easy.

BTW, one of the VERY FEW benefits of poor eyesight is the ability to have a bigger picture and not be able to tell it is soft or pixelated. I have 20/30 and 20/40 vision due to a degenerative eye disease.

Now my brother-in-law who has better than 20/20 can see the pixels at 12' but not 16' where I can only see them at a couple feet.

My mom always used to say that sitting to close to the television would give me bad eyesight. I guess with your experience to back that up, I'd better scoot back a couple feet

sorry for the edit while you were replying.

Yeah, my problem wasn't sitting to close...rather genetics. My twin brother has also been diagnosied. Sucks for us

I am still trying to under stand about treating the rear wall my room is appox. 13'.5" x 8' x 26' should I put a panel on the rear wall.

I'm obviously far from an expert, but in my limited experience, I found benefits in treating all first relection points (left, right, front, back, ceiling, floor) for both music and movies.

I'd say yes, at least at 1st reflection points.

Treating my back wall made a bigger difference than doing the ceiling or left/right front walls.

Treating the back wall is going to help with nulls and peaks that you would get off the back wall. Treating the side walls is going to help with imaging of the speakers. So yes you do want to treat the back wall and the side walls. For the back wall it might be best to go with a 4" panel spaced off the wall 4". For the side walls a 2 inch panel should work fine.

Glenn