Acoustical Treatments Master Thread - Page 191

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Humyt - diffusion on the rear side walls does not need to be symetrical. I have a GIK D1 diffusor on the rear left side wall and a Skyline diffuser across from it on the right side wall and when one is removed there is very little sonic affect because just one is sufficient to attenuate flutter echo between the rear side walls. So, of course you should experiment but I would predict that having 2-3 on one rear side wall and only 1 on the opposite won't hurt things at all. Dr. Floyd Toole in his latest book shows various HT acoustical setups and there are examples of differing diffusion treatments across from each other (e.g. hemicylindrical, QRD diffusers.)

I agree with Ethan that diffusion on the back wall is where I put my first diffusers before the rear side walls. What kind of diffuser are you thinking of using because it's thickness (aka deepest well or cell depth) should be a minimum of 8" and work down to 300Hz and then use bass traps for <300Hz. One idea is to put a bass trap in the middle of the back wall with diffusers on either side of it, OR build a very deep diffuser and put bass traps beneath it for the floor/wall corner and back wall corners from floor-to-ceiling.

Clear as mud?

Thanks for the advice Ethan and Kevinzoe. I am thinking of trying out the Aurelex T-Fusor which is also 6" thick as the GIK D1 diffusor. The planned locations for them are:

a) 1 panel at each corner of the rear wall at ear height

b) 4 panels at first reflection point on the ceiling

c) 1 panel to each side wall of the main listening position at ear height

Front and rear walls (middle part) will use absorption as per Dr.Toole's book Chp. 22.

1 bass trap at each wall/ceiling corners (Auralex LENRD).

Does this sound right? My usage will be mainly for movies (7.2 channels + DSX wides setup). Room size is 4.3m(W) x 6.5m (L) x 2.5m (H).

Humyt - If you're buying Auralex then don't expect Ethan to respond as he reqpresents a 'competitor' to Auralex.

6" deep diffusers - GIK D1 or Auralex T-Fusor - aren't really deep enough to diffuse really effectively down to +-300Hz which represents your estimated room's Schroeder frequency or transition frequency. Have you considered building a Skyline or hemicyclindrical diffuser which can be customized to your needs and offers greater depth flexibility? Just a thought . . .

Regarding your point "a) 1 panel at each corner of the rear wall at ear height" I think bass traps should go there not diffusion.

Regarding your point "c) 1 panel to each side wall of the main listening position at ear height" I don't think you need anything on the side walls directly beside the listening chair as reflections hitting this spot will bounce ahead or behind you so aren't an issue. Instead try experimenting with the diffusers on the side wall's 1st reflection points which is slightly ahead of the listening position but not quite to the speakers.

Have you read Toole's book as you mentioned chapter 22 . . .? If so, lots of 'sound' advice in it for you.

Room treatment is one area I hadn't even considered, and don't know if I would have even missed it if it wasn't there. That said, I'm picky about the sound and have $$ invested.

If I had $100 and DIY, where would be the first place to put something to have the biggest effect? i may add more later, but for now I've got to keep it small.
ATS has some Roxul Rockboard 60 I could use in 2x4 panels.

My room is 8 foot ceiling, maybe 18-20 deep and 12 wide? Curtains along one side wall, back of room has desk and computer setup in one corner and stairs in the other. Viewing/seating is about midway into the room, center.

I could fit:

-1 to 3 panels along side wall on right.
-several panels on the wall behind the mains and tv (50").
-MAYBE something on back wall center, although WAF would crumble.
-corners behind mains and tv, maybe.

$$ wise $100 would get me about 4 panels of that size with cloth and hardware. Where should I focus energy? Will it even do anything?

Not exactly. In fact, diffusion probably is less necessary if you're very far from the rear wall because the distance alone will spread the sound. Plus, reflections from a distant surface are weaker and so less damaging. My main point is that the side walls are out of the way of the "line of fire" so to speak, so that's a less important location.

--Ethan

GIK's diffusor is a genuine QRD type. The T-Fusor is not nearly as good IMO.

--Ethan

Just as a follow-up, the D1 has a higher cutoff on the top end as some of the well faces are polys to extend it to over double what a standard well face would do.

I would also agree with Ethan with regard to the side wall placement vs behind the seating. Another location that's 'out of the line of fire' is up high on the walls where you're primarily looking to minimize slap echo.

Bryan

OK read much more. Thanks for the articles Ethan.

I'm going to try one panel on the right wall at a reflection point, and bass traps in the corners behind the mains and tv. Would additional panels behind each main speaker be useful?

Not sure on materials and design of the bass traps themselves, but it will be all DIY. Also, not sure if upper and lower corners or floor to ceiling? Would just one 2x4 panel be effective? BTW, the sub is located in the corner to the left of the mains if that matters.

does rockwool (slab form) offer as good or better performance than oc 703 for floor to wall trapping?
i am considering 6" wlde X 16" hi X 10 feet long.( front wall under screen.)
walt
(this is in response to an earlier comment by ethan - bass trap the front under the screen)

Walt - check out this link for absorption coefficients between various products, including OC and Rockwool and Roxl:
http://www.bobgolds.com/AbsorptionCoefficients.htm

By the way, how goes the reading of 'the book?' Your impressions?

If one is to build bass traps and have an air space behind the trap, then why are people using OC 703 when 701 has a higher 125Hz absorption coefficient??? I contrasted OC 701 3" thickness (using the 16" air space specs on the link above) with OC 703 3" and 4" thickness and in both cases the 701 less dense material had better low freq absorption. So why do people seem disposed to get 703 instead?

At 1KHz the trend is reversed with OC 703 being more absorbent than 701, but for bass traps I don't want 1KHz absorbed, I want it either reflected or diffused.

Anyone know what the minimum recommended seating distance is from a BAD panel?

Also if anyone can tell me the diameter of the holes that would be useful.

Really appreciate your advice kevinzoe. Perhaps I didn't phrase it correctly, what I meant to say was placing 1 panel each towards the side of the rear wall. I do intend to place bass traps at the corners.

As for the diffusors at the side walls, I was thinking of following what was suggested in Figure 22.3 (page 506) of Dr. Toole's book, specifically Wall B, where a long array of engineered diffusors lined quite a fair bit of the side wall. Is this a good practice for multi-channel setup?

Thanks Bryan, the D1 looks better too! I will definitely look into it.

BTW what can be used to treat slap echo?

kevin: re: book. pg 86; it's like the bible - cannot read it once and understand it all.

soooo... after reading all of this... what would someone on here charge me to tell me what to put where if I can give room dimensions, etc??

It's likely, though you mention "soundproofing" whereas most of this discussion is not about keeping sound in the room (ie soundproofing), but, rather, about making the room itself better for the sound inside of it (ie acoustic treatment).

It depends on what you actually need. If it's simple acoustic treatment, then the vendors here won't charge you anything. If it's room design, then there are several highly qualified professionals who post here all the time. I'm not privvy to their rates, but you could simply PM them.

Frank

As you probably "got" from Frank's post, there is more to it than "here are my dims, what do I put where?" It *might* be that simple, but then it might not and you do more harm than good.

If you are taking the DIY route to sound treatments, you will need a (free) app like Room EQ Wizard and a (not free) calibrated mic.

Jeff

Hi, in the process of treating my room, and got the following questions:

1. What is the performance difference between a foam corner bass trap and a 4" OC703 panel mounted at the corner?

2. Particularly, has anybody had any experience with this? http://www.prosoundfoam.com/12_in_Pr...p-details.aspx

Thanks very much for any information.

I'm really not being a bit flippant when I say the difference is, 4" of OC703 straddling a corner actually works and foam does not. It simply is not a good source for bass trapping. You really only have to view the lab test data to see the very clear distinction. Even if you were to use foam, by the time you'd used enough to equal the effectiveness of a panel trap you'd have spent much more than you would have on even a commercially purchased panel.

Frank

Frank, thanks very much for the quick response. That makes it pretty simple, I will use panels then.

Try www.realtraps.com where there are measurements of similar devices.

Someone had posted previously about placing a movie poster over a 2' x 4' acoustic panel and if I recall other than as a bass trap, this was Ok. How about something like this?

http://cgi.ebay.com/WISCONSIN-BADGER...item20af12e024

I imagine it's about 1/16" or less think wool banner. Thanks in advance.

Thanks for the link. It really helps me with the basics.

How much would 1.1 life size standups absorb sound? I will have at least three on one side wall and one on the other smaller side wall. The back wall will have curtains covering a bay window. The front wall is the screen wall.

Would I really need acoustic panels if I have these guys blocking most of the wall space?

My Darth Vader:

You're kidding, right?

I *think* what he's asking is that he knows the popups are a reflective surface so would that largely defeat a treated wall behind it. Either way, the answer to "would I really need acoustic panels" is "yes".

PEPAR, no I am not kidding.

NJ, these are not cardboard standups. These are costumes on manniquins. Sorry for the confusion. Do you think they will absorb or reflect sound? I would think that a body ( Human or mannequin ) would absorb sound. I would hate to buy acoustic panels only to be covered up by my mannequins.

Hard and curvy, so in general good diffusers. You could still benefit from acoustic panels, because indirect sound will still reach behind the mannequins and improve reverberation times and dialog intelligibility.

Thank you Terry. That answers my question.