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High WAF "bass traps"

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Posted on August 28, 2009 at 10:57:47
felrob
Audiophile

Posts: 52
Location: Vancouver
Joined: August 7, 2009
 My stereo is in our living room. Whatever acoustic treatment I do, I need to keep the living room a...living room! My lovely spouse has agreed that nicely made walnut framed acoustic panels will look good on the walls at the first reflection points(she gets to pick the fabric), so that is not a problem.

The problem is bass trapping in the corners behind my speakers. Speakers are on stands in the narrow end of the room, which is about 14' wide. That end wall has a brick fireplace in center, which makes 2 - 4' wide, 1.5' deep "alcoves", which have wall mounted shelves in them. I need to do what I can to trap bass in there, without the option of putting big bass traps in front of them. I have read that books and magazines and LPs can do some good - is that true?

I welcome any suggestions you may have.

And the answer is..., posted on September 28, 2009 at 22:58:46
felrob
Audiophile

Posts: 52
Location: Vancouver
Joined: August 7, 2009
 This past weekend we (my wife and I) installed superchunk bass traps in the living room. They look great (very dramatic in the room, and pretty interesting). We haven't installed first reflection panels yet, but we certainly will.

We sat down and listened to a *much* better sound last night - smooth, rich, clear sound, with no holes in the bottom end and way fewer annoying midrange intenisities. The best tweak is on the sofa with your sweetie!

Thanks very much for all the help.

pics???, posted on September 30, 2009 at 22:28:40
Oface
Audiophile

Posts: 995
Location: columbia, south carolina
Joined: May 3, 2003
 Thanks,


-chris

RE: pics???, posted on October 6, 2009 at 16:46:15
felrob
Audiophile

Posts: 52
Location: Vancouver
Joined: August 7, 2009
 I apologize, I didn't take any pics while I was building them (I had the obsession on, and didn't want to stop for anything). I'll take some pics of the finished product and post them.

I built frames out of 1x3 and triangular 3/8 plywood so the front edges would stand about 1/2" proud of the mineral wool. the front edges were cambered to match the wall angle. The plywood made a bottom plate, a plate half way up, and a top plate. I screwed the frames to the walls, filled them with triangular pieces of mineral wool, covered the mineral wool with batting to eliminate dust, and stapled grill cloth to the front of the frames (this way I can change out the cloth easily if we want to change the look of the things). I put some 1 1/2" trim boards around it, and voila!
Update on WAF level..., posted on September 3, 2009 at 14:52:27
felrob
Audiophile

Posts: 52
Location: Vancouver
Joined: August 7, 2009
 So I showed her a picture of built in 'superchunk'bass traps (from another list), and they look pretty good. So now the WAF has eased considerably, and I have the go-ahead to install superchunks in the corners and make the shelves narrower to allow the space.

"If we're going to listen to music", she sez to me, "then let's set up the living room to listen to it properly". Damn! I married the right woman for sure. And there is a local supplier that has 8 lb. mineral wool in stock, and I can do the whole job for about $150. Things just can't be working out this well!

Thanks for all your help

RE: High WAF "bass traps", posted on August 28, 2009 at 16:14:03
felrob
Audiophile

Posts: 52
Location: Vancouver
Joined: August 7, 2009
 Thank you, Ethan and David,

Because of the WAF, I need to take David's suggestion first. Book shortages are not a problem for me - I have more in boxes than I have on the shelves, and I have bookeshelves in almost every room in the house (packrat mentality, I guess). I could never convince myself to get rid of books or tools - so I have a lot of both!

If that doesn't work as well as I need it to, then perhaps I can try a combination of books interspaced with nicely wrapped rigid fibreglass fillers on the shelves...that could look attractive...or am I just getting desperate and trying to fool myself?

Thanks very much for the help.

Curtis

RE: High WAF "bass traps", posted on August 29, 2009 at 00:09:57
David Aiken
Audiophile

Posts: 5109
Location: Brisbane
Joined: September 25, 1999
 Don't know how the fibreglass fillers would go. I think there would be issues with effectiveness due to their small size, plus I'd be worried about the kind of rubbing/bumping they would get and eventual fibre release.

If you could make relatively deep shelves and leave a 4" air space next to the wall, follow that with a 3" or 4" thick layer of fibreglass that spans the width and height of the shelf space, then leave an inch or so—use a low wooden spacer on the shelf or something similar—and then have the books you would have the effectiveness of a large fibreglass trap spaced off the wall and disguised by the books.

Probably even better if there are no shelves there at present is simply to run fibreglass floor to ceiling with the space behind it, and then install the shelves with a gap between the shelves and fibreglass and a lip at the back of the shelf to prevent books being pushed back in contact with the fibreglass. You'll still need to wrap the fibreglass but that gives you a pretty standard panel trap construction hidden by your shelves.

The books will still introduce some colouration but as I said, it should be minor.



David Aiken
RE: High WAF "bass traps", posted on August 29, 2009 at 14:09:46
felrob
Audiophile

Posts: 52
Location: Vancouver
Joined: August 7, 2009
 That's an excellent idea - fibreglass behind, books in front. What is the minimum thickness of fibreglass to make a significan difference?

RE: High WAF "bass traps", posted on August 29, 2009 at 20:56:43
David Aiken
Audiophile

Posts: 5109
Location: Brisbane
Joined: September 25, 1999
 For bass absorption, go for 3" or 4" with an air space of 4" or so behind it.



David Aiken
RE: High WAF "bass traps", posted on August 28, 2009 at 14:43:55
David Aiken
Audiophile

Posts: 5109
Location: Brisbane
Joined: September 25, 1999
 I'll disagree with Ethan on this one. Books can absorb a fair bit and can be useful as I discovered a bit over 7 years ago. I was packing to move from my previous home to my current home and the audio system was one of the last things to be packed. I'd never had books in the room with the system but I ended up with a pile of book cartons filled with books stacked at the opposite end of the room to the system and noticed that the system had never sounded better. That prompted me to put the books in the audio room when I set up in the new home and they certainly helped, but not as much as proper treatments and they've been moved to different rooms since I installed RealTraps.

You will get some benefit but probably not at bass frequencies. You'd need more depth than the average book for that. You'll also need the shelves to be as full as possible and as little wall space exposed as possible so that will take a lot of books since you've got 2 floor to ceiling spaces which are 4' wide to fill, and you will need about 7 shelves per side, more if your books are predominantly paperbacks which aren't as tall as hardbacks or art books. Magazines would probably better if you stack them on their side and fill the space between shelves, but then pulling the issue you want to refer to becomes more difficult.

You'll get more benefit if you place the books so there's several inches of space behind them between them and the wall.

LPs won't be as beneficial since the vinyl won't absorb sound and you'll end up with a lot less paper/cardboard—which is what is doing the absorbing—than with books or magazines.

The other thing to consider is that the "absorption spectrum" of books isn't as broad or as smooth as a good acoustic panel or bass trap so there will be some colouration of the sound. You probably won't notice it unless you swap to proper acoustic treatments since the sound is likely to be better with the books than without them, but that's another way in which books or magazines won't stack up—pun intended—as well as proper acoustic treatments.

If WAF is an issue and you can't go with acoustic treatments, then I'd go with books but be prepared to start reading a lot in order to fill the shelves if you don't have enough books to do so already. I had enough to fill a 13' width of 6' tall bookcases when I installed them in my room after our move so I could fill your spaces but most people don't have that many books. A lot of half empty shelves or a few full shelves won't do much at all, you're really going to have to stack the space with books.




David Aiken
RE: High WAF "bass traps", posted on August 28, 2009 at 12:13:01
Ethan Winer
Manufacturer

Posts: 1554
Location: New Milford, CT USA
Joined: December 3, 2003
 It's a myth that books and LP records are useful as acoustic treatment. They are not useful even a little. What you need is rigid fiberglass as large and deep as you can manage. If you're building this all on top of the existing walls, there are lots of ways you can make large traps look good and blend in. But the key is using rigid fiberglass.

--Ethan

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