Rockwool basstraps and absorbing panels

The only absorbing material I can get in Israel is 2" 80Kg pcm Rockwool. Im going to build basstraps with one layer of this rockwool, infront of it one layer of foam(for the high freqs) and infront of them one layer of felt. How low would these traps get? is one layer of this rockwool enough? Im going to use the same combination for my absorping panels, is it ok? Thank you,

Aloha,

Im going to build basstraps with one layer of this rockwool, in front of it one layer of foam(for the high freqs) and in front of them one layer of felt.

My guess is that you can skip the foam. You may want to use 2 layers of rockwool instead. Depending on how much your cloth (or in this case, felt) reflects and/or allows through, the rockwool does a good job of absorbing the highs.

How low would these traps get?

If you are using the type of units at: http://www.johnlsayers.com/HR/index1.htm then

Depending on the variables used this will create an absorber in the 150Hz - 500Hz range. Calculation for the slot width/slot depth etc. etc. and the frequency created can be done using this calculator at this link

Aloha 8)

Hi, thank you for your reply, unfortunately, the calculator link isn't working. Two layers of 2" 80Kg pcm rockwool, with one or two layers of felt will be enough? how low will it get? Sorry for asking it again and thanks again,

Aloha Eliya, Depends on the variables you're using: how tall/wide/far from wall... Perhaps a little more info on what you are planning on doing would be helpful, yes? :wink: Aloha 8)

Here's one of the few corrected slat absorber spreadsheets I know of - http://www.johnlsayers.com/phpBB2/viewtopic.php?t=1363 The one that was at that broken link has an error, as do nearly all the helmholtz calculators on the web. We still need more info on what you're trying to do before we can help much... Steve

Hi, thank you for your replies! The traps are going to be 1.80 meters long, 60cm wide. They're going to be attached to the corner, so each side of the trap will be 42cm away from the corner itself. The traps are going to be hanged 50-60 cm from the floor, and that's it I think.

OK, so essentially you're builiding broadband corner traps - I think the foam/felt is a good idea since the density is higher than optimum, and for the reasons you stated. However, I'd put at least TWO layers of the 2" 80 kG stuff behind the felt/foam, more if you can. Traps like that will affect things down into the 100 hZ range when they're as wide as you plan - they should go a long way toward evening out the modes in most rooms... Steve

That me again with a new user(couldn't log into the old one). I wasn't able to find 80kg/pcm rockwool sheets, I could only find 60kg/pcm sheets, 2" thickness. How many layers of these sheets should I put in my traps/absorbing panels. Should I build my frames wider/longer? I found fleece, which seems nicer than the felt and cheaper. Would it be okey to use that? Thanks.

60 kG is actually better, and the fleece will help improve mid-high absorption. That will work fine... Steve

Few more questions if I may.. How many layers of the should I put(in the basstraps), If I'd add a plywood panel, would it help? where should I place it, in the front or back? One last thing, the frames I've built are 180mX60cm, is it fine? my ceiling is 2.7m, at what height I should place the basstraps? Thanks again.

Eliya, you've still not responded to my comment earlier - "We still need more info on what you're trying to do before we can help much" - by that, I mean that acoustics is a THREE-dimensional science and you've not given anything but ceiling height; no room shape, no floor plan, etc - we really need MORE info in order to suggest what will work in your SPECIFIC space... Steve

Here's a layout of the room in sketchup. Im trying to make the acoustics in the room suitable for practicing/recording. So I decided that first of all, I'll build bass traps for the room. Then I'd move to building absorping panels that I'd put on the ceiling and walls. I'm going to build "global" bass traps that aren't tuned to specific frequency, if I'll have problems with it, I'd build tuned basstraps. Hope it helps.

eliya, Did you get the package I sent you? Will the materials work with the acoustical materials you have available? I never heard back from you after airmailing those bags off to you. Thanks, Joel Ps. Steve! Shoot me an email!

By the way, here's another thread that I asked a few questions and got no answers. There are more details about the my room in that thread.

So far, the only dimension I've seen is your comment about ceiling height; that shape room will be hard even WITH dimensions, but WITHOUT them I can't even try... Steve

Knightfly, I uploaded an skb file with a sketch of my room, it's in this thread, 2-3 posts above this one. Thanks

Saw that, but still don't see any dimensions :? Steve

Ok, Im uploading it again, now with the diemensions of every wall. Sorry for the misunderstanding..

bump

another bump.. :( Im sorry that I'm bumping this thread everytime, but I'm in the middle of things and waiting for answers so I can finish things up.

Im sorry to bump this again, but please, me and my band already started practicing in this basement and I need to make these basstraps. In the 4th post above this, there's and skb file with the diemensions. Any help will be appreciated! My questions are: 1. The size of the frames i've built(1.80mX60cmX10cm - h,w,d) enough? The center of the traps will be something like 30 cm from the corner of the wall. 2. I only have 60kg/pcm rockwool sheets. How many layers should I put in the traps? Would adding a plywood at the front or back of the trap be any good? Thanks, P.s. Im not a troll or something.

eliya, I just want you to know that no one is ignoring you, and I am sorry I have not had a chance to post a reply. We are incredibly busy here at our workshop. However, I will respond to this post as soon as I can with more detail my friend. Hang in there! Joel

If you've already built your frames, I'd start with that size; but if your basement has concrete walls (most do, unless it's really old and made from separate rocks) then you're going to need quite a bit of absorption to make the room usable. I normally recommend frames that are more like a meter wide; I know it's kind of a waste of insulation material, and if there's room you can even do corner traps that are 4 feet wide; but your 2 foot wide ones will be a good start. There's really no major thought required for first steps in a room, even yours with its L-shape - you just put absorbent diagonally across ALL the vertical corners, find a way to hang more of it a few inches off the ceiling, and maybe a couple of them on any bare walls - it's the total amount of surface area that's important, but I'd also (if you have enough) put TWO layers of your 60 kG stuff in each corner. If you can't, one layer is much better than nothing. In a pinch, you can just lean the stuff up in your corners til you get time to build frames - it doesn't need to be airtight or anything, just THERE. If your room is STILL in need of more treatment after all the vertical corners, partial walls, and ceiling, we may need to figure out other things to add; but these first steps are necessary for EVERY room that's less than 2 or three times the size of yours. HTH... Steve

Thanks for the replies! btw, would adding a plywood help in any way?