Acoustic panel questions

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NashBackslash

NashBackslash

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Hello everyone, I've spent a lot of time searching and reading posts on this forum in my attempt to understand DIY acoustic treatment better, and I think I almost got it all figured out, but I can't resist asking these questions as they still puzzle me. Thank you in advance for your time. :)

1) "rigid" fiberglass VS "not so rigid" fiberglass

What's the difference between them? The one I have purchased isn't rigid, it's fluffy and very messy (and itchy too >;/) but it's the only one available to me. I just do not have access to 703. As far as absorption goes, are there any major differences between the two?

2) Low frequency and high frequency panels?

What makes them different? To me, they both look exactly the same (insulation wrapped in soft fabric). What little I do know is that to trap lower frequencies, you have to make the insulation thicker and place them in corners. Am I on the right track? What exactly differentiates one from the other?

3) Are these any good, or am I better off building my own rockwool panels?

b8_1_sbol.JPG


(Note: I would not be ordering from e-Bay or whatever (as if I could); I would be able to purchase them from a local store in town)

I may have more follow up questions later but these will do for now. :) Thanks!

- Nash
 
Dont quote me on this, i could well be wrong;

Rigid fiberglass is much more compact, and therfore has more mass. It performs much better acousticly than non rigid. I do believe non rigid is fine for sound insulation but doesnt do a great deal for acoustics.

Foam will abosrb very few high and mid frequences, and can often ruin the sound of a room. You might want to put them at reflection points in the room, but I do believe wrapped rigid will do a much better job.

I think the difference between high and low frequency panels can be to do with thickness and placement. Although im not too sure on this one myself.

Hope i was some help =]
 
So does that mean I won't really gain much by constructing panels using rockwool?

Also, another thing that I need cleared up:

When constructing bass trap panels, you intentionally leave some empty space inside the frame. So if you have a frame that is 4" thick, you'd only put in 2" thick fiberglass.

A) Is this correct?

B) Wouldn't the fiberglass sort of tilt back and forth inside the frame?
 
I don't think anyone has this stuff completely figured out. If someone says they do they're probably full of shit. :D

Call insulation suppliers to find rigid fiberglass or rockwool. If you don't find anything useful in the phone book, start searching the web. Call some of the bigger national suppliers and ask about nearby suppliers. Specialty Products Inc. gave me an estimate on shipping to my area and informed me of a couple of suppliers within 60 miles so that I could decide which way would be easier/more economical.

Supposedly, the best method of mounting diy fiberglass/rockwool absorbers is by using no frame at all. I haven't tested this and I doubt anyone else here has, except maybe a couple of the acoustic product guys that come here. It does sound logical though.

The thinner panels are used at the first reflection points on the side walls and ceiling. The thicker panels used for corner bass absorbers are going to absorb the highs and mids as well. I can see why breathable fabric is recommended for the first reflection points but I think it might not be such a good idea for the corner absorbers. If you absorb too much of the high/mid reflections your room is going to sound bad. I've seen mentions from other boards stating that heavy bass absorption can also make a room sound bad. I don't know if that's true but it wouldn't hurt to keep an eye on the room's frequency response before and after treatment to see if some frequencies are being absorbed more than others. For example, what if your bass treatment is absorbing 200hz reflections in greater proportion to other frequencies? Does it sound strange?

The usual recommendation around here and other boards seems to be to cover the 4 wall to wall corners and front wall with bass absorbers and cover your first reflection points with broadband absorbers (bang for buck treatment). Logic tells me that skinning the rigid fiberglass/rockwool to be used as bass absorbers with something that doesn't absorb too much of the highs/mid reflections would be a good idea (I haven't tested this). Something else that seems logical to me for a small room would be to use the thicker panels at the first reflection points for broadband absorption rather than the thinner panels for absorbing only the highs/mids. It might be worth the small extra cost of trying both the thin and thick panels to see which works (sounds) best for your room.

I'd say that unless you buy acoustic products from a company that specializes in such things, you're on your own with finding the best acoustic treatment for your room. Although, covering the corners and front wall with bass absorbers and the first reflection points with high/mid or broadband absorbers would probably give you a noticeably better sounding room than leaving the room untreated.
 
rockwool and fiberglass have nearly identical accoustic properties at similar densities. The key is the density. You want something porus enough to let the sound in but not so airly to do nothing to break up the sound waves. The stuff that you are talking about, home thermal insulation, is too loose, What you are looking for is something in thr range of three to five pounds per cubic foot.

You really want to skip the foam. The cheap stuff is not good and the expensive stuff is still not likely worth the money.

You may need to shop around at more specialty places but 3-5 pound per cubic foot fiberglass or rock wool probably is available not too far away, just not at a home improvement store.

Thin panels, one or two inches, will do a better job of stopping mid-to-high frequencies than low frequencies. Thus they tend to be called mid-range traps. Four inch and thicker panels will absorb well down into the bass range. Thus they are often called bass traps although semantically speaking they are absorbing the full sonic spectrum. Another feature of 'bass traps' is their placement. Bass frequencies develop standing waves between one corner of the room and the opposite corner (because that is the longest distance). Thus the bass trap needs to be placed in a corner to do its job properly.
 
Innovations said:
You may need to shop around at more specialty places but 3-5 pound per cubic foot fiberglass or rock wool probably is available not too far away, just not at a home improvement store.
Click to expand...

Why not the heavier density stuff (6 lb. or 8 lb.)? I'm pretty sure that one of the companies that makes bass absorbers uses the 8 lb. density rockwool.
 
You would probably still benefit from reading "The Master Handbook of Acoustics" by F. Alton Everest. You can piece together some of the ideas in a forum, but, at least for me, there is a benefit to complete immersion in the subject and learning the whole subject from an expert. There is a lot more to proper sound treatment than absorbing bass.

Cheers,

Otto
 
I have another question. :)

For corner bass traps, I see some people NOT covering them with fabric, but instead with plywood.

1) Why is this? What difference does it make if you cover it with fabric or plywood?

2) What dictates how thick the plywood should be?

Thanks guys!
 
If you want to build some rigid fiberglass pannels, call up a place that specializes in insulation. I thought there was nobody around me, turns out i had 3 options. You probably won't find it at your local home depot.

Also, you might not find the owens corning stuff, in my area, it was either special order or I needed to make a large order to get it quickly. Other companies make the same stuff, 703 is the decensity, if i remember correctly. Other manufacturors make compareable stuff.
 
There are no Owens Corning distributors in Malaysia. The only place where I can possibly get any of this kind of stuff is half-an-hours' drive away from my home (they don't even sell them at home iprovement stores!), and they only bring in CSR products (which I think is Australian).

There is another option for me; there is a local Roxul dealer but they are based in another state which is like 2 hours away from me, and it seems difficult to contact them (they look like the kind that only supply stuff to big-time contractors, big buildings etc).

Anyway, it turns out that the rockwool that I've been using all this while has a density of 40 kg/m3. The CSR distributor offered me rockwool which has a density of 80 kg/m3 but she will only sell them to me in rolls.

Would 80 kg/m3 be enough for the acoustic panels? She gave me a sample and sure enough, it was rigid.

Also, can anyone answer my questions about the plywood covering above? =)
 
The bass absorbers covered with plywood are sealed membrane absorbers. They are pressure type absorbers where just fiberglass/mineral wool is a velocity type absorber. The tuned panels are much narrower in range, usually functioning over about 2 octaves or so. The center frequency is determined by the depth of the cavity and the mass of the front membrane (plywood in this case).

Honestly, most rooms aren't large enough to really make this type of absorber a good option - broadband is usually better for the majority of treatments.

Bryan
 
Thanks for the info. Yes, I admit that my control is quite small so I've decided not to bother trying to understand membrane absorbers for the time being. :)

Yeah, broadband absorbers seem to be the best option for me...

I have another question. Would constructing "super chunks" (as demonstrated in http://www.radford.edu/~shelm/acoustics/bass-traps.html#BassTraps ) be more effective than just placing broadband absorbers in the corner?

I'd try all this stuff myself, really, but my rockwool will only arrive next week. :/
 
TravisinFlorida said:
Why not the heavier density stuff (6 lb. or 8 lb.)? I'm pretty sure that one of the companies that makes bass absorbers uses the 8 lb. density rockwool.
Click to expand...
The 6 to 8 pound stuff will do slightly better in bass absorbtion but it is more expensive (in other words the stuff in the cubic foot which is not fiberglass is air, which is free.

So which would absorb more bass...two four inch thick absorbers of four pcf fiberglass or one four inch thick absorber of eight pcf material?

Remember absorbers cannot absorb more than 100 percent of the sound that strikes them. They cannot draw sound to them. If you have an absorber that will get 98 percent of the sound hitting it you are way better putting a second absorber somewhere else in the room to get the sound hitting there than to spend a bunch of money trying to get the last two percent on your first absorber.
 
My 80 kg/m3 rockwool has finally arrived. Now I'd like some advise from you people.

Which would be better (in terms of bass treatment) for corner bass traps? The super-chunk type or a 4"-thick (made out of 2 layers of 2" thick) broadband panel?
 
Super chunk is ideal, I use 4'' panels from ceiling to floor, cause I didnt have enough for chunks.
 
Thanks for your advice. Just wondering though... I thought that for corner bass traps, having as much air space as possible is ideal? With super chunks, I'd be filling the entire corner with insulation touching the walls, which means no air space.

Clarifications please. :)
 
NashBackslash said:
Thanks for your advice. Just wondering though... I thought that for corner bass traps, having as much air space as possible is ideal? With super chunks, I'd be filling the entire corner with insulation touching the walls, which means no air space.

Clarifications please. :)
Click to expand...

You have to start over with your studies. :p All the way from the beginning...

This was conveniently a few threads down: https://homerecording.com/bbs/showthread.php?t=232794
 
So if 4"-thickness right up against the wall with no air space is favoured, why do I see many DIY panel websites stressing the importance of spacing the panels away from the walls?
 
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