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Choosing acoustic material for DIY panels
Old 22nd May 2019
  #1
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Choosing acoustic material for DIY panels

Hi everyone,

I'm relatively new to acoustics so forgive me if I say something that doesn't make sense.

2 years ago I bought some basic acoustic wedges for my front and side walls to treat early reflections. I noticed quite some improvement, particularly with some nasty flutter echo I had. However, I still notice some echo at listening position and I think it has to do with my room being quite tall. I also have some issues with bass nulls that I want to treat before buying a sub.

I'm currently planning on building a few acoustic cloud panels that will be suspended from the ceiling. I saw some tutorials and I think I have a rough idea of how I will construct them. The only problem left is choosing the absorbing material. Because I live in The Netherlands, many products advised on tutorials are not available here. I did some research myself and found a product by Rockwool called "RockSono Solid". It seems to be available only in The Netherlands so I couldn't find an english spec sheet. The Dutch sheet says it's density is around 45kg/m^3. They also included this graph and table with absorption-coefficients.

I hope you guys can still understand it although the legend is in Dutch.

Would this be a good material to consider for broadband cloud absorbers? I plan on making them 100mm thick. I went through some posts here and noticed some posts about the safety of Rockwool particularly about fibers raining down from ceiling panels. Should I be concerned about this? I already plan on wrapping the panels with some fabric as most people seem to do (mostly for looks). Should I also wrap the material itself in some sort of plastic? I know that I'm quite new to this so I want to be sure I do this safely and don't miss anything. Or is there another material I should consider that I can get in Europe?

Last edited by bramlaurens; 22nd May 2019 at 06:18 PM.. Reason: Removed some wrong info
Old 23rd May 2019
  #2
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I'm a novice in this area but I'll reply as this section doesn't seem to get much traffic...

Are you going to place these panels at the ceiling first reflection points? This would be the best plan.

The absorption data for the material you posted looks decent to me, and the density is similar to the OC 703 panels most commonly used here. 100 mm panels placed 100 mm from the ceiling should work well I think.

A major reason for covering panels in fabric is to stop fibre particles falling off. It's not just for the look. You don't need to cover them in plastic though, and particularly at first reflection points it would be bad if you did since the plastic will reflect higher frequency sound.

There are reasons to place a thin membrane of plastic or other material on either the front of back surface depending on the panel purpose, but for the ceiling first reflection point panels I think you are trying to make it is most common to have no such membrane.
Old 23rd May 2019
  #3
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Thanks for replying!

Quote:
Originally Posted by Ultrasonic_UK View Post
Are you going to place these panels at the ceiling first reflection points? This would be the best plan.
I have a pitched roof and my mixing position is placed under the highest part of the ceiling (see pic). I'm currently planning on making clouds above the mixing position to try and prevent sound from going into the big, empty untreated part high up in the room which causes some echo.

The speakers are facing the pitched roof and the sound mostly hits the lowest part of the pitched ceiling in the back of the room. I'm guessing this part of the ceiling has the most first reflection points. Since this wall is pitched, the sound does not directly bounce back to the mixing position like a straight back wall would. I've noticed this is actually beneficial for me as it strongly reduces echo at mixing position. This is why I'll focus on the issue of the big empty space above the mixing position first and the issue with the bass nulls.

The plan right now is to suspend the clouds from the roof, around 2.5m above the mixing position. The space between the ceiling and clouds would be quite bigger than 100mm. Would this make the clouds useless? I'm mostly trying to absorb sound before it goes into the big empty untreated space in the top of the room.

Would this material also work for some corner bass traps? Or would I have to pick something denser than 45kg/m3?
Old 23rd May 2019
  #4
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I think you will still get an early reflection off that ceiling at your listening position but the slope will mean this reflection point will be closer to overhead than it would be with a flat ceiling, or even behind you. Something like the attached image.

You could confirm this with the usual mirror test.

The reason reflection point absorbers are not normally spaced more than their thickness away from walls is so that they give an even response over a wide range of frequencies. Suspending what you envisage as bass traps a long way from a boundary is a different question though, and I'm less sure about commenting on. I hope someone with experience of a room like yours comes along to help you out...
Attached Thumbnails
Choosing acoustic material for DIY panels-angled_ceiling_reflection.jpg  
Old 23rd May 2019
  #5
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The sort of panels you are asking about here would be much more effective on your side walls than what you currently have by the way. My understanding is that the sort of thin foam you are using will only help at the very highest frequencies.
Old 23rd May 2019
  #6
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Thanks for the picture, it made me realize I should also treat part of the sloped ceiling for early reflections.

Quote:
Originally Posted by Ultrasonic_UK View Post
Suspending what you envisage as bass traps a long way from a boundary is a different question though, and I'm less sure about commenting on. I hope someone with experience of a room like yours comes along to help you out...
It's indeed not your average box room and it's quite hard to find info on sloped ceilings. I don't necessarily intend for the suspended clouds to be bass traps. The ultimate goal would be for them to be broadband absorbers. I want to make some bass traps in the corners later on. Or am I wrong here and should the clouds be bass traps?

Quote:
Originally Posted by Ultrasonic_UK View Post
The sort of panels you are asking about here would be much more effective on your side walls than what you currently have by the way. My understanding is that the sort of thin foam you are using will only help at the very highest frequencies.
Yeah I heard that quite often. They do their job surprisingly well though. Before I placed them I had a really bad flutter echo and phasing/stereo field issues and they all disappeared after placing the foam. Maybe I will replace them with some diy panels later on.
Old 23rd May 2019
  #7
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Quote:
Originally Posted by bramlaurens View Post
It's indeed not your average box room and it's quite hard to find info on sloped ceilings. I don't necessarily intend for the suspended clouds to be bass traps. The ultimate goal would be for them to be broadband absorbers. I want to make some bass traps in the corners later on. Or am I wrong here and should the clouds be bass traps?
Whatever you call them you are primarily adding them for low frequency control. Generally people only want higher frequency absorption at first reflection points but there is a balance between absorption and the room sounding too 'dead' that I think you'll need to judge for yourself. In terms of panels the only difference would be if you put a semi-reflecting membrane on the front or not.

If you want something that definitely would be called a bass trap then if you could find a way to fill the very top of your ceiling space with lower density insulation this would probably be a good idea. But I'm saying this just from what I've read rather than experience.

Quote:
Originally Posted by bramlaurens View Post
Yeah I heard that quite often. They do their job surprisingly well though. Before I placed them I had a really bad flutter echo and phasing/stereo field issues and they all disappeared after placing the foam. Maybe I will replace them with some diy panels later on.
I didn't say the foam was useless, just that you could do better. If you make some ceiling panels you could try placing them at the sides first to see the effect.

You'll get a MUCH better idea of what is going on if you make measurements, using a suitable microphone and software like Room EQ Wizard (which is free).
Old 23rd May 2019
  #8
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Quote:
Originally Posted by Ultrasonic_UK View Post
If you want something that definitely would be called a bass trap then if you could find a way to fill the very top of your ceiling space with lower density insulation this would probably be a good idea. But I'm saying this just from what I've read rather than experience.
Never thought of this actually, thats a good idea. If I make 3 ceiling/cloud panels I'll have 3 pieces of Rockwool left. I could use them to fill up the very top of the room!
Old 25th May 2019
  #9
You could probably staple a few moving blankets to that part of the ceiling. I'm sure a proper fiberglass panel would be better but definitely more difficult to mount.
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