Bass Traps Q. Combining 96kg and 48kg compressed fibreglass (glasswool) in same panel

[mingar]

Hello to those with experience in bass traps,

I'm trying to give some advice to a friend who wants to build his own traps in a home studio/drum room. -Both in one room.

The budget is not huge so I was wondering if it is a worthwhile venture to combine 96kg density panels with 48kg panels in the one bass trap in order to make them thicker.

At this stage budget allows for 8 120 x 60 96kg glasswool traps at 66mm depth. (Two 33mm sheets). I am toying with suggesting he add 50mm of 48kg to those as they are a little thin compared to most seem to be.

Is this a good idea? Will is add to their effectiveness? Am I simply much better pushing for him to fork out for another layer of 33mm 96kg? It is possible he would increase his budget if it were clear that this was by far the better option.

If it is ok for the 48 kg, should they be layered from front to back 96 96 48. Or 96 48 96?

I have also recommended he make 8 mid/hi traps using 50mm 48kg glasswool for walls and roof. (It is not a good sounding room as yet and drum recordings sound very 'roomy'. It's a smallish odd shaped room with carpet. I've suggested he remove the carpet and we try to remove a lot of the room from the sound with the above basstraps and mid/hi absorbers. Some diffusion would no doubt be a good idea too).

Sound good?

Thank you for your time and your knowledge.

Michael.

[Glenn Kuras]

I would not mix up the densities on the panels. Just stick with the 48kg and make them as thick as possible.

[norton]

What's the goal? If you're needing to really attack low low end, you'll be best served with some sort of resonating slat bass trap. Check out John L Sayers online. Plenty of info.

[BriHar]

Actually I've seen this technique suggested on the Sayers site. Fill mostly with rockwool and then face with a rigid FG panel, then the fabric cladding.

[avare]

Originally Posted by mingar

Hello to those with experience in bass traps,

I'm trying to give some advice to a friend who wants to build his own traps in a home studio/drum room. -Both in one room.

The budget is not huge so I was wondering if it is a worthwhile venture to combine 96kg density panels with 48kg panels in the one bass trap in order to make them thicker.

At this stage budget allows for 8 120 x 60 96kg glasswool traps at 66mm depth. (Two 33mm sheets). I am toying with suggesting he add 50mm of 48kg to those as they are a little thin compared to most seem to be.

Is this a good idea? Will is add to their effectiveness? Am I simply much better pushing for him to fork out for another layer of 33mm 96kg? It is possible he would increase his budget if it were clear that this was by far the better option.

If it is ok for the 48 kg, should they be layered from front to back 96 96 48. Or 96 48 96?

I have also recommended he make 8 mid/hi traps using 50mm 48kg glasswool for walls and roof. (It is not a good sounding room as yet and drum recordings sound very 'roomy'. It's a smallish odd shaped room with carpet. I've suggested he remove the carpet and we try to remove a lot of the room from the sound with the above basstraps and mid/hi absorbers. Some diffusion would no doubt be a good idea too).

Sound good?

Thank you for your time and your knowledge.

Where to start. Bass traps based on porous absorbers require depth. If you are interested bass absorption, at least 200 mm thick. For such absorbers, lighter material is better and cheaper also. AS an example Bradford Wall Floor batts doubled up would be good.

Andre

[Ethan Winer]

Originally Posted by mingar

The budget is not huge so I was wondering if it is a worthwhile venture to combine 96kg density panels with 48kg panels in the one bass trap in order to make them thicker.

As Andre said, what matters most is thickness. Once you get to a foot thick or so, the density seems to matter less. However, for thinner panels, higher density is useful. Some people use low density in front of high density, because the low density absorbs mids and highs arriving at an angle better, as happens at reflection points. But this is mostly minutiae. If your friend has little money, use the lower density only, and cover more total surface area.

--Ethan

The Acoustic Treatment Experts

[bwo]

Originally Posted by Ethan Winer

As Andre said, what matters most is thickness. Once you get to a foot thick or so, the density seems to matter less. However, for thinner panels, higher density is useful. Some people use low density in front of high density, because the low density absorbs mids and highs arriving at an angle better, as happens at reflection points. But this is mostly minutiae. If your friend has little money, use the lower density only, and cover more total surface area.

--Ethan

The Acoustic Treatment Experts

Do you know if it differs much if one is using 65 kg/m3, 40 kg/m3 or 30 kg/m3 rockwool for panels that are 200 mm (7,87 inches) thick? Flowresistivity is unknown.

[BriHar]

Ethan Winer: "Some people use low density in front of high density, because the low density absorbs mids and highs arriving at an angle better, as happens at reflection points."

I don't mean to refute what you are saying Ethan, your advice to the OP is absolutely 100% bang on, but just as a perspective on this point let me quote Glenn Kuras from another posting: "When a panel absorbs it does it twice, once then it goes through and a second time when it hits the wall and goes back through it again." The angle of reflection equals the angle of incidence.

Of course you inferred yourself this is not especially important

[mingar]

Thank you all for your advice and time!
Well this does change things. The price difference between 48kg and 96kg at least here in Australia is massive. He will possibly be able to afford floor to ceiling soffit style triangular traps. Full panels come as 1200x2400. Should he cut panels into 60x60x85ish triangles? I will check his room dimensions and see what it comes too. I'm thinking these in the four corners. 4 100mm 48kg traps halfway point along wall/ceiling corners and then 8 or 10 mid/high panels 50mm 40k on walls and ceiling.

How does that sound?

[ciro]

Originally Posted by mingar

l He will possibly be able to afford floor to ceiling soffit style triangular traps. Full panels come as 1200x2400. Should he cut panels into 60x60x85ish triangles?

Ciro

[avare]

Originally Posted by mingar

4 100mm 48kg traps halfway point along wall/ceiling corners and then 8 or 10 mid/high panels 50mm 40k on walls and ceiling.

Forget the 50 mm thick absorbers. Unless you are planning additional MF absorption, you will end up with a absorption deficit in the lower MF range. Use 100 mm as a minimum.

Andre

[mingar]

Ok this is all great advice! I will advise 100mm for all other traps aside from corner triangles. If these will keep the sound more even but also deaden the room then great.

I guess I was thinking of a way to reduce the room sound for his drum recordings and also for his first reflection points while monitoring and I thought 50mm would do...but even is best so thank you Andre!

Some diffusors I know will also help with improving room sound for drums. Yes?
Michael.

[fatgaz]

Originally Posted by bwo

Do you know if it differs much if one is using 65 kg/m3, 40 kg/m3 or 30 kg/m3 rockwool for panels that are 200 mm (7,87 inches) thick? Flowresistivity is unknown.

I found that around 60kg seemed best, dense enough to work with easily but still seems to be a fairly broad-band absorber. (ie doesn't seem to skew the frequency balance). This is not based on any proper acoustics knowledge however ! also it was easy to get 100mm thick 'panels' at a good cost from a wholesale place local to me. I left a gap between the panel and the wall when I build panels up.

the other thing i did for bass trapping was to get unopened (DIY store) loft insulation rolls (short and fat ones) and just make a tall stack of them (still squashed in the plastic wrapping) in the corners of one room, floor to ceiling. - I taped some together so they were fairly stable and have wrapped some cheap fabric around them so they blend in with the room (and also partly olds them together too.) I didn't worry about HF reflection as you've got diffusion/diffraction happening instead with the shape. I think the density was probably 40 to 60 kg/m3.
Easy to get cheap volume pricing and very little chance of rockwool leaking and a 5-minute assembly job.


G.

[mingar]

Hi Guys.
I thought I would post some pics and a video of the actual room that I am helping to treat. It is such an unusual shape that I thought I better check your thoughts and see if your advice may be different or added to after seeing the shape of the room. Below is a rough diagram of the shape and some pics.

Here is a link to the video: (70mb in size)

https://files.me.com/mingar/tllz2y.mov


I am advising triangular traps 600x600x850 48k 50mil cheese shapes piled upwards in as many corners as possible. (One corner will be difficult because of window). Possibly also along ground under desk at mixing area and back of room. 100mil thick rectangular traps for ceiling/wall corners, walls and ceiling. See rough diagram attached.
What do you guys think? Any advice/alterations/recommendations?
Thanks again,
Michael.

[BriHar]

You indicate two dimensions, both in the perpendicular, intimating that the ceiling is 5' high at one end and 16' at the opposite. Other than that you offer no dimensions regarding width or height. A more accurate sketch in plan view would be helpful.

As it is I would abandon any idea of using the desk for mixing as the symmetry is not there. In addition, the indicated geometry of the room would favour the desk to be on the lower ceiling end - facing the wall. This would also benefit the drums as they should be in the higher ceiling end - especially if you are recording. As it is, the room appears to be setup exactly the reverse of how it should be!

Diffusors or traps are hard to recommend without any proper room dimensions to work out modal issues etc. I could see hanging absorbers possibly being of some use.

[Ethan Winer]

Originally Posted by mingar

What do you guys think? Any advice/alterations/recommendations?

I got your PM. That's a strange shape. Without being there it's tough to know what to suggest. Your initial urge to get lots of bass traps is certainly correct.

--Ethan

[mingar]

Ok I have the dimensions for the room above. Length: 5000 Width 3500. Height at high end: 3450. height at low end: 170 left and 140 right.
Best approach?
Thanks guys.
Michael.

[Ethan Winer]

Can you build a wall to not use the low part of the room? If you can add a wall, you have a shot at getting a decent modal distribution.

--Ethan

[mingar]

Thanks for the modal info Ethan but I think the positioning of the door may make this hard. I can ask but I think he'd prefer not to.
Michael.