Panel straddling

[Jolida]

I have made 12 panels using 4" rigid fibreglass. Four of them go in the corners of the room, two at first reflection points on sidewall, and two on the wall behind the listening position. As per Ethan's suggestion of straddling the panels on the wall/ceiling junction may definitely yield better results, it looks strange in a room which is used not just as an "audio-only" room while visitors come in. All the above mentioned panels are mounted with a minimum spacing of 4 inches from the wall. Is straddling absolutely necessary or do I mount the remaining four flat on the Walls spaced the same way as others????

[localhost127]

Originally Posted by Jolida

I have made 12 panels using 4" rigid fibreglass. Four of them go in the corners of the room, two at first reflection points on sidewall, and two on the wall behind the listening position. As per Ethan's suggestion of straddling the panels on the wall/ceiling junction may definitely yield better results, it looks strange in a room which is used not just as an "audio-only" room while visitors come in. All the above mentioned panels are mounted with a minimum spacing of 4 inches from the wall. Is straddling absolutely necessary or do I mount the remaining four flat on the Walls spaced the same way as others????

all of this guess-work can be eliminated by using the ETC response (one speaker at a time) to verify the 'wall' broadband panel is placed properly and that it is attenuating the entire specular reflection down to the required level (eg -20dB). if you can space your 4" broadband panels off the wall 2-4", i think that would be sufficient (but please verify with ETC).

for your corner traps (to combat modal/wave issues), straddle them in the corners (preferably horizontally (48" wide x 24" tall) - as the further you space the porous absorber from the boundary (towards areas of high particle velocity), the more effective it will become. however, doing this will require more corner panels to be constructed. is that possible? do you have measurements of the room prior to doing this work? will you be able to take measurements once the treatment has been installed so you can verify whether your issues have been resolved or if they require more attention?

[Jolida]

So u mean to say that the four corner panels 2'x4' be straddled horizontally? Spaced midway between floor to ceiling? Is that correct?

[Jolida]

I have made about 20 panels in total as of now. Each measures 24 inches x 40 inches & 4 inch deep. Out of the lot, I have covered 10 of them with Burlap & the remaining I have sealed with a 4mm plywood sheet having an air gap of quarter inch between the sheet & fiberglass. I had read about this being effective at low frequencies. Also i have made four tri-corner traps to be mounted on the top four corners of the room. Do these need to be reflective or absorptive on the facing part?
With regards to ETC, which software do u suggest be used?

[DanDan]

Those ply fronts have me worried. Panel traps are generally fulled sealed. i.e. the front panel resonates with a sealed volume of air, a spring if you will.
I would avoid doing unusual things unless you are doing research and intend to test them.
Generally, bass is the big one. Four corners floor to ceiling would be just a starting point.


DD

[Jolida]

Originally Posted by DanDan

Those ply fronts have me worried. Panel traps are generally fulled sealed. i.e. the front panel resonates with a sealed volume of air, a spring if you will.
I would avoid doing unusual things unless you are doing research and intend to test them.
Generally, bass is the big one. Four corners floor to ceiling would be just a starting point.


DD

Panels traps are full sealed as in???
I have made them according to this picture...
Started by making a 24"x40" wooden frame 4 inch deep. Filled it with rigid fiberglass & sealed it on one side that faces the room with a 4mm plywood sheet as suggested in the picture. The other side is bare. The panel is straddled in the room corner with the plywood side facing the room. Is the design wrong in any way????

[DanDan]

Those like like Ethan's early design. Note they are attached and sealed with caulk to the ceiling. Or wall if used vertically.

DD

[Jolida]

Originally Posted by DanDan

Those like like Ethan's early design. Note they are attached and sealed with caulk to the ceiling. Or wall if used vertically.

DD

So my construction is done wrong?

[DanDan]

If you attach them to the wall and seal with caulk or weather strip, they should work as Ethan intended. They could still be in the corner, just not straddling. They would also work in the middle of a wall. Best to find where your target mode is max, could be any corner or centre of a wall. Play sine waves to find out.
DD

[Jolida]

Originally Posted by DanDan

If you attach them to the wall and seal with caulk or weather strip, they should work as Ethan intended. They could still be in the corner, just not straddling. They would also work in the middle of a wall. Best to find where your target mode is max, could be any corner or centre of a wall. Play sine waves to find out.
DD

But Ethan's traps are not attached to the wall in his pics right? They are just hung spaces away or straddled on the wall/ceiling junctions. I may be wrong. But is the basic concept of my DIY traps correct or have I made errors?

[DanDan]

Sorry to be the messenger here jol, but no.
Panel traps work by the panel mass and stiffness resonating against the spring of the enclosed air. They have to be sealed.
Ethans ones are sealed to the wall and ceiling.Build a Better Bass Trap

Ethan later came up with MiniTraps etc. which are a very different design, totally open, no panel, just a light membrane bonded to the semi- rigid board of fibre.

DD

[laagman]

But the 10 broadband absorbers (without plywood) will still work, so you didn't loose your time and money building these.

The other 10, with a plywood sheet, can only work as membrane absorbers if they're fully sealed. But even if you do that, they'll probably have a centre frequency between 80 and 100 Hz, based on a 4" deep cavity with 1/4" plywood sheet. Probably not low enough...

I would replace the plywood with burlap and "convert" them into normal broadband absorbers, so you end up with 20 ;-)

Then you can design and build new membrane absorbers that target you lower bass problems.

I just built some membrane absorbers myself without doing enough research first. Now it seems I have to replace them :-( It happens, mate

[Jolida]

Originally Posted by laagman

But the 10 broadband absorbers (without plywood) will still work, so you didn't loose your time and money building these.

The other 10, with a plywood sheet, can only work as membrane absorbers if they're fully sealed. But even if you do that, they'll probably have a centre frequency between 80 and 100 Hz, based on a 4" deep cavity with 1/4" plywood sheet. Probably not low enough...

I would replace the plywood with burlap and "convert" them into normal broadband absorbers, so you end up with 20 ;-)

Then you can design and build new membrane absorbers that target you lower bass problems.

I just built some membrane absorbers myself without doing enough research first. Now it seems I have to replace them :-( It happens, mate

Oh God. I probably misunderstood the drawing. I had earlier used Burlap for the other 10 as well, then after seeing the drawing I removed burlap & installed the plywood sheets recently. Thank God I left the other 10 with the burlap itself. By sealed design, does it mean u want me to put a plywood sheet to cover the other side of the panel as well?? And what material is suitable to be used as a membrane?
Or do I remove the plywood sheet from them & use burlap itself??? Which seems more appropriate?

[RJHollins]

If I may offer my understanding ...

The choices for corner bass traps typically are 2 basic styles [DIY].

1. The 'Chunky Corner Bass Trap' are triangle wedges that are cut from a
usually 2'x4' x2" 703 [or similar]. These are stacked in the corner from floor
to ceiling ... then covered with a fabric'd frame.

2. The 'straddle' method is [typically] a 4" thick panel, covered in fabric.

The do NOT have any other membrane added ... just pure rigid fiberglass.

It is also recommended to place 'fluffy pink' insulation BEHIND the panel.

Granted ... there are other applications, but for the basic corner trapping
these are the two methods I've seen.

For MY new room, I'm going the 'chunky' route.

Hope this helps!

[laagman]

Originally Posted by RJHollins

The choices for corner bass traps typically are 2 basic styles [DIY].

1. The 'Chunky Corner Bass Trap' are triangle wedges that are cut from a
usually 2'x4' x2" 703 [or similar]. These are stacked in the corner from floor
to ceiling ... then covered with a fabric'd frame.

2. The 'straddle' method is [typically] a 4" thick panel, covered in fabric.

They do NOT have any other membrane added ... just pure rigid fiberglass.

So you can "convert" your panels to "type 2". Just buy some extra burlap and take off the plywood.

The "chunky corner bass traps" must be great, but a bit more expensive because of the large quantity of fiberglass.

I understood that for lower frequencies, your panels - straddled or not - need to be spaced a looooong way from the wall. Like 1,50m (5') for 57 Hz. That means you'd loose a lot of space. Membrane absorbers would be more suitable.

I'm curious about how low the "chunky corner bass traps" go. Anyone?

[DanDan]

Jolida, if you add back to the panels it needs to be very rigid/massive.
Ethan's and other designs are attached and sealed to the wall. The wall is the back of the sealed chamber. Many modes cover the whole surface, so you could mount your devices in the corners still. Furthermore you may be able to tune them down by adding weight. Take a look at G.E. 's thread where he does achieve some success over a long series of experiments with panels.


laagman, I recommend you take a look at the Q4Avare thread.
Panel thickness and distance from the boundary are 'significantly' effect at only 1/10 of the wavelength. At 1/4 they are 100% effective, but space dictates that most of us work with 'significant'.
I installed three of the larger 34 inch floor to ceiling SSC's in a room here.
A 34Hz mode was reduced from 1.3S to 0.6S.
Could you give us some details of your panel trap experience here?
Just a little detail will do or a link.
Having both examples here may give pause for thought to those who espouse panel and perf as the 'only' way to deal with LF.

DD

[Jolida]

Originally Posted by DanDan

Jolida, if you add back to the panels it needs to be very rigid/massive.
Ethan's and other designs are attached and sealed to the wall. The wall is the back of the sealed chamber. Many modes cover the whole surface, so you could mount your devices in the corners still. Furthermore you may be able to tune them down by adding weight. Take a look at G.E. 's thread where he does achieve some success over a long series of experiments with panels.


laagman, I recommend you take a look at the Q4Avare thread.
Panel thickness and distance from the boundary are 'significantly' effect at only 1/10 of the wavelength. At 1/4 they are 100% effective, but space dictates that most of us work with 'significant'.
I installed three of the larger 34 inch floor to ceiling SSC's in a room here.
A 34Hz mode was reduced from 1.3S to 0.6S.
Could you give us some details of your panel trap experience here?
Just a little detail will do or a link.
Having both examples here may give pause for thought to those who espouse panel and perf as the 'only' way to deal with LF.

DD

If I had to mount these panels in the corner, how can it be sealed? Only the edges would be touching either Walls right? I understand it could be done on a perfectly flat wall though. In the case of a flat wall, the panel needs to have space behind the fiberglass that's inside the sealed panel & the wall correct? I have made the panel 4inch thick completely filled with 4 layers of 1" thick fiberglass. The only way of adding spacing from the wall is to remove two layers out. Would that be appropriate ?
Or do I just remove the plywood fronts & re-install the burlap?

[DanDan]

Sealed to one of the two walls in the corner.
Like the trap in post 12 here

The ideal would be a light density full fill, not touching the panel.
Whether this touches the wall or not doesn't matter. The panel needs to vibrate, the wall doesn't.
There is detail in making resonant devices work, I know this from failure myself. Furthermore it requires a lot of them do do bass, as it does with any other kind of trap.
I would never recommend pressure devices for DIY.
Your and laagman's unfortunate experiences clearly support that view.
Overall Jol, remove the ply.

There are commercial products that work. Modex Plate for instance.

DD

[laagman]

Originally Posted by DanDan

I would never recommend pressure devices for DIY.
Your and laagman's unfortunate experiences clearly support that view.

There are commercial products that work. Modex Plate for instance.

DD

Haha, I agree. Building normal broadband absorbers (just some fiberglass on a frame and some fabric) was an easy and cheap DIY-job, but membrane absorbers are being a headache to me.

I live in Salvador, Brazil and I don't know any dealers/distributors here. If anyone does, let me know!
Importing large panels from Europe or the US would be very expensive because of the shipping costs. So I guess I'm forced to go the DIY way...

But hey, we all learn from failure and I appreciate the advice from the specialists on this forum!

[laagman]

Originally Posted by DanDan

laagman, I recommend you take a look at the Q4Avare thread.
Panel thickness and distance from the boundary are 'significantly' effect at only 1/10 of the wavelength. At 1/4 they are 100% effective, but space dictates that most of us work with 'significant'.
I installed three of the larger 34 inch floor to ceiling SSC's in a room here.
A 34Hz mode was reduced from 1.3S to 0.6S.
DD

That's impressive! I've been reading the Q4Avare thread, but I have to admit that a part of it is way above my level of understanding.
Anyhow, I'm interested in alternatives to membrane absorbers, especially if they're easier to understand, predict and build. From all the information I had read so far, I had the impression membrane absorbers were the only practical solution for a small (lwh: 3.17m x 2.58m x 2.64) room.

Originally Posted by DanDan

Could you give us some details of your panel trap experience here?
Just a little detail will do or a link.
Having both examples here may give pause for thought to those who espouse panel and perf as the 'only' way to deal with LF.
DD

I attached a floor plan, showing 3 membrane absorbers (Ethan's early design) on the left (yellow) with the following specs:

length: 148 cm (58")
width: 50 cm (20")
depth: 13 cm (5")
membrane: 6 mm, 3.38 kg/m2 (1/4", 0.69 lbs/ft2)
fiberglass sheet: 25 mm, 60 kg/m3 (1", 3.75 pcf)

The theoretical centre frequency is 93 Hz, I believe but I hear 86 Hz when tapping them. The most mode annoying mode in the length of the room is at 55 Hz and these panels don't resonate at this frequency. Now I understand I made some critical mistakes when choosing the dimensions and damping.

Because ready-made panels aren't sold in my city (Salvador, Brazil), I'm looking for a better design (pressure device or not) to replace these unsuccesful panels.

The ceiling cloud and the corner traps (green) worked out fine. If I can improve the 55 and 109 Hz modes in the length and the 62 and 124 Hz modes between floor and ceiling, I think my room will be "good enough" for me.

[DanDan]

Well I hope we do learn something from these two failed attempts at panel absorption. Learning to not recommend them for DIY would be a start.

From looking at the design, it seems to me that the VPR type of bass trap should be possible to DIY. It doesn't appear to have any of the problems of the tuned panel or perf.
It appears to be a sheet of steel glued to a 100mm sheet of Basotect.

DD

[laagman]

Originally Posted by DanDan

Well I hope we do learn something from these two failed attempts at panel absorption. Learning to not recommend them for DIY would be a start.

From looking at the design, it seems to me that the VPR type of bass trap should be possible to DIY. It doesn't appear to have any of the problems of the tuned panel or perf.
It appears to be a sheet of steel glued to a 100mm sheet of Basotect.

DD

That sounds a lot easier than an airtight construction. I did a search on this forum but didn't find information on building a VPR bass trap. Anyone?

[DanDan]

Search again. Fraunhofer (Germany) have a patent. The RPG Modex Plate and Broadband are a direct implementation of that patent.
The RPG site doesn't exactly hide any design secrets.
I am in two minds about the patent. I don't like the idea of copying somebody's work, but on the other hand this is a sheet of steel glued to a sponge, glued to the wall. Furthermore these are the people who invented MP3.....

The don't require airtight, and more importantly they are not really tuned.
It seems one could use 1mm steel for higher bass, 2.5mm for the super lows.
The sponge is Basotect, no idea what density or if there are different ones available. Spray glue has been suggested for the steel side, and carpet glue for the back. I reckon there is an issue with mounting. I expect one would need to glue them to a pretty rigid wall or to a heavy rigid backing, e.g. MDF.


Like all bass devices, size is everything. I wouldn't expect one of these to do a lot. Four maybe. I seem to recall 38 were used at Blackbird studio.

This is the crux of the difficulty with DIY bass traps. Nobody is going to build 4-16 of the various types and compare their performance. So we will probably never know.

DD

[laagman]

Originally Posted by DanDan

Search again. Fraunhofer (Germany) have a patent. The RPG Modex Plate and Broadband are a direct implementation of that patent.
The RPG site doesn't exactly hide any design secrets.
I am in two minds about the patent. I don't like the idea of copying somebody's work, but on the other hand this is a sheet of steel glued to a sponge, glued to the wall. Furthermore these are the people who invented MP3.....

Thanks. In case anyone else is interested, searching on "Fraunhofer" got me some links to useful information on VPR, posted on this forum and elsewhere:

- This document has some interesting and accessible information on Compound Baffle Absorbers and Broadband Compound Absorbers: http://www.landtop.com/landtop/shfw/...5173880847.pdf

- On this German forum there's a great project documentation by a guy that built 3 VPR's with specs from the Fraunhofer Institute. It's very accessible if you speak/read intermediate German: Verbundplattenresonatoren

I don't think it's too evil to use some of Fraunhofer people's findings for non-commercial use. However, if I lived in Europe or the US, I'd consider buying Modex Plate or Broadband absorbers. I'd save me a lot of time and they look 10 x better than DIY...

Originally Posted by DanDan

They don't require airtight, and more importantly they are not really tuned.
It seems one could use 1mm steel for higher bass, 2.5mm for the super lows.
The sponge is Basotect, no idea what density or if there are different ones available. Spray glue has been suggested for the steel side, and carpet glue for the back. I reckon there is an issue with mounting. I expect one would need to glue them to a pretty rigid wall or to a heavy rigid backing, e.g. MDF.

The information I found confirms the above mentioned advantages of VPR's compared to DIY membrane absorbers made of wood:
- design is almost idiot proof (good news for non-acousticians)
- no tuning, so they can be useful in another room
- no (long-term) problems with humidity, air leakage, wood termites, knots etc.
- better removability (if glued to MDF)
- LF absorption in less space (from wall)

So, what are the cons?

Maybe the material costs (steel, Basotect) or their weight (51 kg for the 2.5mm type)?
Or does one need to cover a significant larger surface with VPR's to achieve the same level of absorption as other resonators can provide?

[laagman]

Originally Posted by DanDan

Panel thickness and distance from the boundary are 'significantly' effect at only 1/10 of the wavelength. At 1/4 they are 100% effective, but space dictates that most of us work with 'significant'.
I installed three of the larger 34 inch floor to ceiling SSC's in a room here.
A 34Hz mode was reduced from 1.3S to 0.6S.

DanDan,

That's impressive. 34" front width and 2' along the walls to the corners? And what density? 1,5 pcf / 24 kg?

[DanDan]

The dimensions and cut patterns for SSCs are at studiotips.com
I used 48KG Isover High Performance Duct Cladding.
On newer builds I do use light attic insulation in a frame.

Seriously good news on the VPR front over here
Perforated Panel with Porous Absorber trap
DD

[laagman]

Originally Posted by DanDan

The dimensions and cut patterns for SSCs are at studiotips.com
I used 48KG Isover High Performance Duct Cladding.
On newer builds I do use light attic insulation in a frame.

Do you use the lighter stuff on newer builds because it's cheaper or because it offers more LF absorption with larger SSC's (like 34" front face)?

[avare]

Originally Posted by laagman

Do you use the lighter stuff on newer builds because it's cheaper or because it offers more LF absorption with larger SSC's (like 34" front face)?

Easy one, even though I am not Dan.

It is used because it is the right material for that application. It happens to be cheaper than what many people think is the right material.

Rightly and cheaply,
Andre

[laagman]

Originally Posted by avare

Easy one, even though I am not Dan.

It is used because it is the right material for that application. It happens to be cheaper than what many people think is the right material.

Rightly and cheaply,
Andre

Thanks Andre for bringing some good news. It doesn't seem to happen very often that cheaper is better ;-)

In my city big rolls (12,5 m roll of 600 x 50 mm) of fiberglass are a lot cheaper than panels. Has anyone tried to cut flat triangles from fiberglass that was on a roll?

[ritelec]

Originally Posted by laagman

In my city big rolls (12,5 m roll of 600 x 50 mm) Has anyone tried to cut flat triangles from fiberglass that was on a roll?

And where do we eat our lunch.






It will cut flat.

You can also try cutting them one 34", one +/- 28", etc... to have layers going from front of straddle to the corner horizontally face facing forward. And rows from floor to ceiling.