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Treating Space + Panel Experiments
Old 1 week ago
  #1
Gear Head
 

Thread Starter
Treating Space + Panel Experiments

Hello Fellow Acoustics Fans,

After a lot of time researching acoustics and figuring out logistics, the time has come to tackle my own room. As you can see, not an ideal space for many reasons. But I like it for writing so would like to make it work and am prepared to invest in that!

Edit: looks like I can't upload images. They're in the dropbox as well:

https://www.dropbox.com/s/cuuv8kxnm8...room1.jpg?dl=0

https://www.dropbox.com/s/69sfc6c4et...room2.jpg?dl=0

To that end, would love feedback from any and all, particularly those with hands on experience using panel absorbers as I plan for those to provide the bulk of my low-end treatment. (See below for more.)

Measurements

Preliminary measurements of the room generally empty (but including gear) are too large for the site but can be downloaded here: https://www.dropbox.com/s/4rqbbhxxp5...5.17.mdat?dl=0

Using an EMM6 from Cross Spectrum Labs. You can see a lot of rolloff +10k which is either the speakers (ancient Event 20/20BAS v3) or the mic but I'm not particularly concerned about that right now. I'll be swapping the speakers if I can get the room under control.

There are two sets of R/L speaker measurements. R6/L6 through R10/L10 are facing the North (Window) wall, with various speaker and listening position configurations. Set 6-8 is with the speakers directly up against the wall, Set 9-10 with the speakers pulled off the wall and into the room. I have exact measurements should anyone need them but I'm not sure they serve a direct purpose right now.

The second set, SWR1/SWL1 through 6, are with the speakers facing the East wall, or Short wall, again changing speaker distances and listening positions in between. Measurements 1-4 are against wall, 5/6 are pulled away from the wall and into the room.

Listening Position Orientation?

So my first question is, which orientation would you choose? In a normal space I understand the importance of choosing the short wall, but there are some extenuating circumstances here (much more symmetry using the Window wall orientation, and a full rear wall available for treatment) that made me think twice.

From my analysis, it looks like facing the short wall should still be fine, and that is my preferred option from an aesthetic/comfort standpoint, but I see pros and cons in both sets of data and I'd love some more experienced eyes to offer input on my views and "down the road" implications that I may be missing.


Steel Panel Absorption

I have managed to drag

(9x) 60" x 40" 20GA steel panels
(9x) 60" x 40" 12GA steel panels

Into my room. I do not recommend doing this alone.

For my metric friends, these are rough American approximations of the familiar 1.5m x 1m and 1mm and 2.5mm panels, somewhere around ~.95mm and ~2.78mm). I am hoping the 2.8mm is not too high to be effective, but since I have low issues and the next size down was 13GA at 2.38, I took the gamble.

While I have all the mass (steel) I need, the bad news is I'm missing the springs! I have a quote for Basotect G+ (new formulation of Basotect), but the prices are very high from this particular dealer. (Roughly $100 a panel for 2" thick, or $200 a panel for 4" thick + transit fees). Anyone have Basotect USA dealer recommendations?

At those prices, I would much rather pay for Isobond, but unfortunately I cannot find a distributor selling panels that are large enough, and don't want to spend a lot only to receive reduced performance from using foam smaller than the steel. So does anyone have recommendations for US dealers that will go 1.5m x 1m in size?

I do have access to a few different open-cell foams (a charcoal poly, latex, and some auralex) that I will be conducting experiments with. My hope is that the cheaper poly foam offers enough performance that I can get where I'd like, even factoring in the inefficiencies. It seems others have had success with this so I'm encouraged. Open to any and all suggestions regarding foams, experiment locations, etc.

I'll be sharing my measurements so this can be a learning experience for all.

Thanks for reading and any advice you have to give!
Old 1 week ago
  #2
Gear Head
 

Thread Starter
After a bit of haphazard experimenting (speaker and panel position was chosen more or less at random, all measurements were simply relative), two of the 12GA VPRs and some Auralex I was able to achieve a promising result -- major squashing of decay across a range of 30-500hz. Based on the decays I observed and A/B testing with and without foam this thickness steel appears to be most effective at ~30 to ~70 hz.

I also discovered how finicky these devices can be -- there were many configurations that resulted in measurements that were arguably worse than the empty room, and I struggled to get as good a result as I did after moving the panels. It appears things must be precise, and since I've been testing without gluing the absorbent to the plate it's a little more difficult to get things positioned optimally.

Next task is to find the optimal empty room listening/speaker position first (if anyone has input on that it'll be much appreciated!), then determine where the low frequency buildups are greatest and test the VPRs in those areas. I've also sent an email to an Isobond distributor to inquire about larger panels, but I'm not optimistic about that one.
Old 1 week ago
  #3
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DanDan's Avatar
Easy

There are some good VPR threads here. Check out the work of G_E, Gernot, and Audiothings. Also UK Mastering if I remember correctly.
I have been keeping an eye on this topic and I think you will find the following things I noticed very helpful.
1 Other fibres work. I would assume the springier Melamine and Polyester are probably best suited though. There are many other manufacturers of Polyester. https://www.gearslutz.com/board/stud...ing-acoustics/
2 The fibre does not have to be glued to the plate. Double sided sticky tape here and there will do it. Or just pressure caused by containment or other factors.
If I ever try this I intend hanging steel from the ceiling, but a bit closer to the wall than the fibre depth. This may cause enough inward pressure to keep the fibre in place.
3 These device work best at the hot zones of the modes. Play Sine waves at the modal frequencies and you will find the hot zones without the heavy lifting.

Location of speakers and listener is best guided and really much easier if test the options using your software.
DD
Old 1 week ago
  #4
Gear Head
 

Thread Starter
Thanks for jumping in, Dan! I have read as many threads on this as I could find before ordering the steel, so I feel fairly aware of the various methods and alternatives out there. Unfortunately I have yet to see threads using non-Basotect/Isobond that were reported to my liking, aka details of specific products used, their dimensions, and A/Bs showing successful performance.

Please let me know if there are any threads like this that I have missed. Part of my reasoning in starting this thread is to hopefully provide a better resource for the DIY camp than what currently exists, but it's entirely possible I missed some things on the way. I've included a general summary and links to what I've learned below, so you can see the threads that I found of greatest reference.

And yes, my plan is to continue using REW (you'll see initial MDATs in the first post) to find the listening position and then the time-honored generator-while-I-walk-around-with-SPL-meter to find the hotspots once that is established.

--- Summary of VPR Findings ---

This document https://www.gearslutz.com/board/7236925-post16.html provides information on the formulas (VPRs are two part systems). Ultimately the size, thickness, and stiffness of the steel plate, the individual properties of the foam, the mounting position and method, and the number of individual VPRs assembled in the room will all influence the final result.

Unfortunately there are very few examples on the web that include BOTH measurements of a room, and actual dimensions/materials of the VPR, in such a way that provides practical advice or guidelines. Sadly many examples include one or the other, or neither, they just say it worked or it didn't. So this requires a lot of assumptions to be drawn from what is known scientifically and what is seen anecdotally.

As best as I have figured out:

The Steel


Plate size: It is unclear exactly where critical importance lies in terms of (A) total sqft of VPRs placed in room vs. (B) sizing of individual VPRs.

Some open questions I have — what are the differences between a single 2m x 1m VPR vs. two 1m x .5m (or smaller) VPRs? What is the minimum effective size? Maintaining a 3:2 ratio is ideal for distribution across the plate, but what is the impact of straying from this ratio? https://www.gearslutz.com/board/8690620-post171.html

(Further complicating this question is the mounting and position in the room, which will be covered later.)

VPR performance depends on modal density of the plate, which in turn depends on the plate’s stiffness and density.

Plate thickness: The most commonly used are 1mm (roughly 20 GA, for those in US) and 2.5mm (between 13 and 12 GA, for those in US), but it is possible to use something in between, or even heavier.

Again, hard to draw exact conclusions (seeing the theme here?) about respective performance because of a lack of head to head testing, but it is accepted that 2.5mm plates are capable of reaching down to lower frequencies than 1mm.

Exactly where the effectiveness "crossover" between 2.5mm and 1mm lies is hard to say. https://www.gearslutz.com/board/8402739-post153.html

Anecdotally, dor baruch (who has built several VPRs) offers "i go with 1.2mm for 60hz+ and 2.6 for 40hz+" https://www.gearslutz.com/board/9403680-post8.html

Another user built 16 VPRs but only used 1mm and has remaining issues at 45hz and below. https://www.gearslutz.com/board/11554197-post7.html

Plate material: Most recommend Cold Rolled steel sheets, but it appears that is primarily because of dimensional tolerances / replicability / cost. I haven't seen conclusive testing on the impact of using Hot Rolled, Stainless, with powdercoat, etc.

The Damping Material (Foam)

This one is tricky too.

The VPR in its classic form was initially developed with Basotect G, a melamine foam. (Basotect now sells only G+, which is a formulation of G with less formaldehyde, but appears generally the same, acoustically.)

Somewhere down the line an opinion was formed that Isobond is "better for VPRs", and Isobond likely what the most common/successful commercial application (RPG Modex) uses, so it is certainly a valid material.

There are a few users (Dor Baruch, audiothings) who have made multiple VPR installations and downplay the ultimate material used for the damping. They have used Isobond, Basotect, and Poly foams all successfully, and suggest that perhaps a combination of foams may be optimal, depending on plate thickness: https://www.gearslutz.com/board/9313660-post991.html

Factor in world location (much easier to get Isobond in Europe vs. US/ROW for example), cost, time, etc., What the actual measured differences are between these various materials has not been established, nor is it clear exactly which properties of the foam control the result. For reference Basotect G density is 8-11kg/m3 http://www.indicaindustries.com/pdf/...tect_g_eng.pdf, and Caruso WLG 035 is 40kg/m3 https://www.gearslutz.com/board/atta...rber-scan.jpeg , so it's not all down to density.

All this is to say -- if you need something that's guaranteed to work, Isobond or Basotect will get you results. If you're willing to take experiment, you can take risks on locally sourced foams, and ultimately the more experimenting you do, the better ultimate result you can finally obtain.

Finally, it has been observed that the damping material should be larger than the plate for optimal performance. (E.g. the sheet of steel is smaller than the foam that surrounds it.) https://www.gearslutz.com/board/9159400-post11.html and https://www.gearslutz.com/board/7319670-post190.html
Old 1 week ago
  #5
Gear Guru
 
DanDan's Avatar
Simple

You are welcome rathabar, I applaud your diligence but I am pretty sure you will not get accurate data of the type you desire. I think that Melamine was a commonly used material, I doubt that Fuchs tried many. Others later found CIB to be better. If one cannot get CIB, I think Polyester with similar density would be a sure bet. If you search the BBC R&D you will find their Zintec whole wall design. Quite a perspective. Also I entirely concur with the comments regarding the EMT plate. Mere proximity of 705 varies the decay over a very very wide range.
Audiothings:-
Quote:
When it comes to VPR, the best thing is that it is forgiving. I find it amusing that people are still breaking their heads over Basotect and Caruso and so forth. BBC published fantastic results with 'zintec' (steel coated with zinc) and rockwool. If you simply see it as a plate reverb working in reverse, it becomes very easy. In a plate reverb, the steel sheet vibrates to create reverb - with VPR, the steel sheet vibrates to absorb reverb. I think EMT used OC705 as the dampener - but I sure many other materials would have worked.
Search for audiothings threads on VPR. I think he shows actual materials and before and after tests and so on.

Some quick thoughts on your questions.

1mm steel has a peak resonance at 80Hz or so. 2.5 down lower, but I get the sense that the thicker plate is much less efficient also. Unfortunately.
I am curious as to the various mounting methods. I haven't seen anyone try a suspension as I have in mind. Perhaps hanging on springs even.

Where are you located. Let's see if there is a local Poly.

DD
Old 1 week ago
  #6
Gear Head
 

Thread Starter
Quote:
Originally Posted by DanDan View Post
You are welcome rathabar, I applaud your diligence but I am pretty sure you will not get accurate data of the type you desire.
Well that's why I'm hoping I can measure it myself!

Quote:
If you search the BBC R&D you will find their Zintec whole wall design.
This is new to me, I'll look for it.

Quote:
Search for audiothings threads on VPR. I think he shows actual materials and before and after tests and so on.
Yes, I included reference to audiothings' efforts in my summary above!

Some quick thoughts on your questions.

Quote:
1mm steel has a peak resonance at 80Hz or so. 2.5 down lower, but I get the sense that the thicker plate is much less efficient also. Unfortunately.
The thicker plate may have a narrower Q, but it reaches frequencies the 1mm simply can't reach so for rooms with issues below ~45hz it becomes somewhat of an apples to oranges comparison. You're simply going to need both.

Quote:
I am curious as to the various mounting methods. I haven't seen anyone try a suspension as I have in mind. Perhaps hanging on springs even.
Theoretically this makes sense. Unfortunately I live in an old building in earthquake country and also don't trust my ceiling joists enough to try it!

Quote:
Where are you located. Let's see if there is a local Poly.
LA, California -- great availability, but the film / prop industry must have sent the market skyrocketing because costs for 4" open cell poly are absurd compared to what I've found online. If anyone has any insight into suppliers that'd be great.

I do happen to have a sheet of 1.5" of this Solid Foam Charcoal Padding Sheets - Open-Cell - FoamByMail.com that I used to line the interiors of equipment cases. Unfortunately I'm not sure it'll be enough to get a really effective test, but we'll see. If I can produce any kind of result I'll be motivated to order a few more panels in the 4" for testing.

I've also gotten ahold of an Isobond distributor that may be able to work something out, but that conversation is going back and forth.
Old 1 week ago
  #7
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DanDan's Avatar
Gut

Just instinct, but I don' think Q is the issue with the 2.5. I think it is just harder to move, so less absorptive. Low absorption has always been an issue, thus the membranes, hangers, etc.

DD
Old 1 week ago
  #8
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Thread Starter
Quote:
Originally Posted by DanDan View Post
Just instinct, but I don' think Q is the issue with the 2.5. I think it is just harder to move, so less absorptive. Low absorption has always been an issue, thus the membranes, hangers, etc.
I seem to recall all the thick plates being reasonably close to 1.0 at their peaks but that could be wishful remembering on my part!

Edit: Finished off first set of measurements then went back to compare and realized I somehow selected a sub-optimal range to begin narrowing my focus. On the plus side I have gotten pretty good at hitting measure, turning on the correct speaker, and running out of the room. More measuring to do tomorrow!

Last edited by rathabar; 1 week ago at 07:36 AM.. Reason: remove items
Old 1 week ago
  #9
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Big

Old 1 week ago
  #10
Gear Head
 

Thread Starter
Quote:
Originally Posted by DanDan View Post
I think the 2.5 deliver Alpha 0.8, while the 1mm goes to 1.14.
https://www.gearslutz.com/board/6532503-post40.html
DD
Ah, not the worst but I remembered it a little better. Thanks for the clarification.

So, some random test results. (images below, MDAT here:https://www.dropbox.com/s/eqlcqtuwmr...%201.mdat?dl=0)

Pleased to report the plates are at least doing something! Not knocking back the ~35-45 hz area as much as I wanted, but there may be some reasons for that:

This was a total of 3 plates, straddle "mounted" (read: leaned) in the corners, against ~60cm of Auralex (2 corners) and a few random scraps of 30cm poly foam (1 corner). No adhesive, plates and foam were not in complete contact with the wall or each other, basically just me trying things out to see if they made any difference at all while trying to make sure I didn't crush myself.

These were all the heavier 12 GA / ~2.8mm thick plates.

Consistent with GE, I also found the straddling superior to laying flat on the wall. (You can see that measurement in "2 Flat"). Although the laying flat did not alter the frequency response nearly as much.

Now, questions/comments for the group:

  • Introduction of the steel did some interesting things to the SPL graph.(Green is empty room.) Thoughts? Something that may change with proper adhesion/mounting? Edit: in thinking about it, it's possible part of the steel is now in a first reflection point... Would that have that impact?
  • On the foam front, I have been talking to an Isobond distributor who is open to trying to get larger panels from Caruso (~1m x ~1.5m, a little larger to account for US common dimension of 60" x 40"). They're reaching out and I'll keep folks updated as I hear more. Have also placed an order for some 100cm Poly blocks, that will hopefully arrive sometime next week.
  • Can anyone who has worked with Basotect tell me if you're able to roll it up without damaging the material? Or is it more rigid?
  • Finally, anyone have any mounting ideas/suggestions? I'd really love to build a perforated face/frame to enhance the broadband capabilities. Anyone have good resources for those?
Attached Thumbnails
Treating Space + Panel Experiments-screen-shot-2017-10-09-9.41.30-pm.jpg   Treating Space + Panel Experiments-screen-shot-2017-10-09-9.41.15-pm.jpg   Treating Space + Panel Experiments-screen-shot-2017-10-09-9.40.59-pm.jpg   Treating Space + Panel Experiments-screen-shot-2017-10-09-9.40.51-pm.jpg   Treating Space + Panel Experiments-screen-shot-2017-10-09-9.40.06-pm.jpg  

Treating Space + Panel Experiments-screen-shot-2017-10-09-9.39.45-pm.jpg   Treating Space + Panel Experiments-screen-shot-2017-10-09-9.39.22-pm.jpg  
Old 6 days ago
  #11
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barbaroja's Avatar
 

Subbed. Thanks for the brief about VPRs.
About foam... My gut feeling is that the formula used to calculate the resonant freq is somehow adapted to minimal conditions or a certain type of material. That may confirm what Dan posted about Isobond and Basotect having such a different density. I feel that for this type of panel, the elastic or Young modulus should be of importance due to the proximity of the panel to the foam. Don't quote me on this, as I say, it's just a gut feeling
Old 6 days ago
  #12
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DanDan's Avatar
LF

@rathabar, some observations which I hope will be helpful.
I would assume the Lowest Mode, the Length, is the one in the 30-40Hz region.
They are usually very long and often loud too, but not at all in your graphs. I wonder is that because it is unusually weak, or is it because your LF drive is much lower than the rest of the spectrum? It would be difficult to achieve successful treatment if you do not have an actual problem! Note the considerable success with your graphs presented differently below. Note also that the height mode is the least successful. I would bet if you place one on the floor or the floor wall corner, this would change. Gernot has probably already tested this, but I would have thought that the best place to trap the lowest mode would be in the middle of the short Front or Back walls.

DD
Attached Thumbnails
Treating Space + Panel Experiments-screen-shot-2017-10-11-23.52.41.jpg   Treating Space + Panel Experiments-screen-shot-2017-10-11-23.52.36.jpg  

Last edited by DanDan; 6 days ago at 12:02 AM..
Old 6 days ago
  #13
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Thread Starter
Quote:
Originally Posted by DanDan View Post
@rathabar, some observations which I hope will be helpful.
I would assume the Lowest Mode, the Length, is the one in the 30-40Hz region.
They are usually very long and often loud too, but not at all in your graphs. I wonder is that because it is unusually weak, or is it because your LF drive is much lower than the rest of the spectrum? It would be difficult to achieve successful treatment if you do not have an actual problem! Note the considerable success with your graphs presented differently below. Note also that the height mode is the least successful. I would bet if you place one on the floor or the floor wall corner, this would change. Gernot has probably already tested this, but I would have thought that the best place to trap the lowest mode would be in the middle of the short Front or Back walls.
This is helpful, thank you!

Given the asymmetry of the room (~35% opens up to a longer area as seen in the attached photo, taken from the perspective of the front wall "behind the speakers"), and relatively light walls, perhaps that could play a part in producing a weaker signal. Or the speakers may not reach down well below 40hz.

I do have a random hi-fi subwoofer that I can try to figure out a way to drive with REW to see what happens. I'll also try some tri-corner speaker position testing with the speaker on the floor to see if I can make things any worse.

In testing I did try one plate at the "closer" back wall and it didn't have as much effect as the ones in the front/corners did, but I'll see what a panel in front of the "2nd" (farther one) does next testing session. Will also try one on the floor (although that was my very first test and IIRC it did almost nothing causing me to panic!)

My second batch of thicker Auralex arrived today so I can add a few more panels to the testing batch once it is sufficiently offgassed. It's soaking up some rays outside right now.

My only real holdup at this point is figuring out a permanent mounting solution & finding more panels, although you have potentially uncovered another source with your Autex recommendation in the other thread, Dan! I canceled my order of cheap Poly upon reconsidering my willingness to surround myself with fire accelerants. Would effectively be doing this: Foam on Club's Walls Was Decorative Packaging - The New York Times Definitely not worth a couple hundred dollars!
Attached Thumbnails
Treating Space + Panel Experiments-room2.jpg  
Old 5 days ago
  #14
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DanDan's Avatar
Symptoms

If you do not have problematic 40Hz action, I reckon lighter steel would perform better in your room.
Mounting is clearly a thing. There are a few VPR threads here. Check out audiothings and UKMastering in terms of actual working units with measured success. I would like to see how Renz mount the plate.
If I ever try these myself I will certainly try some sort of hanging system.

DD
Old 5 days ago
  #15
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Thread Starter
Quote:
Originally Posted by DanDan View Post
If you do not have problematic 40Hz action, I reckon lighter steel would perform better in your room.
Mounting is clearly a thing. There are a few VPR threads here. Check out audiothings and UKMastering in terms of actual working units with measured success. I would like to see how Renz mount the plate.
If I ever try these myself I will certainly try some sort of hanging system.
Your instinct was correct, Dan -- I set up an empty room comparison between subwoofer (red) and speaker (tan) in the corner with the mic in the opposite corner and the speaker is quite anemic in the low end. On the plus side, now we'll be able to see if these plates really do reach down to 40!
Attached Thumbnails
Treating Space + Panel Experiments-screen-shot-2017-10-12-3.19.42-pm.jpg   Treating Space + Panel Experiments-screen-shot-2017-10-12-3.19.58-pm.jpg  
Old 2 days ago
  #16
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Thread Starter
Good news is the plates do go sufficiently low. This is a tricorner setup with sub in bottom corner one, 12GA plate straddling corner 2, and mic in top corner 3.

Don't see much point in further testing until I can get the absorbent and mounting squared away.

On that front, one thought I had -- open cell spray foam. Has anyone experimented with something like this?

https://sprayfoamkit.com/products/open-cell-spray-foam/

12kg/m3 (close to Basotect), solves the adhering to the plate issue (it's sticky), fire rated, and very cost effective -- 300 sqft @ 100mm rise for $900. Comes out to roughly ~$60 per panel for 16 1 x 1.5m panels.
Attached Thumbnails
Treating Space + Panel Experiments-screen-shot-2017-10-15-10.49.45-am.jpg  
Old 2 days ago
  #17
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Please keep these coming. Nice
Old 1 day ago
  #18
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Quote:
Originally Posted by barbaroja View Post
Please keep these coming. Nice
I hope to but I'm really struggling to find a suitable damping material! Based on my informal testing I'm pretty sure the Auralex doesn't work as well as other materials (I recall some Eric Desart, RIP, posts from a while back that suggested as much, but I wanted to see for myself) as a VPR "spring".

Unfortunately that's the only material I have access to in substantial quantities. I've sent out a bunch of emails trying to source melamines/polyesters but no concrete replies so far.

If anyone has any leads or suggestions, I'm all ears!
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