Hi
This is the first post in a build thread. I'm building a rehearsal sometimes also a recording room, at least for drums. It's about 700 sqr feet or 60 sqr meters. I'm going to use an insane amount of VPR's and diffusors. VPR's to do the improbable case of increasing absorption the lower you get, and diffusion just because I like it and a Live room should preserve energy, not waste it with absorption. So I have ordered 175 cubic feet of Caruso Iso-Bond to be used both as a velocity absorber with low kPas for ceiling and back wall, and higher kPas for use in VPR's on the walls. Caruso Iso-Bond is fleece wool which has enourmous strength so when glued to a metal plate it can hold it, without tearing. Let's see how it goes. Since I'm in Europe I'm so lucky that I can buy this directly from the factory in, as always Germany.

Do you have a question?

The WLG-045 is best for deep porous absorbers, i think about 3k rayl; about 50cm of it is the most efficient, gets you absorption down to 50Hz easily.

If you want even lower absorption, with porous, we're talking about 1m of 1.5/2k rayl material, however I have not yet come across sourceable material in the BeNeLux with that low GFR.

Tom, polyester filling (Polyester-Füllung in German), aka Dacron, the best known brand of polyester filling, has a GFR in the 2k rayl region, eg. see here.

Top, I was not aware that Dacron was the common name for these, the examples are from NZ, but you have experienced similar GFR numbers from the Dacron sourced in Europe?

Diffusion has a not unsubstantial amount of absorbsion, which needs to be accounted for.

Getting tuned membrane traps correct is not a particularly easy task and should be handled by a qualified professional or experienced non professional, unless experimentation is the goal.

I don't really have questions yet, it's just a build thread. I know about flow resitivity and all that stuff, and diffusor absorption etc. I imagine the questions will pile up later... A VPR is not a tuned trap, just so that is clear. I'm on my own so experimentation is the rule of the game. A room covered with VPR's and diffusors is not a room I've seen built here before? Or?

Thx, I'm gonna use this stuff on the back wall and the ceiling, WLG 40 on back wall and 45 in the ceiling, as a bass/ sub bass absorbers, with a lot of air behind them, like about 1,2m. I've done the modelling in Pourous Absorber Calculator, Multi Layer. I'm gonna use 2 layers of these with air gap in between to get the best result. The room is 205kubic meters so I mostly need the lower part absorbed.

I have a room plan, but I don't know how to show it???? New in here, kind of...

VPR
"This Absorber technic is invented and well documented by the German Fraunhofer institution. The VPR Absorber is made with a Don Caruso WLG035 100mm thick porous absorber panel and a steel plate. The Absorber thickness, the steel plate size and thickness plays a role and is calculated to have most effect on your target frequency. "

https://www.don-audio.com/Acoustic-room-treatment-guide


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The reason you don't see rooms covered with diffusion and VPRs is because it would leave a gigantic hole between the effective range of the VPR and the lower limit of diffusion (which is shroeder frequency at best).

You would not have enough surface area to manage the entire range below the diffusers limit, even if one knew how to calculate the array properly according to the modal distribution and strength in the room.

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It's best when learning to stick with the fundemtals, and forgiving methods if one wants near guaranteed decent results. The basics cover so much ground. It's moving from 'good' to 'better, or great" that takes knowledge and experience.

If your goal is to experiment and learn with end result taking the back seat, by all means follow thru on your idea and the necessary additional treatment it will take. Or stick with simple tried and true, and be much more confident that the end result will be good.

My polyester filling is a different brand, Vatelin Fobos, it weighs 150g/m2 at 2cm thick, which makes it 7.5kg/m3. I didn't find the brand Dacron by DuPont in Europe although that does not mean it is not available in Europe.

As for GFR, I had made a note that it ranges from 2.0 to 2.7 rayls/m but I didn't make a note where I had come across that, so no, I cannot prove my comment.

Have a look at posts 165-172 in the topic Common Gas Flow Resistivity numbers as capoeira made a number of interesting posts regarding PET (polyethylene terephthalate), which is what Dacron is.

If I have 1200x3600mm arrays or larger of Jens Eklund's Optiffusor they will go down to 300Hz according to his measurments. A 1mm steel plate VPR will absorb that high, but not much under 70Hz, if I remember correctly, (have to double check), 1,5mm maybe not, 2mm steel place absolutely not. So the gigantic hole from range of VPR to lower diffusion limit might not get to be so big
It's a LIVE room and not a control room, so decay in bass and controlled return from mid range and up, is a priority, even frequency respons in a given spot is not a priority at all. I will build it as planned and take it from there... i will have some wheeled/mobile velocity based absorbers to test with to. So I have material for 7 x 1,25 to 1.5m wide and 2,5-3m high VPR's and 3 full peiod 1,2x3,6m diffusors. Might not get to be perfect but it wont cost mpre than 5 grand...

As I can understand VPR's from inventor used Iso-Bond because of strength and it's used to dampen physical movement of the steel plate. Air flow resistivity don't matter as I can figure out. I cut an 1 x4 inch strip of this stuff once and thought it would be easy peasy to tear it in 2 pieces, no f...... way. Strong as a tank. The producer calls it fleece wool, so it must be the same chemical stuff as fleece used in clothing.

It would be interesting to see the absorbsion coefficient of the unit across the 70-300hz range.

If decay in bass is a primary concern you need to treat under 70hz. Kick drums range from 40-60hz as their fundemtal and bass guitar can dip below 40hz.

This is why broadband absorbsion is a popular choice in conjunction with other means of treatment.

I highly recommend you discuss with Jen's about how to best integrate your diffusers.

You currently have enough to cover a bit more than a standard size piece of drywall. At 400hz they'd need to be located over 10' away from the mic/source to diffuse properly if they work like most diffusers. I don't own his products but from my experience here he's very knowledgeable, and a great resource.

Lack of treatment under 70hz is a gigantic hole, and what typically is associated with a boomy room.

I hope not to sound discouraging, but rather encouraging to investigate further since there are some very apparent red flags in your current plan.

I don't see how to post pictures here, so in text follows..
On the lower half of the back wall (sloped ceiling) 1.8x6.6m, I will us 5000kPas IsoBond, 5 cm 1,3m from back wall, then 10cm Isobond 40 cm from back wall. The front 5 cm part will be mounted as sliping doors so the inside space will be used as storage.
In part of the ceiling/low attic 2,4mx6.6m full width kPas 3000 IsoBond WLG-045, 10cm on ceiling, 30cm air, another 10cm Isobond then 30-80cm to underside of roof. Last 2 absorbers will be mobile screens 1,8mx1,8m 10cm Isobond 5000kPas fronted with light EPS diffusors, placed diagonally in front of front wall corners, approx. 1.2-1.5m from corner, containing things I have to keep, namely window and doors.
As always excuse any lyrical deficiencies describing a driving in words...

These are all sub-bass/bass absorbers according to Pourous absorber calc multi layer.

Hopefully these will make decay and resonnances beetween 45 and 80Hz good enough, not great but good enough. If there still is major problems in this area, it'll bite me in the tail and I will have to use thicker plate VPR's on the wall, which makes them absorb lower in frequency, but also less because thicker steel plates requires higher volume before they apparently seem to work. Wall VPR's will ideally be 1mm plates to to work in 80-250Hz area, this mid-upper bass range is my highest priority, I'll trade a 100-200hz decay problem with a 40Hz decay problem any day, if held at gun point.

the air gap extend the lf cut.
the air gap degrades performances above the lf cut.

measures is the judge.

The air gap is a price and space compromise, between 40-100hz effectivness was the priority.

the air has never attenuated the bass frequencies..
between 40 and 100 Hz, it is useless. if you have chance you extend the lf cut but with a poor result.
the absorption will always be around the maximum of the cycle - all the room is concerned - can you predict it?

where is the Space compromise with an air gap?

for the price compromise, you reduce the thickness without air gap for the space compromise.

Drawings of room attached

It looks better with air between absorbers in pourous absorber calc, if you split a total amount of 20cm absorber available with kPas 3000 with air inbetween. Its also better than only one 200mm absorber, its even better than 400mm absorber, aka absorber covering the whole first air gap.
Red is air gap, blue is 20cm continious absorber, green is 40cm continious. I have anyways already bought only 20cm for a size of 2,4mx6,6m so it's a done deal.

For the other back wall absorber, you see from the drawings, air gap works as storage room, a space compromise. This also measures good, a little better than the ceiling in mid bass, otherwise pretty equal.. It uses 5000 kPas, as you can see in the second screendump, red is the red from the ceiling, backwall is a little better with 80cm of air space between absorbers and then 5000kPas instead. Velocity maxima from surface for different wave lengths explains this, one far from wall and one closer to wall spreads the absorption out in frequency...

it looks bad. have you seen the size of the ondulations before the lf cut frequency?
it means : no work.

advise: Only build absorbers where the AC curve looks very even.
Air gaps should never be larger than the depth of absorbent material, there is a limit to how much lower in frequency you can make an absorber absorb with an air gap.
Example on 400mm absorber: http://www.acousticmodelling.com/mli...&s22=1&d22=350

Okay I didn't know about that problem! Is there anywhere I can educate myself on this? What problem does it make, how does it sound like?

This chart from build it like the pros edition 1, shows the old OC tested, and includes a set of measurements using 16" airspace. It can be compared to the measurements with it flush mounted.

Thx, so old OC much better, as expected! Other than that the others incl 16" airgap seems in the same ballpark? The airgap would show results below 125Hz. Do build it like a pro advise against using a 16" airgap?

The largest air gap I've heard of so far for 4" semi rigid material was Galaxy Sound using 4" with an 8" air gap. I'm not 100% cuz I wasn't there but did read it from a credible source.

Rod doesn't make any recommendation afaik about whether to use the gap or not. I think 16" was chosen because it's a common deapth for a drop ceiling. Rods deep bass trap is filled with fluffy. His corner Helmholtz is an empty cavity about 19" deep, but the frame is filled.

If you really want have an effect on the lower frequencies you really need a deeper, lower GFR material. 4" of 703 is usually used for broadband treatment not bass. The exception would be using it straddled across a corner. But even then there's better options for cheaper.

12" of 5k GFR material with 12" airspace is very good bang for the buck, and 24" of 3k material is a very high performance solution with very simple implementation.

Thx Kyle...... I have 3kPas material but not enough. So I have an absorber that does not have a flat AC curve as advised, but they are flat around 50-120Hz where I need them. I can try an model a solution with flatter curves.... These absorbers are away from the live end so what they do above 150Hz will be overshadowed by the diffuse return of closer walls. If I was sitting in a mix chair with these 5 feet away, case would be different. I can partially cover them with something to return some over 150-200Hz. This problem is not mentioned in F.A.Everest book or Kleier/Tichy, I will check Tools book ++ later. I have an 4" absorber hanging 24" in front of a window, works wonderful. All the worlds 16" suspended ceilings will have this problem and rendered not working? Is there no proof of this in text somewhere???

Back wall in fixing mode, so called isolation camp ������
All the old-timer English GM cars are still not out yet....

Haha, Desart used a 1:4 ratio (absorber : gap) f.e. in the Galaxy.
And a suspended ceiling with 25 mm compressed wool and a 400 mm plenum is by far not useless in most cases.

in this business that used the yam ns10 as opposed to the instruction manual and found it smart and good, nothing surprises me anymore.