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johndykstra
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1st April 2011
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FWIW,

to draw the panels. I saved an RPG template as a jpeg, and used it as a "fill" to paint on a square in sketchup. The result is a multi-tiled repetition of the design. Dummy me, I misinterpreted the tiling, and as a result, the panel is drawn wonky. In the original design for the bad panels, you will notice a solid row of holes down the center. In my rendering, this row is absent, and what should be the left side of the sequence is on the right, and vice versa. Also, the bottom row of the sequence is on the top

D. I. Y. Polys-flipped.jpg Name: flipped.jpg Views: 216 Size: 508.8 KB ID: 228123" style="margin: 2px" /> D. I. Y. Polys-rpg-pattern-full-size.jpg Name: rpg-pattern-full-size.JPG Views: 542 Size: 214.1 KB ID: 228124" style="margin: 2px" />


Well. My gut tells me i would need to build the panels following the proven pattern. But, having studied it, the RPG pattern is uglier, and I plan to leave the panel exposed, and not covered with fabric. It may seem shallow, but the full row of holes down the center of the RPG design really detracts from the aesthetic... and at the same time creates a very flimsy fault line, as my masks are being created from 1/8" finished luan, as opposed to mdf.

Gotta chew on this.
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1st April 2011
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Won't the colour behind the panel affect the aesthetics as well? Just put an acoustically transparent suitably coloured fabric behind the panel. This will improve the look.
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2nd April 2011
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Hey Sebg,

The panels are already covered in a "carpet" of sorts... grey in color. It's not really carpet, as it's practically see through. Very breathable.

I want to keep this fabric, as there will be two panels (the ones closest to the corner with the drums) that are going to remain unfaced. Aesthetically, it makes sense to place the carpet layer over the mask on a few other panels as well, to keep it from looking hap-hazard.

Ideally, the panels would be reversible, to provide options. The way they are currently mounted prohibits this, but I'm giving it some thought.
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4th April 2011
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The panels and their being reversible is great. Bear in mind that as you add diffusion, the room will become drier.

Andre
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Add anything to a room and it will absorb more or less, except for maybe stuff like this:

http://www.synergisticresearch.com/i...RTHomePage.jpg

But a diffuser will, if correctly manufactured, at least absorb as little as possible (while naturally it can still be a considerable amount which shouldn’t be ignored) but considering the positive effects (the diffused field) it’s usually worth the trade of, at least if there’s temporal diffusion going on as well as spatial.


EDIT: But Andre is absolutely correct in the fact that diffusers can absorb quite a lot and especially deep, fined, phase grating diffusers with narrow wells (and even more if not sealed properly).

Last edited by Jens Eklund; 4th April 2011 at 05:34 PM..
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Quote:
Originally Posted by Jens Eklund View Post
Add anything to a room and it will absorb more or less, except for maybe stuff like this:

http://www.synergisticresearch.com/i...RTHomePage.jpg

But a diffuser will, if correctly manufactured, at least absorb as little as possible (while naturally it can still be a considerable amount which shouldn’t be ignored) but considering the positive effects (the diffused field) it’s usually worth the trade of, at least if there’s temporal diffusion going on as well as spatial.


EDIT: But Andre is absolutely correct in the fact that diffusers can absorb quite a lot and especially deep, fined, phase grating diffusers with narrow wells (and even more if not sealed properly).
I was stunned when I first read the above post. The attribution to my remarks about absorption and 1/4 wave absorption are basic acoustics. Thank you for revising your post to make it more acoustically accurate.

I am afraid that your
Quote:
a diffuser will, if correctly manufactured, at least absorb as little as possible
will be misquoted by others because it sounds logical.

Andre
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Quote:
Originally Posted by avare View Post
I am afraid that your

...

will be misquoted by others because it sounds logical.


It is actually true; a correctly designed and constructed diffuser should absorb as little as possible (in the effective bandwidth and above at least).
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4th April 2011
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Quote:
Originally Posted by avare View Post
The panels and their being reversible is great. Bear in mind that as you add diffusion, the room will become drier.

Andre
really?

huh.

I guess I figured adding 64 sq. ft. of reflection and subtracting 64 sq. ft. of absorption would brighten the room. (minus a few 1000 holes of course)

having gone through my ply supply, I would cover all of the panels with fabric. I already exhausted the pretty sheets on the polys.
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If you’re replacing absorbers with diffusers, it will (almost) certainly add to the decay times (life).
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4th April 2011
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Ok,

Well, the absorption will remain, just facing it with amplitude gratings.
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5th April 2011
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Any diffusor (not speaking about the BAD diffusor but conventional - time domain - diffusors) is a considerable absorber too, simply because you offer a lot of surface to the sound. A lot more than when using flat panels or polys. This is relevant for the later sound field that is more diffuse than the first impact.

One might think that this absorption should perhaps not be the case if the diffusor is made from wood or the like. However if we look here

Coefficient Chart

we will find that wood can be astonishingly absorptive. As an example plywood will have a typical absorption around 0.2 which does not sound like much but that means it reflects 2 dB less than what it receives.

Now if you offer more surface with a diffusor (say two times for a finless model or at least four times the surface with fins) then the absorption will be in the range of 4 to 10 dB which means absorption of roundabout 35 to 70 % ... quite a good absorber already.

If you don't like too much absorption then finless diffusors are in advantage, and 1D models are better than 2D models.

Now it is understandeable why RPG not only submit absorption data for their diffusors (red line in the attached picture is valid for their wooden model QRD 734) but also market fabric coated diffusors as absorbers. I bet they were quite puzzled when they found out but turned their findings to their advantage.

RPG Diffusor Systems
Attached Thumbnails
D. I. Y. Polys-qrdacousticaldatachart.jpg  
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Last edited by Hannes_F; 5th April 2011 at 12:29 AM..
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Last edited by Jens Eklund; 5th April 2011 at 12:37 AM..
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Quote:
Originally Posted by Jens Eklund View Post
I was going to link to the exact same chart while saying that approx. 0,2-0,4 is common absorption coefficients for diffusers (1Ds).

Acoustic absorbers and diffusers ... - Google Böcker
+1

Here are the absorption coefficients for the 2D Omniffusor (a little higher than the 1D model as expected) and the Abffusor (the fabric coated model).

My estimation above was only rough of course but it is good to be in the same ballpark with over-the-thumb calculations and measured data ... means we are prinicpally on the right trace.
Attached Thumbnails
D. I. Y. Polys-2d_abs.jpg   D. I. Y. Polys-abff.jpg  
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Side remark about diffusors:

Quite some people see pictures of diffusors used in studios, build some and are then astonished that they can not hear them.

Obviously they expect the diffusors to do something magic to the sound (I admit that I have been there as well).

The point is however that usually you don't want to hear a diffusor (in a control room situation, this changes in a tracking situation).

With other words, at the place where you had an ugly concentrated reflection before you avoid this by placing a diffusor there. Basically the same effect like with an absorber, except that it does not cost so much sonic energy and lets the sound live longer.

A diffusor is a problem solver. It makes the wall behind it 'invisible'. That is what it does. No problems -> no diffusors.

The only case where you perhaps can and want to 'hear' a diffusor in a control room would be if your room is already highly absorptive (for example a non environment room or a FTB room). It seems that in this case diffusors are supposed to add some orientation reflections but others are certainly more qualified to talk about that than me.

As I said this all changes in a tracking situation.
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Overlooked in the discuusion of diffuser absorption modes, as in physical manner the absorption occurs, is the 1/4 λ muffler effect of the wells acting in a tuned resonator manner. More starting at pdf page 41 in the attachment.

Resonantly,
Andre
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Well now I'm totally confused.

I would expect my panels are not a tuned device. Currently, they consist of this sandwich:

breathable fabric
2" 703
breathable fabric
1" air gap

my alteration would be

breathable fabric
binary amplitude grating
2" 703
breathable fabric
1" air gap


Understood one should expect some amount of absorption loss on the reflection. Particularly in a diffuser that is more complex (thin wells) or deep, or consisting of more surface area. This all makes perfect sense.

I wonder if the thread has not taken a tangent on general behaviors of diffusers (that's fine of course), while forgetting that my suggested treatment is neither complex, nor deep, nor excessively surfaced. So the face of the mask should provide .2 absorption. I would expect with all the holes, there's a certain amount of diffractive loss as well. Despite all of that, I can't imagine the absorptive losses can possibly match or exceed the absorptive characteristics of 2" 703... at least not in the 1k and up range... the range I'm seeking enhancement of.

My goal is a variation of an already quite excellent recording space. I've found, that while tracking acoustic instruments, some quite drum passages, percussion,...etc... I wish my room had a bit more sonic imprint in the recordings. Currently, the RT60 of the room measures nearly flat at .2 (five mic and two speaker locations) with no variance below .1 and nothing above .3 I have a lot of data on this room. But out of respect of the forum member who aided me in calculating the data, I'm opting not to provide the graphs until I get his permission.

I'm quite happy with the space. If the addition of amplitude gratings to the face of my absorption were to impart some life (added RT60 above 1k) it is a task I would find easy and importantly, free. If the solution is to design "simple" temporal diffusion, honestly I'd just as soon leave well enough alone and continue using a dry space, and heading toward the stairwell when I desire room as an effect. (understood that 8 binary masks will never create the same room sound of a stairwell... I just want more options. The stairwell will still be there.) Something in between "dry" and "effect" would be a welcome tool.

Now, I'm off to brainstorm a swing/hinge mechanism to allow these panels to be reversible. Without this capability, I'm not comfortable with loosing my dry ability.


Thanks guys, and by all means, please continue the discussion.
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panel reversibility mounting #1

D. I. Y. Polys-latch-1.jpg D. I. Y. Polys-latch-2.jpg

pros:

affordable
sturdy

cons:

time consuming change over
no ability to alter panels angle to wall
requires precise installation of latches
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panel reversibility mounting #2

D. I. Y. Polys-pivot-1.jpgD. I. Y. Polys-pivot-2.jpg

D. I. Y. Polys-pivot-3.jpgD. I. Y. Polys-pivot-4.jpg

D. I. Y. Polys-pivot-5.jpgD. I. Y. Polys-pivot-6.jpg

pros:

angle flexibility
even more affordable
quickly adjustable
would require a larger air gap (see below)

cons:

time consuming (router work is not my strong point)
while quicker than the latch method, this too is likely to be "clunky" changeover
somewhat flimsy/ prone to scratching
would require a larger air gap, because of panel's proximity to each other, to get a panel to flip, I would need more angling ability. This would require some calculation to determine spacing/gapping to allow enough range of motion to accompany the transition.

Last edited by johndykstra; 5th April 2011 at 10:22 PM..
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What a beautiful versatile concept!

Andre
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Thank you Andre.

Here's a refinement:

D. I. Y. Polys-pivot-refinement.jpg

It occurred to me, that simply increasing the air gap wouldn't fix my panels inability to slide side to side fully, as not only would the panel next to it be an obstacle, but because my panel heights are staggered, the bracket would be too.

To solve this, I would need to arc the brackets to achieve the clearance. However, in doing so, the panels are far more susceptible to tilt, or coming off the rails if you will, because there isn't as much horizontal bracket surface to keep the panel vertical during transition. As a fix, I would attach the top hinge through the bracket, and mounted to a removable plug. This way if the panel does come off the rails, I could relatively easily remove the top hinge to remount the panel
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panel reversibility mounting #3

D. I. Y. Polys-wing-nut-1.jpgD. I. Y. Polys-wing-nut-2.jpg

D. I. Y. Polys-wing-nut-3.jpgD. I. Y. Polys-wing-nut-4.jpg

D. I. Y. Polys-wing-nut-5.jpg

Pros:

widely variable angles and depths of air gap
easiest in terms of manipulation
simple execution of design

Cons:

duribility?
by far the ugliest of designs yet
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very impressive !!
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Sometimes I wish I were the kind of person that would be satisfied with a long length of picture wire and a screw in the wall, and simply flip it over. Done and done. However, I'm the guy that comes to practice and takes care of all the recycling, sweeps the floor, and you know... generally gives a $hit how things look. Life could be much easier if I would let it.
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panel reversibility mounting #4

D. I. Y. Polys-chains.jpg

(not shown- "s" hooks)

Pros:
CHEAP
EASY
I've always liked the 'hanging from chains' look, though our space doesn't really fit the S&M aesthetic

Cons:
no angle adjustment
not in a metal band



I really would like angle ability, as I've been told that these (bad panels) tend to behave rather specularly when the incident angle is increased.

Also, worth repeating. My walls have a layer of 5/8" mdf under the drywall. This allows me to hang nearly anything, nearly anywhere.
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8th April 2011
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Attached is the pdf binder of analysis provided by Jeff Hedback.

There are 5 measurement locations, a close, mid, and far mic from a speaker in the drum corner. And a mid and far from the opposite (organ) corner. Unfortunately, I neglected to realize a 1k notch engaged on the test tone channel strip during capture. Jeff and I are executing a new capture soon, but thought I would share this in the meantime.

A big thanks to Jeff, he's a top notch dude.

Binder1 J Dykstra TR Acoustical Data.pdf
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18th May 2011
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Happy accident

Well not an accident really, but a discovery based on necessity. We have always located the drum set in the "dead" corner of the room, as it seemed the obvious location. Recently, we had a new resident move into the house (duplex), and he wanted to set up his drum kit as well. Being ones never to turn down more instruments, we set up his kit under the secondary small cloud in the "live" corner... very poly heavy. It sounded incredible. So, well, lively. So good in fact, that we've taken to using this corner for drum recording. Here's a few shots of a session we did recently of a friend's band. Also shown, is our make shift "control" station while we work in the attic for the new control room.

D. I. Y. Polys-recording-mr.-hawk-fight-kit-close.jpgD. I. Y. Polys-recording-mr.-hawk-fight-kit-close-2.jpg

D. I. Y. Polys-recording-mr.-hawk-fight-kit-far.jpgD. I. Y. Polys-recording-mr.-hawk-fight-kit-far-2.jpg

D. I. Y. Polys-recording-mr.-hawk-fight-mix-position.jpg
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18th May 2011
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Great! Thanks for sharing with us your experience.

Slightly OT, I am pleased that you share with us your experience with polys in a small room. It is difficult to explain to people the effect that they have, even in samll room.

Andre
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Awesome! Really nice polys and I think I'm gonna try to rip off one of the suggested constructions of the reversible panels for my small project studio. Would be a perfect choice for a part of the wall where I want a surface reflecting to the back when mixing and sometimes an absorbent surface when recording in the same space. Many thanks John.

.christian
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25th July 2011
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I'm glad the reversible panel assembly gave you some inspiration. As it turns out, I don't think I'm going to worry about it.

This project is just underway though:

D. I. Y. Polys-babyblue.jpg

As I think I stated before, the plywood that I have remaining after the poly construction is rather "ugly"... bad knots, weird seams... I was going to just put it under the fabric, but doing all that work to never be seen is such a waste.

I've decided instead to flip the wood over, and prime and paint it. Yesterday, I wood puttied all the cracks and knots, sanded, primed, sanded, primed, sanded them. I want these babies smooth as glass with a high gloss top coat. The powder blue face, with the wood reveal in the holes, and the grey fabric... I'm hoping these look really killer all said and done.

After installation, if the room proves "too live" for some applications, I may revisit my hinge mounting, but I doubt it will be necessary.
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16th November 2011
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Hey.

Anyone thinking of building their own bad panels: Don't.

Related, anyone thinking this is clever tool, it's not:

Drill Guide and Chuck-36/37 at The Home Depot

Piece of monkey $h!T. After countless hours of prep: painting, drawing the grid, mapping the hole pattern.... this "tool" drills about as accurately as a wild guess from a blind man. The rods have too much flex and the harness slides like poop on 'em and the chuck has a ton of play in the bearings. A little play at the chuck translated to the end of a 6" long bit... Oh. Then it ceased up completely.

I first attempted an oak block with a cross hair, and 1/2" hole through the center to aid me in drilling straight through all the panels. That was going gang busters until it wore out after ~20 holes... that when I bought that thing.

I still plan to see this through, but after a few crooked holes, my excitement level has dwindled to "near unmeasurable".

I plan to build a similar jig as the first wood block, but with washers countersunk into the wood. Will probably wear the drill bit out quick, but.... I 'm at a loss at this point. Maybe I just need 100 more oak block jigs.
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