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RPG Bad Panel -- Detailed Plans
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#31
6th February 2010
Old 6th February 2010
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The caveat above(also stated in the wiki link) would hold true for 2D binary diffusion as well.. IF... the big if, it was a construction with two layers of reflective surfaces. This is not. It's one layer reflector, one layer absorber. A different sort of animal!
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#32
6th February 2010
Old 6th February 2010
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As Lupo suggested, a hybrid surface is different. It can be used to absorb low frequencies and provide some combination of diffusion and reflection for higher frequencies. The BAD panel (which is based upon a 2D binary MLS) does exactly this. A BAD Panel with a 4 inch absorber absorbs well into the bass frequencies while providing moderate diffusion all the way to the upper limits of human hearing.

A 1D hybrid surface seems to be more limited. However, it can provide the same double punch of low frequency absorption and high frequency diffusion and/or reflection. The one I just built should diffuse from 1Khz to 4.5 Kz, absorb below that, and reflect above. Of course, theory and reality are two different things, so we'll see how it goes I guess. One thing I have noticed already is that the reflective slats cause the trap to resonate. The resonating is not audible, but it can be felt if I put my ear right up against it. I guess it could be resonating at the frequency where the bass begins to pass through the reflective patches, although I am not really sure. The combination of slats in and of itself probably produces a resonance too. So like I said, we'll see how it goes. But I'm thinking that resonance in combination with 17 inches of absorption probably isn't a bad thing, since the absorption is sucking all the energy out of the resonance before it can travel back into the room. But if my opinion on this changes at some point, I'll redo things, as it could well be resonating a frequency where I do not need the absorption.

EDIT: After more consideration, it appears that my homemade 1D hybrid absorber/diffuser is not the source of the resonance at all. As it turns out, it's the wall of my room that is resonating and communicating some of its energy into the panel. Compared to the actual wall, the panel is hardly vibrating at all.
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#33
8th February 2010
Old 8th February 2010
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Update: Okay, well, if I put my ear right up to one of the reflective patches on my hybrid 1D diffsorber, there is a definite resonance coming from the panel itself. Of course, with my speakers pumping, everything in the room is resonating, the walls much moreso that the panel. But what concerns me is that these hybrid diffsorbers are straddling corners and I fear I may be messing up my much needed bass absorption there (I really need it below 500hz). They are 100% absorptive on the bottom half of the corner, and hybrid diffsorber/abfussor on the upp half. I'm concerned that the reflective patches are resonating and potentially ringing. Of course, they are sitting over 17 inches of insulation straddling a corner, so I can't imagine they are releasing that much energy, but who knows. That corner is certainly much more alive than the other one, in which I've not done the reflective patches yet (the other corner is basically a super chunk.)

I guess the only way to know for sure what's going on is to measure. But my room is a total mess right now, and there's no way to measure with all the construction stuff everywhere.
#34
25th March 2010
Old 25th March 2010
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Did anyone ever try building a 2d based on the attached, and if so, did you find an economical or easy way to cut holes in the 1/8" mdf? I imagine you could just use a box cutter (X-Acto knife), no?

I know a laser engraver can alternatively cut 1/8" mdf. eg. Canadian Laser Engraved Products Maybe that would be easier to hire depending on what they charge.
Attached Thumbnails
RPG Bad Panel -- Detailed Plans-rpg-bad.gif  
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#35
25th March 2010
Old 25th March 2010
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Quote:
Originally Posted by mobius.media View Post
Did anyone ever try building a 2d based on the attached, and if so, did you find an economical or easy way to cut the 1/8" mdf? I imagine you could just use a box cutter (X-Acto knife), no?

I know a laser engraver can alternatively cut 1/8" mdf. eg. Canadian Laser Engraved Products Maybe that would be easier to hire depending on what they charge.

I've built 1d Panels, but I don't have the patience to try building the 2D panels. However, before I gave up on the idea, I did give it a bit of thought. I think the easiest way to do this would be with a drill with a half inch bit. You could lay the board down on a couple of 2x4 support rails and punch out the pattern with a handrill (although you might have to go with thicker material so it wouldn't sag inbetween the rails while you were drilling).



It is A LOT of work to drill all those holes. For a little less work, you could use the alternative pattern in the patent doc (there's a pattern with fewer holes that only diffuses up to about 4500hz).

A 1D MLS pattern is much easier to deal with. In fact, it's pretty darn easy!
#36
25th March 2010
Old 25th March 2010
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I built them myself two years ago, 14 panels + big front panel, LOTS of holes... but wonderful results.





I used 4mm MDF for the grate, packed together 6 panels and drilled the holes through them. LOTS of holes, literaly thousands, but it was worth it.
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#37
25th March 2010
Old 25th March 2010
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Quote:
Originally Posted by Pawel View Post
I built them myself two years ago, 14 panels + big front panel, LOTS of holes... but wonderful results.





I used 4mm MDF for the grate, packed together 6 panels and drilled the holes through them. LOTS of holes, literaly thousands, but it was worth it.
Very nice work! Are those BAD panels above your mix position? If so, how do you feel about having diffusion instead of pure absorption up there at the first reflection points?
#38
25th March 2010
Old 25th March 2010
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Quote:
Originally Posted by Pawel View Post
I built them myself two years ago, 14 panels + big front panel, LOTS of holes... but wonderful results.

Nice work ! I've been thinking of doing the same over the upper parts
of corner absorbers.

Paul P
#39
23rd April 2010
Old 23rd April 2010
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Absorbentbobs is offline
BAD Alternative

In case this option has slipped between the cracks, Kinetics sells a product with slightly different math. However, the template (as in the part of the product with the holes) can apparently be purchased separately for $17 each - that's for a 2' x 2' btw. The RPG BAD "template" runs closer to $48 each. The specs ARE different but not radically so. And BOTH companies have produced papers slamming the others product - see attached.

AB
Attached Files
File Type: pdf tad_analysis.pdf (1.38 MB, 697 views) File Type: pdf Kinetics_Absorber_Diffuser_Panel vs BAD.pdf (285.9 KB, 1073 views)
#40
23rd April 2010
Old 23rd April 2010
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Quote:
Originally Posted by Absorbentbobs View Post
In case this option has slipped between the cracks, Kinetics sells a product with slightly different math. However, the template (as in the part of the product with the holes) can apparently be purchased separately for $17 each - that's for a 2' x 2' btw. The RPG BAD "template" runs closer to $48 each. The specs ARE different but not radically so. And BOTH companies have produced papers slamming the others product - see attached.
Thanks, Bobs. That's interesting. Can anyone make sense of those documents as to which is truly more diffusive? The scattering coefficients seem small, but maybe I'm reading wrong (?).

I was going to drill some RPG type myself. I put together some basic drilling templates attached here, based off the RPG patent schematics. I PM'ed Pawel and he said he used a 0.5" drill bit for each hole on a 0.66" grid pattern, which matches the attached.

But it would certainly be easier to just buy TAD ones pre-drilled from Kinetics if they are as good.

Is that something you have to contact them for? I don't see it listed as a purchase option on their site.
Attached Thumbnails
RPG Bad Panel -- Detailed Plans-rpg-pattern-full-size.gif   RPG Bad Panel -- Detailed Plans-rpg-pattern-full-size-inversion.gif  
#41
23rd April 2010
Old 23rd April 2010
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Absorbentbobs is offline
Kinetics TAD template pricing

I received a quote from the local Home Theater distributor. Go to the "Locate a Rep" button at the Kinetics site and find your closest HT person/company.

I don't believe the template only option is discussed on the websites of either Kinetics or RPG - however, they both provide them.

AB
#42
23rd April 2010
Old 23rd April 2010
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Quote:
Originally Posted by Absorbentbobs View Post
I received a quote from the local Home Theater distributor. Go to the "Locate a Rep" button at the Kinetics site and find your closest HT person/company.

I don't believe the template only option is discussed on the websites of either Kinetics or RPG - however, they both provide them.

AB
So, when you say "Template", I assume you mean an actual drilled piece of HDF? Or is it literally a template that would be used to drill the holes yourself?

Can these pre-fab templates be ordered "scaled" to different sizes?
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#43
23rd April 2010
Old 23rd April 2010
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So here's another question: How does absorber depth affect the FR of these things.

Is there a limit to the depth one can use behind the panel? I would assume that absorber depth would mainly affect low frequency absorption coefficients, and not so much diffusion coefficients or high frequency absorption coefficients.

Anyone know?

I'll have to study the Antonio/Cox book more to see if there's anything in there addressing these questions. But from what I remember, there wasn't much there.

-MM
#44
23rd April 2010
Old 23rd April 2010
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So, when you say "Template", I assume you mean an actual drilled piece of HDF? Or is it literally a template that would be used to drill the holes yourself?

Can these pre-fab templates be ordered "scaled" to different sizes?



"Templates" are the drilled section. Although I don't have pricing info, both companies will provide custom sizes.

AB
#45
23rd April 2010
Old 23rd April 2010
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Quote:
Originally Posted by Magickman View Post
Is there a limit to the depth one can use behind the panel? I would assume that absorber depth would mainly affect low frequency absorption coefficients, and not so much diffusion coefficients or high frequency absorption coefficients.
Exactly. At low frequencies (where the web dimension between the openings is less than a wavelength) the entire system acts as if the panel is not there.

Andre
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#46
23rd April 2010
Old 23rd April 2010
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So, I'm thinking of using BAD panel scrims on the splayed walls for my RFZ.

The RFZ side walls are splayed 15 degrees. They are "false" walls filled with wool.

Bad idea?

Opinions?
#47
24th April 2010
Old 24th April 2010
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Bad Panel LF Absorption with E Mount

Quote:
Exactly. At low frequencies (where the web dimension between the openings is less than a wavelength) the entire system acts as if the panel is not there.

Andre
From The Bad Panel CSI doc............

Random Incidence Sound Absorption Coefficients (a): Tested by independent, accredited, NVLAP facility according to ASTM C 423 and ASTM E 795 for an E-400 mounting.

Thickness 1”

125 Hz 0.67

250 Hz 0.77

500 Hz 0.77

BTW, E-400 mounting is approximately a 16" gap between the product and (usually) the ceiling.

I'm not certain but I believe an E-400 mounted 6lb density, 1" semi-rigid fiberglass panel actually absorbs slightly more in the LF region. Perhaps someone can clarify.

AB
#48
25th April 2010
Old 25th April 2010
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Quote:
Originally Posted by Absorbentbobs View Post
From The Bad Panel CSI doc...
And your point is?
#49
25th April 2010
Old 25th April 2010
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Quote:
Originally Posted by avare View Post
And your point is?
Andre, might you would consider reading the documents Bobs posted here and sharing your opinion on which you think could be a superior approach?
#50
25th April 2010
Old 25th April 2010
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My point is.........

Quote:
And your point is?
...I agree with your post. I thought some verified specs might amplify your comment.

I'm still interested in knowing whether an E-400 mounted 6lb density, 1" semi-rigid fiberglass panel actually absorbs slightly more in the LF region than the BAD panel.

Any comments???

AB
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#51
25th April 2010
Old 25th April 2010
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Quote:
Originally Posted by Absorbentbobs View Post
I received a quote from the local Home Theater distributor. Go to the "Locate a Rep" button at the Kinetics site and find your closest HT person/company.

I don't believe the template only option is discussed on the websites of either Kinetics or RPG - however, they both provide them.

AB
I sent RPG an email a while back asking if I could purchase the binary mask separately, and they told me no.
#52
26th April 2010
Old 26th April 2010
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Quote:
Originally Posted by Absorbentbobs View Post
I'm still interested in knowing whether an E-400 mounted 6lb density, 1" semi-rigid fiberglass panel actually absorbs slightly more in the LF region than the BAD panel.
"semi-rigid" has nothing to acoustically. Aside from that, the absorption for the material you are describing can be found in Bob Golds Absorption Coefficients.

Andre
#53
26th April 2010
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Quote:
Originally Posted by mobius.media View Post
Andre, since you're reading this and seem to have a pretty good, independent handle on things, might you consider reading the documents Bobs posted here and sharing your opinion on which you think could be a superior approach?
My thoughts are that RPG designed their product with acoustic priniciples applied, and Kinetics Noise product appears to be a "me too" product based on random design principles.

Andre
#54
26th April 2010
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Quote:
Originally Posted by SAC View Post
I apologize if this sounds a bit obtuse, but the 2 papers seem to go to great lengths to avoid directly discussing and comparing the underlying 'randomization' strategies, although RPG would have the advantage here...and the silence regarding this becomes a bit deafening.
+1 and quite hilarious with the BAD panels being patented!

Andre
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#55
26th April 2010
Old 26th April 2010
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Quote:
Originally Posted by SAC View Post
Without wanting to dive too deeply into the issue, regarding the test comparisons, they are choosing to focus upon an aspect of diffusor design of which many may not be very familiar - and that is the power spectrum.

A 'maximally' diffuse sound field exhibits a flat power spectrum. This is characterized by the spatial distribution of the reflected 'wavelet' amplitudes along a planar surface that are scattered into the different diffraction orders all being equal.

The complementary goal is to then to employ a sufficiently high order (N) diffusion pattern to maximize the distribution to render the low order specular wavelets into a complex high ordered set of specular wavelets featuring much greater diffusion as is offered by the quadratic residue models.

The test results in the papers do not present the more 'usual' (familiar) view of the 2 or 3 space volumetric polar lobing plots or event the ETC that we often associate with diffusion plots. Instead, they state the results in terms of the power spectrum. And in this view, the 'flatter' distribution accompanying the diffusion/scattering indicates a flatter power spectrum which is a direct indication of the more uniform diffusion which displays less specular 'wavelets'. And in so doing, provide a bit of cover for each of the two design approaches while simultaneously casting aspersions on alternative implementations.

You might think of it as similar to the situation when viewing a display of Q or dispersion as compared between a traditional polar plot and a spectrograph display of the same phenomenon. While they will at first seem disconnected, they display much of the same information from different perspectives.


Thus what becomes quickly apparent is the lack of a maximally flat power spectrum in the TAD diffusion plot indicating a slightly more pronounced degree of specular beaming in the resultant diffuse soundfield.

And one might wonder as to whether the TAD product doesn't employ either Galois field (e.g.: MLS) or Gaussian or Eisentein prime sequences as their 'random' pattern, that, while working very well, result in a slightly higher degree of specular energy distribution due to their limited frequency optimization, and hence a slightly less flat power spectrum response than does the RPG quadratic residue based low specular reflection patterns. These would be an excellent, although not quite as optimal, alternative to the quadratic based systems employed by RPG.

I apologize if this sounds a bit obtuse, but the 2 papers seem to go to great lengths to avoid directly discussing and comparing the underlying 'randomization' strategies, although RPG would have the advantage here...and the silence regarding this becomes a bit deafening.

OK, enough fun...back to the salt mines...
One of these papers around here discusses the randomization strategy of the BAD Panel. I believe it's in the Patent Doc, but I could be wrong.
#56
26th April 2010
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Basic agreement with what you wrote SAC. It is now known that it can be done. It is just a matter of applying physics and math to it to determine how to it predictably. One could do worse than to apply the basics of diffusion occurring about an ocatave around a sharp surface, and surfaces with an open area of 20% with the covered surface less greater thatn a wavelength long to develop effective open area strategies.

Wholy,
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#57
27th April 2010
Old 27th April 2010
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I have used both the RPG BAD and Kinetics TAD panels multiple times.

The 4" version of both offer near linear absorption down to 100Hz (approx 1.0 NRC).

The 2" (actually 2.125") version of both have a WONDERFUL midrange absorption quality.

The diffusion is NOT like a quality QRD or PRD. They do sound more open and "rich" from 800-3K. But they can absolutely still yield specular glare if the sound source is reasonably close (depends on source type and amplitude) and if at non-normal angle of incident.

The BAD ARC is in a class of it's own as it combines a polycylindrical scattering that takes away the specular glare concern. This is one of my personal favorite widgets.

They're great tools. Both companies offer data of the highest standards and care tremendously about their products being used successfully.

To Gremmy, RPG does offer the "mask". However, they tend to do so only to and through projects with a known designer or consultant at hand. I don't think this is a slight to you, more a reflection of their brand intregrity and that they're really not a typical retail company (more of a consultant spec support business model). If you are in US, feel free to PM me and I may be able to help you in this regard.
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#58
27th April 2010
Old 27th April 2010
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Quote:
Originally Posted by Jeffrey Hedback View Post
The BAD ARC is in a class of it's own as it combines a polycylindrical scattering that takes away the specular glare concern. This is one of my personal favorite widgets.
This gives me the idea to take a fairly large sonotube, drill the BAD pattern
on the upper part of the front and a bunch of larger holes lower down and
around the back side, fill it with light insulation, cover with fabric and stick
it in a corner.

Paul P
#59
7th June 2010
Old 7th June 2010
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Hi,

i'm newbie to this forum..need some help about BAD panel.

as i red from the patent and try to understand the sequence of the panel, i still don't get it.

so in the sequence like Fig 5 or Fig 6, number of "0" or "1", is representative to hole or not?
what i mean is, the "0" means hole or "1" is hole?

what is the size of the hole? and if i'm want to build leght of 15 or 32, how do i decide the size of the hole and gaps between holes?

i've been trying to calculate how many holes, can be fit to 2' x 2' panel
which is 32 length.

i'd try to figure out the RPG BAD and try to make it, but the sixe of the holes it still not fit to the panel, or it will be fit but not in a right measure.

i hope my quetion can be understand.

thanks for your help and share your time.

Regards,

Bonar Abraham
#60
4th February 2011
Old 4th February 2011
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FWIW I have several of these panels. They definitely have the 1/8" grid. You can feel it through the cloth.

It's funny. I got these by accident. They were listed as absorbers on ebay. I bought them and they were BAD panels. I'm just starting to treat my room so I'm still trying to figure out how to use them. Right now I have two on the ceiling and the rest temporarily sitting on TV tables in the front corners! They did tighten up the room significantly but I haven't done any measurements and I know that they are not being used as intended yet. I have to build some proper bass traps, first and then figure how to use them. Sorry for the blather - I just wanted to be clear that while I have them I can't give an honest opinion on how they work.

Neil

Last edited by jacktiki411; 4th February 2011 at 01:28 PM.. Reason: Signed name twice?? What a dummy!
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