SPACE COUPLERS. Theory, construction and effectiveness on traps.

[Greg B]

Originally Posted by dandeurloo

From what I can tell from a slap test the bare Space Couplers on a wall alone do help. I noticed the peaky/painful slap off of the dry way was attenuated by just placing 2 of them on directly on the way. I wonder if it would preform even better with an air gap between the wall and the diffuser.

Auralex claimed their couplers reduced early HF reflections by 10dB when simply hung against a wall, and added that the benefits are increased when adding space behind them and varying the angle, which would make sense intuitively.

[Jeffrey Hedback]

Love it SAC...btw, I think it is fair to share that a certain person to be unidentified by purple eye band suggests that this same 3" grid with 4" airspace in front of glass will effectively negate discrete reflection issues.

The Auralex tests (performed by Jeff D Szymanski) showed usable absorption (forgive me for not looking up the numbers) with Coupler spaced 2" in front of hard surface (parallel).

DD, I would be totally amazed if you found any tangible benefit of Coupler front of SuperChunk (corner application that is).

It is a versatile tool, not voodoo but not a cure-all.

And...we've barely touched on the loosely coupled space applications.

[localhost127]

Originally Posted by Greg B

Auralex claimed their couplers reduced early HF reflections by 10dB when simply hung against a wall, and added that the benefits are increased when adding space behind them and varying the angle, which would make sense intuitively.

i was under the impression you wanted early reflections -20dB or more...so why pay all of this extra money to only get -10dB, when you could add broadband absorption for much cheaper and be more effective at first reflection points?

and if you place the coupler over broadband absorption at first reflection points, wouldnt you have to worry about reflections from the frame itself bouncing to the user?

[Greg B]

Originally Posted by SAC

You have repeated this multiple times and each time it is worth as little as the previous time.

I repeated the Auralex results again only because he asked which low frequencies were effected. SAC, I know you've been in the conversation since the beginning, but some folks have just joined in and might not have read the whole thread.

Not once have I claimed that the marketing out their is all true and that we should blindly believe. I've simply repeated what other supposed experts have claimed. I bring up these claims only so that folks like you have a chance to dispute/confirm/explain them. I'm just learning as much as I can about how other experts have utilized them before deciding if and how I should attempt to use them myself.

[Greg B]

Originally Posted by localhost127

i was under the impression you wanted early reflections -20dB or more...so why pay all of this extra money to only get -10dB, when you could add broadband absorption for much cheaper and be more effective at first reflection points?

and if you place the coupler over broadband absorption at first reflection points, wouldnt you have to worry about reflections from the frame itself bouncing to the user?

Again, I'm just repeating the information given. Not saying whether or not it's worth buying just to hang against your bare walls.

The idea is that these couplers also can DELAY and diffuse the reflections, and not simply reduce them, which can create a feeling of more space to a smaller room. They are most effective at this when there is a space between them and the walls, and angles can help too. As everyone else is saying, there are many uses for these, and we're not trying to simply suggest one perfect way to use them to solve all acoustic problems.

[SAC]

Stating a percentage at a frequency is worthless without stating the remaining variables that are not only contributory, but causal.

There is no advantage to reading that they add 45% absorption at 125 Hz if folks then get the idea that all they have to do is add a collimation grating to a non-gapped 2" porous panel or to the carpet that so many think works as meaningful absorption and that they will somehow achieve meaningful bass absorption.

The problem is that specific results in a specific configuration are not portable and valid used in general.

On the other hand, the concept of the grating and its myriad applications is a marvelously effective and flexible tool (as reinforced by Jeff above ) - although it is not a simple one size fits all tool that can be used without consideration being given to the specific use and the particular configuration and scale.

And THAT is the BIG caveat that one must understand before going to the hassle or expense to make or buy them. And the 3" variant that was markets was primarily aimed at the loosely coupling spaces in order to augment/increase the latter arriving decaying soundfield. And while effective for other uses, one should be aware of the dimensional issues that are contributory - as one size is not optimal for all applications, although the tool 'category' might be.



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Oh, and to address the issue raised above - you are generally not going to be using these or any diffusor to reduce early arriving first order reflections in a small acoustical space in order to establish an Initial Signal Delay (ISD) gap! Nor are you going to want to use then where the predominate incident energy arrives at a near normal (perpendicular) angle to the surface.

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"Some of the things you are saying the couplers can't do, Auralex and others have claimed they can do"
I'm a bit tired of the circular argument.

But here we see the same simplistic approach based upon over generalization! No one said that "couplers can't do" things - we said that one size of coupler cannot do all things! A 3" coupler will not even be seen by low frequencies! But you know, a larger grating might, but it will not be as effective at other frequencies. They do not operate linearly at all frequencies! Add to that that they have a more significant effect on large oblique incidence angles - which make less and less 'sense' the lower in frequency one goes... We have not overcome the laws of physics yet! Nor did the 'source' of these make that claim!

And as far as with what they are claimed to be effective, apparently you did not recognize the picture that had been posted. And to render this a bit more absurd, I wonder where Auralex -who was not the 'developer' but only the marketing distributor - became familiar with these devices? So what does Auralex -who does not even make the full information regarding tests available claim who cites only percentages? And the tests are "confidential"!? ROFLMAO! Gee Bernie Madoff, So just what percentage return did my investment accrue last year? You say my investment increased by 43%! Wow! And no, that does not mean that the absorption coefficient increased by that amount - it means the difference is a percentage change of yet another unstated set of reference variables - a percentage of a percentage. And just how much is 7dB???

[DanDan]

Stating a percentage at a frequency is worthless without stating the remaining variables that are not only contributory, but causal.

There is no advantage to reading that they add 45% absorption at 125 Hz if folks then get the idea that all they have to do is add a collimation grating to a non-gapped 2" porous panel or to the carpet that so many think works as meaningful absorption and that they will somehow achieve meaningful bass absorption.

The problem is that specific results in a specific configuration are not portable and valid used in general.

While this may be ultimately true if viewed in macroscopic pedant, Lab tests (and our own in situ) are frequently all we have, so why not work with them?

My understanding of the Auralex '43% increase at 125Hz' claim is that the absorption coefficient increased by that amount in that band.
Without divulging confidential information, the test confirms this.
Furthermore, absorption coefficients are available, so the actual numbers are entirely obvious.

The lack of corner action is perplexing. I will test that shortly myself. If it did work, surely the ideal front for an SSC.

DD

[Greg B]

Originally Posted by SAC

The category of tools is amazingly powerful and flexible. But this urge to try to 'make' one variant do all things and be all things for all applications simply displays a fundamental misunderstanding of the the underlying physics they they do not at all modify!

But these attempts to broadly and absolutely make conjectures while looking for "the answer"....

I don't think any of us have suggested that any one tool or technique will solve all problems in all applications. I think we're all just trying to discuss SOME of the ways that they can be useful (and why), and then hopefully move forward a little better informed. Some of the things you are saying the couplers can't do, Auralex and others have claimed they can do, and so I'm just trying to keep an open mind until I have more experience using and testing them myself. Your input has been incredibly helpful, and I still plan on asking your opinion on my specific rooms when I get a little further along in planning how I will want to use the new space I'm adding.

[localhost127]

if you had a large enough room with massive (deep) pink fluffy corner traps, you could always pull your bookshelves against the traps

the ikea expedit 4x4 would work nicely,
ikea expedit - Google Search

[localhost127]

or the 2x4 with a 31" width would fit nicely in front of a 34" superchunk

[SAC]

Now all you need is a preponderance of oblique incidence low frequency energy.

Anything incident between 45 and 90 degrees in the effective band will simply function normally (as usual) as it will be incident directly upon the underlying surface. And much of the energy incident at lower angles of incidence will function as usual as well, as without the grating, they would still be incident on the surface at the same angle only in a non-redirected manner. The net gain will be from energy that might otherwise not be incident upon the absorptive surface without redirection. And one should note that a portion of the 'near side' energy will be precluded from being incident upon the absorptive surface as well - nearly equal to that 'far side' energy captured that would ordinarily miss the absorptive surface.

It will assume a larger role (up to a point) by being spaced out from the underlying surface whereupon diffraction will play a larger role - but not one that will overshadow the reflective component.

[Hannes_F]

Stop the press!
The secret is to mount the coupler behind the absorption!

From the BBC Guide to acoustics practise:








....




Who can explain why it is there?

[Magickman]

Originally Posted by Hannes_F

Stop the press!
The secret is to mount the coupler behind the absorption!

From the BBC Guide to acoustics practise:



Who can explain why it is there?

Hannes, can you post the document from which this excerpt originates?

Thanks!

-MM

[localhost127]

http://www.bbc.co.uk/rd/pubs/archive...icpractice.pdf

[Magickman]

Thanks much!

Don't think I have this one yet.

[localhost127]

hmm, the expedit bookshelf is 15" deep.
id be interested in seeing some testing with rigid fiberglass on the inside and outside of the bookshelf, and also testing with the bookshelf spaces filled with 15" of pink fluffy stuff...and then the bookshelf slide into a corner.

[Magickman]

Originally Posted by Magickman

Thanks much!

Don't think I have this one yet.

Oops! Guess I do already have this one. But thanks just the same.

I'm sure there are others who may be reading who don't have it!

[Hannes_F]

Guys, I meant it as a joke. Of course.
Still, putting the coupler behind the absorber in the indicated way would be a more effective way to increase the bass absorption than putting it in front of it, so there is some truth in this joke.

[Hannes_F]

Originally Posted by localhost127

hmm, the expedit bookshelf is 15" deep.
id be interested in seeing some testing with rigid fiberglass on the inside and outside of the bookshelf, and also testing with the bookshelf spaces filled with 15" of pink fluffy stuff...and then the bookshelf slide into a corner.

Yep, however I would replace the inner of the side walls by slats or use a more open rack alltogether. A closed rack would make more sense if you plan to put a perforated panel in front of it or the like.

[PaulP]

Originally Posted by SAC

Anything incident between 45 and 90 degrees in the effective band will simply function normally (as usual) as it will be incident directly upon the underlying surface. And much of the energy incident at lower angles of incidence will function as usual as well, as without the grating, they would still be incident on the surface at the same angle only in a non-redirected manner. The net gain will be from energy that might otherwise not be incident upon the absorptive surface without redirection. And one should note that a portion of the 'near side' energy will be precluded from being incident upon the absorptive surface as well - nearly equal to that 'far side' energy captured that would ordinarily miss the absorptive surface.

That is one heck of a paragraph .

With respect to gratings used for light, isn't the ratio of wavelength to grating cell size orders of magnitude different compared to these space couplers and sound ? Won't that make a huge difference in behaviour ?

[DanDan]

Well Hannes, I appreciated the joke....;-)

I wouldn't be so sure that those little card partitions would increase LF absorption by 43%. It is the airgap and the chamber which is effective here. The partitions simply enhance the void by diminishing some internal resonance. A full fill of fibre would surely be better.

The size thing keeps coming up. These are 3 inch wells, the absorption of a two inch panel fronted by a Coupler is around 0.8 at 125Hz. This alone is interesting. The size differential between the device and the wavelenght is vast. However the bigger story is the slope of the resulting absorption and consequently the sound in the room. Small rooms are boomy. Tons of fibre will fix this but the Mid and HF will be unnatural. The Space Array seems to address this very nicely. The 'diffusion' appears to be useful even at extremely close range.

DD

[Magickman]

Originally Posted by Hannes_F

Guys, I meant it as a joke. Of course.
Still, putting the coupler behind the absorber in the indicated way would be a more effective way to increase the bass absorption than putting it in front of it, so there is some truth in this joke.

Thanks Hannes. I (clearly) don't really have whole lot of investment in this discussion. I was mainly interested in adding the BBC document to my collection. As it turns out, I already have it. thumbsup

At any rate, my interpretation of the grating behind the face is that it would increase the efficiency at grazing angles only when using a perforated panel in front. The BBC build these boxes as modules, and face them depending on application: Sometimes with a purely porous facing, and sometimes with perforated mask (i.e. - Helmholtz). I would not assume the grating would have any effect at all without a perforated mask in front.

[localhost127]

so, pretending i had a large room to do this in...

the 4x4 expedit is 58" wide (149cm) and 58" tall (149cm)



straddled in a corner, that would give you a 29" deep trap (74cm) that you could fill with pink fluffy insulation.
if you include filling some of the bookshelf spaces, that gives you another 15" depth !!

since it is only 58" tall (149cm), you could stack 2 on top of each other to cover floor-to-ceiling corner (straddled).

now -- could you then fit arrays of 1D QRDs within each of the bookshelf openings? and modulate them with barker code? or possibly make 2 large QRDs (per bookshelf), and have the bookshelf divider be part of the QRD divider well (it would be a little thicker than the QRD divider well, but it's only 1 divider well that's wider than the others)...

would having the qrds within the bookshelf openings then defeat the purpose of using the bookshelf as a coupler? what about for frequencies below the QRD cutoff, which are also smaller wavelengths than the opening size of the bookshelf.

edit: actually it would probably make sense to install qrds in a few (alternating) bookshelf openings, and leave the other openings empty so energy can pass through into the coupler and into the absorption...

[Magickman]

Originally Posted by localhost127

so, pretending i had a large room to do this in...

the 4x4 expedit is 58" wide (149cm) and 58" tall (149cm)



straddled in a corner, that would give you a 29" deep trap (74cm) that you could fill with pink fluffy insulation.

since it is only 58" tall (149cm), you could stack 2 on top of each other to cover floor-to-ceiling corner (straddled).

now -- could you then fit arrays of 1D QRDs within each of the bookshelf openings? and modulate them with barker code? or possibly make 2 large QRDs (per bookshelf), and have the bookshelf divider be part of the QRD divider well (it would be a little thicker than the QRD divider well, but it's only 1 divider well that's wider than the others)...

would having the qrds within the bookshelf openings then defeat the purpose of using the bookshelf as a coupler? what about for frequencies below the QRD cutoff, which are also smaller wavelengths than the opening size of the bookshelf.

edit: actually it would probably make sense to install qrds in a few (alternating) bookshelf openings, and leave the other openings empty so energy can pass through into the coupler and into the absorption...

Give it a shot and let us know what you discover!

[localhost127]

Originally Posted by Magickman

Give it a shot and let us know what you discover!

just gathering ideas/knowledge

[johndykstra]

Hey localhost127,

I can't help but wonder...

You are suggesting a complex multi-tiered treatment plan, that is centered around the limitations of a commercial bookshelf. The construction of the diffusors within the wells would be a custom build, suggesting you are comfortable with your handy work. So, why limit the build to the confines of a melamine product that is likely more expensive than a ground up construct and design?

I would wonder what if any benefit a phase grating with (roughly) 1'x1' cells would even be able to provide to be honest.

[TornadoTed]

I am in the early stages of extending my live room and have been tossing ideas back and forward with Dan. We have discussed the possibility of having traps on the ceiling with space couplers.

Anyway I made this the other day from square drainpipe. It is just under 600 mm square and 75 mm deep. It cost me £15 and took just under an hour to make, I reckon I could make them quicker once I got a system together.

[DanDan]

Cool, this looks very 'Pro'.
How are the cuts done so evenly and burr free?
What glue?
DD

[johndykstra]

I'm speechless.

Bravo sir. I may stop at the home depot on my way home.

[TornadoTed]

Originally Posted by DanDan

Cool, this looks very 'Pro'.
How are the cuts done so evenly and burr free?
What glue?
DD

I have a chop saw with a fine 40 tooth blade, cut slowly and it gives a very clean cut. I pulled a piece of cloth through the middle after to clean all the bits out.

I used an all purpose glue from the building centre. It's called 'The works' it said that it sticks most plastics so I thought I would give it a go, it seems very strong. I have gently abused it and no joins have come apart.