Decaware vs. Gik: How to Choose Which Diffusor for My Room

[Seamus TM]

DECWARE - Room Acoustic Treatments
GIK Acoustics: GIK QRD Diffusor

So, how would I go about choosing which diffusor I should get for the back wall of my control room?

I'm not asking which one I should get.
I'm asking about the criteria involved in choosing.

Thanks,
Seamus

[avare]

Originally Posted by Mumblesound

I'm asking about the criteria involved in choosing.

The frequency range you want diffused, and the lobing on the Decaware from being 2 cycles.

Andre

[Seamus TM]

Thanks, Andre.

...but, how do I know what range I want diffused?

What do you mean about the lobing on the Decaware "from being" 2 cycles?

Thanks,
Seamus

[andrebrito]

Decaware acts at higher frequencies than GIK

Decaware is an higher prime number diffuser

Completely different stuff

Usually for small rooms high frequencies diffuser are a better choice since the distance from the listener to the diffuser is small and therefore you want a diffuser where the lowest wavelenght does not interfere negatively with the listener's perception.

[Seamus TM]

OK, interesting.
The listening position would be about 12' from the diffusion.

[bpape]

The DECware will reach higher than our QRD. It won't reach higher than our D1 due to the polys on the face. The D1 is good up to about 10kHz

Bryan

[Seamus TM]

So, for argument's sake, I would want the Decaware because it reaches higher.

What is the lobing issue that Andre mentioned?
Would it be an issue to have 3 of these in a row?

[Jens Eklund]

Originally Posted by Mumblesound

What is the lobing issue that Andre mentioned? Would it be an issue to have 3 of these in a row?

Probably not. Lobing usually isn’t a problem unless the repeat period reaches approx. 5-6 or above (depending on design naturally).

Sincerely Jens Eklund

[Seamus TM]

Great.
Thanks, Jens.

[bpape]

Originally Posted by Mumblesound

So, for argument's sake, I would want the Decaware because it reaches higher.

What is the lobing issue that Andre mentioned?
Would it be an issue to have 3 of these in a row?

That's fine - just understand that you're trading off extension in the highs for lack of extension on the lower end - hence Andre's initial question.

Bryan

[Seamus TM]

So, what about using both the Decware and the Gik qrd?

[tonio]

Originally Posted by Mumblesound

So, what about using both the Decware and the Gik qrd?

awesome !!

[bwo]

If you're not on a strict budget and have the distance, you can consider RPGs Diffractal:
RPG Diffusor Systems

[SAC]

The GIK QRD would be the overwhelming best choice with a frequency range of ~350 Hz to 3kHz.

The optimal range of diffusion is in the modal-specular transition zone between fc (the Schroeder critical frequency where modal behavior begins to change to specular behavior - and where you will have a mixture of decreasing modal and increasing specular behavior relative to the variations in surface dimensions) and 4fc.

Thus, if fc is 300 Hz, the region between 300 and 1200 Hz is the most critical region for diffusion, with their optimal effectiveness extending to ~2000 Hz. The practical LF extension will be limited primarily by the QRD's depth.

For substantiation, see Bolt, Beranek & Newman's "Controllers of Steady State Room Acoustic Response".

The energy content is so low above ~7500 Hz (wavelength = ~1.8inches) that we generally don't really 'care' about treatment in that region. (let alone at 12,000Hz where the wavelength is ~ 1.1 inches.).

The DECWARE unit fails to even be effective in the majority of the critical region where diffusion is most effective between fc and 4 fc.

[Seamus TM]

Originally Posted by SAC

The GIK QRD would be the overwhelming best choice with a frequency range of ~350 Hz to 3kHz.

The optimal range of diffusion is in the modal-specular transition zone between fc (the Schroeder critical frequency where modal behavior begins to change to specular behavior - and where you will have a mixture of decreasing modal and increasing specular behavior relative to the variations in surface dimensions) and 4fc.

Thus, if fc is 300 Hz, the region between 300 and 1200 Hz is the most critical region for diffusion, with their optimal effectiveness extending to ~2000 Hz. The practical LF extension will be limited primarily by the QRD's depth.

For substantiation, see Bolt, Beranek & Newman's "Controllers of Steady State Room Acoustic Response".

The energy content is so low above ~7500 Hz (wavelength = ~1.8inches) that we generally don't really 'care' about treatment in that region. (let alone at 12,000Hz where the wavelength is ~ 1.1 inches.).

The DECWARE unit fails to even be effective in the majority of the critical region where diffusion is most effective between fc and 4 fc.

Thanks, SAC.
Exactly what I was looking for.

[Seamus TM]

Here's the room.

Frequency Regions:
- No modal boost: 1hz to 27hz
- Room Modes dominate: 27hz to 101hz
- Diffraction and Diffusion dominate: 101hz to 404hz
- Specular reflections and ray accoustics prevail: 404hz to 20000hz

So, it would seem that the GIK would start working just before the transitional period ends.

[andrebrito]

SAC; I would like to know where you got the range fc to 4fc ,is this knowledge from some book or part of your experience ?

On large spaces the Schroeder frequency is very low and we still use diffusers to treat such spaces.. something like the FlutterFree from RPG only works above 2kHz, QRD 374 from 500 Hz up which is well far higher than the Schroeder frequency...

Place a Flutter Free in a small room and you will notice a difference where it acts which is higher than 4fc

Sorry I have the upmost respect from you, you are one of the few people here that keeps pushing the level up but on this one I am not 100% in agreement. :-)

[SAC]

Hi Andre!

First, the primary treatment of a control room back wall is Not for flutter echo!

Secondly, the source of the data was cited was listed, and I can locate it in numerous publications (ranging from Sound System Engineering) and in the actual seminar notes and presentations where I was first made aware of it by Don Davis and Peter D'Antonio themselves, with the original source being Leo Beranek. So, one might say its a bit difficult to get 'closer' to the 'original' sources. I have also posted it in numerous previous posts.

Additionally, the concept was very definitely presented and verified experimentally with complete measurements in the fall, 1984 LEDE (and subsequent) workshops led by Davis, D'Antonio, Berger, Neil Muncy and others.

No one is debating whether QRDs can be used to address flutter echo - provided the grating is small enough (despite it being akin to using a shotgun to hunt roaches) - as one will note when examining the actual size of the hybrid units featuring components nested within the larger wells designed to be effective with regard to flutter echo (Diffractal) or of the (lack of depth) of the wells in a dedicated product like the Flutterfree..

But flutter echo is a trivial concern relative to the high energy low-mids and mid frequencies that are critical to music and speech intelligibility which is dominate and of primary concern in the treatment of the rear wall of a control room. And generally speaking, based upon the information that was (or was not) expressly provided, I would not assume that the rear wall of a small to medium sized control room would only be treated for flutter echo.

And one might also note that the 374 QRD is a 'general' product that is whose effective bandwidth is not accidentally targeted to 320 Hz, placing its lower extension precisely in the region referred. And while the 374 is perhaps the most widely generally used QRD utilized in MANY environments, it is seen less often in many spec built studios where higher order QRDs/PRDs are the norm. This in no way denigrates the 374, but simply illustrates that it is not necessarily the optimal choice for many critical environments.

--------------------

And in a totally unrelated aside... - Its a bit frustrating , given both my time limitations trying to type my posts during 10-15 minute breaks, and those who loudly lament any post that exceeds 4-5 sentences or that employ the use any 'technical' terminology (meaning 'words that mean things' that serve as shorthand for very precisely defined concepts), as well as those who eschew anything remotely actually pertaining to "acoustics", to adequately explain a concept from first principles; while a Much smaller group is bored senseless by having to again listen to a definition of what constitutes sound.

So what one gets is a distilled synopsis (...that may employ terms that are objectively defined and 'mean things'; for which the meanings are always available through independent sources or via PM if anyone wishes to actually know - and not just complain. But for the record, I can count on one or two hands the number of times, let alone the number of folks, who have actually asked (and they are never the ones who complained!)...and it would take substantially more resources to tally those who only complain.).

But coming back after being out of town for the large portion of the week its interesting to be informed by 2 other folks of a few comments and complaints that were made. its funny, as if anything I write is unclear, anyone is always welcome to talk to me directly for either clarification or elaboration or for just about any reason regarding just about any topic. And as anyone who has actually spoken to me can attest, I am very mean and scary!

Well, we're off again for the week...

[andrebrito]

OK I now understand what you are referring to !

Yet I am not entirely convinced about that chart to be honest.

Diffusers are related not only for preventing echoes but to increase ELEF and at least in large room acoustics ELEF is measured and increased at frequencies well above 4*fc

I know that chart is "applied" to small rooms but a kind of find it limited...

[Seamus TM]

Originally Posted by Mumblesound

Here's the room.

Frequency Regions:
- No modal boost: 1hz to 27hz
- Room Modes dominate: 27hz to 101hz
- Diffraction and Diffusion dominate: 101hz to 404hz
- Specular reflections and ray accoustics prevail: 404hz to 20000hz

So, it would seem that the GIK would start working just before the transitional period ends.

So, I basically want something that will start diffusing as low as possible, right?

[Glenn Kuras]

Originally Posted by Mumblesound

So, I basically want something that will start diffusing as low as possible, right?

Just to point out one thing. Ours are NOT a DIY kind of deal. Once you get them you just hang them on the wall.
As far as which is better for your room, I would recommend contacting each of us to help you guide you through your room. You can contact us through the following page which will give us the info we would need to give you the best advice.
GIK Acoustics: Room Setup

[Seamus TM]

ok, Glenn.
Done.

[Seamus TM]

Originally Posted by andrebrito

OK I now understand what you are referring to !

Yet I am not entirely convinced about that chart to be honest.

Diffusers are related not only for preventing echoes but to increase ELEF and at least in large room acoustics ELEF is measured and increased at frequencies well above 4*fc

I know that chart is "applied" to small rooms but a kind of find it limited...

If I'm reading the chart correctly, I would be hard pressed to find diffusion that would be useful for my room...