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Old 10th June 2016
  #18
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Hey mushroommunk,

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Originally Posted by mushroommunk View Post
Hey Boggy,

I'm also majorly inspired by your design, and plan to use it as a basis for building a home theater and listening room at some point (house shopping at the moment). If I hadn't come across your design, demolishing the entire house and building a mini Blackbird studio was my backup plan.
Blackbird studio cannot be "mini", and still working, as a concept. LF absorption is crucial in the Control Room treatment... And with less space you will loose required LF absorption.
Also, phasing effect can happen because ear proximity to the too deep diffusers. Three or four wavelengths of lower working frequency are minimum distance from the ear.
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I was hoping if it wasn't a bother just to clarify a few points from your paper and make sure I'm on the right track.
It won't bother me, this is a reason I started a thread... I don't sell anything here
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Originally Posted by mushroommunk View Post
1) Your hexadecimal diffuser design can be any length. So that 4 meter one you mention in the paper was say a PRN of 0's and 1's 2,048 digits long (or however many used), converted to hex, and then each digit is the slat height (And the maximum slat height is based only on targeted diffusion frequency?).
Yes, basically.
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So you can make an 8meter diffuser just by adding more 0's and 1's at the start. It isn't built of smaller diffuser units, its one long diffuser (so I'm thinking its along the lines of one single QRD using a large prime number, vs an array of QRD 7's that need to be adjusted to avoid periodicity). Correct?
Yes, but you don't need to make one single 8m diffuser, you can make more smaller, but different, modules, and then include it in one long diffuser.
The problem with QRD is because their formula makes too many different well heights, when you increase the order of the diffuser (EDIT: YES! to avoid periodicity), what make diffuser more expensive. I needed something with similar complexity as our very first design (RES Media Studio), which diffuser modules had 13th and 7th order. So 4,8 or 16 possible slat heights were a good choice

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2) This continuous diffuser is the main upgrade to your design, along with ditching Newell(?) hangers for the absorption right?
Yes, yes, together with possibility of more controlled room liveliness with strong diffuse field, with less building complexity and less price.
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3) If one were to leave the number as is, and not raise it with the offset, would this just lower diffusion and add absorption, or does this affect the helmholtz system too much too? (More open surface area to the treatment behind where Hex number is zero).
You can imagine where this will go if you look at absorption modelling results in paper... this will go to something we already had... more close to MyRoom Design Mk I.
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Originally Posted by mushroommunk View Post
4) Related to 3, does raising the slats with the offset not change the Helmholtz affect noticeably, or is that the point and I missed it? (You just mention it doesn't affect principle of the work for the phase grating, and strengthens the thinnest slat) I'm just wondering if the added offset adds enough air/mass into the system to change tuning just as changing gap width lowered it, similar to lengthening the neck of a coke bottle before blowing on it since a Helmholtz resonator is dependent on the length of the neck right? It seems this is semi-accounted for in h=Hmax/2+Hoffset in your simulations, or am I barking down an empty rabbit hole?
I believe Helmholtz absorber, described in paper, doesn't know too much about the diffusion function of it, and will work (something) with or without offset.
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5) To optimize the slat/gap ratio, was it an iterative process of simulations changing slat gap to narrow in on the desired absorption graph, or was a "simpler" method used (like actually calculating the frequency of the Helmholtz resonator formed with a neck cross sectional area using average slat height and gap width)? Was Hmax and Hoffset chosen in a similar manner or as asked in question one is this based solely on targeted frequency?
This paper describes a basic concept of acoustic design. Anybody is free to use it and to try to design it in his/her own way.
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6) In the old MkI design, you had a gap between the air transparent diffuser and the absorber, and air transparent fabric attached to the back of the diffuser, it looks like that is gone now correct? It was there before due to using a different type of absorber right?
Nope, the gap may reappear or not... Depending of design conditions.
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7) Is the thickness of the air gap between the porous absorber and the stiff back important? I've read that you can get *close* to the same absorption values by using X inches of porous absorber and X inches air gap to reduce cost, instead of X+X inches of all porous absorber. Is this the only thing in affect, or is it related to the helmholtz calculations here? I'm also assuming that if the room is built properly the room wall becomes the stiff back correct?
Gap is important, even if it doesn't exist... Everything you ask is dependent of particular design condition. After seven Control Rooms designed in the described way, I saw no simple formula.
Adding strong slat absorber function before wideband porous absorbers, gives the possibility to have ~10% less thickness of that porous absorbers... This is just the scientific conclusion of some benefit of this concept... After some analysis.
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8) And final one for now, in your pictures of Studio M2932 the diffuser doesn't run from floor to ceiling, or wall to wall, is this because you need the remaining surface area for pure absorption (or some other bass control)? Or is this purely aesthetic design (which I am even more clueless on than acoustics )
Well, there are even more different conditions... Depending on customers, acoustic and non acoustic things... Until now, I tried to meet everyone's wish, without bothering acoustics in the room too much.
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Originally Posted by mushroommunk View Post

Apologies if these questions seem basic or are asking for too much info. I've done a fair bit of reading on forums and your papers, but unfortunately with driving six hours a day to get to/from work, plus the work itself, I haven't had time to read the copies of Sound Reproduction by Floyd Toole, Master Handbook of Acoustics, or D'antonio's book on diffusers, all sitting next to my bed so my knowledge is still limited. If there are any other resources that might help please let me know.

Again, Boggy you rock.
NP, thank you very much!



Last edited by boggy; 11th June 2016 at 06:48 AM..