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Simulate QRD 1D with Reflex? Can you check my design pls? Dynamic Microphones
Old 5 days ago
  #1
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Simulate QRD 1D with Reflex? Can you check my design pls?

Im planning to do a QRD 1D for the back of my room ( My small production room )

120 cm (W) x 60 (H) x 15 cm

So I came up with this using QRDude:


Data for One Dimensional QRD (Quadratic Residue) Diffuser

Standard N23+0,0 Panel

Design frequency 896 hz

Number of wells: 23

Deepest well in mm: 150

Fin width in mm: 5

Width of wells in mm: 45

Ratios 0 1 4 9 16 2 13 3 18 12 8 6 6 8 12 18 3 13 2 16 9 4 1

Well depths in mm: 0 8 33 75 134 17 109 25 150 100 67 50 50 67 100 150 25 109 17 134 75 33 8

Block heights in mm: 150 142 117 75 16 133 41 125 0 50 83 100 100 83 50 0 125 41 133 16 75 117 142

Phase shift in degrees 0 15 62 140 250 31 203 46 281 187 125 93 93 125 187 281 46 203 31 250 140 62 15

Scatter 448 Hz Diffuse 896 Hz HF cutoff 3822 Hz

Period width 1150 mm

Minimum distance to seating position 1.15m (3 times wavelength of lowest diffusion frequency)

Good result: Period width of 1150mm is is not less than the design wavelength of 384 mm

Good result: The well width is large enough to avoid viscous losses

Good result: Plate frequency of 20608 hz is higher than HF cutoff of 3822 hz, so it has no effect

Good result: The HF cutoff frequency of 3822 hz is 4.2 times the design frequency of 896 hz

True diffusion frequencies: 896 1792 2688 3584 hz

Current strategy for recommending well width of 25mm: Recommend well width so that wells are at least 25mm wide to minimise viscous losses


So far so good. I think. But, how to simulate this design with Reflex?
Demo version is limited to only 20 geometrical elements...

If you experts tell me it's an OK design. I will go with it.
If you have any comment, please, feel free to comment it before I build it




Many thanks

J.
Old 5 days ago
  #2
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Jens Eklund's Avatar
Even if you could do 47 pieces (needed for an N23 QRD) in the demo version, you would still need to model an array of them in order to evaluate performance (at least in the lower frequency range). A single relatively small object will cause diffraction regardless of shape. 3,6 meters is considered the somewhat of a standard total period width and another limit states that minimum width needs to be at least 16 times the sample height.

QRD and Skyline Well Dividers?
Old 5 days ago
  #3
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Jens Eklund's Avatar
Also;

If you can make it deeper that would be good since your current design will reflect more or less in a specular manner below the effective range (still above the modal range). If you only do one panel you might be fine (since it´s still relatively small compared to wavelength, and assuming the surrounding areas are absorptive) but the use of such a small section of diffusers is questionable. I would say minimum surface area to be useful is at least about 2 m2.
Old 5 days ago
  #4
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Ah. I was hoping you read this thread Jens.

Quote:
Originally Posted by Jens Eklund View Post
but the use of such a small section of diffusers is questionable. I would say minimum surface area to be useful is at least about 2 m2.
If 2m2 would be the minimum hmm...I will re-think and see if I can make it wider. Won't be 2m2 though.

Width of the room is 310 cm at the back.
Because of the room (non asymmetric shape) at the back: the red line is the only place to get a diffuser. (Am I wrong?)
Distance from listening point and red line is 1m80(the picture get the impression it's closer though)

Old 5 days ago
  #5
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And,

I wanted to try a finless design but with the demo limitation I can't :(
Old 5 days ago
  #6
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Jens Eklund's Avatar
You’re a bit close to the rear wall for a diffuser to be useful. About 12 ms is considered to be a lower limit regarding ISD-gap. Can you move further towards the front wall? Ideally, in front of the middle of the room (so you’re avoiding the first null due to first axial mode related to length). Normally, it´s better to keep the speakers as close to the front wall as possible.

2 m2 is not an exact figure. Make it as large as possible (if you still opt for diffuser even if room is a tad too small unless you can move further to the front).

Yes, you want symmetry.
Old 5 days ago
  #7
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Jens Eklund's Avatar
Quote:
Originally Posted by JayPee View Post
And,

I wanted to try a finless design but with the demo limitation I can't :(
Did you check the tread I linked to?
Old 5 days ago
  #8
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Quote:
Originally Posted by Jens Eklund View Post
Did you check the tread I linked to?
Yes. Doesn't mean I understand it...yet! Need time to understand everything. Specially how to interpret Reflex graphic, since I never used it.

Quote:
Originally Posted by Jens Eklund View Post

Freeform (stepped, no fins): positive and negative panel @ 1200mm each, 2400mm total width, 190mm effective depth (220mm total):
Attachment 204083

Screens are from a beta version of AFMG Reflex, posted with permission. More info here:
New EASE Tools Go Beta - AFMG - Ahnert Feistel Media Group


Sincerely Jens Eklund
If I understand it correctly...this design is the best?
Looks like Optiffuser performance (?)
Old 5 days ago
  #9
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Jens Eklund's Avatar
Quote:
Originally Posted by JayPee View Post
If I understand it correctly...this design is the best?
Looks like Optiffuser performance (?)
It is the Optiffuser (or a shape very similar to it at least if not the final version).
Old 5 days ago
  #10
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Quote:
Originally Posted by Jens Eklund View Post
It is the Optiffuser (or a shape very similar to it at least if not the final version).
fantastic result.


I think I will go with a classic QRD 1D design since I can't justify the cost of buying Reflex for only small panel.

If my room was bigger, I would have bought your panel. Definitely.

Thanks Jens!

Quote:
Originally Posted by Jens Eklund View Post
You’re a bit close to the rear wall for a diffuser to be useful. About 12 ms is considered to be a lower limit regarding ISD-gap. Can you move further towards the front wall? Ideally, in front of the middle of the room (so you’re avoiding the first null due to first axial mode related to length). Normally, it´s better to keep the speakers as close to the front wall as possible.

2 m2 is not an exact figure. Make it as large as possible (if you still opt for diffuser even if room is a tad too small unless you can move further to the front).
I will answer t oit properly later today
Old 5 days ago
  #11
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Quote:
Originally Posted by boggy View Post
QRD may be built without fins, and we still can call it "QRD diffuser" and it still works similar to QRD diffuser with fins.
Will read this paper as well...

DIY fractal diffuser help
Quote:
Originally Posted by Arqen View Post
I agree. Fins make the design more complex, and optimized stepped diffusers without fins often outperform finned Schroeder diffusers.

To support this, I've attached a paper by Trevor J. Cox that assesses optimized profiled diffusers (with and without fins).


Your fractal diffuser looks great, by the way!

I don't know if I love or hate Acoustic.
Old 5 days ago
  #12
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Jens Eklund's Avatar
Quote:
Originally Posted by JayPee View Post
Will read this paper as well...

DIY fractal diffuser help



I don't know if I love or hate Acoustic.
A QRD needs fins to perform as intended.
Old 5 days ago
  #13
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Quote:
Originally Posted by Jens Eklund View Post
You’re a bit close to the rear wall for a diffuser to be useful. About 12 ms is considered to be a lower limit regarding ISD-gap. Can you move further towards the front wall? Ideally, in front of the middle of the room (so you’re avoiding the first null due to first axial mode related to length). Normally, it´s better to keep the speakers as close to the front wall as possible.

2 m2 is not an exact figure. Make it as large as possible (if you still opt for diffuser even if room is a tad too small unless you can move further to the front).

Yes, you want symmetry.
Here is my ETC:



Then I put a plywood panel in front of backwall treatment. Looks like my ISD-GAP is around 16 ms.




Quote:
Originally Posted by Jens Eklund View Post
Normally, it´s better to keep the speakers as close to the front wall as possible.
I know but when I was treating the room. I did lot of measurements before taking any decision...and it worked better with 400mm of rockwoul on the front wall.
Attached Thumbnails
Simulate QRD 1D with Reflex? Can you check my design pls?-etc-gap-2.jpg   Simulate QRD 1D with Reflex? Can you check my design pls?-etc-gap.jpg  
Old 5 days ago
  #14
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Jens Eklund's Avatar
So you’re a bit further away than 1,8 m from the rear wall i o w. 16 ms is an ok ISD-gap. I personally want at least 14-15 ms of ISD-gap. If less, I don’t use diffusers unless the client really wants to. Then 12 ms is my minimum.
Old 5 days ago
  #15
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Quote:
Originally Posted by Jens Eklund View Post
So you’re a bit further away than 1,8 m from the rear wall
Indeed. I'm at 195cm-ish.

Thanks a lot Jens.
Old 5 days ago
  #16
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Looking forward to do that QRD 1D and see how it will look on ETC!
Old 1 day ago
  #17
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Quote:
Originally Posted by JayPee View Post
@Jens, since the ISD-gap is determined by the size of the room (or by 'smart' reflections to the listening position), how is the volume (in dB) of the reflection determined?

In the graph above, returning reflection from plywood pane is around -22db.
Is it the same principe? (determined by the size of the room?)

Thanks,

J.
Old 1 day ago
  #18
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Jens Eklund's Avatar
Assuming flat reflecting surface; distance and size would be the two factors determining the gain of the return.
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