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DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)
Old 28th November 2014
  #511
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🎧 5 years
Hi Arqen, I'm going to build diffuser panels for my listening room, my speakers are full statements ( curt's design ) that have open back/transmission line for the mid range,spaced about 56cm from the wall and on this wall I wanted to put the diffuser panels.
I was looking at the model 12 or model 6, the first seems to have good performance even at low frequencies, but my doubt concerns the depth of the panel, I worry that 20cm depth will force me to move forward the speakers and the listener position too ... unfortunately my room is pretty small, 4x4.5 meter circa with chunk bass traps in the rear corners, and bass traps on the first reflections, side and ceiling.
What model of diffuser do you recommend?
Old 29th November 2014 | Show parent
  #512
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🎧 5 years
Quote:
Originally Posted by verderame ➡️
Hi Arqen, I'm going to build diffuser panels for my listening room, my speakers are full statements ( curt's design ) that have open back/transmission line for the mid range,spaced about 56cm from the wall and on this wall I wanted to put the diffuser panels.
I was looking at the model 12 or model 6, the first seems to have good performance even at low frequencies, but my doubt concerns the depth of the panel, I worry that 20cm depth will force me to move forward the speakers and the listener position too ... unfortunately my room is pretty small, 4x4.5 meter circa with chunk bass traps in the rear corners, and bass traps on the first reflections, side and ceiling.
What model of diffuser do you recommend?
Hi Verderame,

I don't think I'm familiar with the model 12 or model 6, but I suggest you don't bother trying to diffuse low frequencies in your room.

I don't know the polar response of your particular open back speakers, but most other speakers are quite directional above 500 Hz, which is close to the frequency that most diffusers start kicking in. In this case, the amount of direct energy from the speakers that's actually being diffused would be modest, and the choice of diffuser is not critical.

While 1D diffusion is usually preferred on the back wall, on your front wall you have the option of using 1D or 2D diffusion. I would probably choose 2D diffusion (e.g. a wooden "Skyline" type build) here, to disperse some energy out of the plane of listening and help build a highly diffuse sound field as sound decays in your room.

But it depends on how much energy your speakers are radiating backward, and at what frequencies. Front wall diffusers often interact more with indirect reflections (e.g., sound that reflected off your back wall and returns to the front of the room) than direct sound.

I recently wrote a tutorial on speaker placement and boundary interference from your front wall.

As explained in the guide, in small rooms I would typically move the speakers close enough to the wall to raise the frequency of the quarter wavelength cancellation (so that it can be dealt with using absorption). In this case, with the speakers close to the wall, if there is room for anything behind them I would choose broadband bass absorption instead of diffusers. Meanwhile, diffusion can be used in the middle of the front wall.
Old 29th November 2014 | Show parent
  #513
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🎧 5 years
Quote:
Originally Posted by Arqen ➡️
Hi Verderame,

I don't think I'm familiar with the model 12 or model 6, but I suggest you don't bother trying to diffuse low frequencies in your room.

I don't know the polar response of your particular open back speakers, but most other speakers are quite directional above 500 Hz, which is close to the frequency that most diffusers start kicking in. In this case, the amount of direct energy from the speakers that's actually being diffused would be modest, and the choice of diffuser is not critical.

While 1D diffusion is usually preferred on the back wall, on your front wall you have the option of using 1D or 2D diffusion. I would probably choose 2D diffusion (e.g. a wooden "Skyline" type build) here, to disperse some energy out of the plane of listening and help build a highly diffuse sound field as sound decays in your room.

But it depends on how much energy your speakers are radiating backward, and at what frequencies. Front wall diffusers often interact more with indirect reflections (e.g., sound that reflected off your back wall and returns to the front of the room) than direct sound.

I recently wrote a tutorial on speaker placement and boundary interference from your front wall.

As explained in the guide, in small rooms I would typically move the speakers close enough to the wall to raise the frequency of the quarter wavelength cancellation (so that it can be dealt with using absorption). In this case, with the speakers close to the wall, if there is room for anything behind them I would choose broadband bass absorption instead of diffusers. Meanwhile, diffusion can be used in the middle of the front wall.
Thanks for the reply.
Model 12 is 36 optimized stepped diffuser 35 wells
Model 6 is optimized stepped diffuser B2-LF array of 5 modules
They come from your pdf available for download!
I'll try to get more informations about speakers backward radiation, now I'm reading your tutorial and it is very helpful.
Old 30th November 2014 | Show parent
  #514
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Quote:
Originally Posted by verderame ➡️
Thanks for the reply.
Model 12 is 36 optimized stepped diffuser 35 wells
Model 6 is optimized stepped diffuser B2-LF array of 5 modules
They come from your pdf available for download!
I'll try to get more informations about speakers backward radiation, now I'm reading your tutorial and it is very helpful.
Ahh! Makes sense. I used third party software (AFMG Reflex) to verify the performance of the designs, and those numbers were automatically generated by the software. Model 12 simply means that it's the 12th model I've tested in that session. In the end those labels add to the confusion but unfortunately it would not let me relabel them in.

BTW, instead of B2-LF you're better off building 5 or 7 A1-LF (Leanfuser) panels and mounting them using the recommended profiled modulations. A1-LF panels are easier to build than B2-LF, and if you mount them using the profiled modulations, they perform better too.
Old 2nd December 2014 | Show parent
  #515
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🎧 5 years
Quote:
Originally Posted by Arqen ➡️
Ahh! Makes sense. I used third party software (AFMG Reflex) to verify the performance of the designs, and those numbers were automatically generated by the software. Model 12 simply means that it's the 12th model I've tested in that session. In the end those labels add to the confusion but unfortunately it would not let me relabel them in.

BTW, instead of B2-LF you're better off building 5 or 7 A1-LF (Leanfuser) panels and mounting them using the recommended profiled modulations. A1-LF panels are easier to build than B2-LF, and if you mount them using the profiled modulations, they perform better too.
Thanks again Arqen, I decide to build a 7 A1-LF.
When it will complete I'll send you a picture of it.
Old 3rd December 2014 | Show parent
  #516
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Quote:
Originally Posted by verderame ➡️
Thanks again Arqen, I decide to build a 7 A1-LF.
When it will complete I'll send you a picture of it.
Awesome. Hope the build goes well and I look forward to seeing it!

-Tim
Old 10th December 2014
  #517
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Hi Arqen,
New member here. I'm working to make a basement listening room sound acceptable. My main problem is low ceilings (about 7'). I'm using waveguide speakers, so direct sound path is strong, but there is still reflection off the ceiling. Can I ask some advice?
1) Is this a good application of diffusers, or should I just fill in between the floor joists above with absorptive material? The room is already relatively well damped (rugs and furniture in the listening area) so I'd like to preserve the liveliness of the sound.
2) If diffusers is a good idea, I'd like to try your Leanfuser design as woodworking area is limited to the rest of the basement, and I like the low height and efficiency of the build. If I went that way, which way should the lines of the Leanfuser run? The speakers are strongly toed-in (about 45 degrees). Should the lines run parallel to the seating row or perpendicular? Or separate diffusers, each parallel to a speaker?

Thanks and sorry for all the newbie questions!
Bill

Last edited by bwaslo; 10th December 2014 at 10:55 PM.. Reason: found answer to one of the questions on further reading - deleted
Old 11th December 2014 | Show parent
  #518
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Quote:
Originally Posted by bwaslo ➡️
Hi Arqen,
New member here. I'm working to make a basement listening room sound acceptable. My main problem is low ceilings (about 7'). I'm using waveguide speakers, so direct sound path is strong, but there is still reflection off the ceiling. Can I ask some advice?
1) Is this a good application of diffusers, or should I just fill in between the floor joists above with absorptive material? The room is already relatively well damped (rugs and furniture in the listening area) so I'd like to preserve the liveliness of the sound.
2) If diffusers is a good idea, I'd like to try your Leanfuser design as woodworking area is limited to the rest of the basement, and I like the low height and efficiency of the build. If I went that way, which way should the lines of the Leanfuser run? The speakers are strongly toed-in (about 45 degrees). Should the lines run parallel to the seating row or perpendicular? Or separate diffusers, each parallel to a speaker?

Thanks and sorry for all the newbie questions!
Bill
Hey Bill,

Welcome! Since your ceiling is low I recommend you focus on absorption at the ceiling first reflection points. If you do use diffusers on the ceiling I recommend 2D diffusers, or hybrid absorber-diffusers.

My designs are 1D diffusers, and they are best used in the plane of listening (for example, on the rear wall). If you want to use them on the ceiling you could build lots of square panels and orient them in both directions (in a chess board pattern). However, they are not designed to be used like this, so if you do this I suggest you don't do it at critical locations (namely, the ceiling first reflection points).

From what I'm hearing about your room, possible candidates for diffusion are the rear wall, front wall, rear part of the ceiling, rear part of the sidewalls, possibly the front part of the ceiling and sidewalls.

Whether you use diffusion at the sidewall and ceiling first reflection points depends on how large your room is and how accurate you want it to sound. Usually, if a reflection point is close to you (like your ceiling first reflection points) I recommend broadband absorption there. But if you're less concerned about accuracy and more concerned about creating an enveloping listening space, a blend of absorption and diffusion may be suitable there (e.g., hybrid surfaces that provide absorption at mid frequencies and diffusion at higher frequencies).

I wish I could give you a hard recommendation for your first reflection points, but it's a balancing act that depends on your room and your goals. The easiest approach is to use absorption there, but it's not the best approach for everyone. You can always start with absorption there, see how it sounds, and then experiment with diffusion.

A more scientific approach is use energy time curve measurements (see Section B) to help you choose treatments for the first reflection points. But this is pretty advanced stuff.

Let me know if anything I've said does not make sense!

Cheers,
Tim
Old 13th December 2014 | Show parent
  #519
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🎧 10 years
Hi Tim (and everyone),

Hope you are great.

I refer to my own post from 2 years ago:

https://gearspace.com/board/8567591-post195.html

I learned from you and I made models in Reflex.

You liked my model using 6mm ply and 35mm wells - N7 with 7 periods modulated.

I promised I'd show you and everyone the build.

Well, it took me two years to do it, but I finally have. Just touching up the white stain finish.

So this is just a heads up to say that some build pics will be incoming!

Nolan

Old 13th December 2014 | Show parent
  #520
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Quote:
Originally Posted by unqlenol ➡️
Hi Tim (and everyone),

Hope you are great.

I refer to my own post from 2 years ago:

https://gearspace.com/board/8567591-post195.html

I learned from you and I made models in Reflex.

You liked my model using 6mm ply and 35mm wells - N7 with 7 periods modulated.

I promised I'd show you and everyone the build.

Well, it took me two years to do it, but I finally have. Just touching up the white stain finish.

So this is just a heads up to say that some build pics will be incoming!

Nolan


Nolan, this is great news!

Your version of the design looks like a good approach for people who want mid-high frequency diffusion, but don't have the time or ability to build the little fractal cells in the standard Leanfractal.

I can't wait to see the build pics!
Old 13th December 2014 | Show parent
  #521
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🎧 10 years
Module assembly pics.

Note for peeps who never followed the earlier stages of this thread:
This model has some positive attributes.
It is shallow. It can work in a small room more easily as a result.
It is fairly economical as the ply is only 6mm thick.
The thin wells are wide enough to not end up causing too much absorption, but thin enough to encourage good HF diffusion.

More to come.
Attached Thumbnails
DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-1-organising-parts.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-2-organising-parts.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-3-wife-not-happy.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-4-hard-rock-glue.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-5-completing-modules.jpg  

Old 15th December 2014 | Show parent
  #522
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🎧 5 years
Diffuser well width and absorption

Quote:
Originally Posted by unqlenol ➡️
Module assembly pics.
It is shallow. It can work in a small room more easily as a result.
It is fairly economical as the ply is only 6mm thick.
The thin wells are wide enough to not end up causing too much absorption, but thin enough to encourage good HF diffusion.
Yes, thanks for bringing that last point up.

For anyone who does not know this, one potential pitfall with HF fractal designs is that they introduce extra absorption. With narrow wells, the viscous boundary layer becomes significant compared to the well width, meaning for each well of the diffuser you get significant absorption due to friction.

The minimum well width to mostly avoid this effect is about 2.5 cm.

With a well width of 3.5 cm this version of the design gives a good balance of med-high frequency diffusion with minimal absorption.
Old 15th December 2014
  #523
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🎧 5 years
Threads like this just remind me how little I know about the world I live in. Thanks OP for the info though! I may give this a go myself once I read and re-read

PS when do you get your results for the thesis?
Old 15th December 2014 | Show parent
  #524
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Quote:
Originally Posted by zigziglar ➡️
Threads like this just remind me how little I know about the world I live in. Thanks OP for the info though! I may give this a go myself once I read and re-read

PS when do you get your results for the thesis?
Glad you appreciate everything we've accumulated here!

By results, do you mean grade / professor feedback, or something else? I got those results a couple years ago and I'm happy to say it was very well received with top marks. I later found a programming glitch (thanks to feedback from Jens) but it does not effect the practical results.

At the end of the day, the marks are just numbers and I was most happy with the practical designs that the optimization code spit out. If not for those, this thread would not exist.

That justifies the effort and many sleepless nights that went into it.

It's opened a lot of doors.
Old 15th December 2014 | Show parent
  #525
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🎧 5 years
Quote:
Originally Posted by Arqen ➡️
Glad you appreciate everything we've accumulated here!

By results, do you mean grade / professor feedback, or something else? I got those results a couple years ago and I'm happy to say it was very well received with top marks. I later found a programming glitch (thanks to feedback from Jens) but it does not effect the practical results.

At the end of the day, the marks are just numbers and I was most happy with the practical designs that the optimization code spit out. If not for those, this thread would not exist.

That justifies the effort and many sleepless nights that went into it.

It's opened a lot of doors.
Ahhh old news then. Well I'm glad it went well - I would've been surprised if it didn't from the depth of research involved in developing the designs. Once I've got the first stage of acoustic treatment positioned (broadband panels and corner bass traps), I'll run some REW tests and check out the graphs to see where this kind of diffusion could help.

I've got two rooms to choose from. One is 3 x 3.5 x 2.4m (WxLxH) and the other is 6 x 3.5 x 2.4m. Naturally the larger, rectangular room will have less modal issues in the seating position, but the room is ... more desirable to keep as a second lounge room from the wife's perspective. A difficult balance of priorities to weigh up haha Either way, the low profile diffusion will be of benefit.
Old 16th December 2014 | Show parent
  #526
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🎧 10 years
Ok, some more pics. Unfortunately I was too stressed during the build to take pics of how I made the standoffs for modulation, mounting everything to the backboard etc.

Some points to note:

I stuffed the raised modules with Isotherm insulation blanket to reduce any chamber resonances and to help add some absorption for the lower frequencies that would reflect but not diffuse.

If I were to build this again I would lose the side pieces of the frame and rather have a curved top and bottom plate to 'cap the array'. Especially since I see how guys on this thread have done such lovely clean work with design and mounting.

The finish is a white stain/sealant. One can see a bit of grain peering through.
The idea was to get a fresh look which ties in with a studio desk which I built at the same time.

Eventually I will add slats over my corner traps ('superchunks') to tie it all in with the diffusor.

Any comments, criticisms or feedback welcome.

And Tim....thanks man.....
Attached Thumbnails
DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-2014-12-14-22.31.49.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-2014-12-14-22.28.34.jpg   DIY Sound Diffusers—Free Blueprints—Slim, Optimized DIY Diffuser Designs (+Fractals)-2014-12-13-20.12.18.jpg  
Old 16th December 2014 | Show parent
  #527
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🎧 5 years
Room ratios

Quote:
Originally Posted by zigziglar ➡️
Ahhh old news then. Well I'm glad it went well - I would've been surprised if it didn't from the depth of research involved in developing the designs. Once I've got the first stage of acoustic treatment positioned (broadband panels and corner bass traps), I'll run some REW tests and check out the graphs to see where this kind of diffusion could help.

I've got two rooms to choose from. One is 3 x 3.5 x 2.4m (WxLxH) and the other is 6 x 3.5 x 2.4m. Naturally the larger, rectangular room will have less modal issues in the seating position, but the room is ... more desirable to keep as a second lounge room from the wife's perspective. A difficult balance of priorities to weigh up haha Either way, the low profile diffusion will be of benefit.
If only a petition signed by Gearslutz members would persuade her to give up the big room.

FYI, if you want to check your room ratios, here's a good resource.
Room Sizing Tutorial | Acoustics, Audio and Video | University of Salford

It gives lists of good ratios for rooms that are 50m3 (directly applicable to the larger of your two rooms), 100m3 and 200m3.
Old 16th December 2014 | Show parent
  #528
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🎧 5 years
Quote:
Originally Posted by Arqen ➡️
If only a petition signed by Gearslutz members would persuade her to give up the big room.

FYI, if you want to check your room ratios, here's a good resource.
Room Sizing Tutorial | Acoustics, Audio and Video | University of Salford

It gives lists of good ratios for rooms that are 50m3 (directly applicable to the larger of your two rooms), 100m3 and 200m3.
Thanks for the link, although I have no idea how to apply the data to my situation haha I'll have to read up.
Old 16th December 2014 | Show parent
  #529
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🎧 5 years
Quote:
Originally Posted by unqlenol ➡️
Ok, some more pics. Unfortunately I was too stressed during the build to take pics of how I made the standoffs for modulation, mounting everything to the backboard etc.

Some points to note:

I stuffed the raised modules with Isotherm insulation blanket to reduce any chamber resonances and to help add some absorption for the lower frequencies that would reflect but not diffuse.

If I were to build this again I would lose the side pieces of the frame and rather have a curved top and bottom plate to 'cap the array'. Especially since I see how guys on this thread have done such lovely clean work with design and mounting.

The finish is a white stain/sealant. One can see a bit of grain peering through.
The idea was to get a fresh look which ties in with a studio desk which I built at the same time.

Eventually I will add slats over my corner traps ('superchunks') to tie it all in with the diffusor.

Any comments, criticisms or feedback welcome.

And Tim....thanks man.....

Nolan,

Great work and thanks for sharing your ideas and your build!

Looks very cool and I really like the smaller form factor.
And good call using absorption inside the raised modules.

Also, nice to see big corner bass traps in your room. That's the way I like to see superchunks built... BIG. I think slats over the bass traps is a good idea and will look good.
Old 17th December 2014 | Show parent
  #530
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Quote:
Originally Posted by zigziglar ➡️
Thanks for the link, although I have no idea how to apply the data to my situation haha I'll have to read up.
To save you the time, your ratios for the larger room are 1:1.46:2.5, which does not land on any of the *best* or *second best* ratios for 50m3 rooms.

But of course, the larger room is still the better option.

In this case checking ratios was more out of curiosity than anything else. I guess if the room had the worlds best ratios, you could try using that as an argument that the room is acoustically gifted and is destined to sound amazing... and to deny it that destiny would be a moral travesty.
Old 18th December 2014 | Show parent
  #531
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Quote:
Originally Posted by Arqen ➡️
To save you the time, your ratios for the larger room are 1:1.46:2.5, which does not land on any of the *best* or *second best* ratios for 50m3 rooms.

But of course, the larger room is still the better option.

In this case checking ratios was more out of curiosity than anything else. I guess if the room had the worlds best ratios, you could try using that as an argument that the room is acoustically gifted and is destined to sound amazing... and to deny it that destiny would be a moral travesty.
Thanks! One last option is 4750x3650x2600mm. I'll see if I can figure this one out. Fingers crossed it's better!
Old 18th December 2014 | Show parent
  #532
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Quote:
Originally Posted by zigziglar ➡️
Thanks! One last option is 4750x3650x2600mm. I'll see if I can figure this one out. Fingers crossed it's better!
It's almost certainly better than the smallest one, simply due to the extra length and volume.
Old 24th December 2014 | Show parent
  #533
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🎧 5 years
Hey there Arqen!

Thanks so much for opensourcing your designs! And also for giving all this advice publicly! I'm sure many people have learned much from you about acoustics, as I have.

I'm building the simplest design (the A1 Stepped Diffuser) right now with a little help from my friend who has more tools and experience at building stuff than myself.

My room is quite an unusual one and probably smaller than most, measuring 370cm*250cm*220cm (the ceiling is angled, so the 220cm height is actually an average of 246cm at the back wall and 193cm at the front wall). It has more peculiarities which I omit for now.

So the apparent dimensions are as follows:
average (middle): 1:1.68:1.14
front: 1:1.92:1.3
back: 1:1.5:1.02

Room volume is about 20.35 cubic meters if my calculation is right. (comparing to the spreadsheet of the "second best room ratios", it is 2.5 times smaller than the 50 cubic meters smallest one mentioned there)

As you can see, on the back end it is almost quadratic . Up until now, I had my speakers positioned at the longer wall. That is due to convenience considerations (the window and the door are on the short opposite walls), as well as due to the fact that the 2 longer walls are made of different materials (one of them is stone, the other one is wood). The ceiling is also wooden. Predictably, the "quadratic" part of the room had much stronger resonances in the low- and mid-frequencies, which I tried to tame with absorption (to limited success). However stereophonic image still didn't feel "right", so I decided to rearrange the room. I covered most of the stone wall with wood (about 2/3ds of it's length), and I placed the speakers on the "window" (lower) side of the room, so the "door" (higher) side is the back wall now.

Now what I'm planning to do is having plenty of absorption on the front (window) wall, especially in the corners, and even more on the back wall's corners. Also some absorption on the first reflections spots. Then, as soon as I finish building the stepped diffuser, I will mount it on the back wall. I can only have as many as 3 modules there due to the wall being too short. Even then it won't fit, so I had to reconsider parts of the design in order to make the diffuser narrower, to keep the door accessible (it's located in the corner). I decided to give up some of the base width, so every module is going to be 38cm wide, instead of 42cm as designed. The rest of the diffuser is built to your specs.

I wonder how this plan sounds to you and if you have any additional advice. Besides moving somewhere else

Thank you again!

tangerine
Old 26th December 2014 | Show parent
  #534
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Quote:
Originally Posted by tangerine ➡️
Hey there Arqen!

Thanks so much for opensourcing your designs! And also for giving all this advice publicly! I'm sure many people have learned much from you about acoustics, as I have.

I'm building the simplest design (the A1 Stepped Diffuser) right now with a little help from my friend who has more tools and experience at building stuff than myself.

My room is quite an unusual one and probably smaller than most, measuring 370cm*250cm*220cm (the ceiling is angled, so the 220cm height is actually an average of 246cm at the back wall and 193cm at the front wall). It has more peculiarities which I omit for now.

So the apparent dimensions are as follows:
average (middle): 1:1.68:1.14
front: 1:1.92:1.3
back: 1:1.5:1.02

Room volume is about 20.35 cubic meters if my calculation is right. (comparing to the spreadsheet of the "second best room ratios", it is 2.5 times smaller than the 50 cubic meters smallest one mentioned there)

As you can see, on the back end it is almost quadratic . Up until now, I had my speakers positioned at the longer wall. That is due to convenience considerations (the window and the door are on the short opposite walls), as well as due to the fact that the 2 longer walls are made of different materials (one of them is stone, the other one is wood). The ceiling is also wooden. Predictably, the "quadratic" part of the room had much stronger resonances in the low- and mid-frequencies, which I tried to tame with absorption (to limited success). However stereophonic image still didn't feel "right", so I decided to rearrange the room. I covered most of the stone wall with wood (about 2/3ds of it's length), and I placed the speakers on the "window" (lower) side of the room, so the "door" (higher) side is the back wall now.

Now what I'm planning to do is having plenty of absorption on the front (window) wall, especially in the corners, and even more on the back wall's corners. Also some absorption on the first reflections spots. Then, as soon as I finish building the stepped diffuser, I will mount it on the back wall. I can only have as many as 3 modules there due to the wall being too short. Even then it won't fit, so I had to reconsider parts of the design in order to make the diffuser narrower, to keep the door accessible (it's located in the corner). I decided to give up some of the base width, so every module is going to be 38cm wide, instead of 42cm as designed. The rest of the diffuser is built to your specs.

I wonder how this plan sounds to you and if you have any additional advice. Besides moving somewhere else

Thank you again!

tangerine
Hi Tangerine,

Great to hear that you're building the stepped diffusers!

Sounds like you're on the right path, but mid-high frequency absorption on your front wall is typically not necessary because your speakers are mostly directional at higher frequencies. I.e., they don't radiate much mid-high frequency energy backward toward the front wall. That front wall absorption may be put to better use on the ceiling or sidewalls.

Of course, you need bass traps in the corners and absorption at your first reflection points, as you mentioned.

I recently wrote a big bass trap placement tutorial here. I recommend you use the tips in that guide to make sure you allocate your absorption properly. I also recommend you check out the guide to speaker placement here, especially the part about speaker-wall distance (the second page of the guide).

If you're planning to add front wall absorption at mid-high frequencies, make sure you have a good reason for it. Three scenarios for which I would consider broadband absorption on your front wall are:
1) You've strategically put your speakers very close to the front wall, such that the speaker boundary interference cancellation notch is moved to higher frequencies, and you want to target that notch by using absorption behind the speakers. (See page 2 of my speaker placement guide for details on this).
2) You're trying to fix a slap / flutter echo problem.
3) You're trying to lower the decay times in your rooms at mid-high frequencies, and you've already applied bass traps + treatments to your sidewalls, rear wall and ceiling.

Hope this helps and I wish you the best with your build!

-Tim
Old 26th December 2014 | Show parent
  #535
Gear Head
 
🎧 5 years
Hey Tim,

Quote:
Originally Posted by Arqen ➡️
I recently wrote a big bass trap placement tutorial here. I recommend you use the tips in that guide to make sure you allocate your absorption properly. I also recommend you check out the guide to speaker placement here, especially the part about speaker-wall distance (the second page of the guide).
Actually I have read both of these guides and I find them very useful!
BTW, regarding speaker-wall boundary interference, I remember you mentioning the effect of low-shelving as a result of speaker proximity to the wall, akin to "proximity effect" of pressure-gradient microphones. I'd like to learn more about this subject and how to deal with it. Blindly finding the correct EQ curve to balance the frequency response can be very difficult. Also I wonder if low-shelving is indeed what's going on there, because that's definitely not the case with pressure-gradient mics:
http://www.neumann.com/download.php?...d=docu0002.PDF
(Page 15)

Quote:
Originally Posted by Arqen ➡️
If you're planning to add front wall absorption at mid-high frequencies, make sure you have a good reason for it. Three scenarios for which I would consider broadband absorption on your front wall are:
1) You've strategically put your speakers very close to the front wall, such that the speaker boundary interference cancellation notch is moved to higher frequencies, and you want to target that notch by using absorption behind the speakers. (See page 2 of my speaker placement guide for details on this).
This is indeed the case. In my small room, I have no other choice. Reinforcing this are two aditional factors:
1) This wall has a large window over all it's length, which I'm still looking into best way to deal with, as it makes impossible to work with computer monitors put against it. I guess a big opaque reflecting surface would be best acoustically-wise, however I want to be able to fold it when not mixing in order to let the light in. Not sure if there is any [accessible] material satisfying both terms (reflecting and foldable).
2) This wall has a significant "step" in it's lower corner over all it's length. This step is about 35cm high and 37cm deep, and I think it's going to add to the boundary interference effect, unless I have absorbers covering it. My speakers' woofers are only about 110cm from the floor, and considering this step, they are only 75cm high.

Have great holidays!

tangerine
Old 29th December 2014 | Show parent
  #536
Gear Addict
 
Arqen's Avatar
 
🎧 5 years
Quote:
Originally Posted by tangerine ➡️
Hey Tim,


Actually I have read both of these guides and I find them very useful!
BTW, regarding speaker-wall boundary interference, I remember you mentioning the effect of low-shelving as a result of speaker proximity to the wall, akin to "proximity effect" of pressure-gradient microphones. I'd like to learn more about this subject and how to deal with it. Blindly finding the correct EQ curve to balance the frequency response can be very difficult. Also I wonder if low-shelving is indeed what's going on there, because that's definitely not the case with pressure-gradient mics:
http://www.neumann.com/download.php?...d=docu0002.PDF
(Page 15)


This is indeed the case. In my small room, I have no other choice. Reinforcing this are two aditional factors:
1) This wall has a large window over all it's length, which I'm still looking into best way to deal with, as it makes impossible to work with computer monitors put against it. I guess a big opaque reflecting surface would be best acoustically-wise, however I want to be able to fold it when not mixing in order to let the light in. Not sure if there is any [accessible] material satisfying both terms (reflecting and foldable).
2) This wall has a significant "step" in it's lower corner over all it's length. This step is about 35cm high and 37cm deep, and I think it's going to add to the boundary interference effect, unless I have absorbers covering it. My speakers' woofers are only about 110cm from the floor, and considering this step, they are only 75cm high.

Have great holidays!

tangerine
Hey Tangerine,

Sorry for the delayed reply. Just got back from a ski trip.

You're right that accurate correction is more complicated than simply applying a shelving filter.

I'm certainly no expert on speaker design but free standing speakers have baffle step compensation built into their circuitry. If you were to flush mount such a speaker into your wall you're effectively giving it an infinite baffle, so you would need to remove the baffle step compensation. The exact shape of the EQ curve needed would depend on the original baffle step compensation (which in turn depends on the design of the speaker and baffle).

Likewise, if you put the speaker close to the wall you need to apply a correction, and to find the "exact" correction you would need to run measurements.

Some speakers have boundary gain compensation control, which lets you apply an approximate correction. But a more accurate way is to use a calibrator to create an EQ curve that compensates for the boundary interference you're experiencing.
Old 21st January 2015
  #537
Here for the gear
 
🎧 5 years
So how exactly would one go about making a fractal diffuser? The tiny ribs on the half-rounds look tough to duplicate. Any ideas? I'd love to try!
Old 21st January 2015 | Show parent
  #538
Here for the gear
 
🎧 5 years
I want to try these on my left and right walls in my home theater, btw. I'm building a Skyline for the back convex wall.
Old 22nd January 2015 | Show parent
  #539
Gear Addict
 
Arqen's Avatar
 
🎧 5 years
Building fractal diffusers

Quote:
Originally Posted by leafthelucky ➡️
So how exactly would one go about making a fractal diffuser? The tiny ribs on the half-rounds look tough to duplicate. Any ideas? I'd love to try!
I've seen several nice fractal diffuser builds.

Here's how to build my favorite fractal design, the Leanfractal (A1-Frac). The Leanfractal is my personal favorite because you can mount it using the same profiled modulations that are given for the Leanfuser. Mounted this way it can perform better than my other fractal diffuser design, the Stepfractal (B2-Frac). The Leanfractal is also easier to build.

Step 1: Build Leanfuser modules according to the A1-LF fabrication drawings.

Step 2: The tedious part: mill the small fractal cells. Details about them are given in the FAQ here. One way to make them is on a milling machine, like Schaap has done here and here. I recall at least one person used a table saw to do this.

Step 3: Mount the fractal cells onto the Leanfuser modules.

Step 4: Mount your Leanfractal panels using the same profiled modulations recommended for the Leanfuser. See the FAQ for this.

See the diffuser build gallery for example fractal diffuser build photos.

Leanfractal (A1-Frac) built by Pablo Crespo:

Dry assembly of Leanfractal panel (prior to gluing):


Stepfractal (B2-Frac) built by Steven Mazzotta at Kalakula Studio:




If you decide to build a fractal diffuser, please let us know how it goes!

Good luck!

-Tim

Last edited by Arqen; 22nd January 2015 at 04:30 AM..
Old 23rd January 2015 | Show parent
  #540
Here for the gear
 
🎧 10 years
I have read all the pages in this topic but it seems like most people are only interested in form, in "how to build" the diffuser like it is some kind of furniture and not in its main function, the sound itself. So, how does it SOUND? What difference did it make? Did you compare it to QRD (with fins) or PRD diffusor? Did you calculate its depth right or it didn't perform as you have expected? Do you think that you needed to build more of them to make the same difference as with classical PRD diffusors? Or you didn't even noticed any difference in sound vs. bare wall at all?
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