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Rudy81

Poly-Cylindrical Diffuser and LF Absorber

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Here are the initial results of the project once hung on the walls at the reflection points.  I did run sweeps for the three main speakers as well as the subs.  Have not had time to study the results, nor had time to listen to anything.  More to come.

 

 

Poly_Stack_sm.jpg

Poly_Rt_Wall_sm.jpg

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Nice Rudy! I genuinely look forward to when you get bored with these and give them away in a few years. I'll be there! :D

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1 hour ago, Thaddeus Smith said:

Nice Rudy! I genuinely look forward to when you get bored with these and give them away in a few years. I'll be there! :D

 

Well, if I end up using poly diffusion on the back wall, you can have the quadratic diffuser I currently have there. 😁

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Could you maybe elaborate on difference between the so cold BBC diffuser and the one that you have built? I have been thinking of fabricating the BBC kind to my requirements, but your diffuser nay be easier to build.

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27 minutes ago, parlophone1 said:

Could you maybe elaborate on difference between the so cold BBC diffuser and the one that you have built? I have been thinking of fabricating the BBC kind to my requirements, but your diffuser nay be easier to build.

 

If you are talking about the 'skyline' type diffuser I think that is way more complicated to build, particularly on a large scale.  As I understand it, the poly vs. the quadratic diffuser are very different in operation.  The poly uses the curved surface to diffuse the sound and keeps the sound timing, phase and amplitude more 'coherent' than does a quadratic diffuser.  Since the quadratic diffuser has varying well depth, it changes the timing of the reflected sound.  There is quite a bit of discussion on this topic on the net.  As you can imagine, there are many opinions on the subject.  Both ideas have their detractors and supporters.  Based on how long this project has taken, it is well worth doing some intensive research before you commit to one type or the other.  This project has taken way longer than I anticipated, but seems to be well worth the time and materials....at least for me.

 

Looking at my plots, the poly's definitely do tame some, but not all, LF resonances.  In my case, some is better than none. I still have not had time to really listen to music in the room.  As soon as I have some time to dedicate to critical listening, I will report back. For sure, it sounds 'different' than my original setup with just absorbers at the reflection points.

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Thanks a lot.

Yes I was referring to the skyline type. 

You are right about the difficulties about building these to cover larger areas. 

Taming the low freques with skyline type should not be such a problem, but then the depth of the particles should be rather large, making the whole thing pretty heavy hanging on the wall. 

That is why I am following your build closely.

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I don't believe the skyline diffusers will do anything for bass frequencies.  AFAIK, they are strictly HF diffusers.

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On 8/13/2019 at 4:18 PM, Rudy81 said:

hung on the walls at the reflection points.

 

That looks good. Your speakers will probably sound more precise.

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16 hours ago, Rudy81 said:

I don't believe the skyline diffusers will do anything for bass frequencies.  AFAIK, they are strictly HF diffusers.

 

I know you get get/build QRDs for as low at 600 Hz, but the lower the freq. the deeper the wells have to be.  I would like to hear what the room below is like when they are doing a mix. It is Studio C in Blackbird Studios in Berry Hill, TN. The have quite a lot of rooms (A thru I) and hardware, and actually do classes on recording and engineering.

 

 

blackbird_studio.png

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Generally speaking, most rooms have the biggest problems with bass and it is the hardest to tame.  I am talking about bass below 300hz or so.  My goal with this build was twofold.  First to tame some of the bass room modes and second, to improve the room 'sound' by not just absorbing the HF frequencies.  I'm still in the early stages of listening to the new room, but it seems very promising. 

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They sure look nice.  I've got a question which I'm sure would be answered by a little investigative work on my part, but I'm here now, am a tad lazy, and only mildly curious.  I believe I clearly "see" what the intents are and how they're meant to get accomplished, so am not seeking clarification beyond one aspect.

 

So you've got a relatively floppy and "massive" membrane, which, I guess, at least for a time could be "tuned" to particular frequencies via installation tension.  At any rate, the goal is to have these membranes absorb, thus cause to cease at least to some extent, "low" frequencies.

 

It appears as though the membrane was installed at a slight recess (1/8 to 1/4 inch?) from the rear plane of the device.  How far from the wall are you placing the backsides?  I think I've gotten the impression that these are being hung on the wall (it appears so in the photos) and if so, what provision is being made to allow the low-frequency airborne pressure waves' "access" to the membranes?  Are the units mounted to the wall with standoffs?  2, 4, 6, etc. inches?

 

 

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I have not explored how to 'tune' the membrane at all and although I'm sure it would be possible to figure that out, I'm not looking at that right now.  The curved surface is also flexible to some extent when you put pressure on it since it is bendable plywood and it is very pliable. 

 

The recess is 3/4" which is the 18mm plywood frame.  I cam up with this since the back of the frame rests against the wall surface. I figured the MLV needs room to 'breathe' as the LF pressure strikes the MLV surface.  The LF will transfer across the curved surface, so that is how it gains access to the MLV membrane. 

 

Units are mounted with french cleats flush with the wall.  In actuality, I didn't need to create the MLV mounting frame since the french cleat by itself creates a 3/4" space behind the frame.  So now, the MLV membrane is about 1.5" from the wall surface.

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