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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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It has been a while  since I updated this post. I liked the sound from the reflection point polys so much, that I wanted to build some for the back wall.  However, they are oriented ninety degrees to those on the reflection points. Pics to follow. The back wall build took a while, so have not posted much while that was in progress. Last night I had an opportunity to do some real listening to the room changes and to take some Audyssey measurements. 

 

The sound in the room is a definite uptick from what it was.  The soundstage is wider and simply more realistic.  Imagining is spot on.  It was pretty good before, but this is on another level.  Walking around the room while bass is playing definitely shows that the poly's do absorb bass and prevent some of the nasty room modes. Not all modes however, as some of the lower frequencies do still exhibit room mode interaction.  At this point, not much I can do about that. I have looked at the Acoustic Fields carbon absorber units, but the price is prohibitive for treating the lowest of frequencies.  Not to mention those units take up a lot of room, and as crazy as it sounds, I am running out of room in the HT.

 

A close look at the Audyssey Pro measurements I took last night do show that the bass frequencies exhibit a flatter response in the room vs. before the polys were added. 

 

So far, this project has been very worthwhile and relatively inexpensive on a DIY basis.  When I get a chance, I will post pics of the finished product.

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I've been following along and I enjoy your work. I'm curious as to the size of your room. I'm looking to the future where I will most likely have a smaller space, so I like to use other peoples' work as a point of reference as to what I may or may not be able to do. Thanks for sharing this!

 

Jeremy

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2 hours ago, capo72 said:

I've been following along and I enjoy your work. I'm curious as to the size of your room. I'm looking to the future where I will most likely have a smaller space, so I like to use other peoples' work as a point of reference as to what I may or may not be able to do. Thanks for sharing this!

 

Jeremy

 

IIRC, the room is 24' wide and 27' long. Ceiling height is 9' and a few inches.

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I am interested in how this turns out, as I am also thinking of making some of these.

Question: My ceiling is 33' high, and curved. Would it be any benefit to treat the walls above 13'...or just below 13'?

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1 hour ago, Ron E said:

I am interested in how this turns out, as I am also thinking of making some of these.

Question: My ceiling is 33' high, and curved. Would it be any benefit to treat the walls above 13'...or just below 13'?

 

  •  I remember seeing pictures of your place in Mexico (I think), but there is one thing I don't remember.  Is the curved ceiling concave or convex?
  • I'd consider some kind of hemispheric diffusion (probably convex, diffusing in several directions, like mushroom heads aimed into the room) on the walls between the 13 foot high level and the 33 foot ceiling, perhaps just some poly-cylindricals orientated in several directions different than the orientation of those below 13 feet, some made of hardwood, some of something harder (more reflective).
  • I really don't know if random directions of a snaggletooth diffuser would be better or worse than mathematically designed ones.
  • A room the size of yours should sound big, IMO. 

Mushroom diffusers (no psilocybin involved, but magic nonetheless)

image.png.ca1c56f1c3e1ac34159cfc24a3b89271.png

image.png.6e252be5cc8054cf166cb86ce3584c5f.png

 

image.png.9f553696ac0848c3faac55a2717178ae.png

 

OR

image.thumb.png.a6f2be57c1077560d3a351d4d436127d.pngimage.thumb.png.ee620244ae498e06a0367a5042207473.png

The Human Condition series of sculptures by Lawrence Sheraton -- so your diffusers will be talked about.

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  •  I remember seeing pictures of your place in Mexico (I think), but there is one thing I don't remember.  Is the curved ceiling concave or convex?
  • I'd consider some kind of hemispheric diffusion (probably convex, diffusing in several directions, like mushroom heads aimed into the room) on the walls between the 13 foot high level and the 33 foot ceiling, perhaps just some poly-cylindricals orientated in several directions different than the orientation of those below 13 feet, some made of hardwood, some of something harder (more reflective).
  • I really don't know if random directions of a snaggletooth diffuser would be better or worse than mathematically designed ones.
  • A room the size of yours should sound big, IMO. 
Mushroom diffusers (no psilocybin involved, but magic nonetheless)
image.png.ca1c56f1c3e1ac34159cfc24a3b89271.png
image.png.6e252be5cc8054cf166cb86ce3584c5f.png
 
image.png.9f553696ac0848c3faac55a2717178ae.png
 
OR
image.thumb.png.a6f2be57c1077560d3a351d4d436127d.pngimage.thumb.png.ee620244ae498e06a0367a5042207473.png
The Human Condition series of sculptures by Lawrence Sheraton -- so your diffusers will be talked about.
The ceiling is a concave, and I cannot go any higher than 18' on the walls, and overhead treatment at all at this time. I am putting in 18' high corner traps on tue front 2 corners, and I have heavy stage curtains covering the front wall, and about 7' of the front side walls.
I just am not sure if it is worth it to put treatment 18' up or not.

Sent from my SM-T550 using Tapatalk

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