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Diffusors: opinions about EPS polystyrene?
Old 3rd October 2012
  #61
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Glenn Kuras's Avatar
Quote:
Also, the "terracotta" brown colour tone turned out to be more of a diarrhea than terracotta.



Old 13th December 2012
  #62
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n0nspaz's Avatar
 

Jens & Glenn & others-

1. is it true that these type of diffusers need to be mounted flat against the wall, tightly so there is no movement/buzzing/etc. ? how do you accomplish this?

2. also is advantageous to give up an additional 1" or 2" behind the diffuser for porous absorption? by this configuration i mean for example, starting from the rear wall in a control room where the diffuser is to be mounted, say 1" OC703 mounted to wall, then diffuser mounted to this. we are giving up precious studio space and porous works better spaced away from the wall anyway, so i assume it is no help to add the 703.
Old 14th December 2012
  #63
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Jens Eklund's Avatar
I frequently use EPS diffusers as a ”lid” on membrane absorbers targeting problematic first/low order modes, so no; they don´t need to be mounted firmly against a solid wall. The only thing that might cause a problem, is panels that are mounted next to each other very close so they are touching, but not glued together: This might cause buzzes, so always glue adjacent panels together.

Note that I have no experience with EPS diffusers made of low density EPS (about 25 kg/m3 or lower). If very low density, noise due to flexing might become a problem in the material itself, I don´t know.


EDIT:
building membrane absobers
Old 18th December 2013
  #64
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jim1961's Avatar
 

Quote:
Originally Posted by Jens Eklund View Post
A common misconception about diffusers made of EPS is that they don’t reflect as good as wood or other dense materials. This can be true if low-density EPS is used and not painted. I did some measurements on my panels and the effect of a coat of paint is obvious:

Attachment 239364

In the low frequency region, the only thing affecting absorption is the mounting, which can actually be used to create a membrane absorber to battle modal issues. More information on the effects of mounting and the membrane effect here:
Flooring question
What panel type and construction material was compared to what in this graph?
Old 18th December 2013
  #65
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Jens Eklund's Avatar
Quote:
Originally Posted by jim1961 View Post
What panel type and construction material was compared to what in this graph?
Optiffusers (EPS); painted vs. unpainted. Not mounted at all, just lying on the floor.
Old 20th November 2015
  #66
rds
Gear Addict
 

Hi guys,

Actually i have a very well treated room with laminated floor but i got still flutter echo in the ceiling right above my listening position and behind me as well. No rugs or carpet in the floor.

I was thinking to cover the rest of the ceiling with this kind of polystyrene panel of 600mmx600mmabd because i need something to be very light and easy to place.




Do you think that it will be enough to kill the flutter echo ?

Thanks
Old 20th November 2015
  #67
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Bjorn Omholt's Avatar
 

You don't to treat the whole ceiling with such a poor treatment. You treat the specular reflection points between speakers and mixing position, using thick absorbents. That will take care of the flutter-echo in that place too. If you need to treat flutter-echo at other places due to instruments/recordring etc. the treatment will depend on your goal but a combination of diffusion and absorption (RPG BAD products) could be one option.
Old 20th November 2015
  #68
rds
Gear Addict
 

As i said the room is well treated and all first reflection points are ceiling included. But still i have that flutter echo just above me when i snap my fingers from my listening position. So that's why i though to add some of those panel to decrease the flutter echo.
Old 20th November 2015
  #69
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Bjorn Omholt's Avatar
 

If you have treated early reflections from the ceiling, I'm surprised you still have flutter-echo in the listening position. How much surface area did you cover? Can you show some pictures please?
Old 22nd November 2015
  #70
rds
Gear Addict
 

Quote:
Originally Posted by Bjorn Omholt View Post
If you have treated early reflections from the ceiling, I'm surprised you still have flutter-echo in the listening position. How much surface area did you cover? Can you show some pictures please?

The room is pretty much fully covered. Corner traps, tricorners, all wall ceiling corners, all frp, back wall, and about the ceiling frp the traps are between monitors and my listening position so right above me there is nothing.

Initialy i had the above listening position treated as well but after measurements it didnt't work well, with the trap above me i had a dip of 6db around 300hz, when removed it was gone.

Also note that my laminate wood is highly reflective.

So i have space above my listening position for 2x 600mmx600mm panels and in back i have still place for 6 panels of the same size.

Actually my main concern is to damp the flutter echo and i prefer to make it by diffusion rather absorption because the room is quite small and have already a lot of absorption. I could place a big carpet to face the parallel ceiling wall but again i prefer to keep the floor reflective.

So actually i would need a total of 8 panels and with some searches i came across those ones.



They sell them by set of 8 pcs which is all what i need.
The question is do they would work for damping the flutter echo ? Their density is set to 20kg/qm.

If someone already use those diffusor for flutter echo purpose could he give me a feedback ?

Appreciate
Old 22nd November 2015
  #71
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Bjorn Omholt's Avatar
 

If both early and late reflections are treated well, it will take care of flutter-echo. Treatment of early reflections need to be broadband, which means very thick absorbents (minimum 15 cm) or a hybrid product like BAD Panel/Arc. The products also need to be large enough in size due to wavelengths. And it's important it's placed surgically to attenuate the reflections arriving in listening postion and not spread out randomly in the room.

Late arrival reflections can either be diffused or a combination of absorbed and diffused depending on the distance.
I don't recommend diffusers for treatment of early reflections.

The combination of this and proper bass treatment will avoid making the room dead.
Old 16th October 2018
  #72
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Sorry to bump this old thread but, Im building a QRD 1D N31 diffuser

fins are 5mm plywood
block heights are extruded polystyrene (XPS) (30mm width)
I need an alternative to PVC to cover the wells....wanted to use some nice white PVC like this (see attached) but the shop where I used to buy them don't make them anymore :( It was really really really cheap.

I know Jens recommends to paint his EPS diffuser.

I need something thicker to smooth out the rough texture of some bad cut.
I'm sure painting won't mask it. But will test it meanwhile finding a good alternative.

Any ideas? What could I use? Maybe some primer before painting...? I'm on a budget! Can't buy wood panel and paint them etc

Cheers!
Attached Thumbnails
Diffusors: opinions about EPS polystyrene?-capture-d-ecran-2018-10-17-00.34.50.png  
Old 17th October 2018
  #73
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The use of a primer on the EPS before painting might also improve the coating.

From Optiffuser manual:
http://www.resonatorstockholm.com/Op...ser_Manual.pdf

Cheap and easy!!!
Old 17th October 2018
  #74
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Last question...if I use primer, will it add 1mm or 2mm?
The whole block heights will be shifted by 1 or 2mm. Will it change diffuser performance?

Very frustrating not to be able to test it with Reflex
Old 17th October 2018
  #75
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Wow super cheap option if it works
Old 17th October 2018
  #76
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Jens Eklund's Avatar
First of all, 30 mm is a very aggressive (small) well width for a finned diffuser. I would not use a narrower well width than about 40-45 mm since smaller well width results in excessive absorption. You might end up with a very expensive, complicated absorber if using that narrow well widths.

A primer does normally not add any significant mass to the surface unless intentionally used with some kind of filler (that one might want to do in order to fill the porous surface of for example EPS better). But even if it did, I wouldn’t worry to much about an increased height of each well of 2 mm, especially if the same height increase is added to all wells.

If you need something that covers a rough/porous surface better than normal paint, you can use normal PVA glue (“white glue”) and add a cement-based filler (in Sweden, Casco´s “Husfix” works well) to it until it reaches a consistency of ketchup (still “paintable” but covers well).
Old 17th October 2018
  #77
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Question

Thank you Jens. I do appreciate your posts

I'm really confused now:

1D QRD diffusors (Can I use a well width of 0.75 inches?) Viscous Losses?!

"I build couple of N41 QRDs with 19mm wells width... and this diffsors works well."
Boggy

Need advice with DIY QRD diffusers for medium-sized project studio

"but i never built diffusers with well width smaller than 18mm." Boggy


In the Master Handbook of Acoustics (5th ed.) p. 265; (Schroeder Diffusers section)

"Numerous commercial diffuser products incorporating quadratic residue theory are available from RPG Diffusor Systems, Inc. Figure 14-9 shows a QRD-1911 above and two QRD-4311 models below. In the model numbers, the “19” indicates that it is built on prime 19 and the “11” specifies well widths of 1.1 in. (The sequence of numbers in the prime 19 column of Fig. 14-3 specify the proportionality factors for well depths of the diffuser.) The QRD-4311 in the lower portion of Fig. 14-9 is based on prime 43 with well widths also of 1.1 in. (For practical reasons, the columns of Fig. 14-3 stop at prime 23; primes between 23 and 43 are 29, 31, 37, and 41.)
This particular cluster of quadratic-residue diffusers offers excellent diffusion in the horizontal hemidisc, as shown in Fig. 14-10A."


1,1 in=2,794cm !


I'm no expert as you know. I don't defend any point of view. Just wanna learn.
Attached Thumbnails
Diffusors: opinions about EPS polystyrene?-capture-d-ecran-2018-10-17-13.09.22.png  

Last edited by JayPee; 18th October 2018 at 09:09 PM..
Old 17th October 2018
  #78
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Jens Eklund's Avatar
More wells packed tighter results in more absorption (assuming diffuser with well dividers, stepped designs are a bit different and this is one of the benefits):

A greater number of wells leads to more energy flow between wells in addition to a greater density of ¼ wave resonance as well as more losses due to viscous boundary layer effects. *

This is pure speculation, but if you look at the current range available from RPG; you´ll notice that they don´t offer any product with such aggressive well spacing (at least not for deeper wells). There might be a reason … again, just speculating.


* from Acoustic Absorbers and Diffusers, 2nd ED
Old 17th October 2018
  #79
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Or the other option:
Maybe their QRD diffuser was sooo big that it was hard to sell/send it?
Just speculating!


In this Brian Lucey's video, the widths of wells seem around 30mm I think.
I couldn't find these infos on Realtraps website.

Thank you Jens.
Old 17th October 2018
  #80
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by JayPee View Post
Or the other option:
Maybe their QRD diffuser was sooo big that it was hard to sell/send it?
Just speculating!
Considering RPG offers custom diffusers that are much heavier and bigger, that wouldn't be the cause.
Old 17th October 2018
  #81
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double post
Old 17th October 2018
  #82
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Quote:
Originally Posted by Bjorn Omholt View Post
Considering RPG offers custom diffusers that are much heavier and bigger, that wouldn't be the cause.
"Custom". Exactly. That was my point.
Old 27th October 2019
  #83
Gear Head
 

Quote:
Originally Posted by Ciaccona View Post
Sry guys, a quick one:

What would be my best choice of weapon to cut a 2'*2' polysterene diffusor in two parts without making a mess of crumbs? Assuming I don't have a sword by Hatori Hanzo handy.
an electric knife (for bread) maybe!
Old 16th February 2020
  #84
Gear Addict
Bump.

Is the Optiffuser still a good choice in 2020?

Is it available outside of .se ?
Old 17th February 2020
  #85
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Jens Eklund's Avatar
Quote:
Originally Posted by r.staettler View Post
Bump.

Is the Optiffuser still a good choice in 2020?

Is it available outside of .se ?
A very good choice if you ask me

Send an email to: [email protected] if you want to order or have any questions.
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