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Question about polycylindrical diffusion

Discussion in 'Room Acoustics / Isolation / Treatment' started by DonnyThompson, Jun 5, 2014.

  1. DonnyThompson

    DonnyThompson Distinguished Member

    Okay... so I've been researching poly-cylindrical diffusors...

    Someone check me on this please:

    From what I understand, diffusion itself does not lessen the energy of frequencies, but instead, actually creates more reflection(s)... but in doing so, it lessens the intensity of these frequencies.
    The smaller, scattered frequencies will have random phase as a result of their individual and random "throw" around the room, and this can result in a smoother RT decay curve in the room.

    So first of all, am I correct in the basic understanding of a diffuser's main purpose?

    Here are some details about the room, should they be required:

    Room Materials:

    older type sheet rock on the walls and ceiling. The house was built in the 1940's. There is insulation in the walls, although not much. It appears to me to be the cheap blown-in style of material. Between the ceiling and the floor upstairs, there is OC R19. (I know this because I put it in myself).

    The floor is hard wood - oak, stained and sealed.

    There is one door, pretty sure it's pine, stained and sealed.

    There are two windows - L 52" x W 32"; both are newer (within the last 4 years) double pane, energy efficient.

    Room dimensions:

    14' 6" L x 12' 3" W x 7' 11" H


    The walls on both the L and W dimensions vary from end to end by up to two inches.
    The floor and the ceiling differ in height by 2 inches... but not on an end to end basis. The difference is in the middle of the room where either the floor has settled or the ceiling has sagged.

    So the room is not exactly square.

    The most obvious question is, do I need diffusion of any type at all?

    If the answer to this is yes, or probably, then I'll continue...

    Before I continue with my questions, I should tell you that I have been doing a lot of research on my own... I'm not trying to be lazy here. I have looked on the web to find the answers to these questions, but I've either not been able to find the answers, or I have run into contradictory information. It's also very possile that I'm not asking the correct questions... That being said...

    If diffusion would be beneficial in my situation...

    1. would I be better off using a poly-cylindrical form of diffusion as opposed to the "skyline" type that I have already built?

    2. if I can - or should - consider using poly diffusion in my room, does anyone know where I could find the formula needed to calculate the size and/or amount of the poly cylindrical diffusion that I need... width, depth, curve, etc.

    3. can I make a diffuser of this type that serves 2 separate purposes - those being diffusion and absorption?

    For example, along the wall behind me, where the wall meets the ceiling, could I run a 12' length of poly diffusion along this section, but in doing so, also add absorption material inside the diffuser?

    If this is possible - because I'm dealing with a half cylinder shape - I would think that something like Roxul would be better to use, than trying to fit and meld rigid glass with the shape... (and also allowing myself enough room for a 2" air gap between the insulation and the wall).

    Would any of this serve a purpose that would be worthwhile? Or am I into a more esoteric type of treatment which leans towards diminishing return?

    Any info would be greatly appreciated ;)


  2. Audiofreek

    Audiofreek Active Member

    Poly cylindrical diffusers aren't really that complicated. They are the poor mans solution to diffusion, and there is no formula per say, but it is nessesary to put some fluffy insulation behind them to dampen any resonances if you are sealing off the tops and bottoms. If you have the time and patience to build skyline diffusers they do a much better job at actual diffusion, rather than just scattering the reflections. I guess you could calculate the resonance of the diffuser if it is sealed, and tune it to trap a specific frequency as well. They do not have to be one half of a circle, they can be bent into a gentle arc as well. It it not recommended the two be placed side by side without any gap as they create a focusing parabolic effect. If you need to place them side by side some absorption between.
  3. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    I'm not aware of any sort of calculations or formulas for diffusion, as there are for like absorbstion coefficients. I think it gets pretty complicated pretty fast, and I've never seen anything like that in any of the books I've read. Although I do believe there are requirements for the volume (physical room volume) for you to actually achieve a "truly" diffuse environment/diffusion. You really should check your local library d, and see if they have the master handbook of acoustics, by f Alton Everest. That's where I got it, and had it for a few years lol. It covers a lot of the stuff you've been investigating lately, and you don't need a PhD to understand it.

    I'd really be more concerned about bass trapping, than management of the mids highs. What you have built already for diffusors is probably gonna be just fine, considering the size of the room.
  4. Audiofreek

    Audiofreek Active Member

    There will be some absorption with the type of polys I have seen. The thin 1/8th plywood will allow bass to penetrate and be absorbed somewhat by the fluffy fibreglass,as well a consuming some energy while entering and exiting the diffuser.Mids and highs will bounce off, but who knows what the cut off frequency will be, and phase relationships at the the cross over point will have changed, due to the exiting waves starting at zero, and the reflected waves keeping the same relationship with themselves.
  5. DonnyThompson

    DonnyThompson Distinguished Member

    See "Donny's Acoustics Project"... this is a new thread topic I have created to attempt to reign all of my other posts into one thread.

  6. Space

    Space Well-Known Member

    blah, blah blah. Read a book Audiofreak.

    Heck read this PDF file on polys given link by Andre:

    While I respect a persons attempt to make the complicated uncomplicated as you suggest AudioFreak, you have to know the complicated first:)
  7. Kurt Foster

    Kurt Foster Distinguished Member


    check this out
  8. audiokid

    audiokid Staff

    Here is one for us - Do we even need to be this concerned at lower volumes?
  9. Kurt Foster

    Kurt Foster Distinguished Member

    you can't just mandatorially set a listening level and get accuracy. the human ear hears flat at or near 85dB. refer to Fletcher Munson curve ....

    at lower levels of 60dB you will not hear a flat signal. the chart shows an astonishing attenuation @ 1 Khz. of 60 dB. we really should at least reference a mix at 85dB at least once in a while. we cannot compensate for bad rooms by simply turning down the volume. no magic bullet.

    here's what a diffuser does according to Acoustic Ramps site;
  10. audiokid

    audiokid Staff

    Damn, I forgot about that. Now I remember why I wanted one of those Radio Shaft meters that aren't available here anymore. I still mix at lower levels but do enjoy blasting it up near the end of when I am wondering how she sounds! But, I should be doing it at 85db to be precise eh?

    Well, an Acoustic Ramp diffuser is my next to do. Thanks for sharing that Kurt. I've not been paying attention to this enough. (y)
  11. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    You still need to have enough room for the sound to scatter and coalesce into something relatively even across the spectrum. I'm not aware of any way to calculate this, or to say type in the dimensions of the room, then the distance of the diffusors from the speakers/listeners, and estimate what you'll, get. If there is some sort of a thing it'd be really cool and I'd love to know about it. I'm honestly not being a smart a$$, I really would like to know cuz I haven't seen anything like that.

    Rods book, basically doesn't get into it because a typical home studio is too small for diffusion to be practical, so I'm guessing it's either too expensive/time consuming, ineffective, or some combination of the two.

    Those things sure do look pretty tho :)
  12. Kurt Foster

    Kurt Foster Distinguished Member

    not an expert but i really don't think a small room precludes diffusion. i've seen many booths and small control rooms in very nice studios that included diffusion. if you deaden the room with absorption then diffusion may not be necessary. but no one likes a completely dead room. the cool thing about the ramp is it is broadband. somewhere along the ramp are depths that will apply to almost any room ... my dream C/R would be almost all diffusion with very little absorption and large enough to negate the need for bass trapping.
  13. audiokid

    audiokid Staff

    My C room is 28' and already one defused nightmare lol. But I would love to try more. Something like this looks simple. But wow, that looks like about $2000 for the right amount I'd need. I like the idea of portable and light weight though.

    View: https://www.youtube.com/watch?v=FBHTlO8TTgw
  14. Kurt Foster

    Kurt Foster Distinguished Member

    that is the one drawback ... as of yet, no one had designed a cost effective solution. diffusion is expensive. sounds to me like opportunity.
  15. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    I'm not an expert either, for from it. How I've interpreted it is that, if the room isn't large enough for "true diffusion" for lack of a better phrase, then there are issues on how to predict its effects. But I dunno if I am thinking about it correctectly.

    Would it look like this ?


    That's George massenburgs place. Pretty cool huh? I'm equally jealous of, and glad I'm not, the carpenter who had the tedium of this job.
  16. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    There's plans for QRD and the diffusors similar to top what Donny made, in some books and on the web, I'd be curious to know how much he spent on the lumber.

    Definately ain't cheap either way, but they are significantly more expensive when buying pre made stuff. Same thing for acoustic doors. Very very expensive pre fabbed. About 3-5x the cost, according to my research, comparing overly doors, to something like in build it like the pros.
  17. audiokid

    audiokid Staff

    We have saw mills around here, this would be pretty simple to get but what a PITA to instal it indeed! Looks like it would feel pretty ugly to be in. I would like to walk in there, just to hear what it sounds like.
  18. audiokid

    audiokid Staff

    plus shipping. A case of RealTraps cost $800 to ship.
    My Acoustic Amp box cost $650 to ship. Shipping it the setback for this stuff. But those in the youtube I posted, look like they are really simple and very easy to ship.
  19. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Man, I didn't even ask them how much it was to ship the doors. Probably in the 500-1k price range. Those things just looked like plywood strips w some screw holes drilled in them. When your talking reflective properties of wood, the amount of coats of poly you put on them, has a significant effect on its frequency response. I've heard of a couple of studios that put up wood panels, then poly-ed them one coat at a time till they were happy.

    The DIYer in me, would just try to find the dimensions of something like this, and just build it myself. But I've been like that my whole life. Lol I build a half pipe skateboard ramp in my back yard when I was 10. Lol I had a scale model made out of cardboard and everything.

    I hope someone(s) could post some reading material about diffusion, and the implementation/calculation of it. In this area, of acoustics, I personally feel like one of the people who post the "best LDC for under $200" type things. Any info would surely be welcomed.
    bigtree likes this.
  20. audiokid

    audiokid Staff


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