Styrofoam diffuser design - thoughts?

[DoomedMan]

Hi all,

A friend of mine can order styrofoam products cut to custom shapes which gave me the thought of designing a simple diffuser. I am very much a newbie in this. From the small amount of research I have done I have come up with a design based on a N11 QRD diffuser. I am aware this will not be a true QRD diffuser, the stryofoam has its limitations regarding wall width. The styrofoam is available in different densities from packaging style up to very dense foam. I understand that a denser foam would be better, anyone know how dense **kg/m^3???

Attached is a PDF which I drew up with some software. It is to scale 1:1, hence is on A0, but you get the idea.

Any thoughts would be appreciated.

DM

[Glenn Kuras]

When you redesign a QRD (like we did with are d1) it is always best to have it tested in a lab to see how it reacts. You can have a ton of lobbing (not a good thing) if you do not do things right.

[SAC]

While your design 'looks very nice', may I suggest that you spend a little time with QRDude and design a proper QRD that will actually perform as intended.

As Glenn stated, the quadratic math upon which QRDs are based is very specific. Random variations do NOT perform in the same manner, and often create larger problems in the form of more troublesome specular reflections. And if you vary from the proper design, you would do well to know exactly what they are doing - as you will most likely need to treat the problems they create, as they will be a source of additional focused reflections - the very thing a true diffusor attempts to spatially and temporally mitigate.

[boggy]

DoomedMan, I look your pdf, an I agree with others. That diffuser shape isn't tested, and I don't see any reason to abandon classic design.
If you (really) like to do something "different" it's better to try fractal qrd diffusor, or diffractal (keywords: diffractal, Peter D'Antonio)

regards

boggy

[DoomedMan]

Thanks for the replies. I know that there is little maths backing up my attempted design. I was after anything that would just help partially diffuse and absorb the midrange in my room and since it would be pretty cheap for me to get these made (~$30aus each, maybe less) just thought I would have a go.

Is there a difference between scattering and diffusing?

[PaulP]

Originally Posted by DoomedMan

Thanks for the replies. I know that there is little maths backing up my attempted design. I was after anything that would just help partially diffuse and absorb the midrange in my room and since it would be pretty cheap for me to get these made (~$30aus each, maybe less) just thought I would have a go.

Is there any reason why you can't supply a valid shape ? QRDude will give
it to you for free.

Paul P

[SAC]

But Paul, using QRDude takes time!

And to quote a sage: "people here are not interested in turning them rooms into laboratories in which they spend the rest of their lives conducting acoustical experiments" in "time consuming" experiments for which each configuration does not already have validated test results performed by someone else at someone else's expense.

[PaulP]

Boy, you're a real baby aren't you SAC. You're the only person for which
I've used the ignore feature on this site and had just recently let you out of
your cage since you seemed to be behaving. I guess not. Bye.

Paul P

[SAC]

Paul, PLEASE ignore me!

I haven't the time nor the desire to spoon-feed someone who actively discourages others efforts and who laments the notion of folks actually trying a procedure in order to learn, allthewhile personally refusing to take the time to try things themselves as you do little else but demand others supply them with 'pre-measured' solutions designed to specifically solve their own personal issues - as apparently its OK if others waste their time solving your issues...

Would you be happier if I simply demanded answers and proof from you of that which you refuse to do, but of which you are so proficient at expecting of others?

[SAC]

Originally Posted by DoomedMan

Is there a difference between scattering and diffusing?

Put very simply, scattering simply breaks a higher intensity specular (focused) reflection spatially into several lower intensity discrete specular reflections.

Diffusion results in both increased spatial and temporal dispersion of energy.
The arrival times of the resultant dispersion of energy and the spatial distribution becomes both more uniform and more dispersed. And the ability to localize the source of said energy decreases with the increased diffusion.

Additionally. later arriving high intensity reflections cause image shift and tonality variation.

[DoomedMan]

Originally Posted by PaulP

Is there any reason why you can't supply a valid shape ? QRDude will give
it to you for free.

Paul P

I have had a play with QRDude, just looking at the default settings and not getting too in depth with it. I'm not really sure what design frequency I should be aiming for. I am very time poor and don't have much spare time to be making it myself and was looking for simple solution rather than buying a ready made product. There is no retailers of such products anywhere near where I live for me to audition.

The main reason I haven't gone for a "valid" shape is because I was worried about the fin width being to thin to be made out of styrofoam. I suppose I could put some slots into the styrfoam and put some balsa wood fins in.

I might get some quotes for both styles and just see how it turns out since it won't cost me much.

I have been looking at shaman's DIY absorber threads using pre-IKEA made frames. I might give these a go as well to use on the early relfection points.

[gremmy]

Originally Posted by PaulP

Is there any reason why you can't supply a valid shape ? QRDude will give
it to you for free.

Paul P

Maybe I am completely missing the point, but I think the OP is looking for a shape that can be easily pressed into a custom shaped piece of styrofoam by some sort of automated process. In my mind, this means no well walls.

To the OP: What about a skyline?

[boggy]

Originally Posted by gremmy

Maybe I am completely missing the point, but I think the OP is looking for a shape that can be easily pressed into a custom shaped piece of styrofoam by some sort of automated process. In my mind, this means no well walls.....

Well walls isn't a problem, but shape:

[gremmy]

Originally Posted by bozoel

Well walls isn't a problem, but shape:

There are no well walls in the pic above. Normally, all the well walls would be the same height, so that you could lay a straight edge across the front of the diffuser and it would contact the front of all the well walls. In the pic above, what you have are block heights of varying depths with no walls.

Also, in a previous post, the OP said this: The main reason I haven't gone for a "valid" shape is because I was worried about the fin width being to thin to be made out of styrofoam. I suppose I could put some slots into the styrfoam and put some balsa wood fins in.

[boggy]

Originally Posted by gremmy

There are no well walls in the pic above. Normally, all the well walls would be the same height, so that you could lay a straight edge across the front of the diffuser and it would contact the front of all the well walls. In the pic above, what you have are block heights of varying depths with no walls.

Sorry! I mean "well walls isn't a problem... if he don't have it".

regards

Boggy

[0bazooka_joe0]

Just an observation but isn't a symmetrical diffuser panel a bad idea? If you're going to design your own without the heavy research at least make it more random than that. Putting symmetrical diffusers next to each other is going to cause some funny acoustic anomalies.

[boggy]

Originally Posted by 0bazooka_joe0

....Putting symmetrical diffusers next to each other is going to cause some funny acoustic anomalies.

You're right, "anomaly" may be called aliasing. I don't build/design symmetrical diffusors. I even use different orientation scheme (some pseudo random sequence) if three or more identical diffusors are mounted near each other. If you build it symmetrical.. there isn't a way to do some random orientation.
But i see also that many commercial designs don't care about this.

regards

Boggy

[gremmy]

Originally Posted by 0bazooka_joe0

Just an observation but isn't a symmetrical diffuser panel a bad idea? If you're going to design your own without the heavy research at least make it more random than that. Putting symmetrical diffusers next to each other is going to cause some funny acoustic anomalies.

You could design two different panels (one of them being an inverse of the other) and use a barker sequence to modulate the response. You can also modulate by turning the same panel in a different direction, instead of using an inverse, although the response will not be as smooth. This is generally what is done in applications where low cost (relativey) commercially available panels of a single order are used.

[PaulP]

Originally Posted by gremmy

Maybe I am completely missing the point, but I think the OP is looking for a shape that can be easily pressed into a custom shaped piece of styrofoam by some sort of automated process. In my mind, this means no well walls.

I based my comment on the fact that all the commercial styrofoam 1D QRD
diffusers I've seen have no well walls. Probably for the reason you state. How
well they work without walls is another matter. Very thin walls could be added
after the fact, along with an outer frame.

Paul P

[boggy]

As far as I know, QRD without walls is noted 1983. in AES publication The Schroeder Quadratic-Residue Diffusor: Design Theory and Application by Peter D'Antonio and John H. Konnert.

regards

Boggy

[gremmy]

Originally Posted by PaulP

I based my comment on the fact that all the commercial styrofoam 1D QRD
diffusers I've seen have no well walls. Probably for the reason you state. How
well they work without walls is another matter. Very thin walls could be added
after the fact, along with an outer frame.

Paul P

Yes, good point.

To the OP: The QRDude info pages discuss QRDs without wells. In general, the higher order, the less the wells are required (per my undersanding based on that page). Once you get some estimates back, I'd be interested in seeing what they are. If it's not unreasonable maybe some of us would be interested in going in on it with you.

I need a some lightweight diffusers to cover my ceiling and rear walls, and the ones from Auralex don't have very impressive numbers (except the T fusor, which looks like something out of a science fiction movie).