jimmyman
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diffusers
I'm just pondering a why question here. Back in the old days you saw a lot of "half round" diffusers filled with damping materiel. The surface was almost always A hard surface such as bent wood panels. At one time I had a bunch of them in my recording environment but now have since gone to a different type diffusion. I do still use (some) Half round diffusion but the surface is soft. Maybe it's because the radius of a of a half round diffuser has to be pretty large to be effective. Or could it be they are more reflective than flat panels? Edit: Maybe I sound a little "Off the wall" here. But when I went searching for round absorbers I found out what a "sabin" is. It's a unit of measure named after the man.
post edited by jimmyman - 2009/10/05 10:25:33
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gamblerschoice
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My understanding is a diffuser does exactly that, it diffuses sound inside the room, so that there are no direct, side to side reflections. With that in mind, a curved surface would work best, with maybe a group of flat surfaces aimed at varying angles. The softer surface might be for taming frequencies, but I am not at all an acoustic expert, just throwing out the guesses based on memory.
Later
Albert
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wst3
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How strange... my mentor and I were just discussing poly-cylindrical diffusers at lunch today (and why is it all the tables surrounding us are always empty?)
I don't know why they fell out of favor, I still like them and they are part of the design of my next studio. If I had to guess I'd guess that other solutions that take up less space have beaten them out.
If what you need to do is diffuse the energy coming from a surface any diffuser will do. If you need a specific diffusion pattern then you have to use the tool that creates that pattern... but in my limited experience there is seldom a need to create a specific pattern.
One of the benefits of the poly is that it can also act as a membrane absorber if you need additional absorption.
Modern thinking is that one should use diffusers to diffuse, and absorbers to absorb (and reflectors to reflect) with no double duty applied, and in a lot of ways that makes designing a room easier, but maybe a little more expensive... depending on what it is that you need.
Two cents worth...
-- Bill Audio Enterprise KB3KJF
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batsbrew
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bitflipper
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Polycylindrical diffusors are popular because they can be easily and cheaply made.
The BBC came up with a novel concept, which was polys on vertical axles that could rotate. The backside was flat and exposed the absorbent material. This allows you to fine-tune the absorption-to-reflection ratio for the room, making one room more versatile for multiple purposes.
Polys, unfortunately, are not the best diffusors because they do not reflect in a truly random pattern. That's why they've been replaced by quadratic residue diffusors in studios that can afford them.
They remain a viable alternative for the DIY crowd, though, since they can be made with basic tools and materials.
I have never seen it done, but it occurs to me that a polycylindrical diffusor in a corner could do double duty as a Helmholtz resonator.
 All else is in doubt, so this is the truth I cling to. My Stuff
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jimmyman
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Thank you all so very much for the remarks, info and
references. I consider myself blessed to have at least
a modestly decent recording environment. Nothing great
or fancy at all but it sure beats "bare walls".
Most of the materiel used is from what would be stuff
thrown away from building sights. (new materials that is).
I find it interesting that materiels thrown away every day
could be of good use to those of us who need some "room
treatment".
And you sure can't beat "free". It's a small bedroom
turned into a devoted recording environment. I had
taken the closet door completely off (hum? is that sort of
a bass trap?) and usually leave the intrance door open
as well.
That may have much to do with the room not being too
boxy sounding along with the treatment. Now the word
term "sabins" takes on a whole new meaning. I think
maybe after all these years I'm starting to at least
understand something about something whatever that
is.
Maybe this is the equal to learning to play music
by ear. I've done much of my room treatment by
what it sounds like after doing things. Sometimes
I did things that either made things worse or only
shifted the problem.
If there is any moral to this story I'd guess at saying
a person gets a small amount of success with a small
amount of treatment and more is better until one
reaches a point of satisfaction.
Thanks guys
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wst3
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Polys, unfortunately, are not the best diffusors because they do not reflect in a truly random pattern Keep in mind that true random diffusion is but one solution<G>... there is a place for the predictable diffusion approach. Oh, and indeed a poly can do double duty as a resonator...
-- Bill Audio Enterprise KB3KJF
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mattplaysguitar
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The Maillard Reaction
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Is not every voluminous container a Helmhotz resonater?
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jimmyman
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Is not every voluminous container a Helmhotz resonater? That may depend on what type the "container" is. If the container can produce a measurable amount of a resonate frequency then I guess the answer would be yes.
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bitflipper
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Is not every voluminous container a Helmhotz resonater? More or less, yes. What makes it a resonator is that it has a relatively high Q. Not every enclosed space will have the narrow bandwidth necessary to efficiently absorb a target frequency. So while every voluminous container has the potential of being a bass trap (including an empty room next door), not every container qualifies as a resonator.
All else is in doubt, so this is the truth I cling to. My Stuff
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jimmyman
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More or less, yes. What makes it a resonator is that it has a relatively high Q. Not every enclosed space will have the narrow bandwidth necessary to efficiently absorb a target frequency. So while every voluminous container has the potential of being a bass trap (including an empty room next door), not every container qualifies as a resonator. Bitflipper this makes ask myself the question of a resonator and absorber. In my mind I think of a resonator as something that "produces" a sound. Yet it "in this case" it "absorbs a sound? but then again maybe you cleared it up by saying: Not every container qualifys as a resonator. Does this mean that the container must have a High Q to quality as a resonator?
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bitflipper
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Does this mean that the container must have a High Q to quality as a resonator? That's basically what defines a resonator. It's analogous to an electronic bandstop filter, which is why we use the same terminology for resonators as with equalizers. Mike is, of course, absolutely right that every enclosed space has resonances (plural). But most spaces have a large number of resonances spread over a broad range of frequencies, and each resonance is "fuzzy", not sharply focused on a narrow range of frequencies. A resonator, such as a drum or a trumpet or a Helmholtz resonator, has one specific narrow frequency (plus that frequency's harmonics) that it responds to.
All else is in doubt, so this is the truth I cling to. My Stuff
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