curved wall panels

[dymaxian]

Hey guys- another wall-treatment thought occurred to me...

I'm aware that diffusion does little good unless you're more than 10 feet away from the wall, and I'm aware that making a curved wall panel doesn't really act as diffusion per se...

But I'm wondering if it might help in the non-parallel wall category. I have a couple panels I've built for the space I'm currently in, similar to the panel Ethan has pictured on his website; just a 4x8 sheet of plywood held curved by a frame of 2x2 lumber, basically.

If the low frequencies aren't going to be affected so much (I'll have to absorb a lot down there, parallel walls or no) and angled walls aren't possible (for a renter, etc), standing a few of these against the walls would at least keep mid and high flutter echoes from happening without deadening the room.

I know we can hear our keyboardist at practice a lot easier with those up, as opposed to all the absorption we had before.

Just thinking out loud again. No real question, just throwing that idea out there...

Kase
www.minemusic.net

[John Sayers]

standing a few of these against the walls would at least keep mid and high flutter echoes from happening without deadening the room.

yup - use them mate - it's sure better than having a dead room and they do work as diffusers.

cheers
john

[barefoot]

I'm aware that diffusion does little good unless you're more than 10 feet away from the wall

I've heard others say this..... but why? I think it must be a misinterpretation of the 20ms rule.

Diffusors certainly do work at distances less than 10ft. They disperse reflections over a wide angle, therefore reducing the reflected energy at any particular location. If you have a problem with early reflections from a nearby wall, a diffusor will definitely help. It won't eliminate the problem. And it could possibly be more effective to use an absorber, or try to angle the wall differently. But a diffusor will certainly improve the situation over a straight wall reflection - even at short distances.

Thomas

[lovecow]

Thomas,

I'm aware that diffusion does little good unless you're more than 10 feet away from the wall

I've heard others say this..... but why?

You might check this PDF:

http://www.rpginc.com/news/library/Tech ... itList.pdf

Page 6 starts the description of the "working distance" for scattering (diffusing) surfaces. It might answer some questions. It is the source of the "10' rule."

FWIW, I find the argument is sometimes economic. Even the lowest cost commercial diffusors are usually 1.5 to 10+ times more money than the equal area of absorption. If you have a 12'x10' bedroom and a $500.00 budget for treatments, it usually comes down to getting the most bang for your buck.

(That's leaving out, of course, the many handy people who put their own diffusors together at a fraction of the commercial costs.)

Best regards,

Jeff D. Szymanski
Chief Acoustical Engineer
Auralex Acoustics, Inc.

[barefoot]

Thanks Jeff.

Personally, I don't think RPG needs to be so conservative in their recommendations. Coherent hemispherical wavefronts are nice, but not a requirement in my opinion. The complex spatial and temporal response you get closer to a diffusor is still a far cry better than the coherent plane wavefront you get from a flat surface reflection. The comb filtering effect will be much more pronounced with a flat wall.

Like I wrote before, diffusion isn't necessarily the best solution at close distances, but it is also far from useless - particularly in a live room. If you're recording instruments that are less than 10ft from a wall, and you still want some natural ambience, diffusion is still quite valid. However, since the wavefronts from the instrument will not be planar by the time they reach the wall, an expensive RPG type diffusor isn't really necessary. These types of diffusors require planar incident wavefronts in order to produce hemispherical scattered wavefronts in the far field. Close in situations provide neither, so any DIY complex diffusive surface will do. Of course, the same rules apply with respect to size, feature depth, and low frequency limit.

Thomas

[lovecow]

Thomas,

I agree.

It's amazing the effect of some shelving with assorted books, CDs, knick-knacks, etc. can have on recording quality - even in a room with some degree of absorption in place. (Something that's no secret in these types of forums. Or is that "fora"? Only if the singular of "flora" is "florum" I guess... )

As a manufacturer of commercial diffusors, we tend to stick by the 10' or 12' suggestion, but we avoid stating it as a hard and fast rule. (As I mentioned, it's usually more about the money!)

In fact, we often find that control rooms with 7' or 8' ceilings benefit considerably from diffusion above the listening area. The listener distance in those instances is typically 4' or less. There is a certain degree of taste - the "art" of our science - involved, of course.

Best regards,

Jeff D. Szymanski
Chief Acoustical Engineer
Auralex Acoustics, Inc.

[impact_kent]

don't get me wrong, I don't mean to resurrect such an old post, but I was reading around the forum........

Anyway, If the "full effects," that being a hemispherical wave front, of a diffusor is to be expected at a listening (mic'ing) distance of 10 feet, what would be the effect of diffusors on any amount of 1-4 walls of a 20 x 20 ft. room?

I know that this isnt a question of prediction, but a question of "try it and find out," but would an acoustic instrument placed and mic'd in the center of such a room be likely to sound a)fantastic, b)the same as if no diffusion were applied or (c) god-awful, full of new room modes created by parallel diffusion from the walls.

I'm asking because my room is 20x20, and as I treat the corners absorptively, I'm ironing out a 1D quadratic residue diffusor about 4x7 feet for one live wall, opposite a completely absorptively dead wall.

Just curious about this 10 foot thing.

Sorry to bring back such an old post, but it was a good one ;]


I did a job over the week in NYC by the way, and this event space used to be a recording studio. Nice large room, about 40x40x 30 or so, and the entire side of one wall, at least from 8ft (doors) to the ceiling, was composed of three large curved sections, the side 2 covered in what appeared to be fabric wrapped 703 and the center in a nicely finished hardwood, a laminate possibly.

Anyway, that room sounded fantastic. It looked like there was no other treatment, although the black painted ceiling may have had some rows of 703 or similar alternating with the HVAC.

Can't help but feel that those curved walls played a big role in the incredible acoustics and intelligibility of speech in that room.

Anyway, curved walls would be nice and all for a live room, but i'm more interested in this 10 foot deal.


Thanks to anybody who has any input,

Billy Dixon

[AVare]

The guideline is three times the wavelength of the lowest frequency diffused. Not ten feet absolutely.

Andre

[impact_kent]

thats completely not what i meant
but thats cool

i'll read books when i can find some cash to buy
library doesnt have much

[impact_kent]

but thanks, that is quite handy.

i'm just wondering if anyone else thinks about what happens when two quadratically diffused wavefronts clash in symmetry.

Are new modes created? peaks? nulls? Is the point lost?

[knightfly]

I'm not enough of a mathmatician to postulate what happens quadratically, but dead center in a square room will absolutely SUCK, no matter WHAT is on the walls. If you follow Andre's rule on lowest wavelength per unit depth, you can't GET deep enough diffusors in a 20 x 20 foot room to handle the LF MODAL problems a square room will introduce.

IF that were my room (and it was NOT being used as a CR), I'd be looking at angled slat absorber solutions for one wall, 3 or 4 4'x8' POLY's on the adjacent wall, and a few patches of absorbent here and there to adjust liveness to taste - a "cloud" over areas that need flutter control, and you should hear a huge change in your room's "signature". Place instruments in the room according to how "live" you want the recordings, and how "big" - close to absorbers for dead, closer to poly's for "big", and closer to the slat absorbers for something in between... Steve

[AVare]

but thanks, that is quite handy.

i'm just wondering if anyone else thinks about what happens when two quadratically diffused wavefronts clash in symmetry.

Are new modes created? peaks? nulls? Is the point lost?

I don't understand you. There is no "thinking" about what happens. Cox, D'Antonio and others have published papers showing what happens, and one of the course curriculums for Salford even includes diagrams and questions on the exam about that! They are on the web, but I don't rrmember the URL. Sorry.

Andre

[knightfly]

Here's the link I have to Salford;

http://www.acoustics.salford.ac.uk/

But I've yet to find any useful info there for study purposes, it's more of a "we're great, come and study here" site - that's why I bought the Cox/D'Antonio book, expensive as it is... Steve

[AVare]

I tries to find the link to the course material but no luck. I will post it when I find it.

Andre

[drew.n]

This one is interesting.
Might challenge ones thinking tho, especially the second order list


http://www.acoustics.salford.ac.uk/acou ... izing2.htm