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Author	Topic: appropriate diffuser behind Apogee
gallant_diva Full Member	posted February 01, 2008 09:19 PM The picture of the wall behind the speakers in current form is shown below. The picture of the system and room is shown below. See the Auralex diffusors behind the MR/TW panels. Toine: You are a great guy, pal, but this diffusor was just not my cup of tea. IP: Logged
ThingMan Full Member	posted February 02, 2008 04:34 AM quote: Originally posted by gallant_diva: Toine: You are a great guy, pal, but this diffusor was just not my cup of tea That's okay Ish... I prefer espresso too! IP: Logged
henk Full Member	posted February 02, 2008 05:28 AM He Toine, In that case: I do always have fresh espresso, and I think your diffusors work wonders in my room I have to admit I turned up the tweeter level a bit (1.5 dB if I remember correct). I'm guessing that wood and MDF are too soft to build an effective hgh-frequency diffusor. I'm going to treat my diffusors with epoxy to make them harder. (and easier to paint properly ) So when are you coming by for a listen? IP: Logged
Dr Rock Full Member	posted February 02, 2008 11:24 AM Hmm, how about building them out of acrylic sheet instead of wood/MDF..? IP: Logged
gallant_diva Full Member	posted February 02, 2008 06:01 PM Toine: Do you think we can change the width of the wells in this QRD diffusor? What would be the effect of that. Thanks. IP: Logged
ericpeters Full Member	posted February 03, 2008 04:39 PM I was just wondering, if the range of the diffuser 700 - 4900 Hz what does actually happen with all the sound above 4900 hz? Absorbed or what? IP: Logged
ThingMan Full Member	posted February 05, 2008 04:56 AM quote: Originally posted by ericpeters: I was just wondering, if the range of the diffuser 700 - 4900 Hz what does actually happen with all the sound above 4900 hz? Absorbed or what? It will be reflected, as a diffuser will act as a flat surface outside its working range. Toine IP: Logged
ThingMan Full Member	posted February 05, 2008 05:01 AM quote: Originally posted by gallant_diva: Toine: Do you think we can change the width of the wells in this QRD diffusor? What would be the effect of that. Thanks. Wider wells = lower top-end frequency = smaller working range narrow wells = higher top-end frequency In the case of this particular diffuser any change in the well-depth or -width will compromise the design. If well-width is a target, you must design a new diffuser around this parameter. IP: Logged
ThingMan Full Member	posted February 05, 2008 05:02 AM quote: Originally posted by Dr Rock: Hmm, how about building them out of acrylic sheet instead of wood/MDF..? Very good idea, but quite expensive... IP: Logged
Dr Rock Full Member	posted February 05, 2008 08:26 AM They'd look good though. I can feel another project coming along.... I think I'll price them all up first though! IP: Logged
sea-speak Full Member	posted February 05, 2008 01:22 PM Black acrylic would look totally awesome. I have been nosing around on the subject of DIY roomlenses. There's a guy on the Asylum who set up his roomlens pipes as if they were the wells of a QRD diffuser (that is, the pipes are staggered front to back rather than in a single plane). He liked the staggered pipe configuration better than the standard one. I've written him to ask the exact layout of the pipes he used. I've also ordered the book he recommends, Everest's Master Handbook of Acoustics. I suspect that if he writes back he'll tell me to get that book and look up some QRD well depths... :) I'm working on getting diffusion into my room, yes I am. cheers, B IP: Logged
etienne New Member	posted October 08, 2008 02:10 AM Hello , just reading this interesting stuff . Is the picture (diffuser plan ) in the first post of this thread not available anymore ? [This message has been edited by etienne (edited October 08, 2008).] IP: Logged
McEnroe Full Member	posted October 18, 2008 12:15 PM Anybody going BAD?? http://www.rpginc.com/products/badpanel/index.htm IP: Logged
diffused Full Member	posted March 16, 2009 05:59 PM Long time lurker, etc etc. Great resource here. I'm curious about this: I've noticed on commercial diffusers that the outer side-walls usually seem to be excessively thick, and this statement: "Width of outer wells, which are actually the sidewalls of the panel and should measure at least half the well width in a symmetrical design" would seem to confirm that observation. I'm curious about this because I'm building some diffusers that I'd like to hang, and extra weight is not a good thing (I'm looking at a fairly wide well width) not to mention the extra cost for the lumber (they're gonna be pretty deep). Can anyone explain to me why the outer side wall needs to be so thick? If it was a matter of containing the sound waves within the region in front of the diffuser or something, I can't see why an inch or even half an inch of plywood wouldn't be fine... Many thanks for any replies! IP: Logged
muralman1 Full Member	posted March 16, 2009 06:14 PM I still prefer nearly nothing in my room. IP: Logged
sebastia Full Member	posted March 16, 2009 10:07 PM quote: Originally posted by muralman1: I still prefer nearly nothing in my room. Are your listening sessions clothing optional Vince? IP: Logged
muralman1 Full Member	posted March 16, 2009 11:22 PM I thought nudism was acceptable in New Zealand, no? Sorry if I offend. IP: Logged
Dexter Full Member	posted March 17, 2009 12:02 AM quote: Originally posted by muralman1: I thought nudism was acceptable in New Zealand, no? Sorry if I offend. Only on the farm mate! ------------------ Vinyl, superior sunscreen technology. IP: Logged
ThingMan Full Member	posted March 17, 2009 03:19 AM quote: Originally posted by diffused: I'm curious about this: I've noticed on commercial diffusers that the outer side-walls usually seem to be excessively thick, and this statement: "Width of outer wells, which are actually the sidewalls of the panel and should measure at least half the well width in a symmetrical design" would seem to confirm that observation. The observation is correct. quote: Originally posted by diffused: I'm curious about this because I'm building some diffusers that I'd like to hang, and extra weight is not a good thing (I'm looking at a fairly wide well width) not to mention the extra cost for the lumber (they're gonna be pretty deep). I don't know what "fairly wide well" means, but any well width exceeding 2 inches will be useless for most music-purposes, except on the wall behind loudspeakers (provided they're not dipolar speakers). quote: Originally posted by diffused: Can anyone explain to me why the outer side wall needs to be so thick? If it was a matter of containing the sound waves within the region in front of the diffuser or something, I can't see why an inch or even half an inch of plywood wouldn't be fine... The outer well is part of the design: it is half the seventh well in a symmetrical QRD-7 diffuser. In a non-symmetrical diffuser one side wall will have the full well width while the other side wall can be very thin. So the outer well is an essential part of the design of any QRD-diffuser. In a symmetrical design you would place half the well width on each side. A diffuser is never used as a standalone thing; one always should use at least 4 periods together. So if you visualise 4 diffusers next to eachother, you can easily understand how two sidewalls together form a complete well. IP: Logged
diffused Full Member	posted March 17, 2009 01:08 PM Brilliant. Thank you so much, ThingMan. These are actually intended for a live recording room (including drums), and I'm monkeying around with a few different ideas for treatment (I may not end up having wells any wider than 2"). The design I'm going by, though, has all 7 (or 11, or 13--whatever I end up using) together in the design and the outer walls are sort of irrelevant...which is why I was confused. Thanks a million. IP: Logged
diffused Full Member	posted March 20, 2009 03:44 PM Actually, now that I think about it...if an individual is using only one diffuser--say, one based on a large prime number that's going to cover quite a bit of space on its own--does anyone know whether or not you would leave it exactly as is? What I mean is, would you leave one outside well with a depth of zero whereas the other outside well has a depth of say, 3/4" (depending on the diffuser's design frequency)? It's not symmetrical that way, but it is the way the quadratic formula is written and the way the model will come out if you design one... IP: Logged
ThingMan Full Member	posted March 21, 2009 04:22 AM quote: Originally posted by diffused: What I mean is, would you leave one outside well with a depth of zero whereas the other outside well has a depth of say, 3/4" (depending on the diffuser's design frequency)? It's not symmetrical that way, but it is the way the quadratic formula is written and the way the model will come out if you design one... Isn't what you describe just the asymmetrical version? What you say is correct indeed. The only reason to opt for a symmetrical design is better looks. As a matter of fact, it doesn't matter where you start. You could start with the deepest well and choose it to be the outer well of the design, as long as one diffuser covers a whole period. Choosing the zero-depth well as the outside well makes building a diffuser easier, but you can choose any well to be the outer well. But like I said: there's no use applying only one diffuser (period), whether it's a large prime number based panel or the simplest QRD-7. The area you have to cover with diffusers should at least be covered by four periods, regardless of dimensions. Periodicity is one of the parameters to obtain even diffusion. One period will never be able to deliver even diffusion. Toine. [This message has been edited by ThingMan (edited March 21, 2009).] IP: Logged
diffused Full Member	posted March 22, 2009 02:36 PM Ah, I thought the reason for using 4 periods was a matter of most diffusers being too small to make much of a difference, and I thought maybe having the asymmetrical version would give uneven scattering or something... Thanks a lot for sharing your knowledge, you've given me a lot to think about. IP: Logged
adrianyardley Full Member	posted September 02, 2009 08:47 AM Tiny Tim, gallant_diva, Dr. Rock... would you comment on using QRD to expand the acoustic size of your listening rooms. Which location worked best? Cladding the wall behind the listener, or placed behind the speakers? Any suggestions for improving QRD? eg. - using narrower wells to diffract up higher in frequency? --> to spread the higher frequencies - using more periods? (eg. easier when using narrower wells) --> finer "lobing" in the diffraction that might be less upsetting for the critical mid-range frequencies IP: Logged
Dr Rock Full Member	posted September 03, 2009 05:38 AM QRD's go behind the speakers. My own listening room has sloping roof behind the speakers so I can't get the QRD's back as far as they should go. I just used Thingman's dimensions and built 'em 4ft high and a touch wider than the speakers (same height as Calipers). They seem to have made the side walls disappear to some degree. I haven't experimented with positioning as I can't. I'll leave it to the experts to talk about changing dimensions.... Making my own bass traps and wall panels of various sizes from 2x2 and rockwool covered with fabric made a bigger difference! [This message has been edited by Dr Rock (edited September 03, 2009).] [This message has been edited by Dr Rock (edited September 03, 2009).] IP: Logged

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