DrWho Posted July 30, 2008 Share Posted July 30, 2008 I'm not convinced that the skylines are effective QRD devices, based on theory. Have you seen the measurements? I think there might be some posted somewhere at www.rpginc.com... If you look at the impulse response of, say, just two given wells, one is delayed compared to the other (different depth). Thus you have a phased array antenna elements which dictates an off-axis lobe. Hence, dispursion. It's actually more complicated than that because sound waves move slow, whereas electrical waves (RF) move fast. Also, the size of the wavelengths matter too....which is why RF designers are starting (or rather have been) taking into account the time that it takes the electrical waves to travel... (2) are not "hard" being styrofoam, and (3) don't have well walls (necessary for making sure that each well element causes a delay). (2) The absorption coefficients for materials vary all crazy style at different frequencies. I am pretty certain the engineers designing the QRD's to solve specific problems know what they're doing...which can actually be seen in the measurements. Though I would love to see hard data that shows the ineffectiveness of certain materials. (3) The goal of the QRD is to diffuse a specular reflection, which is to say the goal is to turn a single spike in the ETC into a series of "random" reflections...which is to say reflections that have different angles at different frequencies with different amplitudes. I guess I don't see how any of the existing QRD products don't satisfy that? Perhaps you could provide an example? Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted July 31, 2008 Share Posted July 31, 2008 "I'm not convinced that the skylines are effective QRD devices, based on theory." Gil The Skyline is not a QRD diffuser but instead a PRD (primitive root diffuser) and one of its most important benefits is the specular reflection rejection that this design affords which is especially helpfull in smaller rooms. One of the most important benefits of RPG products is the theory/performance is tested and verified with their products more than any company I'm aware of. I encourage anyone to take alot of time and explore all the articles available on their website since they are one of the leading research and developers of products for acoustical design and treatments. Like all acoustical treatments(absorbers and diffusers) caution in how and where they are used is important if benefits are to be maximized and negative results avoided. http://www.rpginc.com/products/skyline/index.htm mike tn[] Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted July 31, 2008 Share Posted July 31, 2008 Here is an example of one article on the RPG site that might interest some. RPG is exploring much more interesting/complicated diffusers than the orginal QRD designs if you explore many of their research papers. mike tn tyndall_paper.pdf Quote Link to comment Share on other sites More sharing options...
Arkytype Posted July 31, 2008 Share Posted July 31, 2008 Mike is correct---the Skyline uses primitive root sequence theory as opposed to quadratic residue sequence theory to determine the well depths and locations. The DIY sites cited have plans that differ from the genuine Skyline in that the ersatz versions use a12 X 12 matrix whereas the Skyline uses a 12 X 13. It appears the DIY versions also use a random placement of too few lengths of 2" X 2" blocks. Here's a link to Peter D'Antonio's Skyline patent. http://www.google.com/patents?id=gFQdAAAAEBAJ&dq=5401921 He has been awarded several patents and each will teach you something about the science of diffusion. Lee Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 1, 2008 Share Posted August 1, 2008 Thanks for your comments, including Mike Tn, Arketype, and Dr. Who. I'll start reading. I've look at the article and have downloaded the patent. Best, Wm McD Quote Link to comment Share on other sites More sharing options...
damonrpayne Posted August 5, 2008 Author Share Posted August 5, 2008 So, it seems that there is more than a grain of skepticism regarding using blue foam to make a diffusor? Not worth a $60 experiment? It seems the RPG stuff is grounded in good science, but I could buy another set of speakers for what it'd take to buy their products! Quote Link to comment Share on other sites More sharing options...
michael hurd Posted August 6, 2008 Share Posted August 6, 2008 Damon... I would definately "roll my own" diffusors... but then again, I am a kinda DIY guy for most things. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted August 6, 2008 Share Posted August 6, 2008 So, it seems that there is more than a grain of skepticism regarding using blue foam to make a diffusor? Not worth a $60 experiment? It seems the RPG stuff is grounded in good science, but I could buy another set of speakers for what it'd take to buy their products! Hey damon I don't want to discourage you from diy diffusers. I actually think the $60 experiment is well worth a try. Just make sure that any diffuser you design is glued/assembled good so that it doesn't become a source of rattles at certain frequencies. I did want to point out that the operation of the skyline diffuser and some of it's benefits(especially the specular reflection rejection feature) were being misunderstood/overlooked. What you get with the RPG products is very well researched/verified products kind of like the Palladiums if you will and that is were the real value of their products are IMO. I'll tell you my experience over the years is that every room needs at least some modest bass trap treatments (usually best placed in the corners of the room) and diffusion (with even the less than ideal diffusers most likely being better than doing nothing). True well designed bass traps help to clean up the muddy, ringing nature of some frequency bands which are often at their worse in the crucial frequency range of approximately 60Hz to 400Hz. What you should notice with well placed good designed bass traps is an increase in clarity and definition which equals a much more natural/realistic reproduction of good recordings. I actually have used bass traps in a room where the reproduction/clarity was much improved but an especially nasty room mode was revealed which needed a sharply tuned helmholtz resonator to remove it's audibility. Some people mistakenly think that bass traps will cause a reduction in bass level perception but in reality the perception will be of a stronger, tighter better defined bass reproduction and improved tonality. Now the benefits of diffusers when properly placed is again an increase in clarity, tonality and envelopment with a decrease in the piercing to the ear tendency of some frequency bands (especially in the 500Hz to 10kHz range that many people believe is the fault of their speakers but is often room acoustics at play. Absorption is the most often used treatment by people but it is also the most abused and misused treatment option we have. Many times I've seen it cause worse problems/colorations than it helped and very often I've used redirection or diffusion of a reflection to a much better effect. I believe for the most part that you will find that even less than ideal diffusers will still be a very worth while benefit to you. I also believe ideally it's best to measure the room to identify the problems areas and using only the amount of treatments(Bass Traps, Diffusers, Absorbers....etc...) necessary to treat them. Congratulations on getting the Palladiums damon and I hope you enjoy them as much as I enjoy my Jubilees! Both awesome speakers by Klipsch! mike tn[] Quote Link to comment Share on other sites More sharing options...
damonrpayne Posted August 7, 2008 Author Share Posted August 7, 2008 So, I went to home depot over lunch and they didn't have the 2" blue foam I was looking for. I'll have to trek around a bit but I had decided to give it a whirl and see how they look. I'll have to take another crack at interpreting what RPlusD is telling me. Quote Link to comment Share on other sites More sharing options...
damonrpayne Posted August 11, 2008 Author Share Posted August 11, 2008 DrWho and I went to Home Depot again, and it seems we're extremely skeptical that the variuos foam products would have the level of reflectivity they'd need to be useful. Anyone else have thoughs on materials that are lighter than wood? Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 11, 2008 Share Posted August 11, 2008 aluminum, polycarbonate, titanium, fibreglass, carbon fibre, balsa...??? [] Quote Link to comment Share on other sites More sharing options...
damonrpayne Posted August 12, 2008 Author Share Posted August 12, 2008 Balsa wood! Why didn't I think of that... Since the results of DrWho's measurements seem to indicate that there's not much going on in my ceiling due to some irregular shapes already being present, I'm probably going to go the wood route for side/rear walls when I get back from vacation. There's one ceiling place that will get the masonite treatment. My reading in a tiny bit of spare time today seems to indicate that the size of the arc will matter so I have to look up those equations. I'm going to look into borrowing a table saw with the lazer for precise cuts and digging through Master Handbook of Acoustics for the prime number theory QRD calculations. Stain-grade wood will surely still be cheaper than buying RPG products. Quote Link to comment Share on other sites More sharing options...
WMcD Posted August 19, 2008 Share Posted August 19, 2008 I have an alternate plan. We should build several hundred models of the F-117 in various sizes (?) and place them on walls and suspended from the ceiling of the listening room. These shapes should have no direct spectral reflection and thus must increase dispursion of sound waves. We will get some return on our tax dollars this way. http://www.ece.cmu.edu/~koopman/airplanes/f117/f117.pdf Smile, Wm McD Quote Link to comment Share on other sites More sharing options...
picky Posted August 22, 2008 Share Posted August 22, 2008 If making the diffusors out of ridgid styrofoam, I would be concerned that they might vibrate and make a noise of their own. In automotive, we sometimes have issues with two pieces of styrofoam (or other similar ridgid materials) moving against one-another in a relative fashion, thereby creating noise; usually what we refer to as an "itching" sound. I fear putting a bunch of them togther and touching would result in a virtual "chorus" at certain frequencies. Wood is much more dense and foam is soft enough to where I doubt either would cause this issue. -Glenn Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 24, 2008 Share Posted August 24, 2008 I dunno if I'd go with balsa wood....doesn't it get its light weight from being a very porous material? And if it's porous, then it's not going to be very reflective at all... I was also thinking about that masonite suggestion for directly above your listening position....I wonder if a phase grating wouldn't be a better alternative. Quote Link to comment Share on other sites More sharing options...
damonrpayne Posted August 24, 2008 Author Share Posted August 24, 2008 I'm reconsidering wood on stands for the front early reflections. I was going to roll with the "stuffed" masonite idea for above the listening position and the back of the room above the popcorn machine. I can always, uh, donate them if I change it to something else. What's your favorite food DrWho? I'll make you a series of 5 course gourmet meals to entice you to come back and remeasure, reposition, remeasure.... Quote Link to comment Share on other sites More sharing options...
michael hurd Posted August 24, 2008 Share Posted August 24, 2008 Damon... here ya go, just use sausages of differing lengths.... just on strings, worked for Tom Green... Damon would you like some sausages... LOL... Quote Link to comment Share on other sites More sharing options...
Rewind Posted March 16, 2009 Share Posted March 16, 2009 Hi, I'm building three Skylines and a more or less exact copy of the Real Traps. I have heard praise for them both and I think each has its qualities. I wonder, do you have schematics for the wells in the Real Traps QRD diffuser? And do I really have to make the wall of the wells go all the way (15 cm) when a particular well is only 2 cm deep. //Joni Quote Link to comment Share on other sites More sharing options...
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