black box diffusers

Hey, can anybody explain to me how these things work? I spose for a start they are more "deflectors" than "diffusers". Do they just reflect anything high enough to reflect off the hard surface and just let the rest be absorbed by the stuff on the back (except bass frequencies, i'd imagine). What sort of formula's would be used to figure out the hole spacing?? thanks Matt

they certainly look cool!

I am not clear on what your desire for knowledge is. For an in depth analysis of holes in thin materials look at the IPERF document on perforated materials. Holey, Andre

They look like a copy of the ceiling panels found in SAE studios. They are purely visual :cry:

hehe I was thinking of using them to break up my ceiling in my studio. The ceiling is 3.6m high but parallel to the floor. ...my full thread on it is at http://www.johnlsayers.com/phpBB2/viewtopic.php?t=10373 so john are you saying that you don't think these would do anything? Although I can't really see it in the picture.. at their website (http://www.blackbox-design.com) the 3D layout of the defectors show that they have absorption material stuck to the top of them as well. This would imply that (depending on the hole spacing) they would reflect some highs and absorb a similar amount of mids (depending on the absorption coefficients of the material on the back. am I even close??

Cargo cult design is not recommended. A well documented and proved cloud is more advisable.

Cargo cult design :), thats funny. I don't think it's accurate but it is funny. David French made an overhead cloud, less the reflective panel that looks similier...less the reflective panel: http://www.recording.org/ftopict-26889.html It doesn't seem to be a completely foreign concept....but I wouldn't buy one of the black box things just because it is kewl, fer sur ;)

I'm looking for a way to break up the parallel reflections between my ceiling and my floor. I was trying to avoid just using absorbing clouds in my live room as I do have high ceiling (3.6m) and want to take advantage of them. What do people in my situation usually do? (see above for side-thread link) I know at my mates studio he had absorbing tiles on his high ceiling and it sounded ok.. but when he put some MDF (not sure what thickness) above the Drum Riser... the drums just started to EXPLODE! that was a sound i liked... That kind of lead me to believe that it was the vertical reflections that gave sound explosion and the horizontals that gave it length. does that sound about right to anyone else?

David Frence made an overhead cloud, less the reflective panel that looks similier...less the reflective panel: http://www.recording.org/ftopict-26889.html

I have actually made a similar cloud.. using a aluminium frame and 2 layers of rockwool 2400x1000. Worked AWESOME.. above my speakers in the control room. But I really am looking to do something more interesting than just absorb the ceiling. And just to clarify.. I'm not just interested because they look cool.. it was more because I thought they might actually do what I was looking for.. which is reflect and absorb. hehe what about this.. whats going on here? did you design this John? http://www.electricave.com.au/Photo_12.html

For an in depth analysis of holes in thin materials look at the IPERF document on perforated materials.

thats really good by the way.. just reading now. thanks! :?

Hey Glenn, I did shoot you a brief email about this but I thought I'd post it here too anyway.. is the concept of these "deflectors" similar to your drum cloud design (below)? Reflecting the highs and absorbing some mids? What kind of sound does this give from the ceiling? Does it tighten the overall sound but keep the room lively??

keeping in mind this could is 4' x 8' by 8" deep - yes it will do a significant absorption job as well as keep some of the high end because of the widely spaced slats.

Assuming I was to make a similar thing to the blackbox "diffusers"... if the total AREA of all the holes I made was equal to the total area of MDF that is left... and then put some porous material on top of the MDF to absorb.. would the "diffusers" technically reflect and absorb the same amount?

I'm not familiar with this specific blackbox design and have never taken the time to seriously investigate these devices, but I would intuitively think there is a rationale behind such perforated panels - especially with porous backing. Maybe my intuition is misleading me, so caveat lector. Consider a 'typical' broadband absorber based on porous media, such as these so called 'clouds' or 'pictures' (i.e. a porous material framed and covered with cloth). Now, adding a reflective front panel would change the 'balance' of absorption between low freqs and high freqs, mostly due to diffraction and mass considerations. The crossover frequency can be derived from the dimensions of the panel and it's mass (what frequencies will 'transparently' move the front panel). The larger the front panel - the lower the crossover frequency (laws of diffraction). The heavier the front panel - the lower the crossover frequency (newton's second law). However, adding a solid front panel presents some new considerations: 1. It may behave as a membrane - hence completely changing the way the device works. 2. May introduce flutter because of high reflectivity of a large panel. Creating holes in the panel should (a) reduce the membrane effect, at least in its straightforward way; (b) create some level of diffusivity, that may be enough to prevent/reduce flutter effects. So I believe that beside cool looks, there is some acoustic thought behind the design of these things. All the best, :) Jon.

We have had great success with ceiling mounted diffusors....Ours are genuine high prime # Schroeder based design. We have actually solved bass standing waves with diffusion, which flies in the face of traditional thinking. See the Hilltop Studio case study on our site. We believe that the bass is improved in two ways: Large diffusors have wider bandwidth, and when you reach the harmonics of a bass standing wave, it reduces the apparent level of the fundamental. The panels we make have a solid high density construction. The resonant frequency is very low, and we can feel the panel vibrate at very low frequency. This also helps dissipate low bass, the combination is very effective.

See the Hilltop Studio case study on our site /quote Would you be so kind as to point me out to this link? Not the www part, the link for the page you mention. I jumped through about three links and never did see it....

Here is some information on your request.... http://www.srlaudio.com/customer_commen ... tudios.pdf

Is that what ya call a "case study?"

Well, I guess so...We were called to solve a common control room problem: Bass Standing Waves causing a null in the center of the room. Traditional ways of working on that problem use "trapping", or removing acoustical energy from the room. We solved the problem with a large ceiling mounted diffusor. This alone is sort of astounding information. Our competitors don't get it, because I have been ridiculed by them for designing panels that are not "easy to ship". The effect of this change in the control room is profound. The bass is solid at the mix position, and the mids and highs are spread over a much wider arc. Panning and setting delays is much easier, and the old monitors (actually Urei 813) came alive! John, the owner of the studio, said that anyone could call and he would tell them his story. There is a photo on our site of John in his control room. The diffusor is mounted in the ceiling grid, the other tiles are 2" thick rigid fiberglass. I just thought that this was relevant to the thread about ceiling mounted diffusion. What do you think???

If to me specifically, I would appreciate seeing it in action.

srlacoustics wrote:

Well, I guess so...We were called to solve a common control room problem:

I had a look at the studio's website and the picture there did not show your diffusor in the ceiling. That started me wondering about accuracy. The monitors in the studio's website are listed as 809s not 813s. Clarification please. Curiously, Andre

I am sorry for the confusion. The 809A's were the single coax version of the 813A, which was actually a 3 way with additional 15" woofer. The good part is that these came from UREI when it was still owned by Bill Putnam (pre Harman). Putnam used an Altec coax with the 1" aluminum diagphragm compression driver mounted on a custom open throat horn and associated crossover designed by The Mastering Lab. JBL destroyed this design when they acquired the company, so it is always nice to find the orginal design around. The picture on Hilltop's website is not updated. Here is the current look: http://www.srlaudio.com/acoustic_images ... loud01.jpg I will be glad to clarify any other questions.

Yup about the UREIs. I was at the AES convention where they were debuted. :D Thanks for the picture clarification. I don't know how many people have perused your website but I was impressed to read that your diffusors are not multiple re-iterations of a smaller sequence but one sequence for the length of the diffusor. It's nice to see things done right. From the depth of your product it's obvious that the low frequency wavelength is greater than the listening distance. I noticed that eight feet is recommended as the minimum height for the bottom of ceiling mounted diffusors. This is obviously contrary to the writings of Cox and D'Antonio about listening position being at least 3 wavelengths distant from the diffusor to avoid lobing, but if it works, that is the important thing! Impressed, Andre

Thank you for your comments. Also pointed out in the Cox studies is the fact that when horizontal sequences are repeated, as many companies do with their one size fits all approach, the diffusion is compromised, and lobing problems develop. All of our products use high prime number theory, which has also been associated with good performance. To make a small unit, you must use a smaller prime number sequence. Draw your own conclusions. :D

They are purely visual

Hello John. I have a question for you. Couldn't those panels, IF used as a perforated face panel on a sealed enclosure like Alton Everest shows on Pg 182-184 of the Masterhandbook of Acoustics(first edition)perform as a Perforated Hemholtz Resonator?In fact, by extention(shown on Pg 181), wouldn't they be the same as your much used SLOT/SLAT WALL design, shown on Pg 181? In otherwords, couldn't these panels be used on a INSIDE OUT WALL? :) fitZ

cadesignr wrote:

They are purely visual

Hello John. I have a question for you. Couldn't those panels, IF used as a perforated face panel on a sealed enclosure like Alton Everest shows on Pg 182-184 of the Masterhandbook of Acoustics(first edition)perform as a Perforated Hemholtz Resonator?In fact, by extention(shown on Pg 181), wouldn't they be the same as your much used SLOT/SLAT WALL design, shown on Pg 181? In otherwords, couldn't these panels be used on a INSIDE OUT WALL? :)

You have Everest. Do the calculations for frequencies where Helmholtz type absorbers are normally tuned. You would need VERY thick panels and/or very small % open ratio. FWIW I went through a similar thought process when starting to learn acoustics. Andre