DIY Diffusors to the Max

[G. E.]

Originally Posted by Lupo

... But if you know for certain that a given area will be filled, isn't it better to avoid repetition? Or am I missing something?...

Sure, I would avoid repetition too but isn't it more about practical reasons? 23x12 will double the weight compared to 13x12. Maybe you get the best of both worlds with "splitting" a 23x12 grid?!

Originally Posted by Lupo

... Another question: would it be much point in building symmetrical arrays? Mirroring one of them, so the L/R sides of the room is identical seen from the sweet spot...

Since the whole idea of a diffusor is about homogeneity of the sound field I tend to think this kind of strict symmetry is more counterproductive than not! But it may as well not be notable at all...

[Nordenstam]

Originally Posted by G. E.

the math behind all this doesn't allow a fixed formula for primitive roots, it's more about "searching" (for the very reason this math is strongly related to encryption theory as well...)

Thank you very much for the hint! Took some time to digest that one. It was an eureka moment when it suddenly snapped into place. Had a look at RSA encryption and it certainly looks familiar by now. Very neat! Is it safe to assume that PRD's is a physical/acoustic implementation of RSA encryption? Or is that way too fast?


Being curious now, hope this isn't a silly question. Do you think there's a way to relate the suppression of the specular lobe in the PRD emmison pattern to some part of the math? Like.. (using math concepts I don't really understand (yet)).. like the least primite root or the relatively prime criteria of the "grid size factorials"?

Perhaps this is really stupid idea, but it can't hurt to ask. You're the first one I've met online that seems to really understand this stuff.

Originally Posted by G. E.

23x12 will double the weight compared to 13x12.

Am going for the cheapo coated styrofoam route, at least for the ceiling pieces. Think it'll work fine from about 5-600Hz up, the base design frequency. It'll be the same amount of work to build a single big as two small, and I'd rather have as much encryption strength as possible for a given area! Really like the thought of making the reverb tail more complex that way. Watch out for Encrypted Sound Field Mastering (TM)!

Originally Posted by G. E.

Since the whole idea of a diffusor is about homogeneity of the sound field I tend to think this kind of strict symmetry is more counterproductive than not! But it may as well not be notable at all...

It shouldn't make a difference to the aural result if it scatters equally well in all directions. I just happen to like visual symmetry details like that!


Cheers,

Andreas

[G. E.]

Originally Posted by Lupo

...Is it safe to assume that PRD's is a physical/acoustic implementation of RSA encryption?... Do you think there's a way to relate the suppression of the specular lobe in the PRD emmison pattern to some part of the math? Like.. (using math concepts I don't really understand (yet)).. like the least primite root or the relatively prime criteria of the "grid size factorials"? ...

Another interesting extra mile to go in this thread yet out of my scope today. Definitely needs some thoughtful advice, hm, could have asked my former (some 20 years ago) applied mathematics teacher at the university when I happened to meet him last week at an exhibition. Ok, we put it on the list... now back to music!

[G. E.]

Calculating the well depths with whatever formula you should not forget to calculate the rod heights afterwards (= height_max - depth). So here's my final working plan:

[G. E.]

I had been too optimistic about the edges when ordering the balsa rods, decided to soften all edges this weekend, kind of meditative working for hours, listened to "Coltrane Live in Antibes (1965)" and the like...

[G. E.]

Prepared the rods for the first diffusor -- I need 7, 12, 13, 12, 13, 12, 13, 12, 13, 12, 12, 13, 12, 13, 12, 13, 12, 13, 12, 7 pieces for the lengths 0-19.

[G. E.]

Originally Posted by G. E.

... So here's my final working plan:

Although the above plan was correct I noticed that I needed to transpose the grid for better "readability" for the assembling (I preferred it over rotating simply because Excel has a built in "Transpose"-command...):

[G. E.]

Mounted two spare BBC-type diffusors (instead of the still unfinished new ones) on the cloud to have some progress and to be able to study their contribution. Still working on the mounting trying to get them as close as possible to the solid concrete ceiling. So the images shall be seen as a temporary solution...

[johndykstra]

I really hope everyone has at least a chance to see this thread, and have a look at what is "behind the curtain" of a very well thought out space.

All the talk regarding what new preamp to get is tiring... this is where it's at!

[greatgreatriver]

Yo super dude! I just wanna say that your space is fakkin' great looking. You have good eyes man - you will enjoy music in there.

Peace out!

/Flash Gordon IV

[bove]

Originally Posted by G. E.

Thanks, Loyd -- actually I've been inspired by a photo of Skywalker Sound! Each of the two portable diffusors/absorbers is 2' x 4'. I've included a second mount for a different height (~1.5' higher). Image shows the "beta" version with small "feet". They broke after 2 minutes of moving, I redesigned the feet afterwards and used much stronger curlings that now survive everyday use.

How much do these weigh? They look fantastic. Nice woodworking!

[G. E.]

Originally Posted by bove

How much do these weigh? ...

Each mobile diffusor weighs around 50kg [~110lbs]! Details show parts of the mechanism to change height (two positions).

[G. E.]

Originally Posted by G. E.

... Next thing would be to replace the rollers with spikes...

The Speakers now have spikes to the stand plus the stand itself "pierces" the plastic-floor with spikes to reach the solid concrete floor beneath. The bass response definitly changed but I'm not sure if it became better or worse... more listening and measuring on the way...

EDIT: in the meantime I've removed some of the spikes -- see later post "Coupling speaker to stand"

[derekberg123]

Sorry I don't have a better picture of it but the diffusor on the right is DIY (as you can probably also see with everything else in the room). I got lucky and ran into a bunch of scrap 2x4's and cut them to varying length. Started by screwing a frame together (more scrap 2x4's) and laying it on flat ground to get ready to build. Then, the smaller cut 2x4's were placed in row by row. As I got each row to fit snug into the frame I would also then nail each piece to the frame or adjacent piece (if it wasn't touching the frame) and usually both to make it stronger. After about 2 straight days of this (it would have taken a lot longer if I didn't use a nail gun) it was done and ready to be hung. The thing weighed way more than I thought it would, so to be safe I used lags to lag the diffusor to the studs in the wall. Came out good. Looks cool and made a previously useless space sound half decent. Add some cheap DIY bass traps and foam for flutter echo and voila!

[jimmieee]

Well I dunno have you ever seen this but I've been using this
"240 step wells" 2D diffuser for a while.... (It has a patent already)
But I'm also looking forward to your work!
(P.S. This is not my studio)

[betserd]

Originally Posted by G. E.

The Speakers now have spikes to the stand plus the stand itself "pierces" the plastic-floor with spikes to reach the solid concrete floor beneath. The bass response definitly changed but I'm not sure if it became better or worse... more listening and measuring on the way...

I always tend to think it is best to couple the loudspeakers to the "stand" to reduce vibrations in the speaker itself and to decouple the stand from the floor to minimise vibration transfer from speaker to the ground. This way you end up with one big heavy speaker which doesn't resonate and does not transfer energy to the floor.

Great post btw!! I like the way you keep us informed on your thoughts thumbsupthumbsup

[G. E.]

Originally Posted by betserd

I always tend to think it is best to couple the loudspeakers to the "stand" to reduce vibrations in the speaker itself and to decouple the stand from the floor to minimise vibration transfer from speaker to the ground. ...

Agreed! I went one step back shortly after the initial post and removed the spikes between speakers and stands -- the bottom of the speakers strongly vibrated (bass-freqencies) with spikes in place which totally confirms your comment.

[Hammer Mark]

Originally Posted by Lupo

It's an impressive effort you've laid down in this! Big cudos for all the work. Got me inspired to finally get around to build some. So I've been re-reading the Cox and D'Antonio book and the PRD patent. As for the math, the formulas are pretty straight forward - the one thing that confuses me is how to find the prime root for a given prime number. Is there any way to get a results directly, or any tables to look it up in? Or do I have to try every possible number from 0 to N-1 for any prime number I choose to use, finding out if there is a suitable prime root the hard and long way? Or is five a magic number that works with them all? (seems that way when using the online calculator, but I'm a bit sceptical to such a quick solution!)

The "primitive root" is the smallest integer that yields no duplicates in the set. I don't think there's a way to calculate this, but you can just use the online calculator, start at 1, and increment until you get the desired result.

[speakercoil]

What a great thread... All these massive diffusers reminds me of working at Blackbird. George Massenburg's room has the biggest diffusers I have ever seen... I used to describe the feeling of the room as if you were surrounded by a bunch of Zulu warriors pointing spears at you... It was weird, because it's a massive room, but I would get claustrophobic at times. What's funny about the picture below is that they obviously moved the desk for the picture. Normally it is pointed the opposite way (toward the camera). I guess they just didn't want to show the doorways. As an intern I have to say cleaning that room was a bitch... It was sooooo hard to get all the dust from under those things... They were quite stunning though.

[johndykstra]

Originally Posted by speakercoil

What a great thread... All these massive diffusers reminds me of working at Blackbird. George Massenburg's room has the biggest diffusers I have ever seen... I used to describe the feeling of the room as if you were surrounded by a bunch of Zulu warriors pointing spears at you... It was weird, because it's a massive room, but I would get claustrophobic at times. What's funny about the picture below is that they obviously moved the desk for the picture. Normally it is pointed the opposite way (toward the camera). I guess they just didn't want to show the doorways. As an intern I have to say cleaning that room was a bitch... It was sooooo hard to get all the dust from under those things... They were quite stunning though.

A very famous photo that has made it's rounds through many a thread on here.

It's funny, everytime I see the room pictured, without fail, someone brings up not being able to imagine having to clean it.

Did you regularly vacuum out the wells, or was that a "once a year" sort of endeavor?

[betserd]

Originally Posted by G. E.

Each mobile diffusor weighs around 50kg [~110lbs]! Details show parts of the mechanism to change height (two positions).

I was wondering why you did not choose to build omniffusors for the mobile devices, they must be much lighter. Any reason for using the skylines?

[G. E.]

Originally Posted by betserd

I was wondering why you did not choose to build omniffusors for the mobile devices, they must be much lighter. Any reason for using the skylines?

I don't know exactly how RPG's Omniffusor®s (they're 2D so aren't they also kind of Skyline-diffusors?) are built so we can only guess they make use of some cavity behind the wells to save weight -- at least that's what I did with my huge 19x15 diffusor. The main difference between the lets say Omniffusor®-"type" and BBC-"type" is, that the first ones usually don't go as deep as the second (don't know the reason why) and therefor have a more limited lower design frequency. Additionally their pretty wide dividers may be seen as a disadvantage. Anyway, I've "designed" my mobile diffusors on the go while building them, not every detail is totally thought out...

[str1ke4ce]

Originally Posted by G. E.

Oh, thanks a lot! Well, I lowered the monitors (2 x 20" in portrait mode) half a year ago and have been working that way since then, got used to it quickly. And you know, it helps the acoustics...

Maybe the 2D-guy in the sketchup-renderings has been misleading, exchanged it for a 3D-model (thanks Google 3D Warehouse):

why is the engineer naked?

[speakercoil]

Originally Posted by dykstraster@gmai

A very famous photo that has made it's rounds through many a thread on here.

It's funny, everytime I see the room pictured, without fail, someone brings up not being able to imagine having to clean it.

Did you regularly vacuum out the wells, or was that a "once a year" sort of endeavor?

It was mainly vacuuming the floor, and underneath it which was a daily thing... Cleaning those involved dusting twice a month, which took FOREVER. What's awful though is those floors. It's the same problem I always had with D... No matter how many times you mop, it still looks dirty. It's just something about that dark wood, it never shines like you want it to. Also that room creates A LOT of dust, I am guessing because it's from the wood of the diffusers. The corner's were a pain in the butt too... You had to move lamps out of the way and get in all these funky angles... It was really mopping below those suckers that was a pain in the ass... Always on your knees trying to push a mop all the way underneath.

On the flip side, that lounge was always the easiest to clean. George is a very neat person, and never messed it up too badly. It was mainly a quick sweep and mop, and a little restocking.

Man... I really miss that place.

-Grant

[G. E.]

Originally Posted by str1ke4ce

why is the engineer naked?

... you choose: ( ) sound is HOT, ( ) spent all the MONEY on diffusors, ( ) she's ENGINEER-OF-NAKED-TRUTH

[G. E.]

Due to a lot of requests about the mobile diffusors I tried to remember how I built them back then. Resulted in a kind of "LEGO®-like" construction description, doesn't it? I connected the wood parts with both glue and screws -- solid as hell. Make sure you use sturdy rollers, because those are the weakest part!

[G. E.]

Some renderings completed with 2x BBC-diffusors in front and a broadband absorber on the back: the two "positions" are shown as I use them, low (drums, etc.) & high (vocals, etc.).

[mshayden]

G.E. I liked your design of the large free standing diffuser, but what do you think about using 2"x2" strips of open cell foam instead of wood? Im going to try is, just wanted some opinion. Thanks.

[G. E.]

Originally Posted by mshayden

... using 2"x2" strips of open cell foam instead of wood?...

As I understand open cell foam may be used for absorbtion which totally contradicts using it for diffusion purposes -- diffusion is based on reflection (though some absorption may occur because of unwanted resonances etc.)

[mshayden]

gotcha. Im new to this, just thought Id give something a try. thanks!