Prime 29 Diffuser Build - Using QRDude

Lonely Raven · 8th November 2009, 08:36 PM

So now that I have a house, and a goodly sized living room for a proper home theater, I've decided to go all out with the room treatments. Huge corner bass traps, broadband traps at key points, flutter breaker diffusers, and proper QRD diffusers.

While researching QRD diffuser designs, hoping I'd stumble into a completed design I could just clone...I stumbled into GearSlutz and all these great diffuser builds, as well as this QRDude software.

QRDude: Quadratic Residue Diffuser calculator

Collo, who writes the software is a member of these forums, who has been kind enough to answer questions and tweak the software to help make it more user friendly for the DIY guys like me. (if you find the software as useful as I have, throw him some $$ for his efforts!)

For better or worse, the following is my Prime 29 build for the rear-side walls of my home theater...used to help break up the flutter reflection between the side-rear speakers, and help liven up the surround sound in the back of the theater. My ultimate goal is a live end - dead end with the speakers in front being the dead end, and the surround being very *live*.

Here is a screen shot of the Specs of my side-rear diffusers.

And the MaxData showing the dimensions (which I have printed out across several 8.5 X 11 pieces of paper, and on a laptop screen in the workshop. On the high rez image, we can easily read the well depth measurements. Note: that's 841 1" wells there...yes, I'm a glutton for my own self punishment.

Once I got this far, I ran to my local lumber yard which is about 45 minutes away, and I stocked up on panels for this and a subwoofer project I have in the works. I'm on vacation this week, so I'm looking forward to making progress on both the diffusers, and the 21" woofer in a 15 cubic foot box! Here are all the panels stuffed into my Scion xB. Poor car, it used to be a show car...now I use it more like a truck. The lumber yard was nice enough to cut all six panels crosswise so I could fit the 4' X 4' sections in my car and not have to rent or borrow a truck.

From here on out, it's all about cutting and assembly!!

Lonely Raven · 8th November 2009, 09:08 PM

OK, now on to the cutting.

Please note, some of what I do is *very* much not safe. As I post some of these photos, I can imagine "millions of (woodworker) voices suddenly cried out in terror and were suddenly silenced". I'll clarify as we go along here.

First off, I decided to rip all the fins, since this is going to be a well type diffuser along the lines of the RPG OmniFussor, but on a larger scale. Something like this:

Here are my fins cut so far. 3.5" + or - 1/64"

I wound up about 8 fins short! Now, had I done a "cut sheet" where you draw out the panels (in this case 4' X 4') and drawn out each completed piece so I could map out the cuts, I would have made enough fins to complete the project. But I simply started ripping the 3.5" fins and kept going till I reached the required 60 fins, or in this case, ran out of MDF. A little planning might have saved me another trip to the lumber yard. But then again, two full sheets later, and it appears I won't have anything left over for the SECOND diffuser!

Once I had the fins cut, I used some scraps left over from the fins to start building and testing a jig for cutting the 1" tiles for my diffuser. One of my design requirements, was that I try and keep the weight down. So instead of buying 160' of 1" X 1" wood blocks, I'm going to cut 841+ tiles out of MDF, and glue them at the correct height. It sounds harder then it is.

So the concept of the tile cutter, is that I rip the 1/8" MDF scraps into 1" wide strips. Then I feed them into the jig and cut them into 1" X 1" tiles with great consistency. The original jig I made for the band-saw (which is the safest way of cutting objects so small), but my band saw apparently can not cut even a 1" strip straight, and all the tiles came out looking like diamonds. I wound up tossing all those tiles in the trash, and started working on the same jig but for the table saw (the absolutely least safe way of doing this).

Here is the jig on the Table Saw. It's literally the same jig I made for the band saw, but shifted down a bit so the table saw made fresh cuts into the scrap material.

This is the part where woodworkers cry out in anguish. The way this jig works, is that the base panel is glued and stapled to the piece of pine, all very squarely. Then the pine fence is screwed to a quality, very square Miter from Incra. Then I place (staple and glue) a 1" X 1" "stop" exactly 1" to the right of the blade kurf in the jig (see the image above). So I hold onto the long 1" wide strip with my left hand which presses it to the stop, while my right hand index finger holds the (future) 1" tile and the whole jig slides forward into the blade chopping off 1" tiles exactly the same, all day long. (and hopefully not taking any figures with it).

Again, this is absolutely the WRONG way to do this. If the wood binds at all, it could kick up and fling my hand right into the blade. And as sharp and true as this $125 blade it, I probably wouldn't notice till I saw my fingers hit the floor. So do as I say, not as I do!! The *correct* way of doing this would be to make the whole jig more robust, and use a toggle (or two) to hold the MDF in place while I put my hands way back on the fence to push the jig into the blade. Toggles look like this:

You can see how that would be much safer to have the toggle hold the MDF as it's run through the blade. I could come up with 100 excuses why I didn't use a toggle and risk my fingers, but they would all be lame. Just be smart and do it right.

Moving on, a little better view of the whole jig:

And the resulting tiles. These are 1/64" under 1" X 1". I'd say I did pretty good, and I still have all my fingers (So far). I still have a bucket load more of these to cut.

Lonely Raven · 8th November 2009, 09:20 PM

Now for the fin jig.

So these fins are going to fit together like a giant tic-tac-toe grid. The best way to do this would be to cut consistent and accurate slots 1.75" into each fin, then the fins would interlock together. If I'm off on these cuts, the tiles won't fit!

So along comes the fin jig. Typically this type of jig is used for making finger joints for building boxes or cabinets. I came up with it while teaching myself to make guitar speaker cabinets as a teen, only to find out woodworkers had been doing this for probably a couple hundred years.

The way this jig works, is that you mount a board to the miter (I used the same miter as before), then you take the 1/8" saw blade, and run it completely through the board at the correct height. This gives you a clean cut, exactly as you want it on the fins. Then I measure 1" exactly to the right of the blade kurf, and make a second cut. In the second cut I glue in a 1/8" "key". So, now that everything is set, you make the first cut on the fins by pressing it up against the "key". This gives you the correct spacing so you have 1" from the end of the board to the first cut (this is assuming your fin ends don't slot into the frame on the diffuser!!). Then you take the cut fin, and slide the cut OVER the key, which gives you the exact 1" spacing you need for your next slot. Then cut, move and repeat till you get to the end of the board! It's that simple! In fact, I was cutting 10 fins at a time using this method. It was hard on my hands, cutting, pulling, moving over one slot, cutting, pulling moving over one slot...but the end result was so accurate, that the 1" tiles I cut fit inside the assembled fins perfectly!!

Lonely Raven · 8th November 2009, 09:31 PM

So here I am with a few of the fins completed. All the slots cut, and a hand full of tiles cut. I figured I'd do a dry fit to see how everything goes together.

Here are the fins slotted together to form a corner of the grid:

It was a bit of a tight fit, I had to use a board laid across the grid, and a small hammer to tap the board to get all the fins to interlock. If I had a saw blade that was a hair thicker, these would fit together a bit more easily. As it is, everything went together pretty well!

Now my concept for getting the tiles spacing exactly (the next "jig I'll be working on later this week). Is to simply use wood dowels that fit into the slots, and I'll have the wood dowels cut equal to the depth needed, minus the 1/8" thickness of the tile. Here is a quick and dirty test example I did. I cut some scrap to different heights, and drop them into the slots:

Then I simply press fit the tiles into the grid till they hit the wood spacers, so I know where to stop. And yes, the cuts were all so exactly on this, that the tiles press fit perfectly with not the slightest gap in the grid. I dare say these are damn near air tight!

Now the bad news....so I was up late last night, I finished cutting the slots in about 25 of the fins, and I figured I'd start assembling a bunch of the grid before I go to bed. Well, while tapping in the fins, a few of the fins tore right at the slots and just fell apart! Keep in mind, as you add more and more fins, it's getting tighter and tighter. This thing could easily hold it's own weight up on the wall once I get all the pieces interlocked. But that tightness came at a cost.

Now, at this point, I'm not sure if I should scrap this project and get 1/8" plywood (ditching the MDF completely) and start over (which would be stronger and lighter, but also twice as expensive), or if I should just continue to assemble the grid, knowing that the broken parts will easily be held in place by the grid itself. My concern is, if this falls apart this easily just putting in 6-8 fins, how impossible is it going to be to assemble when I get to 29 X 29!! I wish I had a saw blade that was just a hair larger then 1/8" thick!!

That's all I have for now...I've lost a bit of steam after this latest issue. I think I need to take a break from it for a day or two and come back with a fresh mind. I was hoping to have one of these done this weekend, but it's not going to happen as frustrated as I am right now.

mobius.media · 8th November 2009, 09:38 PM

Bummer man. These well-based designs seem tricky to implement.

Kudos for pushing ahead.

G. E. · 8th November 2009, 10:13 PM

Quote:

Originally Posted by Lonely Raven

... My concern is, if this falls apart this easily just putting in 6-8 fins, how impossible is it going to be to assemble when I get to 29 X 29!! I wish I had a saw blade that was just a hair larger then 1/8" thick!!...

I ran into the same kind of troubles (see image) with a quite similar PRD-diffusor, 19x15 grid based on the same construction exept that I had the wood prepared by a workshop. I took two of us to get the pieces into place using heavy hammering and screws from the back to fix those which were already in place. Really, it gets harder with every row... maybe you just get a very thin saw blade and "split" the whole grid into more easily workable grids!?

Schaap · 8th November 2009, 10:33 PM

Quote:

Originally Posted by Lonely Raven

That's all I have for now...I've lost a bit of steam after this latest issue. I think I need to take a break from it for a day or two and come back with a fresh mind. I was hoping to have one of these done this weekend, but it's not going to happen as frustrated as I am right now.

You need to construct it from the beginning on a e.g. MDF back plate! When you saw or cut in thin MDF it breaks easily under pressure

.

I have made an Omniffusor and filled the slots full with wood to prevent resonations. Good luck! Nice pictures btw.

terry j · 8th November 2009, 11:24 PM

good work LR!

I completely understand what you are doing, and how the slots get progressively tighter as you go. It will be very hard at the end.

Off the top of my head, this might work.

With your jig, when you make the first slot (which then gets moved over to locate on the lug) you could always do a second pass thru.

Ie, cut the slot and it is exactly a blade width wide (ever so slightly small). Ok, using paper or shim or whatever works it is in place for that first pass.

Then do a second pass, after removing the shim. The slot is now that shim width wider.

When you move the pack over onto the existing lug, you make the first pass with it (the pack) hard to the left, and then the second pass hard to the right and that way you now have the second slot *ever* so slightly wider than the blade width, and the same size as the first slot....and so on thru the pack.

I too second the safety aspect, when I built mine this way I ended up with a saw cut on my finger!! (see the space coupler theory thread, I too show pictures etc of the cutting jigs SPACE COUPLERS. Theory, construction and effectiveness on traps.) I got around that problem by the saw always being 'hidden' within wood, and never exposed. the pics in that other thread may help some.

Can I ask, is there a reason why you did not go deeper?? I know it gets heavier etc etc, but personally for all that work I would have made it 'more' worthwhile and make it diffuse deeper.

You are making more than one?? If so, then with your spacers I would have reversed it. Ie, rather than cut to length the spacers so it 'places' the tiles from 'above', I would have cut the inverse length so that it places the tiles from 'below'.

That way, you can make a full jig that can be used over and over.

The dowels can be permanently glued in place on a backboard, such that your grid can be placed on it. This time when you put the tiles in, you are doing it from the 'back'.

That also now allows you access from the back to the tiles, either for getting the glue in or filling the cavity. Once done, lift off the completed product and place the new grid on and do it all over again.

The way you outlined means every time you want to make one, you need to sort loose dowels and place the spacer manually in the correct location...would not want to get a few out of place!! so lot's of checking etc, then you need to remove the product, turn it over and then do the gluing and filling of the cavity, all the time hoping one or more of the tiles do not move.

Pretty well exactly the same method as you are doing, but without the double handling. just think in reverse.

And only really useful if you are doing more than one.

Not a criticism, hopefully just an alternative look at the method.

PaulP · 9th November 2009, 04:34 AM

Quote:

Originally Posted by terry j

I too second the safety aspect, when I built mine this way I ended up with a saw cut on my finger!! (see the space coupler theory thread, I too show pictures etc of the cutting jigs SPACE COUPLERS. Theory, construction and effectiveness on traps.) I got around that problem by the saw always being 'hidden' within wood, and never exposed. the pics in that other thread may help some.

I was going to say the same thing, get a block of wood in there behind the mitre gauge fence
or you may regret it. Especially since your blade is way high. My neighbour cut off three fingers
just after retiring and setting up a full workshop in his garage. Put an end to that dream.

Other than that great post. Thanks for sharing. Hope you find your way forward.

Paul P

Lonely Raven · 9th November 2009, 02:42 PM

Quote:

Originally Posted by PaulP

I was going to say the same thing, get a block of wood in there behind the mitre gauge fence
or you may regret it. Especially since your blade is way high. My neighbour cut off three fingers
just after retiring and setting up a full workshop in his garage. Put an end to that dream.

Other than that great post. Thanks for sharing. Hope you find your way forward.

Paul P

Actually, I don't go all the way through the miters fence. I did once when I squared up all the material, but after that I glued and stapled another 1/4" panel about 4" forward of the fence. The only area that I'm in danger right now, is holding the material to the jig and running it past the blade.

Thanks for the consideration though. An extra set of eyes is always good!

Terry, I follow most of what you're saying. I'll look into making a spacer somehow to widen the slots. Otherwise, I may have to scrap this for a bit. I'm expecting delivery of my 21" sub driver today, so I'm probably going to get working on that this afternoon.

G.E. I love your thread on all your diffusers...it's part of what inspired me to jump into this project. Great photos in that thread by the way! I would love to see more!

PaulP · 9th November 2009, 02:53 PM

Quote:

Originally Posted by Lonely Raven

I'll look into making a spacer somehow to widen the slots.

The (really thin) spacer is only necessary for the first cut of the first slot
in a batch since the following slots are indexed off the previous one (and
they all now require two passes per slot as terry j mentions. I used a similar
method to make box joints with 1" fingers using a 1/2" jig. A bit too loose
would be better than a bit too tight.

Are you planning some sort of frame around the whole thing ?

Paul P

Lonely Raven · 9th November 2009, 05:31 PM

Quote:

Originally Posted by PaulP

The (really thin) spacer is only necessary for the first cut of the first slot
in a batch since the following slots are indexed off the previous one (and
they all now require two passes per slot as terry j mentions. I used a similar
method to make box joints with 1" fingers using a 1/2" jig. A bit too loose
would be better than a bit too tight.

Are you planning some sort of frame around the whole thing ?

Paul P

Originally I was planning on having a frame around it, but I kinda like it with the edges open. And this will be plenty strong enough once I get it fully assembled. I think I'll consider solid blocks for the end wells.

I forgot to add previously...the reason why these are only 3.5" deep, is because the right diffuser will be on the wall of an isle that people walk past. Even 3.5 inches sticks out pretty far.

If I redo my back wall, I'll probalby do 6-8" deep. This is what I have on the rear wall already:

It's a bunch of flutter breaker diffusers made from vintage oak and pine stair treads, with a pair of 2' X 4' MDF QRD in the middle. Both projects were blatantly stolen from other plans. I just scaled them to my needs, stained them, and screwed them to the wall on 2" X 2" furring strips. The airspace behind the diffusers was then stuffed with 2" rockwool acoustic fire blanket.

Lonely Raven · 9th November 2009, 11:03 PM

OK, I hope you all understand when I say, I'm going to take a short break in the diffuser build, to work on my other project.

Here is the driver for the sub-woofer I'm building for the home theater. It's so big, it's almost perverted!

StudioTinPanAll · 18th November 2009, 04:41 PM

how's the sub and diffusor coming along ?

Lonely Raven · 18th November 2009, 05:33 PM

Quote:

Originally Posted by StudioTinPanAll

how's the sub and diffusor coming along ?

The sub is coming along, and diffusers are on hold till the sub is done.

On an unfortunate note...I may be let go from my job this week...which puts a hamper on finishing any projects and starting new ones.

PaulP · 18th November 2009, 05:40 PM

Quote:

Originally Posted by Lonely Raven

The sub is coming along, and diffusers are on hold till the sub is done.

On an unfortunate note...I may be let go from my job this week...which puts a hamper on finishing any projects and starting new ones.

That's bad news, I hope it doesn't happen. May you get through the week
without too much pain.

Paul P

Lonely Raven · 18th November 2009, 05:49 PM

Quote:

Originally Posted by PaulP

That's bad news, I hope it doesn't happen. May you get through the week
without too much pain.

Paul P

Thanks Paul.

Lonely Raven · 23rd November 2009, 06:16 AM

OK, well, had a "fun" week at work. I basically had to interview with HR for my own job. I don't even want to get into that...I'm just glad that I have a job.

I finished up my sub, and it's setup in the home theater. I can hit 102db at 10Hz with 1500 watts! Watching Star Trek on Blu-Ray was fun! Though I need to EQ it a bit...but that's a whole nother project.

Now that I'm done with that for the time being, I cleaned up the garage shop and collected the pieces from the broken QRD-29. Just for fun, I took I what I had and made an 11 X 11 (actually, it's off by one, but it's just for practice). I just cut the fins around 11 X 11 since that's the largest I could go with what I had, and started assembling. I did go back to my slot jig and spaced like Terry and Paul were talking about. I used business cards to "add some slop" to the slots so they could be assembled without beating them with a 5lb hammer. There is a lot of slop in my 11 X 11 sample, but that's because I took all my practice and broken pieces and just slapped it together. The final product will be much more consistent.

Here is what I have so far:

I took the remnants and pieced together this 11 X 11 grid (actually, you can look at it like a 10X10 or 12 X 12 since I'm leaving the edges open). It's not bad for spare broken parts!

Bringing QRDude on the screen, I used my digital caliper to set the depth of the tiles.

Once I got the tiles set to the correct depth, I used a cheap paint brush and some wood glue to seal each tile in place. When I took these photos, I only had one row done...before I go to bed tonight, I'll have 3-4 rows. I'll probably finish this up over the next few days as it takes about 10-15 minutes per row. All the while, I'm thinking about ways to make this go faster. I still want to do a pair of prime 29 diffusers, but I may do some others using 2.5" tiles and a depth of 6" for my back wall. The advantage of going with a smaller prime is that I have fewer varying depths to deal with...though the adventurer in me wants to do something big and difficult.

I have no idea what I'm going to do with a single 11 X 11 2D diffuser, but it's a fun project and gives me time to think about and better plan the pair of Prime 29

collo · 23rd November 2009, 07:25 AM

Man, those photos with QRDude in the background and the resulting diffuser in the foreground give me a real buzz.....

Schaap · 23rd November 2009, 08:15 AM

Wow, great job!

Please let us know how it works in your room when it's finished.

Lonely Raven · 23rd November 2009, 04:48 PM

Quote:

Originally Posted by collo

Man, those photos with QRDude in the background and the resulting diffuser in the foreground give me a real buzz.....

Thanks! I really enjoy this software...it's been a great help and I'm sure will inspire a wave of projects by many DIY guys.

Quote:

Originally Posted by Schaap

Wow, great job!

Please let us know how it works in your room when it's finished.

It's going to take a while for the final project to get done. Just this little one is going to take me a few days beyond what I already have into it, so I can just imagine the larger pair taking months. Though with some of the suggestions made here, I think I have some great ideas to help speed things up a bit.

It will be a fun winter project!

Lonely Raven · 26th November 2009, 10:29 AM

OK, I couldn't sleep, so I finished this up a few minutes ago. The glue is still wet, but everything press fits together so well, it pretty much holds itself together (except for the edge tiles that are only held in on 3 sides).

Doing this gave me time to think about the best plan of attack for my Prime 29.
I'm going to run the numbers a few different ways using QRDude, and see if maybe I can come up with something a little less time consuming, but still pretty useful for my surround sound needs. I may bump this up to 1.5" tiles and drop down to Prime 23 for example...I hate to cop out like that as I really have my heart set on a complex period, but I'd still like to get these two side ones done before the end of the year!

And if I come up with a plan that helps me produce these more quickly, I may just revamp my whole back wall with 2D diffusers, and make a couple extra for my "office" which is really just a corner of the basement with my computer, guitar amps, and a work bench for building guitar amps.

terry j · 26th November 2009, 10:56 AM

well, one thing is for sure, with the walls they don't look half as sexy as they do at skyline... damn.

Still, well done keep at it.

I kinda agree with your issues with 'making it easier'...half the trouble is the limited effective range etc etc of these type of things...make it easier for yourself by going to 1.5 inches (hey, that's the size I will be using so that means it's good right?) and the effective range will fall.

No free lunch darn it. Oh to be an audiophile at times....then we can ignore physics

Lupo · 26th November 2009, 11:23 AM

It looks cool! All you need now is a lot of small ornamentary objects to put in the wells.. Like this: http://www.styleroom.se/image/scaled...l-småsaker.jpg

Seriously: That's excellent work! :)

Lonely Raven · 26th November 2009, 12:32 PM

Haha, or I can start a thimble collection.

mobius.media · 27th November 2009, 12:17 AM

looks great but i'd add a frame.

Lonely Raven · 22nd December 2009, 04:28 AM

Quote:

Originally Posted by mobius.media

looks great but i'd add a frame.

Great! You can show us when you build one.

Mine will be without a frame.

I'm still making some progress on this. Been busy with family stuff for the holidays. I have some photos I'll download once I get my camera battery charged. But for now, I'm wondering what you diffusion gurus think of something like this.

Collo, any suggestions on how to model something like this in QRDude?

I'm not saying rewrite the program just for this, I'm saying, any recommendations on how to model the individual pieces to make the whole??

Lonely Raven · 22nd December 2009, 06:17 AM

Mini-update. Here is where I'm at with the Prime 29. I had some issues trying to work in a little bit of "slop" to the design so it doesn't tighten up with every row I add. So some of the fins are a little warped. I'll probably break the warped ones out and replace them, since I finally developed a way to cut these with just the right amount of slop so they press fit together, but don't tighten up. Here is how it looks now, before I ran out of material. All pieces are press fit by hand, and it's strong enough to hold it's own weight. Though MDF is still fragile.

And I got a lot of materials for building a bunch more absorbers. I need to build a cloud, and side early reflection points...plus I'm probably going to do another super-chunk in the back corner of the room.

I'm also playing around with some of this 3D wallpaper. This stuff actually diffuses noticeably, and not in a bad way at all. I just pinned it up where the OmniFusers will go whenever I get them done, just for grins. I'll leave them up till the Prime 29s are done.

mobius.media · 22nd December 2009, 06:40 AM

Wow that 3D wallpaper is awesome! Looks like it would be great for places like ceilings or just anywhere that's not otherwise treated (if it's cheap enough)!

Link?

Lonely Raven · 22nd December 2009, 08:09 AM

Quote:

Originally Posted by mobius.media

Wow that 3D wallpaper is awesome! Looks like it would be great for places like ceilings or just anywhere that's not otherwise treated (if it's cheap enough)!

Link?

Sorry, I posed it in another thread. It's a little expensive when you include shipping costs, but it covers a good amount of wall space.

PaperForms Acoustic Weave (12 Tile Pack) - Wallpaper - MIO

8th November 2009, 08:36 PM	#1
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	Prime 29 Diffuser Build - Using QRDude So now that I have a house, and a goodly sized living room for a proper home theater, I've decided to go all out with the room treatments. Huge corner bass traps, broadband traps at key points, flutter breaker diffusers, and proper QRD diffusers. While researching QRD diffuser designs, hoping I'd stumble into a completed design I could just clone...I stumbled into GearSlutz and all these great diffuser builds, as well as this QRDude software. QRDude: Quadratic Residue Diffuser calculator Collo, who writes the software is a member of these forums, who has been kind enough to answer questions and tweak the software to help make it more user friendly for the DIY guys like me. (if you find the software as useful as I have, throw him some $$ for his efforts!) For better or worse, the following is my Prime 29 build for the rear-side walls of my home theater...used to help break up the flutter reflection between the side-rear speakers, and help liven up the surround sound in the back of the theater. My ultimate goal is a live end - dead end with the speakers in front being the dead end, and the surround being very live. Here is a screen shot of the Specs of my side-rear diffusers. And the MaxData showing the dimensions (which I have printed out across several 8.5 X 11 pieces of paper, and on a laptop screen in the workshop. On the high rez image, we can easily read the well depth measurements. Note: that's 841 1" wells there...yes, I'm a glutton for my own self punishment. Once I got this far, I ran to my local lumber yard which is about 45 minutes away, and I stocked up on panels for this and a subwoofer project I have in the works. I'm on vacation this week, so I'm looking forward to making progress on both the diffusers, and the 21" woofer in a 15 cubic foot box! Here are all the panels stuffed into my Scion xB. Poor car, it used to be a show car...now I use it more like a truck. The lumber yard was nice enough to cut all six panels crosswise so I could fit the 4' X 4' sections in my car and not have to rent or borrow a truck. From here on out, it's all about cutting and assembly!!

18th November 2009, 04:41 PM	#14
StudioTinPanAll Lives for gear Join Date: Aug 2005 Location: Antwerp Posts: 517	how's the sub and diffusor coming along ? __________________ Studio TinPanAlley

23rd November 2009, 08:15 AM	#20
Schaap Gear addict Join Date: Sep 2004 Location: Netherlands Posts: 354	Wow, great job! Please let us know how it works in your room when it's finished. __________________ "Poetry and music" http://tinyurl.com/cmtwkp

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lexicon prime time 93 ver. lexicon prime time II 95	dov	High end	7	20th July 2005 11:28 AM

8th November 2009, 09:08 PM	#2
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	OK, now on to the cutting. Please note, some of what I do is very much not safe. As I post some of these photos, I can imagine "millions of (woodworker) voices suddenly cried out in terror and were suddenly silenced". I'll clarify as we go along here. First off, I decided to rip all the fins, since this is going to be a well type diffuser along the lines of the RPG OmniFussor, but on a larger scale. Something like this: Here are my fins cut so far. 3.5" + or - 1/64" I wound up about 8 fins short! Now, had I done a "cut sheet" where you draw out the panels (in this case 4' X 4') and drawn out each completed piece so I could map out the cuts, I would have made enough fins to complete the project. But I simply started ripping the 3.5" fins and kept going till I reached the required 60 fins, or in this case, ran out of MDF. A little planning might have saved me another trip to the lumber yard. But then again, two full sheets later, and it appears I won't have anything left over for the SECOND diffuser! Once I had the fins cut, I used some scraps left over from the fins to start building and testing a jig for cutting the 1" tiles for my diffuser. One of my design requirements, was that I try and keep the weight down. So instead of buying 160' of 1" X 1" wood blocks, I'm going to cut 841+ tiles out of MDF, and glue them at the correct height. It sounds harder then it is. So the concept of the tile cutter, is that I rip the 1/8" MDF scraps into 1" wide strips. Then I feed them into the jig and cut them into 1" X 1" tiles with great consistency. The original jig I made for the band-saw (which is the safest way of cutting objects so small), but my band saw apparently can not cut even a 1" strip straight, and all the tiles came out looking like diamonds. I wound up tossing all those tiles in the trash, and started working on the same jig but for the table saw (the absolutely least safe way of doing this). Here is the jig on the Table Saw. It's literally the same jig I made for the band saw, but shifted down a bit so the table saw made fresh cuts into the scrap material. This is the part where woodworkers cry out in anguish. The way this jig works, is that the base panel is glued and stapled to the piece of pine, all very squarely. Then the pine fence is screwed to a quality, very square Miter from Incra. Then I place (staple and glue) a 1" X 1" "stop" exactly 1" to the right of the blade kurf in the jig (see the image above). So I hold onto the long 1" wide strip with my left hand which presses it to the stop, while my right hand index finger holds the (future) 1" tile and the whole jig slides forward into the blade chopping off 1" tiles exactly the same, all day long. (and hopefully not taking any figures with it). Again, this is absolutely the WRONG way to do this. If the wood binds at all, it could kick up and fling my hand right into the blade. And as sharp and true as this $125 blade it, I probably wouldn't notice till I saw my fingers hit the floor. So do as I say, not as I do!! The correct way of doing this would be to make the whole jig more robust, and use a toggle (or two) to hold the MDF in place while I put my hands way back on the fence to push the jig into the blade. Toggles look like this: You can see how that would be much safer to have the toggle hold the MDF as it's run through the blade. I could come up with 100 excuses why I didn't use a toggle and risk my fingers, but they would all be lame. Just be smart and do it right. Moving on, a little better view of the whole jig: And the resulting tiles. These are 1/64" under 1" X 1". I'd say I did pretty good, and I still have all my fingers (So far). I still have a bucket load more of these to cut.

8th November 2009, 09:20 PM	#3
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	Now for the fin jig. So these fins are going to fit together like a giant tic-tac-toe grid. The best way to do this would be to cut consistent and accurate slots 1.75" into each fin, then the fins would interlock together. If I'm off on these cuts, the tiles won't fit! So along comes the fin jig. Typically this type of jig is used for making finger joints for building boxes or cabinets. I came up with it while teaching myself to make guitar speaker cabinets as a teen, only to find out woodworkers had been doing this for probably a couple hundred years. The way this jig works, is that you mount a board to the miter (I used the same miter as before), then you take the 1/8" saw blade, and run it completely through the board at the correct height. This gives you a clean cut, exactly as you want it on the fins. Then I measure 1" exactly to the right of the blade kurf, and make a second cut. In the second cut I glue in a 1/8" "key". So, now that everything is set, you make the first cut on the fins by pressing it up against the "key". This gives you the correct spacing so you have 1" from the end of the board to the first cut (this is assuming your fin ends don't slot into the frame on the diffuser!!). Then you take the cut fin, and slide the cut OVER the key, which gives you the exact 1" spacing you need for your next slot. Then cut, move and repeat till you get to the end of the board! It's that simple! In fact, I was cutting 10 fins at a time using this method. It was hard on my hands, cutting, pulling, moving over one slot, cutting, pulling moving over one slot...but the end result was so accurate, that the 1" tiles I cut fit inside the assembled fins perfectly!!

8th November 2009, 09:31 PM	#4
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	So here I am with a few of the fins completed. All the slots cut, and a hand full of tiles cut. I figured I'd do a dry fit to see how everything goes together. Here are the fins slotted together to form a corner of the grid: It was a bit of a tight fit, I had to use a board laid across the grid, and a small hammer to tap the board to get all the fins to interlock. If I had a saw blade that was a hair thicker, these would fit together a bit more easily. As it is, everything went together pretty well! Now my concept for getting the tiles spacing exactly (the next "jig I'll be working on later this week). Is to simply use wood dowels that fit into the slots, and I'll have the wood dowels cut equal to the depth needed, minus the 1/8" thickness of the tile. Here is a quick and dirty test example I did. I cut some scrap to different heights, and drop them into the slots: Then I simply press fit the tiles into the grid till they hit the wood spacers, so I know where to stop. And yes, the cuts were all so exactly on this, that the tiles press fit perfectly with not the slightest gap in the grid. I dare say these are damn near air tight! Now the bad news....so I was up late last night, I finished cutting the slots in about 25 of the fins, and I figured I'd start assembling a bunch of the grid before I go to bed. Well, while tapping in the fins, a few of the fins tore right at the slots and just fell apart! Keep in mind, as you add more and more fins, it's getting tighter and tighter. This thing could easily hold it's own weight up on the wall once I get all the pieces interlocked. But that tightness came at a cost. Now, at this point, I'm not sure if I should scrap this project and get 1/8" plywood (ditching the MDF completely) and start over (which would be stronger and lighter, but also twice as expensive), or if I should just continue to assemble the grid, knowing that the broken parts will easily be held in place by the grid itself. My concern is, if this falls apart this easily just putting in 6-8 fins, how impossible is it going to be to assemble when I get to 29 X 29!! I wish I had a saw blade that was just a hair larger then 1/8" thick!! That's all I have for now...I've lost a bit of steam after this latest issue. I think I need to take a break from it for a day or two and come back with a fresh mind. I was hoping to have one of these done this weekend, but it's not going to happen as frustrated as I am right now.

8th November 2009, 09:38 PM	#5
mobius.media Lives for gear Join Date: Jun 2009 Posts: 1,890	Bummer man. These well-based designs seem tricky to implement. Kudos for pushing ahead.

8th November 2009, 11:24 PM	#8
terry j Gear maniac Join Date: Jul 2009 Posts: 243	good work LR! I completely understand what you are doing, and how the slots get progressively tighter as you go. It will be very hard at the end. Off the top of my head, this might work. With your jig, when you make the first slot (which then gets moved over to locate on the lug) you could always do a second pass thru. Ie, cut the slot and it is exactly a blade width wide (ever so slightly small). Ok, using paper or shim or whatever works it is in place for that first pass. Then do a second pass, after removing the shim. The slot is now that shim width wider. When you move the pack over onto the existing lug, you make the first pass with it (the pack) hard to the left, and then the second pass hard to the right and that way you now have the second slot ever so slightly wider than the blade width, and the same size as the first slot....and so on thru the pack. I too second the safety aspect, when I built mine this way I ended up with a saw cut on my finger!! (see the space coupler theory thread, I too show pictures etc of the cutting jigs SPACE COUPLERS. Theory, construction and effectiveness on traps.) I got around that problem by the saw always being 'hidden' within wood, and never exposed. the pics in that other thread may help some. Can I ask, is there a reason why you did not go deeper?? I know it gets heavier etc etc, but personally for all that work I would have made it 'more' worthwhile and make it diffuse deeper. You are making more than one?? If so, then with your spacers I would have reversed it. Ie, rather than cut to length the spacers so it 'places' the tiles from 'above', I would have cut the inverse length so that it places the tiles from 'below'. That way, you can make a full jig that can be used over and over. The dowels can be permanently glued in place on a backboard, such that your grid can be placed on it. This time when you put the tiles in, you are doing it from the 'back'. That also now allows you access from the back to the tiles, either for getting the glue in or filling the cavity. Once done, lift off the completed product and place the new grid on and do it all over again. The way you outlined means every time you want to make one, you need to sort loose dowels and place the spacer manually in the correct location...would not want to get a few out of place!! so lot's of checking etc, then you need to remove the product, turn it over and then do the gluing and filling of the cavity, all the time hoping one or more of the tiles do not move. Pretty well exactly the same method as you are doing, but without the double handling. just think in reverse. And only really useful if you are doing more than one. Not a criticism, hopefully just an alternative look at the method.

9th November 2009, 11:03 PM	#13
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	OK, I hope you all understand when I say, I'm going to take a short break in the diffuser build, to work on my other project. Here is the driver for the sub-woofer I'm building for the home theater. It's so big, it's almost perverted!

23rd November 2009, 06:16 AM	#18
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	OK, well, had a "fun" week at work. I basically had to interview with HR for my own job. I don't even want to get into that...I'm just glad that I have a job. I finished up my sub, and it's setup in the home theater. I can hit 102db at 10Hz with 1500 watts! Watching Star Trek on Blu-Ray was fun! Though I need to EQ it a bit...but that's a whole nother project. Now that I'm done with that for the time being, I cleaned up the garage shop and collected the pieces from the broken QRD-29. Just for fun, I took I what I had and made an 11 X 11 (actually, it's off by one, but it's just for practice). I just cut the fins around 11 X 11 since that's the largest I could go with what I had, and started assembling. I did go back to my slot jig and spaced like Terry and Paul were talking about. I used business cards to "add some slop" to the slots so they could be assembled without beating them with a 5lb hammer. There is a lot of slop in my 11 X 11 sample, but that's because I took all my practice and broken pieces and just slapped it together. The final product will be much more consistent. Here is what I have so far: I took the remnants and pieced together this 11 X 11 grid (actually, you can look at it like a 10X10 or 12 X 12 since I'm leaving the edges open). It's not bad for spare broken parts! Bringing QRDude on the screen, I used my digital caliper to set the depth of the tiles. Once I got the tiles set to the correct depth, I used a cheap paint brush and some wood glue to seal each tile in place. When I took these photos, I only had one row done...before I go to bed tonight, I'll have 3-4 rows. I'll probably finish this up over the next few days as it takes about 10-15 minutes per row. All the while, I'm thinking about ways to make this go faster. I still want to do a pair of prime 29 diffusers, but I may do some others using 2.5" tiles and a depth of 6" for my back wall. The advantage of going with a smaller prime is that I have fewer varying depths to deal with...though the adventurer in me wants to do something big and difficult. I have no idea what I'm going to do with a single 11 X 11 2D diffuser, but it's a fun project and gives me time to think about and better plan the pair of Prime 29

23rd November 2009, 07:25 AM	#19
collo Gear maniac Join Date: Aug 2009 Location: Newcastle, Australia Posts: 179	Man, those photos with QRDude in the background and the resulting diffuser in the foreground give me a real buzz.....

26th November 2009, 10:29 AM	#22
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	OK, I couldn't sleep, so I finished this up a few minutes ago. The glue is still wet, but everything press fits together so well, it pretty much holds itself together (except for the edge tiles that are only held in on 3 sides). Doing this gave me time to think about the best plan of attack for my Prime 29. I'm going to run the numbers a few different ways using QRDude, and see if maybe I can come up with something a little less time consuming, but still pretty useful for my surround sound needs. I may bump this up to 1.5" tiles and drop down to Prime 23 for example...I hate to cop out like that as I really have my heart set on a complex period, but I'd still like to get these two side ones done before the end of the year! And if I come up with a plan that helps me produce these more quickly, I may just revamp my whole back wall with 2D diffusers, and make a couple extra for my "office" which is really just a corner of the basement with my computer, guitar amps, and a work bench for building guitar amps.

26th November 2009, 10:56 AM	#23
terry j Gear maniac Join Date: Jul 2009 Posts: 243	well, one thing is for sure, with the walls they don't look half as sexy as they do at skyline... damn. Still, well done keep at it. I kinda agree with your issues with 'making it easier'...half the trouble is the limited effective range etc etc of these type of things...make it easier for yourself by going to 1.5 inches (hey, that's the size I will be using so that means it's good right?) and the effective range will fall. No free lunch darn it. Oh to be an audiophile at times....then we can ignore physics

26th November 2009, 11:23 AM	#24
Lupo Lives for gear Join Date: Aug 2005 Location: Norway Posts: 1,087	It looks cool! All you need now is a lot of small ornamentary objects to put in the wells.. Like this: http://www.styleroom.se/image/scaled...l-småsaker.jpg Seriously: That's excellent work! :)

26th November 2009, 12:32 PM	#25
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	Haha, or I can start a thimble collection.

27th November 2009, 12:17 AM	#26
mobius.media Lives for gear Join Date: Jun 2009 Posts: 1,890	looks great but i'd add a frame.

22nd December 2009, 06:17 AM	#28
Lonely Raven Gear maniac Join Date: Nov 2009 Location: Bolingbrook, IL Posts: 209	Mini-update. Here is where I'm at with the Prime 29. I had some issues trying to work in a little bit of "slop" to the design so it doesn't tighten up with every row I add. So some of the fins are a little warped. I'll probably break the warped ones out and replace them, since I finally developed a way to cut these with just the right amount of slop so they press fit together, but don't tighten up. Here is how it looks now, before I ran out of material. All pieces are press fit by hand, and it's strong enough to hold it's own weight. Though MDF is still fragile. And I got a lot of materials for building a bunch more absorbers. I need to build a cloud, and side early reflection points...plus I'm probably going to do another super-chunk in the back corner of the room. I'm also playing around with some of this 3D wallpaper. This stuff actually diffuses noticeably, and not in a bad way at all. I just pinned it up where the OmniFusers will go whenever I get them done, just for grins. I'll leave them up till the Prime 29s are done.

22nd December 2009, 06:40 AM	#29
mobius.media Lives for gear Join Date: Jun 2009 Posts: 1,890	Wow that 3D wallpaper is awesome! Looks like it would be great for places like ceilings or just anywhere that's not otherwise treated (if it's cheap enough)! Link?