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Rudy81

Poly-Cylindrical Diffuser and LF Absorber

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This build is of my own design and I would be more than glad to share what I did with any of you who are interested.  I will be taking more pics in the next few days since there may be some interest.  I currently have built 4 different sizes.  Details to follow.



Please if you could send me any and all info you would be willing to share with me and any photos
Thanks


Dollar for dollar Klipsch has no equals
Name one other speaker company that can build a speaker and keep working like new after 45 plus years of service. Answer NO ONE !!!!!!

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I am still in the middle of the build so have not posted more.  I am traveling on business and when I get back I will post a details on the build for you guys.  I currently have 12 units that are waiting for the insulation install.  Life keeps getting in the way.  I need to retire!

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2 hours ago, Rudy81 said:

I need to retire!

I heard that!

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I’m disabled/ retired and only 53. It’s been 5 years or so since I last worked and wish to god I could go back to work full time, hell, even part time for that matter
Lol


Dollar for dollar Klipsch has no equals
Name one other speaker company that can build a speaker and keep working like new after 45 plus years of service. Answer NO ONE !!!!!!

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11 hours ago, carlthess40 said:

I’m disabled/ retired and only 53. It’s been 5 years or so since I last worked and wish to god I could go back to work full time, hell, even part time for that matter
Lol


Dollar for dollar Klipsch has no equals
Name one other speaker company that can build a speaker and keep working like new after 45 plus years of service. Answer NO ONE !!!!!!

 

I am truly sorry you are that young and have been unable to work for so long. Sometimes in my daily focus I become somewhat selfish to what I want and not what is good for me.  Thank you for a timely reminder! 

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Here goes a basic post on how I am building these poly's.  I'm sure I won't cover everything, so please feel free to ask questions.  I am currently building 12 poly's for my side reflection points where I currently have HF absorbers only.  Six total on each side, 3 staked on 3 for an 8' high structure.  I plan on attaching them to the wall with french cleats, thus making them easy to move laterally as required. 

 

I started out by viewing similar designs in the Master Handbook of Acoustics and other ideas commercially available.  I did not want any permanent structures on the wall.  I also wanted something more than diffusion in the high frequency spectrum.  I read various articles on using limp mass vinyl as an LF absorber and did find one commercial product that uses LMV for that goal. 

 

First I used a pencil and string to draw circles of various radii on a large piece of paper so I could determine how large to build the poly curves.  I determined the depth on that same drawing, as shown.  Once I was happy with the sizing, I used my router jig to cur the circle parts in  18mm Baltic Birch. Those are the ends of the poly. Note: I cut two pieces of each size on 12mm BB to be used as templates. I then used those templates to cut the 18mm pieces on my router table.  This was a much faster way of making identical pieces than using a router to cut individual 18mm pieces.  In the future I can easily duplicate the sizes I already cut.

 

PolyCutTemplateS.jpg

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Once the circular pieces were cut, I ripped more 18mm BB into 3" wide pieces and cut the length so that the finished poly would be 48" tall.  This size is perfect for the bendable plywood I used o surface the front of the poly. After my first prototype, I realized that I needed to bevel the outer edge of the frame to allow for a faster and easier attachment of the bendable plywood. I beveled the outer edge of the frame sides to 22 degrees, which worked well with the three poly sizes I chose. Once the frame pieces were cut and beveled, I used pocket screws and glue to create the frame. After the glue set, I used pocket screws and brads to attach the circular ends to the frame. 

 

I originally used only pocket screws on my prototypes thinking I might stain the wood and didn't want to damage the plywood exterior.  However, I later found that the bendable ply does not stain very well and I decided to go with a cloth cover for the polys.  This allowed me to use brads and staples to attach the bendable plywood and the main frame.....a time saver.

 

 

 

 

SizesS.jpg

Basic StructureS.jpg

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Next step was to figure out a simple way to attach the LMV to the back of the poly and leave enough space behind the LMV so it could vibrate freely when the structure is hung on the wall. Simplest way I could find was to rip 1.5" strips of 12mm BB and attach them to the inside of the poly frame with brads and glue. This will provide a method to staple the LMV to the frame and leave a space such that the LMV does not touch the wall.  This method allows me to wrap the bendable plywood to the front of the poly.  Then, glue as much ultratouch insulation as I want to the interior of the poly, and then close it up with the LMV at the end. 

 

 

LimpMassframeEdgeS.jpg

LimpMassFrameDoneS.jpg

View From BackS.jpg

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I used 1/4" bendable plywood for the front.  You can use many other products for the front, but my research indicates that wood has the preferred qualities for HF diffusion and is somewhat flexible for use in LF absorption.  It is also a product that is easy to cut, glue and adhere.  A 4x8 sheet of barrel bendable ply cost me about $20 per sheet. You can also get the 'column' bend plywood which bends along the 4' edge to make an 8' column. I measured the circumference of  the polys and cut the bendable ply a little larger, then use a hand router with a flush trim bit to size perfectly.  Used glue and brads for the larger polys to attach the poly front.  The smaller sizes needed staples to keep the bendable plywood attached while the glue dried (smaller radius polys were at the limit of the natural bend of the plywood and needed to be held in place while glue dried). This is where the time needed to bevel the outer edges of the frame paid off.

 

Here is a picture of a semi-finished poly.  This is the basic structure prior to adding interior insulation, attaching the LMV, adding french cleat and finally adding the colored material to finish the poly.

 

I have finished all the basic structures but need to add the insulation, add the cleat and finish the exterior.  Plan is to take room readings with nothing at the reflection points, with just HF absorbers, and finally with the 12 polys in place.

PlywoodWrapS.jpg

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Very, very nice work.

 

WMcD

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Finally had a chance to get back to this project.  Today I finished trimming the excess bendable plywood edges, sanding all the polys, and filling each with Ultratouch denim insulation.  Next will be cutting the MLV and stapling to the back, adding french cleats to the back and finally covering with fabric.  I used thicker 8" insulation in the largest two sizes.  The 3.5" thick insulation went into the smallest of the polys.  I lined them up for size comparison as shown in the pic.

 

Poly_Sizes_SM.jpg

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Am I correct in assuming that if these were put into corners they would not perform as well as a bass trap in the corners for bass?

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19 minutes ago, Ron E said:

Am I correct in assuming that if these were put into corners they would not perform as well as a bass trap in the corners for bass?

 

Again, I am no expert. But, I have found that my corner traps were pretty much useless for low frequencies. The physics of LF sound dictates that those super chunk traps are actually....useless, which is what I HAD in the corners.  Actually, this type of diffuer/absorber in corners has better ability to trap bass than the super chunk idea.  Eventually I will use a similar design for the corners.  In corners, the LF velocity becomes pressure as it reaches the walls.  You need to 'absorb' the pressure by using a flexible surface that will dissipate the pressure.  That, is the basic idea. The thickness of absorption material in a super chunk required to dissipate LF is so thick, it is impractical in any common listening room.  That leaves things like membranes or helmholtz resonators for true LF absorption.

 

My plan is to keep taking before and after measurements to see what actually works. Plenty of available data on this subject.

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I was just about to make some triangle corner base traps with a 2" thick front. I had thought about making it curved too. Do I need to have wood like you used for the face or could I use a formica type material?

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9 hours ago, Ron E said:

I was just about to make some triangle corner base traps with a 2" thick front. I had thought about making it curved too. Do I need to have wood like you used for the face or could I use a formica type material?

 

Are you talking about the super chunk corner trap?  Floor to ceiling insulation stacked one sheet on top of another?

 

Get a hold of The Master Handbook of Acoustics and it has some suggestions on corner traps. In general, there is a piece of thin plywood or luan that is attached to the side walls running floor to ceiling. Insulation is added behind the panel, but not totally filled.  Just a sheet running vertically floor to ceiling with an air gap.  You should be able to find a copy of the book from many ebook providers if you don't want the hard copy. 

 

It is well worth the effort to really research this before you start your project.  This is my second effort at all this.  The first time I really didn't do my homework and am having to replace some itesm. 

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I ran super chunks in my old theater (new bass traps would be just a 2" thick piece running upwards....no triangles. This would give me a space behind the roxul). This time my bass traps will be about 18' tall...which is still not to the ceiling but will be to the point where the ceiling starts to surve inwards.  I have the master book somewhere in my boxes from the move i believe still. Not sure as i might have given it to a friend. The current room is going to be a nightmare to tune, and I am just trying to get it the best I can without going any higher. My estimates so far on Roxul is about $1500 more Roxul than I currently have in the garage. I am looking at about 50+ panels, and that will only be about 25% of the wall surface treated.

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Cost is certainly a big consideration for all of us.  I personally stay away  from fiberglass or mineral wool and prefer cotton products.  I think it would be worth your time to find the Master handbook and look at the suggested examples of good corner traps.  You may not have to use hard fiberglass or mineral panels due to the way the corner pieces are constructed.  Once I finish the side polys, assuming they actually do work, I will be building some more for the back of my room for diffusion and more bass absorption.  Once that is complete, I will be addressing stand alone bass traps for the front of the room behind my screen, followed by attention to the room corners. 

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More progress today. Finished adding the MLV to all 12 polys. Also added cleats to the top section of each poly.  I did not glue the cleats  in case I ever want to change the hanging method or wish to use the polys in some other configuration.  Next will be adding the material and adding the hanging cleat to the walls. Getting close now.

 

 

MLV_sm.jpg

Cleat_sm.jpg

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Beautiful work!

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All 12 polys are now complete. As soon as I have time, I will begin the process of hanging them at the first reflection points on the side walls.  Plan is to first take full frequency sweeps of each main speaker with the room in its present state.  Then, remove all the side reflection point absorbers.  Another set of readings. then hang the polys and finish with a set of readings with the polys hung floor to ceiling at the reflection points. 

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