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What do you think of this . . .

Link: 

. . . as a speaker cabinet construction technique?  A large sphere would be the ideal shape for a baffle, at least in terms of diffraction.  So, just as long as you do not cut large circular flat spots on the sphere to mount the drivers, you should be OK.  No bracing required, as the pressure build up inside the sphere would be equally distributed.

  The author makes this 19" sphere out of 3/4" birch plywood, so the internal volume would be 1.6 cu. ft.  That would be just about right for a couple small 6 inch woofers mounted on the sides.  I'm thinking MTM with a small 1 inch hole drilled for a press-fit tweeter.  Then flank the small tweeter with a couple small 3" flat membrane type mids.    Thoughts?


jhollander
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Comments

  • For the longest time I wanted to build one of these  http://speakerdesignworks.com/Exclamations.html

    Sourcing a suitable sphere is a problem.  Building those tools would be even tougher.
     John H, thanks to JP I did get that email
  • Paint em' white and put a corncob pipe and a button nose on top and call it Frosty.  B)
    4thtry
  • Pretty cool, checked the price?
  • Those are sweet!
      If you just wanted the spheres it would be fairly easy to cut on a lathe or router jig. Cutting two half sections would make it a lot easier.
  • Kornbread said:
    Paint em' white and put a corncob pipe and a button nose on top and call it Frosty.  B)

    Or I could line them internally with lead roll roof flashing and then call them "The Lead Balloons"  =)

  • 6thplanet said:
    Pretty cool, checked the price?

    Yes, really pricy.  But this would be strictly a DIY affair, if I decide to try it.  I have a nice table saw and a dual bevel sliding miter saw, so making up the basic ball would be a time consuming, trial & error process; but doable.  I don't have a lathe, but once I get the sphere put together, I could hand sand the giant ball into a perfect sphere using my palm and belt sanders.   Time consuming, but doable.
  • kenrhodes said:
    Those are sweet!
      If you just wanted the spheres it would be fairly easy to cut on a lathe or router jig. Cutting two half sections would make it a lot easier.

    I don't have a lathe, so two half sections would not work for me.  A router jig would work; but only if I could figure out how to build one to produce something this big.  I know Nick S. (uglywoofer) made a special router fixture to create his "Stink eyes" speakers, but that was much smaller.    
  • edited June 5
    For the longest time I wanted to build one of these  http://speakerdesignworks.com/Exclamations.html

    Sourcing a suitable sphere is a problem.  Building those tools would be even tougher.
    I was thinking that I would just sand the high points down by hand. Take off most of the material initially with my belt sander.    Then make a bowl shaped concave attachment for my palm sander as the final step. 
  • edited June 5
    If you can get to the geodesic sphere phase then the angle grinder jig and manual turning jig would not be to tough.  Put it all together and I'm not going to get enough enjoyment from the process to make it worthwhile.

    Building a giant plaster tractrix horn seems like more fun.
    rjj45
     John H, thanks to JP I did get that email
  • 4thtry said:
    For the longest time I wanted to build one of these  http://speakerdesignworks.com/Exclamations.html

    Sourcing a suitable sphere is a problem.  Building those tools would be even tougher.
    I was thinking that I would just sand the high points down by hand. Take off most of the material initially with my belt sander.    Then make a bowl shaped concave attachment for my palm sander as the final step. 
    With that much material to remove, it would be a lot easier to use a router planing jig to create a flat spot, then it's an easy matter to finish sand the driver mount.
    Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"
  • There is no doubt that if I decide to go ahead with a project like this, it is going to be a real challenge.  Probably a year from start to finish.

      The author gives some tips in youtube comments as to how to zero in on the proper angles.  You start with 1/8" thick tempered hardboard and then cut up a bunch of small triangles without bevels.  Then you layout an experimental hemisphere by hot gluing intermediate sections together.  Once a perfect hemisphere is obtained, angle measurements can be taken and then transferred to the table and miter saws. 

    I was looking at the exclamations speakers and noticed that this sphere has a fairly large flat spot cut on the front to mount the drivers.  Even though the driver cones are not equidistant to the edges, the edges are still there and will diffract and create phantom images.  On my speaker, I want to attempt mounting my drivers onto the curved surface of the sphere so as to avoid an edge transition.  To do this, I would have to carefully grind off a portion of the plastic driver flanges to match the curvature of the sphere.  There would still be a small amount of flat (or curved) surface created by the driver itself, but that is unavoidable.

  • I recall seeing a geodesic dome calculator online at one time
     John H, thanks to JP I did get that email
  • Thanks, John.   I found several calculators on-line.  These should help to estimate the "strut" lengths that must be used to create the correct number and size of equilateral triangles.  But the bevels will have to be determined experimentally. 

  • Once you know the number of segments for a given diameter seems like simple division
     John H, thanks to JP I did get that email
  •   If you only need a sphere and dont need the cool shapes created by the plywood I would consider laminating rings of mdf.  Mdf is so cheap and depending on how you cut them you should have little scrap/waste.

    4thtry
  • kenrhodes said:
      If you only need a sphere and dont need the cool shapes created by the plywood I would consider laminating rings of mdf.  Mdf is so cheap and depending on how you cut them you should have little scrap/waste.

    That is a great idea!  You can probably take out  1/2 the build time.  The rings could still be baltic birch.  Having the rings CNC would be even better.
     John H, thanks to JP I did get that email
  • An angled cut with a jigsaw or a scroll saw would yeild the least amount of waste. A cnc would yeild the least amoint of waisted time.😉
  • I could try laying out multiple rings in sketchup to see how this could come together, number of rings, angles, etc.  The cutting, however, would need to be precise; a jig saw or scroll saw would probably not work out very well.
  •   How big of a ball would you like? I can try to draw it in fusion. I also have a wood lathe. The lathe would speed tings up a lot if it can swing the diameter that you need.
      I was also thinking, audio is perceived in the horizontal plane. Would a vertical cylinder measure the same as a sphere?
  • looks like you want the diameter a multiple of the wood thickness.  Seem like you can rough cut depending on the inside diameter.  Here's picture

    kenrhodes4thtry
     John H, thanks to JP I did get that email
  • kenrhodes said:
      How big of a ball would you like? I can try to draw it in fusion. I also have a wood lathe. The lathe would speed tings up a lot if it can swing the diameter that you need.
      I was also thinking, audio is perceived in the horizontal plane. Would a vertical cylinder measure the same as a sphere?


    I am looking at a 19" diameter sphere to allow enough room for a good woofer alignment with a couple 6 inch woofers mounted on the sides.

    Based on my understanding, a cylinder will not measure the same as a sphere.  Olson actually compared a cylinder type shape to a sphere in his original paper.  The sphere produced the smoothest overall responce is his tests.

    http://www.aes.org/aeshc/pdf/how.the.aes.began/olson_direct-radiator-loudspeaker-enclosures.pdf

    rjj45
  • Here is what I come up with using Ken's trans laminated ring idea.  This is a 2D cross section showing a total of 13 rings per hemisphere.  Only the exterior bevels are shown, as the interior of each ring does not need a bevel.  Note that the bevels start at 2.3 degrees, then 6.6 degrees, 11.1 degrees, etc.  The bevel angle increases as the ring diameter decreases.  The first 7 ring layers could probably be rough cut with my jig saw.  But the bevel angles above 30 degrees would have to be cut by CNC or some other method.   If I did this, I would probably cut ring layers 7 to 13 all at 30 degrees and then grind off the excess later with my belt sander. 


  • I did some prototype testing on a makeshift 12" diameter styro sphere to see how it would go (or not go, as the case may be).  I wanted to see what kind of internal box resonance problems would be created by an internal spherical enclosure shape.  

    I created my test sphere from two FloraCraft 12" diameter styrofoam domes, available at Michaels for about $12 each.  The domes are about 7/8" thick, so the inside diameter is approximately 10.25"   On-line sphere calculators yield an internal volume of 0.326 cubic feet (9.23 liters).  I used Mortite window caulking cord to "glue" the two domes together to create a sphere.

     I cut holes for a pair of Eminence Alpha 3-8 three inch full range drivers, placing one on each side, 180 degrees apart.  I "glued" them in position with Mortite.  I cut a small 2-3/8" diameter hole on one side for a 2" ID PVC BR port.  I varied the length of the port from 1.5" up to 6" to change the tuning from roughly 100Hz (fairly flat alignment) down to 60Hz or so (very droopy extended bass shelf alignment).


    hifiside
  • When I scale things up for the 19" diameter sphere (17.5"ID) , the peaks and valleys above 300Hz will move to lower frequencies based on the change in wavelength distances involved.  Based on half-wavelengths, I am estimating 1130*12 = 13560 / 17.5 = 774Hz verses 13560/10.25 = 1323Hz.  So, as a guesstimate of what my bigger sphere will do, I need to drop all the peaks and dips by roughly one octave.  So the peak at 875Hz will become 437Hz in the larger sphere.  The peak at 1.8kHz will become 900Hz, etc.  

    In the final system, the crossover will be 350Hz at 12dB/octave electrical.  So this should help to keep these peaks under control.  The nice thing about using two woofers on opposite sides of the sphere is that the wavelengths are essentially cut in half, boosting the peaks and valleys to higher frequencies. This also solves a problem with constructing the sphere, allowing me to leave large 6 inch diameter flat spots on the top and bottom during construction.

    Also, placing the port entrance along the outside circumference of the sphere (instead of at the center of the sphere) helps quite a bit to smooth things out.  This probably has something to due with the fact that a sphere concentrates a great deal of its acoustical energy directly towards the center.   


    hifiside
  • Next up, my plan is to build a small rectangular box with the same volume (.326 cu ft) using internal dimensions of 5.1 x 8.3 x 13.4" (golden mean ratios).   I'll mount the same drivers and ports and repeat the same Z and NF tests to see how this data compares to the spherical enclosure data.   Stay tuned.

    rjj45S7910
  • Even though wood/mdf is an ideal substrait for speakers this might be an ideal use of a 3d printer. Would you like a 3d printed sphere? My printer only has 8 1/2x8 1/2x9 print bed but I might be able to print it in sections. Glue it sand it and paint it and it will look pretty good. Depending on the drivers required I might be able to print a ball with the proper recesses.
  • Thanks, Ken.  I'm pretty much locked into your trans-laminated wooden ring idea using either MDF or particle board.  I've spent about a month now working on a custom fixture that will help me to mass produce all the trans-lamination rings with precise, repeatable diameters and bevel angles.  If the fixture works out as I hope, I should be able to start making sawdust in a week or two. 
    rjj45
  • Very nice. I'm excited to see what your final results will be.
  • I messed up a little bit with my previously posted NF measurements.  In OmniMic, you must check the "ALL" button when making NF measurements.  I accidently left the button set to "blended" which then applied a 5ms gate.  This gate chopped off the NF measurement before the internal box echo had a chance to die off completely on it own.  This gave the peaks and dips more of a rounded off type look.  I re-did the measurements and posted the corrected graphs below.  They use the "ALL" setting, which produces sharper looking NF plots with more well defined peaks and dips. I also fixed a couple air leaks on the spheres which helped to clean up a few strange ripples on the previous graphs.

    For comparison purposes, I cobbled together a test box using the same volume as my test sphere and ran some more measurements.  The test box is 6.5 x 7.25 x 12" internally, which comes out to roughly 0.326 cubic feet.  I was going to use golden mean ratio dimensions, but this is what I had available on the scrap pile.   I mounted the drivers and port in the typical places that you would normally put them if building a small two way speaker (see pics).  As you can see in the graphs, the rectangular box has a nasty internal resonance at about 580Hz, which is the same whether I used one woofer or two woofers on opposite sides of the box.  This resonance comes from the boxes 12" top to bottom dimension.  Using 13560 inches/second as the speed of sound divided by 12 yields a full wavelength of 1130Hz and half wavelength of 565Hz (fairly close to 580).

    The sphere, on the other hand, does not develop a peak until 830Hz, in the case of a single woofer; and about 1.3KHz, in the case of dual woofers (see graphs).  There was no damping material of any kind used inside either the sphere or rectangular box.

    This is very good news, because it indicates that it will probably not be necessary for me to add additional flat partitions inside the sphere to break up low frequency resonant modes.  The larger 19" diameter sphere will have peaks roughly 1 octave lower, but, they should still be high enough so that I can significantly dampen them with the woofer's low pass crossover parts.  In addition, there will be an internal circular partition over the midrange drivers which will tend to mix up the reflective distances a bit more.  I will also be lining the inside of the sphere with 1/2" or so of damping material.

    ThumperTom
  • I took my "styro-sphere" and re-purposed it for a tweeter test.  I have a pair of CSS LD22F's and my 2.85" woofer cutout was an almost perfect fit to the LD22F's flange.  So, I mounted one tweeter into one of the two woofer holes.  After pressing it in, it flattened out to a perfectly flush and level mount using a few strips of masking tape.  (see pic) 

    I think this is the same tweeter that Ani used in his Penguins and JR used in his Vermillions.  Correct me if I am wrong, but I think Ani used the flat flange LD22F version and JR used the LD22C curved flange version.

    I ran up a set of OmniMic horizontals.  Very smooth response.  The ripple notches at 1.3kHz, etc., are a function of my 12" diameter "styro-sphere" unloading into 4 pi space.  Notice how the ripples disappear as you move off axis.  When I build the larger 19" sphere, these ripples should reduce in size and frequency, similar to Olson's original AES paper. 


    kenrhodes
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