Yet Another (3rd!) Way to Construct a 28" Spherical Shell...

Since I was toying with the idea of making another set of spherical speakers (possibly using 8" woofers instead of 6.5"), I came up with yet another way to contruct a 28" dia. sphere from MDF: fabricate 32 "orange slices" and assembly them into a perfect sphere! This design takes advantage (key advantage!) of the coincidental fact that 1/32 of the circuference of a 28" sphere is exactly 2.75" (so at the max thickness part of the "orange slice" this can be done using a 3/4" "core" with 1" pieces on either side, PLUS since used for speakers, it needs to have a 6.5" to 8.25" dia hole at each "pole" and 1/32 of the circumference of an ~8" circular is ~3/4" (so just the "core" there is enough. Basically, I built a "construction jig" (complete with hinged "router table") to assemble each of 32 "orange slices" from three different types of pieces. Each "slice" uses 2 "A" pieces (from 3/4" MDF), 2 "B" pieces (from 1" MDF), and four "C" pieces from 3/4" MDF (see pics). So for two spheres you would need 128 A's, 128 B's, and 256 C's....These are assembled in the "jig" (to ensure uniformity), then with the router table set at exactly 5.625 degrees (360/64), the "orange slice" is tapered (linearly based on distance from N-S pole axis) exactly as needed s.t. when all 32 are assembled, you end up with a perfect sphere (of whatever thickness you want dictated by how "wide" each A, B, C, pieces are). Depending on how many degrees of arc each "A" piece is, you end up with either an 6.5" dia hole (79 deg.) or 8.25" dia. hole (75 deg.) at each of the two N-S poles (and all the other driver holes are just cut using a hole saw as before). I built one "path finder" slice just to see if it feasible. Just as in the "layered" way of making a sphere (which is a LOT harder because each layer basically has different sized pieces which must all be cut at beveled angles unlike this way where ALL cuts are non-bevel and only three different pieces to cut out), it is a lot harder than you think to cut really smooth circular cuts when cutting out these "arch" pieces. You get "bored" and try and go too fast, etc.). Anyone know of an automated way to cut out a bunch of pieces from a 49" x 97" sheet of MDF (medium density fiberboard)? Also had some issues with the router bit not being tight enough so it "rode out" at one point and cut too deep in a few spots. But basically all doable....just a lot of cutting/routing.

A big advantage to making them this way is you could (when assembling the 32 "slices") NOT glue the edges at the boundaries of the four sphere "quadrants" and thus ship these speakers as 1/4th spherical sections (and provide end user with the metal band clamps used to "squeeze" everything together for him to do this final assembly of the four 1/4 sphere sections as a "kit" or whatever - with driver holes cut out/idented and rough sanding done and wiring harnesses/terminals, x-over caps, un-assembled stands, etc. supplied....just add the 28 EPI drivers - used from ePray or "new" from Huw at humanspeakers.com!).

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That looks like a lot of work, you must have a lot of time on your hands!! How many drivers can you fit in a 28" diameter sphere?

See the "other" site (DIY section) for mucho details on these speakers. But for a symmetric distribution of woofs and tweets, it works out to be 14 (6 woofers and 8 tweeters in my case). Also, Huw at humanspeakers.com is going to add pics and "writeup" of these speakers to his DIY section as well... But here's a pic of AOS I ("fat boy" with 1.5" wall thickness) and AOS II ( 1" thick 5.5" squares used to "disco ball" approximate a sphere):

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Jig "router table" re-done using plywood (instead of MDF...too wimpy). Also need to add two more support posts (that set the router table angle to exactly 5.625 deg = 360/(32*2)) on either side of the center one so that this table does not bend down even a little bit during the router operation. Otherwise the "orange slice" will not be exactly tapered as required. I'll make one more "trial" orange slice to see if it is "good enuff". Also made a few improvements to make sure that the "orange slice" remains totally "locked" in place during routering.... This "jig" good for any shell thickness up to ~2", but 1.25" is what I'll use:

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The curved pieces on the jig (under the "orange slice") are just blocks for holding the piece in place after one side has been routered/tapered... Still not sure if I'll build these spheres (for an 8" woofer version of AOS's...), but at least I have the "jig" ready just in case...

Ed, you're the only person I know who could (or would) pull this off~

Thanks (I guess! ) Rabbit. I have to do something at work when I'm bored/waiting for computer jobs to run, etc., so I think about (and design jigs for and even analyze... ) ways to make round speakers... It's a project; something to keep from going (more... ) crazy.... Huw at humanspeakers.com likes the idea...he'd get to maybe sell me 28 EPI drivers.. ...and since his are new (or newly re-furbed/rebuilt), I'm sure they'd sound better than the one's you get from ePray...

That is incredible ---

........ Sure like to test them with Tom's ears --

You must bring them to Carver next year --

Some updates to the "jig"....added a center screw to help hold the "slice" in place during routering. Built a 2nd slice... Researched how to veneer a sphere; very sketchy and doubtful that it can be done (I made a paper pattern of 1/8th of a sphere flat projection and it "crumpled" when trying to curve it in two directions...someone said that it needs to "stretch"). This another HUGE advantage of doing the sphere in 1/32 "slices": each slice is "flat" across the ~2.75" (max) wide slice in the circumferential direction, so it only needs to bend in one direction and therefore won't "crumple". Huge advantage as I really want to HW veneer them if I do another set...pics:

clamping while glueing the A, B, C, pieces:

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The finalized "assembly jig":

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With the final routered "slice":

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Two slices (taped together) = 1/16 of a sphere:

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Where the ends come together to form the 8" dia hole at each "pole":

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Ed...your workmanship is outstanding! Never heard a sphere speaker but maybe some day...

Very impressive!!!

Cool

I think you should start planning on one that's 48 inches in diameter & uses 10 inch woofers~

Ed.....you have the patience of a Saint, and great woodworking and jig skills.

I have built more than a few speakers over the last few yrs and I wouldnt attempt a sphere....wow.
I would of put 2 ikea 14" bowls together and called it a day...

keep the pics flowing.......very cool.

Yeah, but I'm trying to "automate" the process as much as possible so that it's just "turn the crank" without a bunch of careful measurements and angle cuts, etc required. Basically since I have metal patterns for the three (and only three!) basic pieces (with a different "A" piece depending on whether you use 6.5" or 8.25" O.D. woofers), you just need to lay these out on sheets of 3/4" and 1" MDF and then use a scroll saw to cut them out (no bevel cuts!). Per "slice" this takes about 24 minutes, then about another 15 minutes to glue/clamp the eight of these pieces together into the basic "orange slice" shape (the "fan" shaped 1/4" plywood pictured in the "jig" is used in "position 1" during this operation as shims under the "C" pieces out at the ends of the slice because the basic "block" is 1/4" less wide per side out there). After glue drys, then you swing the router table into place and run your router (with bit set to just touch the top of the slice out at the extreme radial distance from the "N-S" pole line) over the slice and this mills it to the proper taper angle. Then flip the slice over and use the 1/4" fans in "position 2" (with the ~1" blocks at the end in position under the newly milled surface s.t. they "wedge" the slice up against the head of the "locator screws" out at the ends of the slice and ensure that the piece is precisely in position for routering of this flip side). All this takes ~15 minutes. So say ~ one hour per slice = ~32 hours per sphere. Sounds like a lot of time/work, but you don't have to think about it and it's probably overall less than the time taken using the other two methods of making MDF spheres that I used previously. And unlike the "disco ball" method, this is a true sphere and can be used with 8" woofers (the 5.5" required flat squares of the "disco ball" can only accomodate ~6" woofers...). But like I said previously, the REAL benefit of doing it this way may turn out to be that you can VENEER each "slice" because each slice only curves in one dimension (longitudenal direction) and is "flat" for the ~2.75" equatorial direction of each individual "slice"). After veneered, one could sand down a bit the slight "ridges" at the boundary of each slice for probably an almost perfect spherical look in that direction as well as the perfect spherical curvature in the longitudenal direction....I think a walnut/maple/cherry/etc. 28" dia spherical speaker would look awesome..especially setting on a contrasting wood stand! We'll maybe see...I'll probably put this all aside for a while as/when I have the "jig" done/perfected and maybe pick this project back up if/when I ever "get to" retire....it would really suck up the time anyway. I've priced NEW drivers for these "AOS-III" speaks from humanspeakers.com and using 8" epi woofers (6) and 1" epi tweets (8) it comes to $816 plus $29 for shipping per speaker. I think that's pretty reasonable for new speakers/drivers of this number...

The Elipson Planet L speaker --

A few other brands have dared to make spherical speakers, but Elipson claims to have been the first; they've been perfecting round speaker design for more than 70 years

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