Constructing a sphere...

[Rocky]

Hi all,

I am designing a set of small BR bookshelf speakers using a full range driver, and I'm looking into how to go about constructing spherical cabinets for them. My initial thoughts is printing out a shell using a part printer I have at school (can print parts up to 30cm*30cm*30cm IIRC), but the printer material is not suited for speaker enclosure.. So I can either dress a thin shell with layers of fiberglass, or I can use it to cast a silicon mold. The latter would perhaps provide the better result, but I have never tried something like this.. Any tips of techniques or molding material from anyone who has good ideas or has gone down this route in the past?

Any feedback will be appreciated..

[planet10]

There is an extensive thread here about a spherical woofer.

Keep in mind that the outside of a sphere is great for minimal diffraction, but quite ugly inside for resonance.

dave

[Rocky]

Thanks Dave! styrofoam and acetone...

[sreten]

Hi,

how about fibreglass over a cheap plastic football ?

Or using the inside of the football as a mould ?

/sreten.

[Rocky]

Originally posted by sreten
Hi,

how about fibreglass over a cheap plastic football ?

Or using the inside of the football as a mould ?

/sreten.

I think styrofoam spheres will be the thing. I plan to intersect it with two planes (cut it) one on the bottom side, and one at the speaker mount. After that, I'll cover them in epoxy and fiberglass or something similar... continue in layers for about a cm, then sand and smooth it, using a planar sander on the bottom side, and finally drill holes for port and driver, and pour acetone in it...

Now, if I could only find styrofoam spheres of the right size... 23-25cm diameter..

EDIT: I mocked up the translation here I think... I wasn't referring to styrofoam, but something we call "isopor" here in norway.. Clue translates it to "expanded polyester". The stuff the chips you put in boxes when shipping triodes are made of..

[xstephanx]

one more vote for one of those cheesy soccerballs you used to get when you were a kid to play in the pool with. usually smooth plastic with a soccer ball pattern printed on it. after you coudl just deflate it to take it out.

[Rocky]

Originally posted by xstephanx
one more vote for one of those cheesy soccerballs you used to get when you were a kid to play in the pool with. usually smooth plastic with a soccer ball pattern printed on it. after you coudl just deflate it to take it out.

Problem will be the planar surfaces... How would you guys do that with a soccer ball..?

[Rocky]

It would be doable with the ball... it could be constructed as a sphere, then sanded down the planar surfaces and reinforced with more fiberglass from the inside after the driver hole is opened.. I might give it a try if I can't find what I need in any of the local hobby stores.

[sreten]

Hi,

for the holes glue a couple of plastic or carboard rings
on the ball, e.g. short sections of 4" PVC waste piping.

sreten.

[Svante]

Now as I understand this project, it does not have a tweeter, but if you are thinking of adding a normal tweeter with a ~90 mm flat and round faceplate in a sphere, there will be a corner on the sphere near the edge of the faceplate. This corner appears at the same distance from the dome throughout all 360 degree directions. This in turn leads to a baffle step that is not very nice.

This is less of a problem for the woofer, where almost all of the non-spherical part (the driver cone) is radiating sound. In the tweeter case, the dome covers just a little part of the faceplate.

Sorry if that was not part of your question.