Techniques and Materials for Spheres and Ovoids

[HK26147]

I see in the past there has been interest in non-rectangular enclosures, with the benefits they offer
How do I make spherical enclosures?
How do I make spherical enclosures?

The 1st DIY efforts I saw ( circa SB mag in the 80's ) were fabricated from slices of wood laminated together to form the rough shape. This was sanded down to final shape.
I did not want to follow this approach, and I wanted to use something other than wood, usually a process of removal from a rough form.
I wanted to be able to create any shape desired, so I would cast from a shape. Others have used hard shapes like glass balls ( ie lawn balls gazing balls etc ), and cast 2 hemispheres which they fused together.
Others use a sacrificial mold, like an plastic ball that can be deflated or popped. Others build a shape from modeling clay.
Fiberglass fabric and polyester resin are predominately used for the shell.

For use as the smallest spherical satellites possible, I borrowed a few techniques/materials from the stage craft world, to create (2) 8" spheres for approx $35.
Very Briefly:
I used a spreadsheet to run volume iterations for various geometric shapes including spheres and determined that minus speaker and port volume that an 8" sphere would be what I needed for some Vifa 4 1/2 drivers ( outsourced for Revel ).
I found an 8" Styrofoam ball at the crafts stores, I cast the initial shape using Tarlatan reinforced with Gloss Medium ( latex ).
That was removed and attached to a plywood ring baffle cut for the drivers.
This shape was layered and built up with plaster bandages ( used to set broken bones ) several layers thick.
On top of that was placed polyester auto body filler and sanded to shape.
Auto Body centers also have a thinner finishing putty for final finish.

The shell of the sphere being comprised of differing layers results in a strong yet inert enclosure. I tuned these to 80Hz f3.
This is almost all hand work with a lot of sanding. The quality and techniques of finish ( including marbling techniques, and auto finish materials ) depends greatly on the skills of the builder.
I invite others to share their work and ideas.

[Moondog55]

I'd love to see the photographic record if you made one as I've been contemplating a somilar project (( At some time in the future))

Regards
Ted

[HK26147]

Ted:
I have been looking through my Hard Drive archives to retrieve and organize the various bits and pieces of spherical & Ovoids speakers:
Until then - this link:
http://modsandends.com/?m=200810

Shows an effort that ends up with result very similar to what I did.

My method and approach was different:

[cirrus18]

Many thanks for the link to get me here, it makes very interesting reading.

My only comment is, wouldn't it have been a little easier, saving on lots of sanding, to make a female mould from half the ball first. Then make the required number of halves, joining them later. This would allow to work laying-up the mould from the inside.
The finished surface of the sphere would then be just as smooth as the original ball. You'll also have a mould that you could use for later productions.

Anyway, very good work, but you didn't say how they sounded which is a very important consideration.

Paul

[Geek]

Bondo is awesome
(wear a dust mask! [mega toxic])

If you can get the "White Lightning" brand stuff, it's a lot more durable, but takes more skill.
(spreads..spreads...sticky...STONE! type thing)

Cheers!

[Saturnus]

The easiest way is to head down to your nearest IKEA (or their online store in whatever country you live in), and pick up a couple of their salad bowl.

For example this one in wood:

http://www.ikea.com/us/en/catalog/products/40057259

But there's another cheap and very good way to make a good mold. Take a plastic football (soccerball) or any sort similarly sized ball, and a tennis ball or another similarly sized ball. Now make a cardboard cone that fit the diameter of each ball on either end. Glue it up. And you have the perfect mold for a spheroid speaker.

[HK26147]

EDIT: My sphere is 6" diameter not 8"
Here is my proto: ( from several years ago )


Google Images for:
speaker "sphere"

And another approach:

http://flickr.com/photos/jonathanwightman/2353542862/
More to follow:

[HK26147]

you didn't say how they sounded

Yes I delayed answering...
I built these in 2003 and have yet to find the specs/notes/etc...

I built these for several reasons:
(1) The audible effects of diffraction has fascinated me since I bought a pair of Focal Eggs in the 80's.
(2) I wanted to explore the possibilities of a small satellite, for back channel speaker (AV) setup
(3) A mini near-field monitor system for computer editing I was doing on a video.
(4) A mini system for kitchen/background/outdoor.
(5) Try out fabricating non-rectilinear cabs using new and non traditional materials and techniques.

When I built mine, I did not have the means to measure T/S so I did it by the numbers and used the PE published specs on this Vifa. I picked the sphere volume and tuned to 80Hz ( it's Bass Reflex ).
More recently WTII measures @ 77Hz

It is used above 80Hz, <80Hz goes to a small sub woofer.
You can't get real bass with a 4" speaker.
It sounds much better with an active crossover, to save it from working on the bottom octaves.
It doesn't have the extended high range ( a better 4 or a coax would probably cure that ). A small boost with the treble corrects for the most part.
It sounds much better than the usual drek sold as mini A/V and PC sound packages. ( but that's not to hard to do anyway ).
It works very well near field. and as a portable outside system
All in all it was well worth the effort and sounds much better than than the same 4" driver in a box.

Obviously my method while very cheap in materials, is labor intensive.
But this was a proof of concept and many of the shapes to cast a mold from were not readily available ( to me anyway ) at that time.
It's certainly easy and cheap enough for virtually any DIYer to build and hear for themselves.

[mayhem13]

Google search 'wooden vase' or 'bamboo vase' and you won't believe how many are suitable for spheroid speaker enclosures ALA B&W.

[HK26147]

from http://www.tokyomango.com/tokyo_mang...-egg-shap.html