Spheres

[ODougbo]

What many folks have been looking for

Capital Garden Geo Sphere Planters

12"s -18"s - 26"s

btw, this was the thought behind the post (thanks to other DIY member)

Baffle Step Compensation

 

[cismc2]

Hi -I've always been interested in spheric /spheroidal enclosures. Any details on materials/thickness as far as rigidity, stiffness, non-resonance?
Thanks - Jon

 

[Ouroboros]

In the UK, the well known DIY/furnishing/garden store 'Homebase' sell two sizes of resin/stone "Terrazzo" spheres of this sort. One with an internal volume of 7 litres, one with approx 19 litres. I have used two of the smaller sizes ones to fit some audax AP100Z0 4" speakers. The internal volume of 7L is just right for a reflex design with the AP100Z0. They work very well, though the AP100Z0 rolls off strongly above 8kHz.

To over-simplify things a lot, I increased the diameter of the hole in the base by using a thin cutting wheel on a Dremel 4000, then cut a piece of FR4 glass-epoxy (single-sided pcb with the copper stripped off) to act as the mounting plate and epoxied this on the now larger hole.

I drilled four holes through the FR4 and into the sphere with a tungsten-carbide router bit on the Dremel, and epoxied four lengths of 4mm threaded rod so that they protruded orthogonal to the FR4, so that the AP100Z0 mounting holes dropped over the studs. A cheap, thin mouse mat provided the gasket material between the AP100 and the FR4.

I'll take a photo or two to put on here in a few days.

As a quick base for the speakers, I bought two of those large diameter rubber rings that dogs like chewing and playing with. The spheres now sit perfectly on a flat surface on these rings!

 

[jerryo]

I noticed some black plastic "Goldfish Bowls" on eBay with an internal volume of 3 litres that are used for party cocktail drinks rather than fish. I thought they might make a quick and easy alternative for the right driver. They do have a raised lip that would be useful for setting a wood baffle into. Not sure what the wall thickness is though.
They are very cheap!

 

[Inductor]

ODougbo,
You can build now Elipson Planets.
[Recensione] Diffusori Elipson Planet L - [Italiano]

I bought two of those large diameter rubber rings that dogs like chewing...

love it.

 

[system7]

ODougbo, you have an EXTREMELY creative mind. Love it. You've got me thinking!

You are now doing what mathematicians who hung on to get to the interesting stuff call Conformal Mapping.

This is a hugely powerful continuous transformation that preserves right angles, and converts spheres into planes and such. This skillful painting in Ryde (IOW) High Street gives a glimpse:

[IMGDEAD]http://img708.imageshack.us/img708/7830/orrerycaferyde.jpg[/IMGDEAD]

Physicists use it to transform one problem into another, and use the same maths. This is Professor Leo Susskind using it to derive some results in "String Theory", mapping circles to rectangles:

[IMGDEAD]http://img153.imageshack.us/img153/2184/conformalmappinglog.jpg[/IMGDEAD]

It's probably my familiarity with Conformal Mapping that allows me to understand this bit of beautiful Steen Duelund thinking about loudspeakers and rooms:

[IMGDEAD]http://img38.imageshack.us/img38/4083/steenduelunddiagram.jpg[/IMGDEAD]

Back to your thoughts about spheres. I've just been pondering how your spherical speakers might work, in a spherical room, of course! Hope I don't get TOO obsessed by this, but I think it leads somewhere and Conformal Mapping gives you a handle on it.

 

[ODougbo]

Thanks Steve; that may be, but only because I'm in the "not restricted by any professional training' category.

The best deal would be to make them with fiberglass; Styrofoam spheres forms are easy to find. i.e. cut front wood ring and fiberglass as one solid speaker. Should be easy to scoop out Styrofoam once done.

Local Walmarts has 8" in stock.

Ebay has 10" spheres (523sq in) in the $23 range:
2 Pieces 10" Styrofoam Ball | eBay

Price jump for larger sizes:
TheCraftPlace.com Store: Styrofoam Balls for Floral and Craft Design. Many sizes.

 

[mondogenerator]

In the UK, the well known DIY/furnishing/garden store 'Homebase' sell two sizes of resin/stone "Terrazzo" spheres of this sort. One with an internal volume of 7 litres, one with approx 19 litres. I have used two of the smaller sizes ones to fit some audax AP100Z0 4" speakers. The internal volume of 7L is just right for a reflex design with the AP100Z0. They work very well, though the AP100Z0 rolls off strongly above 8kHz.

To over-simplify things a lot, I increased the diameter of the hole in the base by using a thin cutting wheel on a Dremel 4000, then cut a piece of FR4 glass-epoxy (single-sided pcb with the copper stripped off) to act as the mounting plate and epoxied this on the now larger hole.

I drilled four holes through the FR4 and into the sphere with a tungsten-carbide router bit on the Dremel, and epoxied four lengths of 4mm threaded rod so that they protruded orthogonal to the FR4, so that the AP100Z0 mounting holes dropped over the studs. A cheap, thin mouse mat provided the gasket material between the AP100 and the FR4.

I'll take a photo or two to put on here in a few days.

As a quick base for the speakers, I bought two of those large diameter rubber rings that dogs like chewing and playing with. The spheres now sit perfectly on a flat surface on these rings!

Great tip on the spheres, im right next to homebase AND have a pair of AP100Z0 woofers and TM25F1 tweeters that need a nice 7 litre home! Halfway thru a blanda bowl build for 3inch fullrangers. Dunelm Mill have some nice 6inch goldfish bowl vases in glass for £5, theyre also worth a look for small volumes.

 

[Ouroboros]

I popped in yesterday and this type of sphere wasn't in stock. The nicely glazed ceramic ones were though. I don't know if more types will be back later on, or whether they didn't sell well enough to re-stock.

 

[jerryo]

There are also 15, 30, 60 litre fish spherical fish tanks made by "Bi Orb" to think about. Paint them on the inside, whatever colour you like for a high quality gloss finish. Got to be strong to support 60litres of water!

 

[Inductor]

More spheres
Ikea bowl speaker drivers - diyAudio

 

[mondogenerator]

I did find a firm that makes acrylic spheres up to 400mm dia but decided they would likely cost too much.

 

[jerryo]

Spherical Perspex fish tanks; 15 litre = £56.99, 30 litre = £79.99 Not so expensive if you take into consideration the purchasing of MDF and all the machining and finishing required to make a conventional cabinet. They might need some sound deadening applied internally which would be easy. Being Perspex, machining for a vent tube ( if required ) would also be very easy.
Cheaper of course if you buy second hand!

 

[system7]

I do wonder if you guys are just designing something as bad as a cube speaker in effect.

[IMGDEAD]http://img716.imageshack.us/img716/416/sphereandcube.jpg[/IMGDEAD]

It's gonna boom everytime the wavelength is an integer of the radius.

People have talked about ellipsoids or oblate spheroids having less pronounced resonances. Golden ratio cabinets an' all that.

This looks like electromagnetism, but it's also how a spherical speaker interacts with a flat wall. The image is later in time, of course, which causes some effects of cancellation. I find it interesting.

[IMGDEAD]http://img825.imageshack.us/img825/6065/electricdipole.jpg[/IMGDEAD]

Good stuff, conformal mapping, eh? Spheres are preserved, albeit they can go to planes sometimes.

 

[mondogenerator]

A Dipole is a dipole...

The problems with spheres have been discussed at length in other threads, as have means to mitigate them. I dont think the OP intended to go over old ground, merely provide a resource to help those that do wish to build with spheres.