Sphere Speakers

[moconnellus]

I'm new at this and was thinking about building sphere speakers. Is a sphere truly the best shape for sound reproduction?

 

[annunaki]

Not neccessarily. It is good, but it would be tough to quantify 'the best'. One of the best, along with the sphere would be the snailshell ( See Here )and tapered tube/sphere. Some speakers do not require an enclosure at all, like electrostatics. They can sound very nice.

 

[Audioholics]

One of the best, along with the sphere would be the snailshell

Well, at least that's what B&W's marketing would like you to believe.

It might be interesting to note that in general, only the people making and patenting spherical loudspeakers make the claim that this is the best shape...

 

[WmAx]

I'm new at this and was thinking about building sphere speakers. Is a sphere truly the best shape for sound reproduction?

It is 'best' only in narrowly defined terms. It is 'best' as far in as baffle step diffraction transition is concerned which results in smoother frequency response and polar response.

In case of using a speherical enclosure, you would need to take special care of the internal cavity resonance -- it will be at a single frequency at a large magnitude. Dense stuffing and/or internal cavity dividers will be required for optimal behaviour. The best shape would be a spherical half for the front and a tapered tube for rear(spreads the resonant modes across a wide spectrum that can more easily be dampened with fill materials) section. Refer to the B&W midrange modules on the 802, 801, 800 Nautilus series or to DIYer Kingdaddy's midrange modules:

http://kingdaddy.linaeum.com/Mains (SST-8)/DSC02829.JPG

http://kingdaddy.linaeum.com/

-Chris

 

[WmAx]

It might be interesting to note that in general, only the people making and patenting spherical loudspeakers make the claim that this is the best shape...

It is demonstrated by credible [1]research that the speherical shape is ideal for the front cabinet shape, in so far as smooth/linear frequecy response is concerned.

-Chris

Footnotes
[1] Direct Radiator Loudspeaker Enclosures
JAES, Volume 17 Number 1 pp. 22-29; January 1969
Olson, Harry F.

 

[Francious70]

Chris,

Dead links.

Paul

 

[WmAx]

Chris,

Dead links.

Paul

Odd. I just tried the links and they work fine.

-Chris

 

[moconnellus]

It is 'best' only in narrowly defined terms. It is 'best' as far in as baffle step diffraction transition is concerned which results in smoother frequency response and polar response.

In case of using a speherical enclosure, you would need to take special care of the internal cavity resonance -- it will be at a single frequency at a large magnitude. Dense stuffing and/or internal cavity dividers will be required for optimal behaviour. The best shape would be a spherical half for the front and a tapered tube for rear(spreads the resonant modes across a wide spectrum that can more easily be dampened with fill materials) section. Refer to the B&W midrange modules on the 802, 801, 800 Nautilus series or to DIYer Kingdaddy's midrange modules:

http://kingdaddy.linaeum.com/Mains (SST-8)/DSC02829.JPG

http://kingdaddy.linaeum.com/

-Chris

Thank you for your input. Question, what do you think about a 1 inch MDF for a sphere enclousure? Do you think that would give high quality sound reproduction?

 

[annunaki]

How in the world would you make a sphere from mdf?

 

[moconnellus]

How in the world would you make a sphere from mdf?

It's difficult but can be done with near perfect results. Before I go forward I want to make sure I am building the optimum shape.

 

[TRADERXFAN]

thinking outside the box...

How in the world would you make a sphere from mdf?

A sphere could be created by gluing mdf panel "faces" to eachother. The centers and edges could be precut to form the desired shape. It would be complicated, but not impossible. Think of the way a CATscan takes pictures in "slices" that stacked together shows the entire brain.

 

[WmAx]

Thank you for your input. Question, what do you think about a 1 inch MDF for a sphere enclousure? Do you think that would give high quality sound reproduction?

As I said, the sphere is optimal for external shape(diffraction). A hybrid shape is ideal to also deal with internal resonances.

A 1" MDF sphere would provide an incredibly rigid(structural law) structure that is many times stronger/resiliant as compared to a 1" MDF box. So, no problems in that respect -- if you deal with the internals with divided cavities and proper damping materials, it will work very well(but I still recommend a hybrid shape).

-Chris

 

[annunaki]

A sphere could be created by gluing mdf panel "faces" to eachother. The centers and edges could be precut to form the desired shape. It would be complicated, but not impossible. Think of the way a CATscan takes pictures in "slices" that stacked together shows the entire brain.

Understood, I forgot about that way. That would be an incredibly rigid enclosure, if not extremely time consuming to build.

 

[philh]

Well, at least that's what B&W's marketing would like you to believe.

It might be interesting to note that in general, only the people making and patenting spherical loudspeakers make the claim that this is the best shape...

It's best, at least in it's ability to get my wife to say not only NO, but H*** NO

 

[moconnellus]

As I said, the sphere is optimal for external shape(diffraction). A hybrid shape is ideal to also deal with internal resonances.

A 1" MDF sphere would provide an incredibly rigid(structural law) structure that is many times stronger/resiliant as compared to a 1" MDF box. So, no problems in that respect -- if you deal with the internals with divided cavities and proper damping materials, it will work very well(but I still recommend a hybrid shape).

-Chris

Two questions:
Lets say I went for the sphere design how would I change it internally to deal with internal resonances?
And when you say "proper damping" what do you mean by that?

I am new at all this.

 

[WmAx]

Two questions:
Lets say I went for the sphere design how would I change it internally to deal with internal resonances?

Because the sphere essentially have an equal distance path centralized around a single primary resonance(1/2 wavelength equaling the diameter), anything you can do to spread out the resonance will be beneficial and as a result make absorbing the lower amplitude(but wider spectrum) resonances easier. A wall along the Z axis, to divide the sphere internally, into halves(leaving a cutout so that the driver can be inserted) will accomplish this.

And when you say "proper damping" what do you mean by that?

I mean a dampening material and density that is optimal for absorbing the modal resonances and also absorbing the higher frequency energy from the upper midrange band that may be reflected back to the speaker cone. In your case, I would fill most of the internal volume with a very dense fiberglass or rockwool packed tightly, then as you approach the driver, use a few inches of poly fill(you can use cheese cloth or hair netting to hold it back off of the driver). The high density materials will be most effective in absorbing the lower midrange and midrange frequencies, while the low density material with an open, wide fiber structure will absorb the upper midrange and treble frequencies that may otherwise reflect back to the driver cone. Note that such a level of filling the enclosure can only be used with a closed system -- a ported/passive radiator system will not work efficiently if most of it's volume is filled with dampening materials.

-Chris

 

[gigabyte]

geodesic domes

hey .i'm thinking of mounting 8 bose drivers ( from the 802 model)
in a 18mm mdf geodesic dome.( made from pentagons & hexagons)


would you have any advice?

thanks

 

[Joe Schmoe]

hey .i'm thinking of mounting 8 bose drivers ( from the 802 model)
in a 18mm mdf geodesic dome.( made from pentagons & hexagons)


would you have any advice?

thanks

If you are going to go to that much time and effort, you should really use better drivers. Bose is not known for even moderately decent quality.
If you want to look at some good multipoles, check out Shahinian Acoustics.

 

[gigabyte]

you are right.these BOSE 802's where given to me. used to be in a bar
they are rated at 1 ohm.it will be an experiment might upgrade later.
are there any decent drivers around with the same diameter ?

 

[Joe Schmoe]

I don't know much about buying "raw" speakers. Some of our DIYers should chime in here.