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Old 11th July 2012, 07:17 PM   #1
lejaybo is offline lejaybo  United Kingdom
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Default Random enclosure idea??

Hello peeps,

been looking into making some ikea bowl spheres as a simple full range speakers

but....................

was wondering what would

BLANDA MATT Serving bowl - 12 cm - IKEA

on top of this

SEKIN Serving bowl - IKEA

would this work good? or is it bad for internal waves and such
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Old 13th July 2012, 08:49 PM   #2
tvrgeek is offline tvrgeek  United States
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Round can be good. Might check out what US Enclosures says about round. You will need some kind of way to dampen it.
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Old 13th July 2012, 10:32 PM   #3
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The best enclousure is the sphere, second is the tube/cylinder, called as Bazooka in automotive sound.
Square/rectangular boxes are the worst sound, a compromise, to favor the convenient use of flat wood/MDF slabs.
A pity this shell is small, What kind of wood is it??
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Last edited by FullRangeMan; 13th July 2012 at 10:36 PM.
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Old 13th July 2012, 11:44 PM   #4
tvrgeek is offline tvrgeek  United States
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Full sphere is smoothest. Cylinder is only good if used on end. Mounting the driver like a Bazooka is horrible. See Olson. Actually, search on "Olson diffraction" and look at the various sites. Everyone sites his original paper because he did it correct the first time and no one has anything much new to say!

Boxes can be made to behave very well with big round over bits or clever application of 1/2 inch thick felt.
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Old 14th July 2012, 12:03 AM   #5
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Quote:
Originally Posted by tvrgeek View Post
Full sphere is smoothest. Cylinder is only good if used on end. Mounting the driver like a Bazooka is horrible. See Olson. Actually, search on "Olson diffraction" and look at the various sites. Everyone sites his original paper because he did it correct the first time and no one has anything much new to say!

Boxes can be made to behave very well with big round over bits or clever application of 1/2 inch thick felt.
HI,
I fail to understand. What you mean say with ''used on end'' and ''Mounting the driver like a Bazooka''??
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Old 14th July 2012, 01:05 AM   #6
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Sphere is the best shape wrt 2pi to 4pi transition ripple of the shapes Olson tested (ie looking only at the outside, the inside is a bad shape). Teardrop (as per B&W) is better and doesn't have the same internal standing wave issues that a sphere has. Driver mounted on the end of a cylinder is bad, driver mounted on curve of cyclinder is much better but not as good as rectangular box with big champhers.

Page 23 Olson

Click the image to open in full size.

OP's suggestion of half-sphere on truncated cone is a good one, this is closer to teardrop (add a duncecap on the back-side to finish it off). And on top of that you save 9 per speaker.

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Old 14th July 2012, 01:09 AM   #7
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The sphere is NOT the best! In order of worst to best..1) Sphere 2) cube....3) all others 4) A calculated best Acoustic ratio 1.2599-1- .7937.
Think about it... the sphere will reflect internal waves from a point source to the walls (At equal distances) & all arrive back to the same place, in phase, equal intensity....This will compound & concentrate the back-wave...Same somewhat with the cube. An acoustic ratio breaks up these frequencies by a mathmatically derived proportion.


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Old 14th July 2012, 01:10 AM   #8
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Quote:
Originally Posted by planet10 View Post
OP's suggestion of half-sphere on truncated cone
One potential complication: the cone needs to be the same diameter as the bowl, no dimensions are given.

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Old 14th July 2012, 01:12 AM   #9
Ron E is offline Ron E  United States
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Beware anyone who cites Olson on diffraction, especially when they mention US Enclosures in the same breath...YMMV.

Olson used a point source (2" diameter) mounted in the center of his ~24" baffles. This overstates the effect of diffraction in most cases.

If you move a piston in the end of a cylinder slightly off-center, diffraction performance becomes surprisingly good, as does the off-center performance on many of his examples. When a source takes up a large percent of the baffle, shape becomes rather unimportant.
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Old 14th July 2012, 01:16 AM   #10
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Quote:
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Olson used a point source (2" diameter) mounted in the center of his ~24" baffles.
Page 22:

Click the image to open in full size.

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