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Old 20th December 2009, 10:16 PM   #1
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Default My sphere in cube idea for reducing standing waves

The best shape for a speaker container would be a sphere, which is difficult to be easily reproduced by a diyer, but with new technology it can be simply done. Make a cubical shape container, example 4 x 4 x 4, buy a 4 inch rubber ball that can be deflated. Spray the rubber ball with cooking oil all over insert the inflated ball that snuggly fits in the cube. Clamp a temporary baffle that has two holes drilled in opposite corners and spray the side that is facing the open part where the ball is located. Clamp the temporary baffle down and the spray in the neat part of this the self sealing insulating foam sold at hardware stores. Following direction for the amount of time needed to let it set and harden. Later remove temporary baffle, deflate the ball and remove. No more standing waves and better response.
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Old 21st December 2009, 01:13 AM   #2
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Originally Posted by mcmahon48 View Post
The best shape for a speaker container would be a sphere, which is difficult to be easily reproduced by a diyer, but with new technology it can be simply done. Make a cubical shape container, example 4 x 4 x 4, buy a 4 inch rubber ball that can be deflated. Spray the rubber ball with cooking oil all over insert the inflated ball that snuggly fits in the cube. Clamp a temporary baffle that has two holes drilled in opposite corners and spray the side that is facing the open part where the ball is located. Clamp the temporary baffle down and the spray in the neat part of this the self sealing insulating foam sold at hardware stores. Following direction for the amount of time needed to let it set and harden. Later remove temporary baffle, deflate the ball and remove. No more standing waves and better response.
REDUCE standing waves???? reduce to one frequency in ALL directions maybe but not reduce them in amplitude--IMHO BAD BAD idea
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Old 21st December 2009, 01:34 AM   #3
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how about a hemisphere?
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Old 21st December 2009, 02:58 AM   #4
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Originally Posted by mcmahon48 View Post
The best shape for a speaker container would be a sphere, ...
I think B&W research on spherical enclosures with tapered tube rear wave absorption is one of the best midrange and tweeter designs. The B&W website has technical information and measurements.

A friend took large styrofoam shapes - sphere + cone - cut them to mimic the B&W shape, sealed them with primer paint, and hand coated this shape with sand-only cement plus fiberglass string mat. When it had hardened he used acetone to melt away the styrofoam. The midrange sound was excellent.


Tony Gee produced a similar shape in his Galactica speaker by stacking MDF cut outs.

The Lumen White Light speaker uses a bulge+taper in a more traditional cabinet claiming it removes the reqirement for (any? most?) stuffing
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File Type: jpg Galactica_html_m204947a7.jpg (74.6 KB, 443 views)
File Type: jpg DeavonAnthony.jpg (48.9 KB, 440 views)
File Type: jpg lumenwhitewhitelightlargefront.jpg (53.8 KB, 440 views)
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Old 13th December 2012, 01:04 AM   #5
pepsi is offline pepsi  United Kingdom
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Quote:
Originally Posted by LineSource View Post
I think B&W research on spherical enclosures with tapered tube rear wave absorption is one of the best midrange and tweeter designs. The B&W website has technical information and measurements.

A friend took large styrofoam shapes - sphere + cone - cut them to mimic the B&W shape, sealed them with primer paint, and hand coated this shape with sand-only cement plus fiberglass string mat. When it had hardened he used acetone to melt away the styrofoam. The midrange sound was excellent.


Tony Gee produced a similar shape in his Galactica speaker by stacking MDF cut outs.

The Lumen White Light speaker uses a bulge+taper in a more traditional cabinet claiming it removes the reqirement for (any? most?) stuffing
Hi,

Do you have a link to the measurements on the B&W website? I cant seem to find them.

Much appreciated,
Matt
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Old 13th December 2012, 01:47 AM   #6
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Standing waves just don't work the way most people think they do.

At frequencies where the wavelength is on par with or shorter than the dimensions of the enclosure things tend to *more like* light bouncing off mirrors, but not really. Sound spreads, it's a wave. Especially when it meets a finite barrier.

The B&W nautilus designs are for the most part an acoustic labyrinth that has been coiled. So for waves that travel back from the driver, it works... waves that travel perpendicular to that plane, it's not quite as wonderful, except to the extent that the "back wall" appears to be nearly infinite.

Round walls are reflectors that focus energy back... so the effects and the problems are different, the pattern of nodes inside the enclosure is different, more so as frequencies go higher.

People have tried the "egg" shape too...

Just about every shape has been tried. There is so far, no magic shape.

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Old 13th December 2012, 01:51 AM   #7
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Quote:
Originally Posted by mcmahon48 View Post
The best shape for a speaker container would be a sphere, which is difficult to be easily reproduced by a diyer, but with new technology it can be simply done. Make a cubical shape container, example 4 x 4 x 4, buy a 4 inch rubber ball that can be deflated. Spray the rubber ball with cooking oil all over insert the inflated ball that snuggly fits in the cube. Clamp a temporary baffle that has two holes drilled in opposite corners and spray the side that is facing the open part where the ball is located. Clamp the temporary baffle down and the spray in the neat part of this the self sealing insulating foam sold at hardware stores. Following direction for the amount of time needed to let it set and harden. Later remove temporary baffle, deflate the ball and remove. No more standing waves and better response.
I'm afraid that as I understand your idea it would not be so good as you think. The spherical shape is a somewhat good shape for the outside of the speaker to reduce diffraction. But it is the worst possible shape for inside the cabinet since the design reinforces all the standing waves at one frequency. It sounds like, from your description, if I understand it, that the sphere would be inside the cubic shape. And would make up most of the internal volume of the speaker. If this is the case it would indeed be bad.

But you could' I suppose, make some kind of a small sphere inside a speaker cabinet that was not used for air volume that could bounce and break-up the waves inside the cabinet. You would however, need to increase the size of the cabinet to make up for the lost space.

Hezz
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Old 13th December 2012, 02:33 AM   #8
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Originally Posted by pepsi View Post
Hi,

Do you have a link to the measurements on the B&W website? I cant seem to find them.

Much appreciated,
Matt
B&W has a few white papers on the development of the Nautilus 801 speaker which include measurements for the midrange and tweeter sphere+taper_tube.

Some of the white papers have been mirror'ed.

http://www.hifiportal.co.uk/Articles...ilus%20801.pdf

Nautilus | technologies - Bowers & Wilkins | B&W Speakers
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Old 13th December 2012, 09:10 AM   #9
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Hello, I just done same thing, still before finishing the enclosure, work not permitting any job done. But tomorrow is my last day abroad i just filed resingment.

So between the holidays i might get the mfinished. You can find my build on the full range forum as I use Fostex 168 Sigmas as drivers.
As they are now, I made the best possible copy of B&W shape. Teardrop on the outside with the inside a sphere with cut of back and prolonged to a funnel with exhaust (insert better description here....)
Anyway, before completing, I make a lot of pics and update the forum post so you can have a look.
I can tell you from initial listening, the sound is impressive. I had a guy over from recording studio, and he was impressed by the clarity of midrange. However they where still not finished, I suspect a little better results when done so.

Anyway, I am more then willing to share construction details.

Fingers crossed to your project. But please consider different aproach to construction as you mentioned. Seems too complicated. Keep it simple and sturdy. Plan well ahead.

Danny
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Old 13th December 2012, 02:22 PM   #10
DeonC is offline DeonC  South Africa
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Originally Posted by mondogenerator View Post
REDUCE standing waves???? reduce to one frequency in ALL directions maybe but not reduce them in amplitude--IMHO BAD BAD idea
One trick everybody seem to miss is that for a sphere, the standing waves due to paralel walls all move through one point- the centre point of the cube. This is easy to break up by simply running a brace through that point (rectangular, not round). Then the sphere becomes a very good shape, IMHO.

Enjoy,
Deon
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Last edited by DeonC; 13th December 2012 at 02:25 PM.
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