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Multi-Way Conventional loudspeakers with crossovers

calculations for spherical enclosure.
calculations for spherical enclosure.
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Old 6th October 2018, 12:17 AM   #11
Galu is offline Galu  Scotland
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Gilbert Briggs of Wharfedale fame discussed a spherical speaker in his 'Loudspeakers' book, of which I have the 1961 reprint.

The 20" diameter spherical enclosure was made of 2" thick polystyrene, an acoustically 'dead' material which allowed little of the internal resonance to be heard through the walls.

The enclosure was fitted with two full range 8" drivers working in push-pull at opposite sides of the sphere to improve the acoustic loading on the cones. The interior was loosely filled with BAF to reduce the main resonance peak.

The result was an omnidirectional speaker whose bass was said to be remarkable in relation to the size, weight and cost of the enclosure.

There's a caveat however. In his follow up book (More About Loudspeakers) Mr. Briggs writes "Having made an expanded polystyrene sphere about 4 years ago, I can confirm that it is a most awkward shape to have about the house. Acoustically, it is better to square the circle and go back to (a cube)."
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Old 6th October 2018, 12:34 AM   #12
krivium is offline krivium  France
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It depends. There seems to be a kind of appeal to spherical enclosure in french's brands: Cabasse's 'la sphere' (which i haven't heard) is clearly inspired by the previous Elipson's range of spherical loudspeakers from 60's/70's:
Enceintes acoustiques spheriques ELIPSON BS302 Vintage sur supports plexiglas

I've heard the 402 as one of my friend used them as mains in a studio. Sounded great imho.
Very fragile though.
The main advantage is about bsc and low(!) edge diffraction.
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Old 6th October 2018, 06:52 AM   #13
Aucosticraft is offline Aucosticraft  India
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A big thanks guys,

You passed lot information on its construction ideas. Although I was looking for the mathematical calculations. You gave me lot more. Yes, my obvious next question was to be about construction help.

Ok, here is some rough Math calculation sheet using smath studio.

Attached :

CapVol.smz (smath sheet)

CapVol.exe ( Smath exe of the worksheet)

CapVol.htm ( How the sheet looks like)
Attached Images
File Type: png CapVol.png (29.7 KB, 180 views)
Attached Files
File Type: zip Capvol.zip (510.9 KB, 4 views)
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Last edited by Aucosticraft; 6th October 2018 at 06:57 AM. Reason: Adding PNG file for quick view.
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Old 6th October 2018, 07:55 AM   #14
Aucosticraft is offline Aucosticraft  India
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Sheets with more clear diagram.
Attached Images
File Type: png CapVol.png (66.7 KB, 185 views)
Attached Files
File Type: zip capvol.zip (629.9 KB, 0 views)
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Old 6th October 2018, 08:17 AM   #15
krivium is offline krivium  France
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Hi,
Please could you explain clearly (with words) what you are trying to achieve? Cause i don't get it, there is not much more difficulties than other kind of box for math given you know what you want.
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Old 6th October 2018, 01:29 PM   #16
Galu is offline Galu  Scotland
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You seem to be OK with the mathematics, so what help do you require with the construction?

Do you intend to choose a ported or sealed enclosure? Have you selected a speaker driver to suit your choice of type and volume of enclosure?

More information please.
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Old 6th October 2018, 08:15 PM   #17
Aucosticraft is offline Aucosticraft  India
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Quote:
Originally Posted by krivium View Post
Hi,
Please could you explain clearly (with words) what you are trying to achieve? Cause i don't get it, there is not much more difficulties than other kind of box for math given you know what you want.

Sorry , I think I didn't explain properly what I am looking for .

I initiated this thread to get help in calculating (mathematical equation)the sphere . Rather the partially cut sphere.

See, the sphere is partially cut to accommodate the driver. and the circumference of the cut needs to be of the circumference of the driver. So after the cutting out the partial part of the sphere the remaining volume of sphere should be the required volume.

Quote:
Originally Posted by Galu View Post
You seem to be OK with the mathematics, so what help do you require with the construction?

Do you intend to choose a ported or sealed enclosure? Have you selected a speaker driver to suit your choice of type and volume of enclosure?

More information please.
The math worksheet is created after I initiated a thread to help me with calculation formulas. And I hope it is correct.
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Old 6th October 2018, 08:28 PM   #18
Galu is offline Galu  Scotland
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Quote:
Originally Posted by Aucosticraft View Post
See, the sphere is partially cut to accommodate the driver. and the circumference of the cut needs to be of the circumference of the driver. So after the cutting out the partial part of the sphere the remaining volume of sphere should be the required volume.
Thanks, I see that now. It actually dawned on me after taking another look at the diagram of the sliced sphere!

To help verify your maths, please clearly state the diameter of the sphere, the diameter of the flat speaker mounting area and your calculated final volume.

If I'm not up to checking your maths, then I'm sure there is someone who is!
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Old 6th October 2018, 08:31 PM   #19
scottjoplin is offline scottjoplin  Wales
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Don't forget the volume the driver occupies
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Old 6th October 2018, 10:48 PM   #20
Richidoo is offline Richidoo  United States
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The formula you want is simple arithmetic, but it requires that you inquire with the driver manufacturer to find out the driver displacement (volume of portion of the driver that is behind the driver mounting flange.) Mfgs know this but it is often not published. You could also make a close enough estimate yourself. Call this displacement volume "D."

Then you need to determine the volume between the driver mounting plane cut into the sphere and the concave surface of the portion of the sphere that is removed. This is a lens shaped volume, so you can determine that volume using this online calculator. Be sure to use the "thru hole" dimension for the diameter of this volume, not the overall flange rabbet diameter that is cut into the sphere walls. Call this lens volume "L"

If you make the speaker ported, then also subtract the volume of the port from the box volume - the outer port tube dimensions and the space inside it. Call this port volume "P"

Volume of a sphere is 4/3*pi*r^3. call this "S"

Your formula for the net volume remaining inside the sphere when you cut the driver hole and install the driver (enclosure working volume) is:

V = S - (L + D + P)

There are some sources of acrylic and polystyrene foam spheres of various sizes online.

When choosing the diameter of your sphere, also consider how it will affect the baffle step for your filter and EQ designs.

Spheres have a lot of volume inside that will usually exceed what you need for good bass alignment. So you can build a more traditional box shape inside the sphere to minimize internal sound reflections acting on the driver. Non parallel walls, etc. You can make these from thin plywood, then just glue them to the inside of the sphere then fill the void with expanding urethane foam through some holes in the plywood. Make a lot of holes so the foam can expand easily, then cut it flat after foam hardens. Or you can just spray the foam in blobs, measure the volume with sand and cut away to achieve the volume you want. Or use liquid concrete to make the walls, etc. If you're doing a sealed speaker the volume is not too critical, but a ported speaker box volume (Vb) is critical.

Have fun! Sphere enclosures sound great! I can easily hear the lack of edge diffraction, if the sphere is big enough to blend smoothly with the driver flange, without much angle to the edge. If you want flat angle at the flange edge, you have to flatten the sphere planar to the front of the driver flange, then roundover the new edge to remove the abrupt angle change. The larger the sphere you use, the easier it is for the sound to make smooth transition to sphere profile. At RMAF2008 a Japanese vendor demoed a 5" full range driver in a spherical wood enclosure of 1 meter diameter! It sounded incredible!
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