Hi!
Maybe this is hijacking the thread but I pass on some more pics from the building process:
It is possible to find the top center by looking at the circles on the surface - here a hole is drilled..
the carving in some traces to guide the saw:
workin with the saw was really troublesome - in the begining it was OK but as the crcle was beeing finished, the whole thing started wobbling - the final resut was far from perfect but the tolerances by not gluing the second halff tigth to the metal took care of that:
I glued (epoxi) some steel bands inside one of the bowlss so to guide the other one when joining them - for this glue was also used but a sealant for marine (sikaflex).
/
Maybe this is hijacking the thread but I pass on some more pics from the building process:
It is possible to find the top center by looking at the circles on the surface - here a hole is drilled..
An externally hosted image should be here but it was not working when we last tested it.
the carving in some traces to guide the saw:
An externally hosted image should be here but it was not working when we last tested it.
workin with the saw was really troublesome - in the begining it was OK but as the crcle was beeing finished, the whole thing started wobbling - the final resut was far from perfect but the tolerances by not gluing the second halff tigth to the metal took care of that:
An externally hosted image should be here but it was not working when we last tested it.
I glued (epoxi) some steel bands inside one of the bowlss so to guide the other one when joining them - for this glue was also used but a sealant for marine (sikaflex).
/
An externally hosted image should be here but it was not working when we last tested it.
«Lets say a cone weighs 50 grammes, and the enclosure weighs 10 kilos, a not unreasonable assumption I feel. If the cone is moving, by Newton's conservation of momentum the forces must balance. The ratio of cone movement to to enclosure movement is therefore 50/10 000, which gives us a maximum possible movement in the box of 0.005% of the movement of the cone. And that's with a box that's not coupled to anything, and is completely free to move. I'm not that worried.»
Well, you missed the main point. It'd be all true for an isolated system, but, unfortunately, there is a dissipative force — the air resistance. At velocities as high as the driver's it makes the main contribution to the force acting at the wall from the driver. So, vibrations really matter.
Well, you missed the main point. It'd be all true for an isolated system, but, unfortunately, there is a dissipative force — the air resistance. At velocities as high as the driver's it makes the main contribution to the force acting at the wall from the driver. So, vibrations really matter.
TNT said:
It kind of is, but it's my fault - I asked!
Great work on the bowls - very clever finding the center. Those bowls must have gotten VERY wobbly cutting with the jigsaw (sticksaw). Thank you for showing how you joined the bowls.
Back to the topic, it does surprise me that the metal spheres don't vibrate. Shouldn't there at least be pulsing from the pressure/vacuum caused when the drivers move in and out? Maybe the sphere is ridgid enough not to pulse?
There was another thread on spherical speakers HERE. On page 6 you can see wooden ball enclosures that Jives made.
Finding the wooden balls isn't easy, but now, thanks to TNT, we know that Ikea has both metal and wooden hemipheres for speaker building. Cool.
I think that the secret is in the sphere shape. All forces are going along the walls, not towards them as in a box. I think this paper gives some insigth into the theory:
B&W PV1 paper
This sub was what inspired me to build the "BBASS" (my name for them) ! And that has nothing to do what they kick, even if they do
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B&W PV1 paper
This sub was what inspired me to build the "BBASS" (my name for them) ! And that has nothing to do what they kick, even if they do
/
panomaniac said:
It wouldn't suprise me that you could rest a car on one of these bowls. They're very stiff. A subwoofer application wouldn't likely generate frequencies high enough to set off the shell's resonances either. I once build a cabinet of !/4" wall EMT steel. It sounds amazing right up to around 1-2 kHz where the internal wall modes take over. Fun effects box.
Yes, yes... A sphere. Reminds me of the old "Bathysphere." Very strong indeed.
It is often written that the sphere is the best shape for a speaker enclosure, the reasons given often have to do with internal reflections and standing waves. Not much is said about the sphere might resisting vibrations, too. It seems so easy to get the flat sides of a speaker box to vibrate that "intuition" would say any shape will vibrate. Maybe not...
The only sphere speakers I have much experience with are the good old Elipson balls. Never did check to feel if they vibrated much.
TNT may have started us down a very interesting path.
It is often written that the sphere is the best shape for a speaker enclosure, the reasons given often have to do with internal reflections and standing waves. Not much is said about the sphere might resisting vibrations, too. It seems so easy to get the flat sides of a speaker box to vibrate that "intuition" would say any shape will vibrate. Maybe not...
The only sphere speakers I have much experience with are the good old Elipson balls. Never did check to feel if they vibrated much.
TNT may have started us down a very interesting path.
Hey guys,
Sorry to revive an old thread.
Been reading up on isobaric, push-pull and push-push configurations. Its confusing at times! I think it got confusing at times because most seemed to talk about the direction the speakers are facing and forgot to mention polarity...
Am i right in thinking:
That even order distortions will cancel for an infinite baffle or a dipole configuration when drivers are connected in a push-pull configuration. This will also work in an enclosure if the box is large enough or the excursion is small enough.
John K... was rather emphatic that cancellation is not guaranteed when push-pull is used in an enclosure. The enclosure introduces nonlinear air compliance and whilst the configuration reduces even order distortion, it is not eliminated.
And then there is the isobaric configuration which can be used to halve the required enclosure volume..... but not have any effect on the even order HD.
Anyway, that was what i gained from the forum. Is that understanding correct?
It got me thinking about some of the crazy designs posted, especially in this forum (TNT, Planet10, Sletol). I came up with this ridiculous and completely impractical creation. I thought it was worth sharing for the fun of it.
.... dunno how good it would sound...if at all... but i bet it would travel really fast
Guy
Sorry to revive an old thread.
Been reading up on isobaric, push-pull and push-push configurations. Its confusing at times! I think it got confusing at times because most seemed to talk about the direction the speakers are facing and forgot to mention polarity...
Am i right in thinking:
That even order distortions will cancel for an infinite baffle or a dipole configuration when drivers are connected in a push-pull configuration. This will also work in an enclosure if the box is large enough or the excursion is small enough.
John K... was rather emphatic that cancellation is not guaranteed when push-pull is used in an enclosure. The enclosure introduces nonlinear air compliance and whilst the configuration reduces even order distortion, it is not eliminated.
And then there is the isobaric configuration which can be used to halve the required enclosure volume..... but not have any effect on the even order HD.
Anyway, that was what i gained from the forum. Is that understanding correct?
It got me thinking about some of the crazy designs posted, especially in this forum (TNT, Planet10, Sletol). I came up with this ridiculous and completely impractical creation. I thought it was worth sharing for the fun of it.
.... dunno how good it would sound...if at all... but i bet it would travel really fast
Guy
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I see this at work alot. working with large megawatt generators, believe me, when we do an shdden short test on the generator, as part of certification, with a few thousand amps on the cable, perhaps 3500 instananeaous current, on a 400 amp cable setup,(4 x say 45mm thick cables) you CAN see them lot jump, the instant the short closes.
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