Archive for October, 2014

Seeing Clearly

Saturday, October 18th, 2014

Transparency is the buzzword we hear these days in political and corporate discussions. The justification we hear for closed-door sessions and secret meetings is that some decision-making processes are nobody else’s business. Or, that in the case of government plans and strategies, success is more likely if opponents are unaware of what is being planned.

I am not in a government or a large corporation, so perhaps I should not pontificate on such matters. My main interests are more personal and scientific. My research into the acoustics of the parallel projection of a hypercube onto 3-space (otherwise known to geometers and mineralogists as the Rhombic Docecahedron) has been hampered by the simple fact that one cannot see into the interior of a functioning loudspeaker because they are most often made of veneered particle board or even metal. When I explain to audiences that hypercube speakers require no internal acoustic padding, unlike other designs, I am often met with skepticism because I cannot easily prove this without dismantling the speakers to let people look inside.

An associate of mine in New York is working on this problem. You can see here a picture (click to enlarge) he sent me of a work in progress constructing speaker enclosures from clear polycarbonate.  When they are complete, listeners will be able to see inside the functioning speakers they are comparing to more standard designs.

Allowing light to pass through the interior of the functioning devices, however, will permit far more than mere visual comparison of padded versus non-padded speakers. For those with the initiative and courage to emulate my associate’s example in accomplishing independent confirmation of my own observations, I offer the following suggestions:

1. Holographic interferometry There was a time when the best holograms were recorded in glass plates coated with photographic emulsions. Nowadays, however, the advent of high-resolution CCD sensors (the kind used in smart phones and digital cameras) allows us to do laser interferometry without having the change the film each time we take a picture. The wonderful thing about this is that it can reveal not only the modes of vibration of solid objects, but also can reveal the details of fluid flow — and air is a fluid. Sending a laser beam though a clear loudspeaker when it is off and when it is running would allow anyone to combine the image data sets to reveal what is going on with the movement of air inside the speaker.

2. Sonoluminescence You may have heard that if a bubble of air is strapped at the center of a spherical flask by sound waves, the collapse of the bubble concentrates energy into a tiny region that emits light. The only difficulty with this experiment is that the container needs to be symmetrical (so that sound waves are converging to the center to keep the bubble from rising or drifting) and that the frequencies used are limited to those which resonate well with the size of the container or flask used.

I have, however, the following suggestion: that radial geometry might not be necessary at all. Perhaps the container need not be round. I believe it should be possible to obtain comparable results using a container in the shape of the rhombic dodecahedron.  Why?  Because converging sound waves from the positive x,y, and z directions should be sufficient to immobilize the bubble.

But why, you might ask, should we do this when a spherical flask is already available from lab supply companies? If, as I maintain, the vibration of a fluid inside a hypercube speaker contains a pressure antinode and a displacement node at the very center, then acoustic confinement of bubbles should occur and the rapid oscillation of pressure there should cause the cavitation that produces light in sonoluminescence.

3. Sonofusion There have been claims made for years now that the concentration of energy in a collapsing sonoluminescence bubble might be adequate to cause fusion reactions to occur. If such a thing could be made to happen and to liberate more energy than is needed to cause it, a relatively clean source of energy would be available to the world — one that might not require the enormous lasers and complex reactors and superconducting magnets scientists have been using for decades to try to accomplish sustainable confinement of the fusion reaction.

It seems possible that the use of a more appropriate geometry could help in such efforts. If inertial confinement can be accomplished by acoustic wave fields, then the rhombic dodecahedron could offer some hope in investigating the possibility of sonofusion.


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