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A tube is fabricated using piezoelectric material, and driven using encircling electrodes. The driving voltage is applied, delayed at the speed of sound, along the length of the tube. Thus a click would cause a pulse of contraction (or expansion) to travel along the tube, from the closed end towards
the open end where it discharges the sound into the open.
The tube can be folded or coiled into a small volume, and allows a large area of actuator to air contact, without the cancellation effects due to a large driver area at high frequencies, yet move a large volume of air to reproduce low frequencies efficiently.
Bose Acoustic Wave
http://www.bose.com...eguide_solution.jsp
Some info about how to put bass in tubes. [Amos Kito, Sep 26 2008]
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Annotation:
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Interesting, but susceptible to a couple of problems:
1) The closed-end tube described will have a 1/4-wavelength resonance peak that may be hard to smooth out. |
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2) While the "phased line array" technique could work well over a limited frequency range, I have doubts about full-range capability. |
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+ for half-bakedness, but I'd like to see a better description of the signal processing required. |
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Would woofer and tweeter tubes solve the resonance problem? I mean with filters for frequency as well (do they do that anyway?). |
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Any tube has a resonant frequency, and stiffer materials create sharper peaks, floppier materials create flatter, wider peaks. Appropriate choices of tube sizes and stiffness can be overlapped in frequency to give a smooth wideband response. E.g. "Shotgun" style highly directional microphones use this technique in reverse. |
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Ported loudspeakers use the port to extend bass response lower that could be accomplished with the same driver in a closed box. |
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I imagine the peristaltic tube speaker could be like a set of pan pipes. |
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Could you get similar results by coiling the tube, then drive the side of the coil, so the tube's whole length is compressed all at once? Bigger amplitude, smaller driver volume. |
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No, the finite speed of travel of sound through the tube will tend to cancel out the high frequency components. |
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"Bass in a small volume" = small fish, or quiet fish? |
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If you coil it in a spiral, you'll get something
approximately disc-shaped. A regular speaker is also
approximately disc-shaped. I think that a speaker of this
type will never be louder, and will probably be quieter,
than a regular speaker of approximately the same size,
used in open air. |
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This phased-array tube speaker produces a higher
pressure, but with a smaller cross-sectional area. This
results in a poor impedance match to the surrounding air,
unless it's driving a small volume. So it could be good for
earbuds, but for an open-air application, it would need a
big
horn to work well, and then you might as well just use a
regular speaker. |
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Peristaltic tube speaker, my arse. |
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