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Tech Page: Cylindrical Sound

September 1, 2009
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The Sony Sountina stands about six feet tall, the top half of which is the Vertical Drive glass-tube tweeter. The  midrange and woofer drivers are in the base, along with an internal power amp. All three transducers radiate sound in a 360-degree pattern.

The Sony Sountina stands about six feet tall, the top half of which is the Vertical Drive glass-tube tweeter. The midrange and woofer drivers are in the base, along with an internal power amp. All three transducers radiate sound in a 360-degree pattern.

Speaker technology has changed very little in the past few decades. An electrical audio signal passes through a coil of wire called the voice coil, which generates an oscillating magnetic field. The coil is placed near a permanent magnet that pushes and pulls it according to the alternating polarity of its magnetic field. The end of the voice coil is attached to a cone or dome diaphragm, which vibrates along with the coil and thus radiates sound waves into the surrounding air.

During the past few years, Sony (sony.net) has developed a new type of speaker transducer with some interesting properties. Called Vertical Drive Technology, it's a tube of glass that radiates sound in a 360-degree cylindrical pattern. This glass-tube tweeter is part of a tall, slender speaker called the Sountina, which also includes a conventional 5-inch woofer and 2.75-inch midrange cone, along with an internal power amp (see the figure above).

The tube is driven by actuators at its base, which vibrate in a direction parallel to the tube's axis, sending compression waves along its length. Amazingly, this launches sound waves from the entire length of the tube perpendicular to its axis in a cylindrical pattern. The woofer and midrange drivers are mounted vertically — woofer pointing down near the bottom of the speaker and midrange pointing down just below the glass tube, with openings for both — so their sound emanates in a 360-degree pattern, as well.

The Sountina provides a stereo pair of analog inputs, as well as co-ax and optical S/PDIF digital audio inputs that support two channels of 24-bit/96kHz PCM. But wait — how can a single speaker reproduce a stereo signal? The low and midrange frequencies are mixed to mono, but there are multiple actuators at the base of the glass-tube tweeter, and they respond to the two channels independently, vibrating different parts of the tube accordingly.

Another fascinating aspect of the Sountina is how the intensity of the speaker's sound behaves at different distances. For a conventional point-source driver, such as a cone or dome, moving twice as far away causes the sound pressure level (SPL) to drop 6 dB in open air. But the SPL from a line-source driver, such as the Sountina's glass-tube tweeter, falls by only 3 dB at twice the distance. Thus, at different distances, the balance between the tweeter and midrange/woofer cones changes.

I'm quite curious about how it would sound to feed the left and right channels of a stereo source separately to two Sountinas or, even better, multichannel audio to five or seven of them. Sony says that can be done if each channel is split and fed to both inputs on each speaker. Would the 360-degree radiation pattern be more enveloping than conventional speakers, or would reflections from the walls turn the sound to mush? I suspect the latter, but it sure would be fun to find out.

The Sountina is clearly intended to provide ambient sound for the consumer market. It's currently available in Japan, Europe, Russia, the United Arab Emirates, Taiwan, Brazil, Panama and Chile, but not the U.S. The price tag is 1,050,000 yen, which converts to just more than $11,000 as of this writing — and that's for a single speaker. Will Vertical Drive Technology find its way into professional or home studios? I don't know, but it's certainly a fascinating concept, and I look forward to following its development.

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