Wood and Dried Squid

Jul 1, 2004 12:00 PM, By Scott Wilkinson

           
 

Forty years ago, Toshikatsu Kuwahata had a dream. As an audio-equipment engineer for JVC (www.jvc.com), he believed that speakers should do more than just reproduce the sound of musical instruments — they should be musical instruments. He noticed that many of the most beautiful-sounding instruments, such as the violin, guitar, and piano, are made of wood, which inspired him to develop speaker cones made from the same material.

Kuwahata's was no specious dream. He was convinced that the materials traditionally used to fabricate dynamic speaker cones left something to be desired. Specifically, he was concerned about the relationship between the speed at which sound propagates through the material and the vibration-damping factor. For example, polypropylene exhibits low propagation speed and high damping factor, whereas aluminum is exactly the opposite. Paper exhibits relatively low propagation speed and a moderate damping factor.

Kuwahata believed that a superior speaker-cone material should have high propagation speed and a modest damping factor, and he found that wood fit the bill perfectly. In addition, sound waves propagate at different speeds through wood, depending on the angle between the direction of travel and the orientation of the wood grain, which tends to minimize resonance within the material.

He was able to pare the cores of birch logs into long, thin sheets, but he didn't know how to form a sheet of wood into a speaker cone. His first prototype was constructed of fan-shaped wedges glued together. Kuwahata heard improvements in sound quality, but he knew there was no way to mass-produce such a driver. He also tried stamping thin sheets of wood into cone shapes, but they inevitably cracked under the strain.

Kuwahata was about to give up on his dream when the answer suddenly came from an unexpected direction. One of the engineers on his team, Satoshi Imamura, was ordering dinner one evening when he noticed that dried squid was one of the dishes offered on the menu. He knew that dried squid is very chewy, and he wondered how it was prepared in order to be palatable. He learned that it was soaked in sake, which transforms it into a delicacy.

Imamura realized that this could be the answer to the wood-cone problem: if the wood were soaked in alcohol, it might soften enough to withstand the pressure of being stamped into a cone shape. Imamura told Kuwahata about his idea, and they experimented with all sorts of liquor. They found that cheap sake worked best, perhaps due to its impurities. (This provides an uncanny parallel to the world of musical instruments — it is said that Stradivarius soaked his wood in a secret liquid, which gave his instruments their uniquely wonderful sound.)

Another problem that Kuwahata had to overcome was that the stamped cone did not retain its shape over time, especially under conditions of high temperature or humidity. After four years of experimentation, his solution was to apply a thermosetting resin after stamping, which succeeded in maintaining the form even in 90 percent humidity at temperatures up to 60°C/140°F.

The first product to incorporate wood-cone speakers is the JVC EX-A1 microshelf system ($550). The cones are 8 cm in diameter, and the wood is only 0.28 mm thick. Each speaker has a long-throw voice coil, which moves a lot of air and enhances bass reproduction, even from small speakers.

Future models include a two-way design with a 10 cm cone woofer and a 19 mm dome tweeter, as well as a floor-standing design with four 8 cm cones and a 19 mm dome tweeter. Kuwahata is also working on 13- and 16 cm cones. It will be interesting to see if this technology lives up to its promise. Pass the sake!