06/13/2014—Back in 2008, when engineers at Panasonic first suggested the use of bamboo in the Lexus CT 200h speakers, the idea raised more than a few eyebrows. At the time, the inclusion of renewable, fast-growing bamboo in audio equipment was unheard of.
Koji Sano, chief engineer at Panasonic, however, knew he was on to something good.
“We’d been experimenting with bamboo since 2007,” he explained, “so we knew the plant—charcoaled bamboo and bamboo fibers, to be precise—would make a lot of difference in our attempt to increase sound quality inside the cabin.”
Lexus speakers are divided into an array of collaborative parts, of which the diaphragm, a cone-shaped membrane that vibrates to produce sound, is one of the most crucial. A diaphragm must be light to create a loud noise; stiff to hit high notes precisely; rigid to minimize acoustic distortion; and flexible enough to dampen its own vibrations.
It’s a quadruple threat for nailing a crystal clear sound, and Sano knew that by using bamboo within the CT’s diaphragm, all of the above could be achieved.
“You often see bamboo sway in strong winds, constantly moving in all directions without cracking,” he says. “That’s the sort of quality we seek in a speaker diaphragm.”
Following initial meetings with Lexus engineers, his team secluded themselves in a lab and conducted numerous phases of intense product development. In 2010 they created their first fully functional prototype, and in 2011 it was installed in the Lexus CT as a standard feature.
But like any Lexus-affiliated innovator, Sano felt more could be done—a bamboo-based diaphragm could be lighter, more rigid, and more flexible so that sound could be even better.
So Sano and his team went back to the drawing board and developed a next-generation speaker, included in the latest CTs, that’s even more advanced.
“The secret behind our latest improvement is a material called plant opal, which we have extracted from bamboo leaves,” explains Panasonic staff engineer Yohei Jin.
Plant opal is a microscopic structure found in the fringes of grass plants, including bamboo. It’s hard and clear, named for a likeness to the eponymous gemstone.
“The type of plant opal we use has the shape of a needle,” Jin explains, referring to the tiny, .2-millimeter-long pieces specifically selected for the job. “We use only a small amount of the material, but as it bites into the diaphragm’s resinous body, we can improve overall rigidity and stiffness.”
Here’s how it’s done. First, bamboo leaves are sourced from healthy trees and tiny pieces of plant opal are extracted:
Next, the plant opal pieces are combined with bamboo charcoal to form a powder, and the mixture is then molded into a speaker diaphragm:
With this latest improvement, the team has managed to improve acoustic velocity—a yardstick by which frequency range is measured—by 10 percent, so the sounds produced through the latest CT speakers are even sharper, especially at high frequency. Plus the midrange has gained more depth.
“Bamboo is the ideal material for speakers,” said Sano, “and its plant opal more importantly so. And we are the only one in the industry that has successfully tapped into the plant’s massive potential. We are also aiming to introduce this plant opal speaker into the highest echelons of our home-audio lineup.”
“Simply because it’s that good.”
—BY SHOGO HAGIWARA/ILLUSTRATIONS BY DANILO AGUTOLI