Pioneer slims down the subwoofer

AUTHOR: Inavate

Pioneer Corp in Japan, has developed a new loudspeaker technology, which it seems will achieve both thinness and high fidelity audio reproduction. The company says it has developed a woofer with a driver only 13.2mm thick, and 16.52mm thick including its diaphragm. This is only about one-third the thickness of a conventional dynamic speaker (about 45mm).

Although the product was developed to solve problems with the design of ultra-thin LED-Lit TVs the first application will be in car stereo speakers. The company has plans to expand the range of applications to audio-visual and computing applications.

Horizontal coil movement

Tohoku Pioneer of Japan, which handled development, moved the voice coil driving the diaphragm off to the sides, to attain the thinner design (see image), dubbing the technique HVT (Horizontal – Vertical Transforming. Normally dynamic speakers stack the coil and the diaphragm, so that the only methods of thinning construction are to use a thinner voice coil or reduce the gap between the coil and the diaphragm.

These approaches of course force a trade-off with sound quality: it becomes difficult to gain voice coil drive performance and the amplitude of diaphragm vibration is restricted, introducing distortion. This situation in turn makes it necessary to use a rigid suspension for the diaphragm, making it even harder to keep the minimum resonant frequency (f0) low.

In HVT, the voice coils are positioned on both sides of the diaphragm, reducing the structure’s thickness, but assuring the diaphragm amplitude. Because a soft suspension can be used a lower f0 is possible, and it is therefore easier to improve fidelity in a lower frequency range. The first HVT product offers an f0 of 75Hz, a pretty respectable bass.