How Low Can You Go?
Sydney Morning Herald
Monday August 13, 2001
``HOW much will I have to pay for a really good subwoofer?" It's a question ducked a dozen times a day in hi-fi stores around the country by salespeople. It's not that they don't know the answer; they just don't want to scare anyone off by quoting a realistic figure. The truth is that playing back low bass at high volume requires a large cone, a large cabinet and a high-power amplifier, none of which comes cheap.
Velodyne's HGS-15 Servo subwoofer is a case study of what you should expect in a sub. For a start, it sports the largest driver cone you're ever likely to encounter. It has a diameter of 381 mm (15 inches), which means more air than any two 304mm (12-inch) drivers or any four 200mm (8-inch) drivers.
One inescapable problem with using a large cone is momentum. Once a large, heavy cone starts moving it's difficult to stop and even more difficult to start off in the opposite direction. Yet, in order to follow a music signal, a subwoofer's cone must go back and forth up to 200 times a second. Velodyne solves this problem very cleverly. It fits a small accelerometer to the driver that monitors which direction the cone is moving and how fast it's going. This information is relayed back to a servo-feedback circuit that compares the actual cone movement with what the cone would be doing if it had no mass at all. The servo then generates correction signals that are fed back to the input and force the cone to track the audio signal more closely. A happy side effect of servo control is reduced distortion: up to 30 times lower than a conventional bass driver.
Yet another benefit of using servo control is a much smaller cabinet than would usually be possible. That said, the HGS-15 cabinet, at 46cm wide x 50cm high x 40cm deep, is far from small. It's attractive, though, thanks to a high-gloss black finish.
The Velodyne has all the inputs, outputs and operating controls anyone is ever likely to need, including a high-pass (40-120Hz) filter that can be bypassed to allow your home-theatre receiver's bass management software to work at its best. There's also a switchable infrasonic filter (15/35Hz) to prevent unwanted signals (inaudible rumble from a turntable or traffic noise on a CD) from causing excessive cone motion. An infra-red remote control lets you make minor adjustments to subwoofer volume without moving from your chair.
There's only one word for the bass produced: awesome. This subwoofer goes lower than is necessary to be able to reproduce the lowest notes produced by any musical instrument, including pipe organ, and plays loudly enough to deliver the most extreme low-frequency effects ever recorded for movies on DVD. Even more impressive is the clarity of sound. In musical passages where other subs sound muffled and indistinct, the Velodyne remains crisp and tuneful.
Not everyone will spend $5,000 on a subwoofer, but if a sub you're considering even approaches the performance of Velodyne's HGS-15, you'll know you're on to a winner.
Greg Borrowman is the editor of Australian HI-FI Magazine.
Info file
Velodyne HGS-15 Servo-Controlled Subwoofer
Price: $5,199
WC Wedderspoon Pty Ltd
3 Ford Street, Greenacre, NSW 2190
(02) 9642 2595
wedderspoon@smart chat.net.au
www.velodyne.com
© 2001 Sydney Morning Herald