Just What Is a Digital Loudspeaker?

This last year has seen several companies proclaim the launch of the "world's first digital loudspeaker." The term brings to mind some exotic new approach that is neither cone nor ribbon nor electrostat---something as different from all of those as, say, a CD is from a vinyl record or cassette tape.

Coming across "the world's first digital loudspeaker" somewhere, one might expect that it must be a major technology revolution in the chain from nature, to bits, and back to nature again. It would also help ward off confusion in such a nascent product area if the phrase were used to describe a single technological approach. But, as it turns out, "digital loudspeaker" applies to several not-so-similar techniques, some of which are not that revolutionary after all.

On the face of it, the idea of a literally "digital" speaker is impossible. At some point, the laws of physics dictate that the digits must be converted to something capable of driving a speaker's physical movement, which then creates sound pressure and therefore sound. In other words, most of the time a "digital loudspeaker" wouldn't look much different from a conventional one, except that the digital-to-analog converters (DACs), crossover, and/or amplifier in such a system might be in a different place or contain more digital processing than is currently typical. But in this world of "digital-ready" marketing, it is those little differences that make for a "world's first." The following are just three examples from many recent pronouncements.

Sony's First-Generation Digital Speaker System
Following HI-FI '97, we reported in Stereophile on a new Sony speaker designed by Dan Anagnos, based on a sophisticated digital crossover. The system, comprising several black boxes connected to a large 572-lb speaker, impressed most folks who had a chance to hear it.

Sony has characterized the new loudspeaker system as a first-generation digital speaker, even though the demonstration models used conventional (although specially designed) cone drivers driven by off-the-shelf (not Sony!) power amps. The external crossover is indeed digital, however, enabling one to hook the output of a digital source such as a DVD/CD player or Dolby Digital stream directly into it. The filtered signal intended for the different drivers in the speaker box can then be rendered by any conventional power amp.

So in this case, a "digital speaker" actually refers to the benefits of a (currently external) digital crossover/DAC.

Altec Lansing's Digital PowerCube Speaker System
What Altec Lansing has done is take a conventional set of small powered speakers, some conventional crossovers, and hooked them up to a personal computer using the recently established Universal Serial Bus (USB). USB is a purely digital connection scheme that allows computer peripherals such as keyboards, printers, and mice to connect with computers and each other with "plug-and-play" ease.

So while the development of a speaker connected to a system using USB cables is cetainly fresh at this point, we still have conventional drivers using conventional amplifiers in an application that currently works only with USB-savvy personal computers. What's different here is that the DACs are now inside the self-powered speaker.

Therefore, this system is essentially a conventional powered speaker with a built-in DAC, connected to a digital source via USB.

1 . . . Ltd.'s Digital Loudspeaker (DLS)
Certainly the most radical of the bunch is the recent digital loudspeaker (DLS) from researchers in Cambridge, England (see current story). The DLS is an innovative technology that rethinks the digital processing, as well as the drivers used to deliver the final sound. In fact, here is an example of a new driver technology that could not work well (if at all) without a digital processor crunching away at the incoming signal.

In other words, the DLS is a fundamentally unique speaker technology supported by groundbreaking digital processing.

In the end . . .
. . . a "digital loudspeaker" appears to be any system in which extensive digital processing is employed close to or inside the speaker box, but not always in the same way. Sony has a high-end digital crossover, Altec Lansing has a powered speaker with DAC built-in, and 1 . . . Ltd. has an entirely new digitally driven driver technology.

But do we need to clarify this term, or just let it evolve for a few years until we get the general idea of what it means? After all, "surround sound" refers to a wide range of decoding systems, yet still works as we move from format to format. As always, time will tell. In the meantime, it may be wise to look carefully under the cover to see just what flavor of "world's first digital loudspeaker" is being showcased this week.