NXT's speakers (left) employ the companies novel audio amplifier module (right) to get the most out of USB-powered sound. NXT

Most of us keep our music on our computers and our computers are increasingly mobile, but there’s a disconnect between the ability to store large amounts of music on a laptop and the portability of said laptop: laptop speakers aren’t worth playing music on. But a clever engineering fix by British company NXT has changed all that, conjuring big sound out of small, portable speakers powered by nothing more than a USB outlet.

Most audio amplifiers – the kind you plug into the wall – maintain a voltage of about 32 volts. That means when the music gets loud, the amp can deliver the required punch. Laptops, which must use power sparingly to preserve their portability, don’t pack nearly the wallop; a USB 2.0 port produces a maximum 5.25 volts to external devices, making it impossible to power larger, high quality speakers from a laptop.

Some engineering trickery from NXT circumvents these problems by relying on the simple premise that the USB can deliver 5.25 volts all the time, even though music is not all crescendos. During quiet passages, a pair of capacitors stores unused voltage coming from the USB. The speakers monitor the music signal a few milliseconds ahead of amplification so they can release that stored up power when the interlude is over and the heavy guitar/drum combo us unleashed.

Of course, this technology is a replacement for weaker bus-powered, desktop-style speakers; pretty much any high-quality stereo speaker has an AC adapter. And the power storage is limited; the extended version of Freebird could run the capacitors out of juice, causing the volume to fall. But NXT says they’ve tested the speakers on a variety of musical styles with consistent success. If they can get some consumer electronics firms to hear them, the technology could be on the market by next year.

New Scientist