Soon, music aficionados can use plug-in USB speakers that produce high-quality sound from the laptop without the need for mains power.

The tinny fizz produced by most laptops' built-in speakers spoils the music quality because the USB port, from which they get their power, can supply only 2.5 watts. Now, the British firm NXT of Cambourne, Cambridgeshire, has come up with a USB-powered system that can deliver up to 15 watts to each speaker, reports New Scientist.

Although power from mains-powered units is held at around 32 volts, a USB 2.0 port can deliver no more than 5.25 volts to a device.

NXT chief executive James Lewis says that most of the time music is quiet enough to be reproduced satisfactorily by circuits running at just 1 volt. So NXT built its USB-powered amplifier to run at low voltage, but able to deliver higher voltages - and more power to the speakers.

This is done by tapping a pair of capacitors that store spare power from the USB during quiet passages. By pre-determining the music signal a couple of milliseconds ahead of the amplifier, the system determines exactly when to raise the voltage and unleash the stored power.

"It's the first time I've heard of using the dynamic reallocation of power for this type of application. It seems like a great idea," said Andy Dowell, a director of Dolby Laboratories in the UK.

"People would love to get more oomph out of the PC speakers." (ANI)