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ROADIES, those beefy humpers who lug stage gear around for rock stars, may
have had their day. Inflatable loudspeakers are on the way, and they鈥檙e light
enough for anyone to shift.

Loudspeakers come in heavy, cumbersome boxes that provide an air enclosure to
absorb unwanted vibration and give a fuller sound. But now two companies,
SoundTube Entertainment of Park City, Utah, and Ellula Sounds of Loughborough in
Leicestershire, reckon an inflatable box will do the job.

Conventional speakers have a 鈥渄river鈥�, which converts electrical signals to
back-and-forth movement and is connected to a cone-shaped diaphragm that
vibrates the air. The driver sits on the front of a cabinet. To make loud or
deep sounds you need big drivers mounted in giant boxes. So rock groups need
roadies to hump and heave them onto the stage.

SoundTube is now developing inflatables that bands can carry flat鈥攁nd
blow up when they arrive. The company is cagey about details, but a patent
describes one way in which an inflatable speaker might work.

A speaker driver is mounted in a flat, rigid board bonded to a large bladder.
When the bladder is inflated, it expands to form a box shape resembling a
speaker cabinet. The bladder has several chambers so that the whole thing won鈥檛
collapse if one is punctured. At the end of each gig, a vacuum pump sucks out
the air.

British company Ellula Sounds has made its own inflatable speakers, on sale
next month. The company is a spin-off from Loughborough University, which
licensed the flat-panel speaker technology developed by NXT of Cambridgeshire.
Ellula鈥檚 speakers resemble brightly coloured audio beach balls and are aimed at
the home, for use with portable stereos and computers.