Stereoscopic developments

So, we've been watching the enthusiasm Hollywood has with stereoscopic video, and pondering ways to take it further. We think we've hit upon a big one: stereoscopic audio.

Adapting existing visual stereoscopy techniques has proved quite fruitful, and neatly avoids the extra expense and inconvenience of requiring more than one speaker. Here are a few approaches we've experimented with:

• Anaglyph: By applying high-pass and low-pass filters to the left and right audio streams, respectively, the two streams can be mixed and played from a single speaker, without crosstalk. It is possible to direct them to the appropriate ear by means of specially-designed earmuffs, constructed from materials that only allow muffled or tinny sounds to the appropriate ear, and the brain naturally reconstructs these to form a "holographic" picture of the 3D audioscape, while still sounding as good as any Bose satellite audio system. Additionally, it is our opinion that a good set of earmuffs looks less dorky than red/cyan glasses, though admittedly we haven't consulted our spouses yet.

• Time-division multiplexing: Similar to the popular LCD shutter glasses idea, this approach plays each audio stream alternately for brief periods, and a synchronised mechanical shutter apparatus on the earmuffs blocks and allows the audio into each ear in turn. When done at a high enough frequency, persistence-of-hearing lets the brain perceive the interrupted audio as almost continuous, and the "jackhammer effect" is soon tuned out and ignored. We did find that some care needed to be taken with the mechanical shutter design; early prototypes with hinged rather than sliding shutters had a tendency to generate sufficient lift that they needed to be tied down with a chin strap (though we feel there's some promise in a hybrid design where lift is carefully managed in order to reduce the otherwise burdensome weight of the mechanism).

• Auto-stereoscopology: With a broad enough radiating surface, audio frequency emitters can use a "lenticular" approach, where tiny baffles direct the sound to specific regions assumed to be in the vicinity of the sole listener's ears. By our calculations, a 3 or 4 metre mylar-based electrostatic strip or ribbon should be adequate for good focus, and should still be potentially cheaper than an equivalent-sized Martin Logan once manufacturing scale is achieved. The use of nanotechnology or exotic materials when constructing the baffles isn't strictly necessary, but it wouldn't hurt either.

• Audio polarisation: It's well-established that light can be polarised into horizontal and vertical orthogonal components, by blocking EM waves oscillating at other angles, and theatre 3D often uses this method. Audio waves oscillate longitudinally rather than laterally, so polarising them involves splitting the waves into forward and retrograde motion, and blocking any air particles moving in the wrong direction. This is not easy with traditional speaker cones, as by their design they must move both forwards and backwards. Luckily, the desired motion is easily achieved by using common household appliances instead; by using a speed-controlled fan for the left stream and a vacuum cleaner for the right stream, in conjunction with opposed one-way air valves on each ear, crosstalk can be kept to a minimum. The primary downside of this method is a tendency to cause listeners to lean to the right, so is probably best suited to political conservatives. Also, testers reported that sound in the left ear sucked less.

Come and see our most exciting stereo audio developments at our NAB stand (since you probably won't be able to hear them).