The mobile phone, that essential modern accessory, makes its user immediately unpopular with those around him. For some reason, talking into such a phone is far more annoying to external listeners than a conversation with a human companion, or even soliloquial muttering. Daedalus reckons that the phone user instinctively projects his voice to reach the distant party. He is now inventing a phone which can be spoken into silently.

Speech is formed by the mouth and tongue acting as an ever-changing resonant cavity for tones produced by the larynx. The tones themselves are very basic; someone who has lost his larynx can speak intelligibly with a simple buzzer as a replacement. Daedalus's brilliant idea is to provide an ultrasonic ‘buzzer’ as a larynx. His ‘Ultraphone’ has a narrow pipe, like a drinking straw, which projects into the user's mouth and injects a set of inaudible ultrasonic frequencies into it. The user whispers or mouths his speech silently, and a microphone detects the modulations imposed by his mouth and palate on the ultrasonic signal. A heterodyne circuit downshifts this signal into the audio range, thus reconstituting the speaker's normal voice, and transmits it to the called party. Like a normal telephone, it also injects a proportion of the speaker's reconstituted speech back into his own earpiece as a ‘side-tone’ for aural feedback. Thus he hears his voice quite normally, and is not tempted to speak audibly. Indeed, any attempt to do so will result in strange distortions as the audio is downshifted and aliased by the heterodyne circuit.

This simple system would produce a flat and toneless speech, rather like that of the laryngectomy patient with his buzzer. But Daedalus hopes to equip the Ultraphone with a program that recognizes the tonal clues implicit in silently mouthed speech, and varies the ultrasonic frequencies in sympathy. This should give far more realistic speaking tones, close to the user's natural voice.

The Ultraphone will sweep the market. Yuppies and poseurs will be able to make truly silent phone calls anywhere, even in concert performances and prayer meetings, without disturbing the proceedings or revealing the important, confidential matters they are discussing. And even in a boiler factory or gunnery range, ambient noise will not distract them. High above the audible clamour, their ultrasonic deliberations will travel clear and unaccompanied.