Daedalus

Muffled furnace

Noise is one of the major nuisances of modern life. Yet the usual sound-absorbing materials are purely passive, and can never damp it out completely. Daedalus now proposes an active absorber, inspired by the observation in a chemical textbook that the carbon monoxide flame “gives a curious impression of silence”. Carbon monoxide, he notes, burns with a reduction in the number of gas molecules. If, like most gas reactions, the burning speeds up with pressure, then a sonic pressure-peak will deplete the gas of molecules at an enhanced rate, and damp itself out. Conversely, when the pressure is low, the depletion slows down. So the flame absorbs the sound. Furthermore, certain flames are extremely sensitive to sound. They were used as acoustic detectors in pre-microphone days. Even a weak sound changed their combustion regime very visibly.

So Daedalus is inventing quiet flame technology. He is devising nozzles and flame-surrounds that optimize this sound-damping effect. He hopes to perfect a gas burner whose nonlinear reaction regime overreacts to sound, and thus absorbs it perfectly. A street lamp that absorbed traffic noise would be welcome on busy roads; victims of aircraft noise or pop-crazed neighbours would love a gas fire that gave out quiet as well as heat.

Even so, nobody would want to keep a fire burning on a hot day, merely to keep the noise down. So Daedalus is taking the argument further. When iron rusts, for example, gas molecules are completely absorbed into a solid. DREADCO's chemists are now studying the oxidation of iron alloys, as well as yellow phosphorus, aluminium amalgam and even lithium (which absorbs nitrogen as well). They are seeking pressure-sensitive reaction regimes with strong nonlinearity, or even a pressure threshold. Their goal is a surface that rusts or tarnishes with total absorption of sound. Ideally it should change colour during the reaction. When fully reacted, it could be regenerated, perhaps by reduction with hydrogen.

This novel decor will be very expensive at first, and will be aimed at acoustics laboratories and recording studios. Gradually it should spread to the more opulent homes, offices and public buildings. A personal version in earmuff form would be widely welcomed; not only for the quiet in which it wrapped the wearer, but for the pleasing warmth released by its slow sonic oxidation.

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Jones, D. Muffled furnace. Nature 393, 740 (1998). https://doi.org/10.1038/31602

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