The Sound of Silence.
Noise is an increasing problem in the densely populated environment of Britain's towns and cities. Damping sounds between interior walls is not at all difficult, and where it is not achieved it owes more to poor standards of construction than to any inherent practical issues. Noise in outdoor spaces is, by comparison, harder to control - whether from traffic or simply next door's over-exuberant social activities. One effective way to eliminate noise is through the use of active noise control ( http://en.wikipedia.org/wiki/Active_noise_control ). A microphone is used to detect incoming sound-waves, and a speaker then transmits sounds of equal amplitude and opposite polarity. The incoming sound is thus attenuated by destructive interference. This method is effective, but requires rather complicated feed-back equipment. If the technique is applied to attenuating noise in a large volume, multiple speakers are required, in which case interference between their outputs is a problem.
Sound-waves, like electromagnetic waves, can to some extent be collimated or focused using parabolic reflectors ( http://www.mattsa.cl/mattsa/productosyservicios/sistemasdeseguridad/hs60.html ). This begs the question- can a highly directional acoustic source attenuate non-directional noise by destructive interference?
If so, it should prove possible to create a noise-damping 'curtain' of directed sound, by constructing a row of white noise emitters enclosed by a container of parabolic cross section, designed to focus the sound to a point in the air, see figure 1:
Figure 1: 'Acoustic Curtain'
While collimation of sound is inevitably less efficient than that achievable with the EM spectrum, it should still be effective in directing the majority of the white noise generated straight up, and away from the listeners behind the 'curtain', at least in outdoor spaces. Destructive interference with the random noises impacting on this 'acoustic curtain' will largely eliminate them, or at least the more distinct sounds among them, such that turning on the system should dull the irritating noise of the outside world, leaving at worst a hushed and indistinguishable background hum. The human brain would serve to complete the damping process.
Noise is an increasing problem in the densely populated environment of Britain's towns and cities. Damping sounds between interior walls is not at all difficult, and where it is not achieved it owes more to poor standards of construction than to any inherent practical issues. Noise in outdoor spaces is, by comparison, harder to control - whether from traffic or simply next door's over-exuberant social activities. One effective way to eliminate noise is through the use of active noise control ( http://en.wikipedia.org/wiki/Active_noise_control ). A microphone is used to detect incoming sound-waves, and a speaker then transmits sounds of equal amplitude and opposite polarity. The incoming sound is thus attenuated by destructive interference. This method is effective, but requires rather complicated feed-back equipment. If the technique is applied to attenuating noise in a large volume, multiple speakers are required, in which case interference between their outputs is a problem.
Sound-waves, like electromagnetic waves, can to some extent be collimated or focused using parabolic reflectors ( http://www.mattsa.cl/mattsa/productosyservicios/sistemasdeseguridad/hs60.html ). This begs the question- can a highly directional acoustic source attenuate non-directional noise by destructive interference?
If so, it should prove possible to create a noise-damping 'curtain' of directed sound, by constructing a row of white noise emitters enclosed by a container of parabolic cross section, designed to focus the sound to a point in the air, see figure 1:
Figure 1: 'Acoustic Curtain'
While collimation of sound is inevitably less efficient than that achievable with the EM spectrum, it should still be effective in directing the majority of the white noise generated straight up, and away from the listeners behind the 'curtain', at least in outdoor spaces. Destructive interference with the random noises impacting on this 'acoustic curtain' will largely eliminate them, or at least the more distinct sounds among them, such that turning on the system should dull the irritating noise of the outside world, leaving at worst a hushed and indistinguishable background hum. The human brain would serve to complete the damping process.
posted by Iansonuk at 12:51 PM
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