| 摘要 |
Until now, sound protection hoods or sound-insulation material have been used for noise attenuation. Both types have, however, the disadvantage that a heat build-up has occurred. The use of crystals brought no technically satisfactory solution, since these point-shaped sound sources effected cancellation of the sound only at the intermediate frequency points. It is the object of the invention to reduce or to compensate noise arising preferably in the case of electrical machines or devices. In this case, the sound-emitting body or the housing surrounding the body is enveloped in a film, known per se, made from a polymeric material. A signal of phase opposite to the sound waves is applied to this film, on the side facing away from the body. By means of this invention it is for the first time possible to provide sound-emitting bodies of large surface area with protection against sound or noise.
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