Noise occurring during such a mode of operation is perceived as particularly disturbing in many areas. This particularly applies to the area of vehicle technology for operating noise of electromechanically driven vehicle components (e.g. electric window lifters) or electrohydraulically driven vehicle components (e.g. automatic hood of a cabriolet). In order to reduce this interference noise, the electric motors are often mounted on elastic elements for damping a transfer of noise in solids and/or are at least partly encased in sound damping, the latter often together with parts of a drive mechanism (e.g. a gearbox). Such insulation devices are particularly suitable for attenuating higher frequency components in the spectrum of the noise. For lower frequencies such insulation devices are large, bulky and expensive.
From the prior art, moreover, the method of the controlled compensation of background noise by active superposition of noise with opposite phase (antinoise) is known. Such active noise attenuation is described e.g. in U.S. Pat. No. 4,677,677 and EP 0 471 290 B1.
However, the range of applications of such active systems for noise suppression, frequently also known as ANC (“Active Noise Cancellation”) systems, is limited in practice.
Apart from the cost of assembly or placement of a device for the active generation of antinoise (loudspeaker), there is a serious fundamental problem in that destructive interference of background noise and antinoise can usually only be achieved for more or less small geographic areas, but not for a long-range environment around the relevant noise sources. Thus such known active noise suppression systems, for example, are hardly suitable for compensation of the operating noise of an electric window lifter in the entire passenger compartment in a motor vehicle. A practical application also fails in this case because a sound sensor that is required for this purpose (microphone) cannot be arranged in a position (e.g. on a passenger's head), which would be particularly suitable for optimal operation of the system. Finally, the functionality of known active noise suppression systems is also adversely affected by the quite frequently occurring circumstance that there is not only one well localized sound source, but multiple spatially distributed sound sources. In this case, in particular mechanical transmission devices are to be considered, which are driven by the electric motor concerned and are therefore arranged after it.