[0001] The present invention relates to an active noise cancellation system for a vehicle
having a sound reproduction system, comprising means for generating one or more electrical
signal(s) proportional to the noise in the target area, an electronic means receiving
these signals, such as an adaptive filter, for generating a noise cancellation signal,
one or more sound sources connected to said electronic means for generating cancellation
noise in the target area, and one or more sensors for detecting residual noise in
the target area and transmitting it in an electrical form to the electronic means
to tune its operation.
[0002] Figures 1 and 2 in the accompanying drawing illustrate the conventional system for
realizing active noise cancellation in a vehicle, such as a car. Figure 1 shows the
apparatus components required in such an active noise cancellation system, and Figure
2 shows the placing of the most essential of these in the vehicle.
[0003] A conventional active noise cancellation system of the kind shown in Figure 1 comprises
first of all detection sensors 1, the purpose of which is to generate a signal proportional
to the noise present in the target area. In practice, these detection sensors can
be for instance microphones. The signals from these detection sensors are inputted
in an electronic means 2, such as an adaptive filter, which in response to said signals
being proportional to the noise in the target area generates a noise cancellation
signal, which is ideally of equal amplitude but opposite phase to the noise signal,
in which case the noise cancellation signal as reproduced through the sound sources
3 will cancel the noise in the target area. In practice, complete cancellation is
not possible for the mere reason that the means 2 for generating the cancellation
noise is not able to function in real time on account of the many delays involved
in the system, but must in practice predict the situation prevailing in the target
area. Thus the cancellation can be directed specifically to periodic components of
noise. However, in practice the noise can be attenuated about 10-30 dB at the motor
noise frequency. In order that the equipment generating the cancellation noise may
adjust itself to changes in the target area, the system further includes sensors 4
for residual noise, which may in practice be for instance microphones adapted to listen
in the target area. On the basis of the signals generated by these sensors 4 of residual
noise, the means 2 for generating cancellation noise can adapt its function to afford
optimum attenuation.
[0004] Figure 2 shows the placing of the components of the system of Figure 1 in a car.
The actual means 2 for generating the cancellation noise is then fitted within the
door panel of the vehicle, and the loudspeakers 3 generating the cancellation noise
are placed in the corners of the interior of the vehicle body. The system further
comprises several sensors 4 monitoring residual noise, being disposed in the upper
part of the interior of the body.
[0005] In practice, the placing of the sensors for cancellation noise in the interior of
the vehicle body constitutes a problem. The placing of these sensors in such a way
that they do not interfere with the other furnishings of the interior of the vehicle
is very problematic, since these sensors and particularly the wiring to be brought
thereto must be fitted within the upholstery of the interior, which requires rather
extensive additional mounting work.
[0006] Thus the object of the present invention is to provide an active noise cancellation
system for a vehicle, wherein the placing of the sound sources for cancellation noise
and particularly that of the sensors for residual noise does not present problems
of the kind described above, but these requisite components of the active noise cancellation
system can be fitted within the vehicle without any additional work being involved.
This is achieved with the noise cancellation system of the invention, the first embodiment
of which is characterized in that the sound sources for the generation of cancellation
noise are constituted by the loudspeakers of the sound reproduction system of the
vehicle, and that the sensor or at least one of the sensors for detecting residual
noise is fitted in conjunction with one of said loudspeakers.
[0007] The noise cancellation system according to a second embodiment of the invention is
again characterized in that the sound sources for generating cancellation noise are
constituted by the loudspeakers of the sound reproduction system of the vehicle, and
that the sensor or at least one of the sensors for detecting residual noise has been
fitted in conjunction with said electronic means.
[0008] The noise cancellation system of the invention will be described in more detail in
the following, with reference to the enclosed drawing wherein
Figure 1 represents schematically the construction of the noise cancellation system,
Figure 2 represents an arrangement according to the prior art for disposing the components
of the noise cancellation system in the vehicle, and
Figure 3 represents a solution according to the invention for disposing the components
of the noise cancellation system in the vehicle.
[0009] In accordance with the invention, it has been realized that almost invariably a sound
reproduction system is installed in a normal vehicle, particularly a car, said sound
reproduction system typically comprising a central unit and four loudspeakers placed
approximately in the corners of the interior of the car. By using these loudspeakers
and their wiring routes which are part of the normal outfit of the vehicle, one can
also realize the noise cancellation system of the invention. Therein the loudspeakers
3 of the sound reproduction system are used as sound sources generating the cancellation
noise of the noise cancellation system, and the sensors 4 of residual noise are placed
in the immediate vicinity of these loudspeakers for instance in the same cabinet with
them. The wiring of the sensors can then be drawn by the same routes as the wiring
of the loudspeakers, or a single multicore cable can simply be used for both the loudspeaker
and the sensor of residual noise pertaining thereto. Thus the fitting of these sensors
does not cause any additional work as compared with the mounting of the loudspeakers
of a normal sound reproduction system.
[0010] Even though the sensors for residual noise are placed very close to the loudspeakers
3 generating the cancellation noise, this does not present a problem. The means 2
for generating the cancellation noise does not directly reproduce this residual noise
signal but only monitors some of its frequency components and is controlled in response
thereto to generate cancellation noise which most effectively cancels noise at the
frequency of noises generated for instance by the motor and tires of the vehicle.
[0011] By placing one sensor for residual noise in conjunction with each loudspeaker --
four loudspeakers being normally provided -- of the sound reproduction system, one
can achieve a system which is fully sufficient for the detection of this residual
noise signal. Further, one sensor can be placed in conjunction with the means for
generating cancellation noise, which also does not require additional work from the
point of view of wiring or mounting.
1. An active noise cancellation system for a vehicle having a sound reproduction system,
comprising means (1) for generating one or more electric signals proportional to the
noise in the target area, an electronic means (2) receiving these signals, such as
an adaptive filter, for generating a noise cancellation signal, one or more sound
sources (3) connected to said electronic means for generating cancellation noise in
the target area, and one or more sensors (4) for detecting residual noise in the target
area and transmitting it in an electric form to the electronic means (2) to tune its
operation, the sound sources for the generation of cancellation noise being constituted
by loudspeakers (3) of the sound reproduction system of the vehicle, characterized in that the sensor or at least one of the sensors (4) for detecting residual noise
is fitted in conjunction with one of said loudspeakers (3) and / or said electronic
means (2).
