Accelerometers as part of the active noise control in the car

Active Noise Cancelling headphones - thing is very convenient and useful. Its essence lies in the generation of sound which is in opposition with respect to the noise coming from the outside. Thus is their effective mutual suppression. Of course, the silence is not fully reached, but the noise level is significantly reduced ear. However, it is relatively easy to implement in a small fully controlled space, which also represents each cup headphones. But how can you make an active noise reduction in the car? The company's engineers Harman, apparently found quite interesting solution.

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Sound insulation in the car can be divided into two main tasks.

The first - a reduction in running noise of the engine. The expensive machines, this problem is solved for a long time and very successfully. Knowing the type of engine, its size and power, as well as the mode of operation, can be fairly accurately calculate its frequency characteristics. Based on this information it is possible to generate a suppressing signal in antiphase.

The second task - isolation from all sorts of outside noise. And here it is much more difficult: Unlike the engine or the same headphones, noise reduction system can not predict when there will be some external noise, as well as its intensity and frequency. For example, the sound of friction of tires on the roadway will be very different depending on the material, flatness and even tire wear themselves. And this is one of the main sources of noise in the car. The traditional method of using a number of sound insulation fairly heavy materials leads to an appreciable weighting car and as a consequence, increase the average fuel consumption. By the way, the adepts of the introduction of "unmanned" cars believe that their widespread use will help drastically reduce the accident rate, which means you can not lay in the design of a certain margin of safety car in the event of a collision. Consequently, it will be possible to make them less of a relatively rigid material that will themselves provide higher sound insulation, will facilitate even more cars and reduce their average consumption.

For obvious reasons, an active noise reduction in the cabin will not use the approach implemented in tactical headphones.

Each cup is equipped with an external microphone (closed foam nozzles). The system detects gunfire and explosions, suppressing noise from them with a tiny delay. In this case, it is enhanced people to soldiers could fully communicate with co-workers in a fight. However, using this approach in the case of a car? Position the microphone on the outside? But then part of the noise transmitted suspension, they will be registered with a different frequency and volume. If you move the microphone inside the cabin, then how to explain the system, you need not have to respond to a number of "internal" sounds, such as conversation occupants?

The company's engineers and Lotus Engineering Harman proposed the original solution. In the cabin installed several accelerometers that monitor vibration in the vehicle. Their analyzes the on-board computer and calculates what soundscape is created in the salon by these vibrations. Low frequency noise is obtained more easily neutralized due to the greater wavelength. In addition to the automotive acoustics easier to generate similar sounds. As for the high-frequency noise, they are blocking around the driver's head is very difficult for the built-in speakers, and even a slight movement of the head may nullify the whole effect of suppression.

The reaction takes a few milliseconds of each of the steps of detecting a vibration to generate sound in phase opposition. Note that the same dynamics can play music that does not need to suppress. A frequently encountered in the compositions of sounds coinciding in frequency with the noise tire and suspension. The developers did not disclose how they have solved this problem, but claim that the suppression of exposed only external "unnecessary" noise, and built-in speakers sound is not distorted in any way. By the way, are not subject to suppression and sirens official vehicles, to avoid unpleasant misunderstanding.

It is possible in a short time is almost complete silence in the cabin will be able to enjoy is not only the owners of cars of a class "lux".

Source: geektimes.ru/post/240984/