For some time now, Bose has been using the car stereo to help cancel out engine noise and give car users a quieter ride. Now the company has announced it's going to extend the system to manage road and tire noise as well, which could have knock-on effects for efficiency and lightweighting.
The history of active noise cancellation is a fun and fascinating one. It dates back to the late 1800s, in fact, when a British engineer found out that it was possible to neutralize sound with another, inverted sound while experimenting with two Bell telephones. In the 1950s, several researchers were experimenting with the idea, but since the integrated circuit had yet to be invented, you had to manually adjust the frequency and amplitude of the cancellation sound to achieve your desired results. That's handy for constant droning noises, but a pain in the butt to use with any noise that changed constantly.
Indeed it was Dr. Amar Bose, the founder of Bose corporation, who invented the first noise cancelling headphones as we understand them today, after enduring the kind of noisy plane flight that has sold so many units since. Here's a great little history. The theory is easy enough to understand; a microphone measures incoming sound waves outside the headphones, then flips those waves upside down and sends them back out through the speaker, phase-shifted enough to perfectly line up given the distance between microphone and speaker. Any additional sound, like music coming through the headphones, is added to the cancellation signal, and the whole thing comes out sounding terrific.
In headphones, it's easy. The ear is always in the same place relative to the microphones and the speakers. Achieving the same kind of effect in a car cabin? Much, much harder. You can't put microphones or speakers near the ears, because there might be five or six different sets of ears, all moving around quite a bit during the drive. Indeed, your speaker locations are pretty much fixed by what suits the needs of the car stereo designers.
So Bose's sound engineers have been battling with a very complex problem: working out which sounds to put through which speakers to phase-cancel sounds from the car's engine and all four tires in such a way as to reduce noise all the way through the cabin, so that it doesn't matter how tall or short a passenger is, or where their ears sit in the environment of the car. Active noise cancellation requires the creation of sound to cancel other sound, so getting it wrong could literally double the amount of noise experienced.
The engine noise side of things has been in effect for some years now. Bose (along with other companies like GM) has been listening to engine sounds and generating signals both to cancel them out, for a quieter ride, and to enhance them, giving drivers a better feeling of connection with their car without adding to external noise pollution. Now, at this year's CES, Bose revealed it's ready to start dealing with road noise as well.
There's basically no situation in which extra road noise is desirable. The sound tires make as they deal with different road surfaces adds nothing to your enjoyment of a car. So Bose's QuietComfort Road Noise Control (RNC) system is designed to integrate with any car stereo to deaden as much road noise as possible.
It does so using a series of accelerometers, microphones and signal processing software, in conjunction with the car stereo's speakers, to produce acoustic cancellation signals throughout the cabin. Mics in the cabin constantly monitor the sound levels the system is producing, and fine-tune the algorithms to account for extra passengers, luggage and even the deterioration of the vehicle over time.
The system will start rolling out in production cars in 2021, says Bose, and once it's established, it could help cars become lighter and more fuel economical, because it'll reduce the need for heavy passive sound insulation all around the car.
We look forward to (not) hearing it in action!
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