quote:I share your puzzlement. Perhaps somone can explain how it works when one person is 1/2 wavelength further from the nose sorce than the other person.
Originally posted by Kestas: I still don't see how noise can be canceled from another source. They are generated from different locations and can only cancel each other at certain locations, just like a moire pattern. At other locations they'd have an additive effect.
quote:But phase does have everything to do with it. If the sound from the speaker is 180 out of phase with the nosie source it tends to cancel the noise. If it's in phase with the source, the sound level gets louder. Sound cancelling headphones work because their microphones are right at the speakers, a small fraction of a wave length away. Move the sense microphone 1/2 wavelength away from the speaker in the headphone and it will make the noise level louder instead of canceling it. I would like to hear how the Honda system works, but it's not the headphone model.
Originally posted by kenw: source has nothing to do with it. freequency does not change by locations, as it bounces around inside the car or wherever, it doesn't change. Amplitude may change, but not frequency. it can only work with repetitive noise, the more "white" the better. Saw article on this in car usage at least 10-15 years ago. I have a pair of headphones that does this quite well. virtually eliminates all road or air noise in cars and planes. it allows me to turn down the stereo since i don't have to overpower wind noise. does nothing to voices, etc or "non-white" noises.
quote:I did a search online and what I found agrees with you. The thread I read said the ANC only works on very low frequency drivetrain rumble. The example they gave was around 50 Hz. If they optimize if for a space equi-distant between the front and rear seat pasengers, there would only be foot or two difference in distance. The press releases an parroting of them makes it sound like general purpose noise cancelation system. It isn't. Instead of spending money on their ANC, they could have left it out and called the rumble SMS (Sound of money saved)
Originally posted by kanling: I think that the system only works at low frequencies where the wavelength is much greater than the dimensions of the car. At 40Hz, the wavelength is about 28 feet, so a few feet difference in the passenger cabin won't matter much.
quote:For a good demonstration of this, wire one, or better yet, two of the speakers in your car backwards and notice that the bass is greatly reduced. This happened in my car due to an incorrect wiring diagram. When I corrected the wiring, all the bass came back.
Originally posted by XS650: But phase does have everything to do with it. If the sound from the speaker is 180 out of phase with the nosie source it tends to cancel the noise. If it's in phase with the source, the sound level gets louder.
quote:Crude, but cheap and effective. Oh the possibilities. . .
Originally posted by XS650:quote:It's already been invented.
Originally posted by ekpolk: I'm not laying out any of my cash until they come out with a system robust enough to cancel out the noise emanating from annoying people. . .
quote:Amazing huh? Active noise cancellation delevered through the stereo speakers. Active fluid engine mounts. Wow. This is from www.greencar.com
"Running a six-cylinder engine on only three cylinders represented a challenge to Honda engineers. VCM required several advanced technologies to mask the vibration inherent in three cylinder engines with their more widely-spaced power pulses. To deal with this, the "drive-by-wire" electronic throttle computer assures that power neither increases or decreases during the switchover. Also, an Active Noise Control system cancels out excessive engine noise using a microphone to detect the noise, and then generating a signal 180 degrees out of phase to cancel out the noise. These canceling sound waves are emitted from the front and rear speakers during three-cylinder operation, idling, and at-start running. The ANC system is not needed when running on all six cylinders. Finally, two active control engine mounts, one in front of the engine and another behind, are controlled by the engine computer, which uses solenoids to damp fluid movement in the mounts. During three-cylinder operation, the computer monitors changes in crankshaft rotation rpms and sends this information to the mounts, which then compress or extend an actuator to dampen the engine vibration. "
quote:That might cause a bit of a surprise if someone hooks up a subwoofer to the factory system. I guess that's not too common on mini-vans though.
Originally posted by kanling: I think that the system only works at low frequencies where the wavelength is much greater than the dimensions of the car.