Active Noise Canceling Mufflers

[emoguitarboy]

Hey,

I was talking with my boss today, and we came up with with a question. I've heard of Active Noise-Canceling Mufflers for use in industrial applications. I was wondering if anyone has made one or is in the process of development of one for cars.

For clarification, a noise canceling muffler would be a system that listens to what noise is coming out, and uses a speaker to cancel the noise.

 

[kenamond]

Are you talking about using this instead of a normal muffler? If so, you need to make "anti-noise" that is as loud as the car would be without a muffler. That's pretty loud. And the speaker would have to handle the heat and be insulated from the elements. Perhaps it would be possible with some sort of massive voice coil bolted to a flexible "lid" to the "muffler". It would only have to drive things up to about 250Hz (4 putts per 2 rev at 7500rpm). But you'd probably need to beef up the alternator to drive that thing (like many do to drive a loud stereo). Also the x-max and area of the "speaker" have to be sufficient to generate sufficiently high pressures (decibels). Might make for huge muffler. Then you'd have to calibrate it so that the anti-noise is as loud as the noise (it'd be funny if you got it in phase instead of out and make the car 2x as loud).

If you look more into this and find that they can do it with folded horns or something compact, let me know. Sounds interesting.

 

[tkelly27]

My dad was telling me they have them on certain lexus models. I think it's a passive system though, so you don't get complete noise cancellation. He said it does get noticeably louder with more throttle though.

 

[AndrewD5418]

Why not just have two resonators on the exhaust, and then the muffler. Quietens it pretty well.

 

[Defiant]

Someone -it may have been Nissan or Mazda- had a noise-canceling system like the modern Bose headphones, for the whole car, back in the eighties. It kind of went away, and I've never run across it.
The other one not used nearly enough is auto-volume adjustment that turns the radio up and down with road noise.
For muffler use, it's probably just economics- in most cases, it's cheaper just to build a differently-baffled muffler than to try and get exotic about it.

 

[TunaTalon]

Here's what a 1996 patent application says about the technology.

From http://www.freepatentsonline.com/5748749.html

"Attempts to use active anti-noise sources on mufflers or other applications involving an exhaust pipe, include the work of Cain, U.S. Pat. No. 5,272,286, which shows an active noise cancelling device surrounding an exhaust pipe in a generally concentric configuration. The problem with such an arrangement is the tremendous expense involved in building something in direct contact with a hot exhaust pipe, the inability to retrofit the system to existing tailpipes and its enormous bulk as well as other problems in its operation. A similar device is shown in Japanese Application, 60-22010, entitled "Exhaust Noise Reducing Device" by Toshiyuki Kaminaga, published on Feb. 4, 1985. Scherrer, in French Patent No. 1,190,317, published Oct. 12, 1959 shows a system very much like Cain, supra, where concentric pipes empty into a mixing chamber. Finally, U.S. Pat. No. 4,487,289, Dec. 11, 1984, entitled "Exhaust Muffler with Protective Shield", shows an extension fitting over a tailpipe, again like Cain."

The company holding the patent does not mention it on their current web site (http://www.nctclearspeech.com/noise-cancellation.htm)