Exhaust and sound waves

[Stan Weiss]

Years ago I read an article where they were working on using sound waves to cancel out the exhaust noise and you would not need mufflers or any restriction in the system that would cost HP. Has anyone seen anything like this?

[LJW]

Run a Google search for "Bose Active Noise Cancellation".

[big block fiero]

In public I sometimes caugh while I pass gas to cover up the sound but the smell allways gives it away.

[rookie]

I want to start by thanking Big Block Fiero for sharing, this sets a good example for the children, I think.
Second, if you cancel out sound doesn’t that make it silence, if so I wonder if it should be called a silence making system?
Last but not least is, David has done a no loss exhaust system for years, you can read about in his books are search the web for exhaust David Vizard and probably find bunches of info.

[big block fiero]

I was just kidding around, but really thou, much is available on this subject and a good source is "the scientific design of intake and exhaust systems". I have read this book completely many times and have even built a morrison multi-point indicator to test exhaust pressure waves. This is a very technical read that is not for everybody and will leave you with more questions then answers. But another book that is for everybody and will leave you mostly with answers is as we all know max performance chevy small blocks on a budget by david vizard.

Basicly sound waves and pressure waves move at different speeds. you tune the length of primary pipes so the sound waves reflect at the end of the pipes and come back to the exhaust valves just as they are closing. These waves are used for A performance benifit but I cant think of any examples where these waves are designed to crash back into themselves other then some of the following that are undesireable.In summary the performance engine as it is today has a design up to the end of the collecter that cannot permit changes so any sound cancelling technology, must happen downstream from there.

Manufacturers have done much testing with exhaust manifold designs that are designed to do as your post suggests. These designs do not follow generally eccepted formulas for nessesary primary or secondary pipe length and this comes at a performance cost that the racing crowd wont afford.

Turbo muffler designs have been designed to do as your post suggests but the parabolic sound deflector or other designs that move the pressure and sound waves from crashing strait back into the incoming flow have gotten more favor and deliver more power. These waves are instead dirrected against flat perferated walls with fibreglass packing to absorb sound and so is the design predominate today.

This all then locks in a set of perameters and is where david vizard comes in and suggests a resonator with a deverging cone feature that reflects waves back against a flat wall then all about the chamber. This is kind of like the turbo muffler example that deverts waves against a wall rather then back into themselves but instead then into fibreglass packing rather then all about the chamber. This on page 129 is what he refers to as a near-zero loss system.

So then I believe what you read describes the properties of A resonator bouncing waves all about the chamber but not dirrectly into themselves wich by the way has been done by the auto manufacturers on stock automobiles for many years. What I do find most interesting thou is the shape of the resonator that david vizard suggests that of its design helps the waves to not bounce back into themselves as much as does the designs done by the auto manufacturers. This improved shape was such a good idea to me that on my fiero where space is limited I built a custom resonator with two inlets and two outlets. Each bank of the engine is joined together then the two outlets go to custom little right angle mufflers then to stock appearing exhaust tips. Motorcycle resonators having two inlets and two outlets also influenced my design as is done on a v-45 magna.

If you find an example of a performance setup that purposly crashes exhaust waves into each other please let me know.

Also, I didn't think kids would have any intrest in this site so I would like to hear from the technical kids out there. Mini bikes and powered skateboards can be hopped up to, so I suppose they may be out there.

Matt.

[rookie]

Matt,
I was being facetious about the kids.

On David’s system, he is actually using the chamber to exhaust the engine so it thinks it is not running an exhaust system at all, this is why you need a chamber of a given size based on engine cubic inches and the pipe has to dump, not merge into the chamber.
Then the exhaust system only has to exhaust the chamber, so the mufflers need to flow a certain amount of cfm based on your engines horsepower so it does not create a restriction, most turbo mufflers rarely flow 400 cfm.

With David’s system, reduced sound is just a plus; its main design was no power loss.

As for mini bikes we use to spray wd40 on the clutch to make it rev higher before it took off, although it was probably slower, we thought it was the fastest thing around, it’s amazing how seat of the pants feel will fool you more times than not.

Skatboards,
Me and skateboards, ends with, that's gona leave a mark.