Has anybody here made a Helmholtz chamber resonator to cure their exhaust drone?

In the picture, the resonator is the larger diameter can. The design of the resonator chamber (or can) is kinda involved. They are designed to cancel a certain frequency....in my case, right around 117hz. The construction has 4 variables, The diameter opening of the spout, the length of the spout, the diameter of the can, and length. (really just volume)

This site has a nice description and a design calculator. Wilhelm Racing - Killing Drone

 

I have not, but i know they work. Take a look at the 2011-2020 5.0 f150 mufflers. Ive done a good bit of research on them, alot of folks seem to have had success with just a smallish pipe cut the the right length

 

A single diameter pipe, coming out at a 90, or with an 90 elbow, is called a 1/4 wave pipe. They work as well, just over a more narrow range.

 

Heres what i was looking for


Is this a similar principle?

Thank you for the link, I will jump on the bandwagon and see what frequency my drone is at tomorrow.

Drone is essentially vibrations in the pipe getting out of control right?

 

Just look at your tachometer at which the drone is the loudest. Mine happens to be 1750.

I gather the formula is. (1750/60) x 4 (the number of combustion events/rev) = 116.9hz

So if you wanted to build a 1/4wave pipe, it would be 116.9/4...or roughly 29 3/16".

Drone is, from my research, the exhaust gases vibrating the pipe at a specific frequency.

 

That reminds me of Honda's ATAC system which is used to broaden the powerband of a 2-stroke engine in conjunction with a tuned pipe.

 

mine is right sround 1750 as well
i will report back frequency tomorrow
its a straight piped stock exhaust system with stock tail no tip

 

I'm very similar to yours, but with a Dynomax 4" round..in the stock location.

I'm building one, I'll let you know how it works.

 

Mine peaks 99 and 125 hz within 1 db of each other on crappy cell app
One shows -25 the other -26.
this is between 1550-1650 rpm or right around 57-60 mph in overdrive. Its not really loud in comparison to some cummins trucks ive owned.

 

I bet it will work - I just installed one for an intake application on a gas motor and it made a nice difference.

 

When building a 1/4 wavelength resonator, I think you may want to convert the target frequency to wavelength.

So for the target frequency of 117 Hz (from your example above), the wavelength in a standard atmosphere would be 1116 (ft/sec) / 117 Hz = 9.54 ft. A quarter of this turns out to be around 29", which is close to what you got above. Not sure if that is coincidence or if there is some science/math there that I'm not thinking of. However, the exhaust in the tailpipe is quite a bit warmer than the 59 deg F of the standard atmosphere so the local speed of sound would be higher. That may drive you to a longer resonator.....

 

Yeah, the temp of the air in the chamber is 1) hard to measure, and 2) changes. It's going to be above ambient that's for sure. The linked calculator has 3 different temp variables.

 

Excuse my ignorance, are the pipes open to the exhaust, or closed off? I thought they were closed off

 

Closed. The sound wave reflects off the back of the tube in a 1/4 wave pipe. The Helmholtz must use a pressure differential..or some rocket scientist thing.

 

After a lengthy drive home, I charted the drone at 160hz. That does not match my math above,