Exhaust Drone removal for ANY exhaust

[midnightsun]

US special forces for instance use noise cancellation on "silent" vehicles. So how do we apply this to a car exhaust? We flip the sound out of phase and have it crash back into its self.
How do we do that? Easiest is building a side branch resonator / 1/4 wave resonator.

Note * The diameter of the side branch should be equal to the diameter of the main pipe *

First we find the frequency of the drone. Using your phone you can download a Spectrum Analyzer app. Then while driving around record the frequency the drone is being produced at and the RPM. It will be a fairly low frequency say 135HZ and below.
Note * Some Cell phones have crappy mics so you might need a good mic to capture the correct frequency."

Picture below is just an example and not my Explorer.

Now that you have this data you can have an exhaust pipe chamber or chambers built that will cancel the frequencies that annoy you.

Pictures i found showing examples of this.

Muffler companies such as Corsa try to do this in the muffler will sometimes limited success and add a large cost.

So for about $70 you can have a muffler shop weld you in a side branch resonator chamber.

So some key points. Notice the 1/4 chambers are angled. This is because water can collect in them. You want the water to be easily removed by gravity.

 

[midnightsun]

I found a good post regarding the math for this being its an engine. http://www.performancetrucks.net/fo...xhaust-resonator-tube-eliminate-drone-489463/

If your local Exhaust installer has no idea what you are talking about, move on to one that does.

In its most basic form it would look like this in Excel. =((1100/135)/4)*12

Change 1100 with the speed of sound in feet.
Change the 135 with the frequency spike you record.

Some sites are saying record the RPM of the drone and then using the above sites math figure out the real drone frequency of the exhaust.
Which one is it? Is odd because lets say cabin drone is 130Hz (caused by resonance) but you are only turning 2000 rpm.
Calculating based on 2000RPM you get 100Hz not 130Hz.
These tube lengths are pretty drastic in length at that point 100Hz = 35 in & 130Hz = 27 in.

Math says our v6 should have a lower frequency at 2000rpm than a v8 because we have less cylinders 3 vs 4 per revolution soooooo....

 

[midnightsun]

More examples.

In this pic of the u bends only 1 opening on each side is actually open to the exhaust tube. The other is welded shut.

 

[midnightsun]

More write ups http://mkiv.supras.org.nz/articles/exhaust_drone.htm

 

[midnightsun]

So i found a calculator here http://ls1tech.com/forums/conversio...t-drone-engine-swaps-solved.html#post18138582
It needs to be modified for v6 engines.

 

[Forddealz]

How do you cancel the noise? Is there some kind of app for that? My friend on his BMW has some kind of exhaust installed, he calls them opening and closing the flaps. He can switch the noise on by pressing a button and then when we want to hear the noise he flips the button again.

 

[Odrapnew]

How do you cancel the noise? Is there some kind of app for that? My friend on his BMW has some kind of exhaust installed, he calls them opening and closing the flaps. He can switch the noise on by pressing a button and then when we want to hear the noise he flips the button again.

I'm sure there's a calculator out there to determine the proper design.

The noise is canceled by creating opposite sound waves in the exhaust. Kind of like walking backward on a moving walkway but with sound waves(that's the easiest to describe it I think). Sound waves are essentially peaks and valleys and this design is set up to create the inverse wave at a specific frequency, essentially canceling out the peaks and valleys so you eliminate the drone.

As for your friend with the BMW, sounds like he has cutouts in the exhaust to bypass the muffler(s) or resonators. Not the same as what's going on here.

 

[midnightsun]

You can find more info here including some useful calculators I created. Any updates will be on the below thread.
http://www.ecoboostperformanceforum.com/index.php/topic,6634.0.html