How to cancel drone with a Quarter Wave Tube

[Supermoto]

oh perfect, btw there is a company that makes them premade incase the shop would only want to weld one on for you.

http://synapseengineering.com/synapseusa/products/nodrone.html

That is actually extremely helpful, thats a gem right there. I have a lot to think about now, but I am glad and end to the drone is in sight.

 

[The Dude]

Rampage does excellent work!

So with the quarter length installed is the drone gone and wife happy?

He and his wife both do fantastic work. I may have him redo the tail end in titanium, just because The drone is gone, but it's still a 3.5 inch exhaust, lmao. It's dailyable for sure. Super quiet idle.

 

[Supermoto]

Something I am curious about, how wide of a band does the QWT help with drone? My GTI drones exactly from 2.5k to 3.5k rpm, so I assume my calculations should be based on 3k rpm.

 

[El_bigote_AJ]

Something I am curious about, how wide of a band does the QWT help with drone? My GTI drones exactly from 2.5k to 3.5k rpm, so I assume my calculations should be based on 3k rpm.

You’re supposed to build it based around the peak of the sound, and it’s supposed affect that full window since is should be a different frequency still at 2500 vs 3500 but still in the same realm of what’s causing the boom sound

 

[Supermoto]

You’re supposed to build it based around the peak of the sound, and it’s supposed affect that full window since is should be a different frequency still at 2500 vs 3500 but still in the same realm of what’s causing the boom sound

Now that I think about it that makes sense. Instead of basing the calculations on RPM I will use a spectrum analyzer to see what frequency is strongest in that range.

 

[The Dude]

Now that I think about it that makes sense. Instead of basing the calculations on RPM I will use a spectrum analyzer to see what frequency is strongest in that range.

Either way accomplishes the same thing, but with a spectrum analyzer, you skip the extra math, and you can visually verify the peak.

 

[The Dude]

This was before the qwt, but it gives you an idea of the tone @GTI Jake

 

[Supermoto]

Alright so I took an audio recording of the drone and analyzed it in audacity. I need advice. The loudest freq that I get is 90hz, but its right at the beginning of the drone range. Should I base my QWT off this frequency since its the loudest, or should I use a frequency from the middle of the range to cancel around both sides (idk if thats how it works).

Graph:

 

[shovelhd]

Based on that graph, I'd target 100Hz.

 

[Faceman]

When I design speakers, calculate the notch filter for the center of the peak.

If you want to get really deep into acoustic science and quarter wave research: http://www.quarter-wave.com/

 

[The Dude]

Alright so I took an audio recording of the drone and analyzed it in audacity. I need advice. The loudest freq that I get is 90hz, but its right at the beginning of the drone range. Should I base my QWT off this frequency since its the loudest, or should I use a frequency from the middle of the range to cancel around both sides (idk if thats how it works).

Graph:
View attachment 174765

I agree with shovel. Target 100 hz, it'll still disrupt above and below. Thats right around what, maybe 2700 rpm?

 

[Supermoto]

Based on that graph, I'd target 100Hz.

Cool, thats what I was thinking. Im glad to have some progress with this exhaust, the drone is pretty bad.

When I design speakers, calculate the notch filter for the center of the peak.

If you want to get really deep into acoustic science and quarter wave research: http://www.quarter-wave.com/

I will take a look. I am not familiar with what a notch filter is, but will do plenty of research and figure it out.

I agree with shovel. Target 100 hz, it'll still disrupt above and below. Thats right around what, maybe 2700 rpm?

Thank you for the response, I will work on building a QWT that targets 100hz. The range of drone I experience goes from 90hz to 125hz, or roughly 2500 to 3500 rpm give or take a few hundred. When analyzing it with an app in the car as I drove I got a peak around 103-107, but I trust the recording in audacity more.

 

[shovelhd]

The reason I suggested 100Hz is that the peak you're seeing doesn't vary by more than 3dB (+/- 1.5dB), and it's a nice round number. If you can get -10dB out of this solution, I'd call that a win.

The best way to eliminate drone is to never have it in the first place.

 

[Supermoto]

The reason I suggested 100Hz is that the peak you're seeing doesn't vary by more than 3dB (+/- 1.5dB), and it's a nice round number. If you can get -10dB out of this solution, I'd call that a win.

The best way to eliminate drone is to never have it in the first place.

I wish I could just not have it to begin with. Not sure how to acheive that.

 

[The Dude]

I wish I could just not have it to begin with. Not sure how to acheive that.

keep the stock exhaust