Ive got a question about building a side branch resonator / 1/4 wave resonator / Hemholtz pipe.
Does one tune for the in Cabin resonance frequency or the actual engine revolution per minute frequency when building one of these?
I cant find a definitive answer on the web. Everyones Math is either or.
Math required for in cabin drone...just put this in a spreadsheet program. =((1100/135)/4)*12
Now you will have the length of pipe required in inches.
Parts of the formula that change.
1100 = is the speed of sound. *This should be calculated using the temp inside the 1/4 wave resonator because temperature affects the speed of sound.
135 = frequency in Hz of the drone in cabin
From what i've learned
* The diameter of the side branch should be equal to the diameter of the main pipe *
* Heat affects the air speed in the wave resonator *
* build it angled so gravity can expel water if collected *
* Corsa exhausts are expensive just to accomplish what $10 in pipe can do.
* Magnaflow recommends tuning a 1/4 wave resonator to the frequency of cabin drone.
* Filling the pipe with some rag wool or fiberglass packing will help remove high frequency as well.
Examples of these 1/4 wave resonators ....
So while i don't have a drone problem yet, i'm anticipating i will in the very near future as i'm building a custom exhaust. Others also might have drone issues or just want to remove certain exhaust notes.
So basically what these do is the drone sound travels down the exhaust, enters the 1/4 wave resonator pipe and bounces off the sealed end flipping the phase of the sound wave. When the sound wave crashes back into the sound wave that isn't out of phase they cancel each other. No exhaust pressure should enter the pipe because its capped at the end. Exhaust pressure follows the path of least resistance so performance isn't affected.
