# Helmholtz for exhaust drone

Copper - Posts: 54
Joined: June 16, 2009
Location: Florida, United States
Posted: April 23, 2018 at 3:56 PM / IP Logged
I’m looking to do a “dead-end” resonator pipe as an add-on to my custom exhaust. Basically a 1/4 wave or Helmholtz resonator to cancel out interior drone.
My car resonates at 129hz at highway speeds (75-90mph).
My math is basically taking the speed of sound at 210° And dividing by 129Hz. Then dividing that by 4 (1/4 wave), then multiply by 12 for inches. I came up with 30”.
I’m planning on teeing off my exhaust pipe just prior to the muffler at about 25-30° and doing a soft bend in the form of a J or U because of space constraints. End is capped.
Theory says the dead-end pipe will receive the 129Hz and return 1/4 wave pulses to cancel the sound.
It’s been done, I’m just unsure of a few things:
- can the pipe come off at that angle or does it have to be perpendicular to the other pipe?
- is it okay to have that much of a bend as long as its “sweeping” and not drastic?
I know this isn’t typical stuff for this site, but you guys are smart!
Thanks!

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