Exhaust Resonator Calculator

Inputs

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Use quarter-wave for a closed side branch/notch tube. Use Helmholtz for a cavity connected by one or more necks.
Drone, intake or duct tone frequency to target.
Hz
Average gas temperature at the resonator. The field stays in deg C so absolute temperature is not mis-converted by unit toggles.
deg C
Engine speed used only to compare pulse frequency against the target tone.
rpm
Dominant excitation order. For a four-stroke engine, a rough exhaust firing order is cylinders divided by two.
pulses/rev
Inside diameter of the side branch or Helmholtz neck.
mm
Acoustic end correction added to physical branch or neck length. Use measured or packaging-specific assumptions when possible.
mm
Physical closed-end side-branch length available in the vehicle or duct.
mm

Results

Default result
Edit inputs
Target physical length(L)
1,111mm
Pass

effective length minus end correction

Also computed

Actual tuning frequency(f_actual)Pass121.2Hz

Tuning error(df/f)Pass0.9976%

0.998% absolute error

Engine pulse frequency(n*Np/60)Pass120Hz

engine pulse is near target

RPM at target frequency(60f/Np)2,400rpm

Speed of sound used(c)539.1m/s

from 450 deg C gas

Effective acoustic length(Le)1,123mm

Method notes 4 notes
  • Quarter-wave mode: f = c/(4*Le).
  • Speed of sound uses c = sqrt(gamma*R*T) with dry-air constants and the entered average gas temperature.
  • End correction, flow, perforations, packaging, temperature gradient and nearby bends can move the real notch frequency.
  • This is a resonator tuning screen only. It does not predict muffler transmission loss, insertion loss, backpressure or durability.

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