Exhaust Resonator Calculator

Inputs

View results
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)
1,111 mm
Pass

effective length minus end correction

Also computed

Actual tuning frequency (f_actual) Pass 121.2 Hz

Tuning error (df/f) Pass 0.9976 %

0.998% absolute error

Engine pulse frequency (n*Np/60) Pass 120 Hz

engine pulse is near target

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

Speed of sound used (c) 539.1 m/s

from 450 deg C gas

Effective acoustic length (Le) 1,123 mm

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.

Powered by MachineCalcs ↗