Exhaust silencer

Build a silencer from chambers, perforated tubes, rock-wool sections and resonators. See its transmission loss against the engine's firing harmonics and its back pressure — at the real exhaust temperature.

FREE · NO SIGN-UP v1.0.0 · verified against 16 reference cases

INPUTmm · °C · kg/s

1 · Engine from its datasheet

Speed [rpm] Cylinders

Cycle Exhaust temperature [°C] at the silencer

Exhaust mass flow ṁ [kg/s] Allowed back pressure [kPa] engine maker's limit

2 · Pipe Pipe inside diameter d [mm] inlet, connecting tubes and perforated tubes

3 · Silencer inlet → outlet

Side branches on a pipe or a chamber, x from the inlet

Add an element

Pipes, plain chambers and the tail pipe are free. Perforated, absorptive and resonator elements are Pro+.

4 · Engine exhaust spectrum optional · L_w per octave, dB

31.5 Hz63 Hz125 Hz250 Hz500 Hz1000 Hz2000 Hz4000 Hz

Distance for the sound pressure level [m]

Example values, not a real unit. Results update as you type.

SECTION · TO SCALE

TRANSMISSION LOSS · dB

TL · 1F 75 Hz10.3 dB

TL · 2F18.3 dB

TL · 1 kHz OCTAVE28.2 dB

BACK PRESSURE460 Pa

Check the fill's temperature rating at 480 °C and keep it behind glass cloth or stainless mesh so the gas does not carry fibres out.
The fill model (Delany–Bazley, Miki) is fitted for 0.01 < ρf/σ < 1; here ρf/σ runs from 0.0002 to 0.061, so the fill's result at the ends of the range is extrapolated.

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HOW IT'S CALCULATED · WITH YOUR NUMBERS

Step by step, with your numbers

01
Equilibrium████ ██ ███████ · ██████ = ██.██
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Reactions████ ██ ███████ · ██████ = ██.██
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Shear force████ ██ ███████ · ██████ = ██.██
04
Bending moment████ ██ ███████ · ██████ = ██.██
05
Deflection████ ██ ███████ · ██████ = ██.██
06
Stress████ ██ ███████ · ██████ = ██.██

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References: Munjal, Acoustics of Ducts and Mufflers (2014) — transfer matrices with mean flow; Sullivan & Crocker (1978) perforates; Delany & Bazley (1970) and Miki (1990) fibrous fill; Morse & Ingard (1968) lined ducts; Levine & Schwinger (1948) radiation.

ASSUMPTIONS & LIMITS

Plane waves: one-dimensional acoustics in every element. Valid below the plane-wave limit shown; above it chambers carry cross-modes the model does not see.
Transmission loss is for an anechoic outlet and a wave arriving from the inlet. Insertion loss also depends on the engine's own source impedance, which is not known here; it is shown for an anechoic source and an open tail pipe.
Mean flow is included in pipes and chambers (convected waves) and in the perforates' resistance; the perforated and absorptive sections otherwise use stationary-medium wave equations.
Noise radiated through the shell (breakout), flow-generated noise at perforations and edges, and temperature gradients along the silencer are not included.
The fill is a locally reacting wall; its datasheet flow resistivity at 20 °C is scaled to the gas viscosity.
Exhaust gas treated as air at its temperature (enter γ if you have the gas analysis).

DISCLAIMER · For education and preliminary sizing only. Results must be reviewed by a qualified engineer before use in design.

BEYOND PLANE WAVES

Shell breakout, 3D modes and a measured spectrum to match — we take the silencer into a full acoustic FE study.

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