Speaker: Sound Generation and Propagation in a Pipe

Speaker Sound Generation and Propagation Inside a Pipe CFD Simulation, ANSYS Fluent

Description

Sound generation in a speaker involves several sequential steps. An incoming electrical signal is sent to a coil, generating a fluctuating magnetic field that interacts with a permanent magnet's field, causing the coil to move rapidly back and forth. This coil is attached to a diaphragm, which displaces the surrounding air as it moves — pressurizing air as it moves forward and expanding it as it moves backward — generating pressure waves. These waves propagate through the air, and when they fall within the frequency range of human hearing, they are perceived as sound. The resulting sound's frequency matches that of the electrical input driving the coil, while its amplitude (loudness) depends on how far the diaphragm physically displaces.

This project models a speaker diaphragm with a maximum displacement of 2 mm, vibrating in a sinusoidal pattern at 500 Hz. The diaphragm's resulting velocity profile was derived from this displacement function and implemented as a boundary condition through a custom UDF hooked into the dynamic mesh solver.

Four receiver points were defined within the domain to track acoustic results at increasing distances from the speaker. The geometry was designed in SpaceClaim and meshed in ANSYS Meshing using a structured mesh totaling 687,500 elements.

Methodology

Turbulence was modeled using the standard k-ε model. Diaphragm motion was captured using dynamic mesh: at each time step, the solver calculates the diaphragm's updated position and remeshes the surrounding domain using smoothing and layering methods to accommodate the moving boundary. The simulation ran as unsteady, using a time step of 0.001 s over 1000 total time steps.

Conclusion

Results include pressure and turbulence kinetic energy contours across the domain's central plane, along with an animation showing the evolving pressure field over time. Static pressure was extracted at each of the four receiver points, and the resulting Sound Pressure Level plots confirm that the generated sound's frequency matches the diaphragm's vibration frequency exactly at 500 Hz.

The results also show a clear amplitude trend: as distance from the speaker increases across receivers 1 through 4, the amplitude of the pressure fluctuations — and correspondingly, the loudness of the sound — steadily decreases, consistent with the expected attenuation of sound pressure as it propagates downstream through the domain.