Hambric Vibroacoustic Demonstrators

A baffled circular piston within a rigid baffle (or wall) generates outwardly propagating pressure waves that resemble those of a simple monopole source. In this demo I'm plotting the radiated sound power and efficiency over frequency on the left, and the far-field sound pressure and intensity distributions at the current frequency on the right (the current frequency is chosen with the slider bar and denoted on the radiated power curve).

We rarely quantify a radiating source by a pressure at a specific location. Instead, we examine total radiated sound power, integrated over a closed surface, usually in the far-field. The sound power is commonly normalized by the surface average of the square of the source velocity (the resistance) and often normalized further by the radiating surface area and acoustic plane wave impedance ρc, which is the radiation efficiency. Here, I'm plotting total radiated sound power transfer function (power/square of source velocity) on the left y-axis and the radiation efficiency σ on the right y axis.

It's also common to plot the radiation efficiency against dimensionless frequency, or ka. k is the acoustic wavenumber 2πf/c and a is the circular piston radius. A ka of 2π corresponds to one full wavelength over the dimension a.

In this demo you can change frequency, the radius of the piston, and the acoustic medium. I am fixing the bottom x axis (Frequency) and the right y axis of the radiated power/efficiency plot on the left. Watch the total power y axis values and the ka axis values change as you adjust the piston radius and the acoustic medium.

Change frequency (using the slider or by clicking on the radiation efficiency plot), piston radius, or acoustic medium and observe the effects on the radiated pressure and intensity fields. The higher the frequency, the shorter the wavelengths and the more 'lobes' there are in the directivity patterns. You can also animate the pressure distribution (the intensities are fixed over time so won't animate).