Acoustic Binary Amplitude Diffuser (BAD) panel scattering скачать в хорошем качестве

Acoustic Binary Amplitude Diffuser (BAD) panel scattering

Time domain #acoustics #FDTD animations of a Binary Amplitude Diffuser (BAD) panel (3 x N = 7 maximum length sequence). Try modelling this diffuser (or other drawn objects) for yourself: https://sparky-10.github.io/code/fdtd-anim... Originally posted on Twitter: https://twitter.com/sparky_10/status/16968... Web page version: https://sparky-10.github.io/animations/bad... More often modelled in the frequency domain, this shows an incident (pseudo) plane wave sine pulse at 0.5, 1, 3, and 7 x f0, where f0 is the design frequency of a Schroeder diffuser from a previous video here:    • Acoustic Schroeder diffuser scattering ani...  . In each case a plane surface of the same dimensions is included for comparison, plus there's a zoomed in example and an analogue slits array. At low frequency (0.5 x f0), scattering from the BAD panel is effectively an attenuated version of the equivalent plane surface. This is because it's overall dimensions are small compared to wavelength. The incident wavefront essentially sees an average absorption coefficient across the panel. At mid frequency (1 x f0 and 3 x f0) wavelength becomes comparable to diffuser panel spacing. The reflected sound comprises an attenuated specular reflection (back to the source, think 'like a mirror'), with spatial and temporal spread in scattered sound to the sides due to manipulation of the reflected amplitude. Note: although offering less diffusive performance, BAD panels can be made much thinner than an equivalent Schroeder diffuser. With increasing frequency the specular component narrows. A BAD panel is designed to scatter equal energy in to the grating lobes (directions where scattering is emphasised due to the repeating diffuser pattern), though at a lower level than the reflection in the specular direction, which is an inherent result of the diffuser altering the reflected sound amplitude and not the phase (like a Schroeder diffuser does). An interesting analagous example is shown at this frequency, comparing the BAD panel to the equivalent transmission through an array of slits in a plane surface. Because we are considering transmission, where the BAD panel has reflecting and absorbing elements the array of slits has a hole and a surface respectively. One advantage of looking at the surface in this way is that it is slightly easier to distinguish the difference between incident and initial reflected sound (for the BAD panel it is their interference pattern that is observerd). At high frequency (7 x f0, the same as the Schroeder diffuser 'flat plate' frequency) the BAD panel response becomes more specular still. However, the BAD does not suffer from the same 'flat plate' frequency as a Schroeder diffuser, and some diffusive efficacy remains.