A possible way to control nonlinear interactions in non dispersive sound waves is to introduce additional absorption of a certain frequency component. It has been shown that selective absorption of the second harmonic of an incident sinusoidal wave results in less damping of the fundamental frequency signal. In an earlier presentation this effect has been investigated for strongly nonlinear plane waves containing shocks. It has been demonstrated that second harmonic selective absorption does not prevent shock formation. Compared to nonlinear propagation in medium without absorption, it results in specific waveform distortion, less amplitude of the shock, and correspondingly less nonlinear attenuation. Here, high intensity acoustic beams, either focused or unfocused, in selective absorption medium are considered. KZK equation in a frequency domain with additional absorption of the second harmonic is simulated numerically for various focusing gains, source amplitudes, and medium absorption. A modified spectral approach that enables to model nonlinear waves, including shocks, with a relatively few number of harmonics N 30 is used. The effect of selective absorption on waveform distortion, shock front formation and structure, harmonic amplitudes, acoustic energy absorption, and amplification factor in focused beams is discussed.
AVA initial attraction to the recently completed building designed by Architects was the prospect of increasing the visibility and perceived transparency of their work. Studios and open plan work zones are arranged adjacent to or facing the public footpath in view of passers-by. The fit out is textured and engaging; teamed with translucent twin walls to create offices and meeting spaces, and exposing much of the raw base building structure. The technical aspects were complex, with the spaces required to accommodate a diverse range of organisational activities and as such any acoustic treatment would have to weave through the building seamlessly. Without a traditional suspended ceiling, AVA acoustic consultants asked manufacturer to develop a solution to create linear white acoustic Baffle Beams, direct fixed between the concrete ceiling bays that once installed blended seamless into the architect’s aesthetic vision whilst controlling the unwanted reverberation. Manufacturer made its acoustic Baffle Beams in factory from high density non-combustible glass wool core wrapped in a 2 ply glass mat composite facing that is cut and folded to give a clean frame-less look. The beams are supplied in standard white, black, grey and wood-grain. Other options include fabric wrapped and PU wood-print veneers. Baffle Beams are available in a wide range of standard and custom sizes.