Read about acoustics

An analysis of 7-year long recordings of sea noise made at the CTBT underwater station off Cape Leeuwin in Western Australia has shown that Antarctica is the major source of low-frequency noise in the Southern Ocean and southern parts of the Indian Ocean. Two different kinds of signals arriving at the Cape Leeuwin station from Eastern Antarctica can generally be distinguished. The most amazing of them are iceberg songs, which are very-low-frequency, from about 3 Hz to 10 Hz multi-harmonic signals lasting sometimes for several hours and which are supposed to be produced by vibrations of the iceberg plate after collision with the seafloor, ice shelf or another iceberg.

Many animals, from grasshoppers in a small field to baleen whales in the open ocean, use acoustic signals to find or attract conspecifics and potential mates, and the farther away you can make yourself heard, the better the odds are for finding mates and transmitting your genes into the next generation. Other animals, such as some primates, birds and meerkats, live in groups where most animals can forage while a few individuals keep watch for predators and raise the alarm in case of danger. Obviously, the distance that these calls are heard plays an important role in group organization and likely places an upper boundary on the dispersion of the group, decreasing foraging competition within the group if alarm calls travel farther and group is more dispersed.

Our objectives for this project include an in depth analysis of the properties of stringed instruments. We strived to understand how different stringed instruments function individually, and how instruments differ in their sound and function. Stringed instruments create the sound in three phases: (i) the source or string, (ii) the medium or body and (iii) the interface, which is the oscillation of the air around the body. These elements interact to create the sound we hear in each instrument.

Students had to ensure the instruments played notes of the Western musical scale and that the timbres of the instruments allowed them to be played together in an ensemble. Finally, the students were required to compose original music for ensembles of these instruments and play them in a public concert in the college’s concert hall.

Acoustic Tim-Reversal-Mirrors (TRM) are, among many other applications, powerful instruments to detect defects in solid materials. Their ability to focus automatically on cracks makes them the most performant ultrasonic devices in this domain. In this paper, we prove that a simultaneous focalization of the different kinds of waves in the solid (transverse and longitudinal waves) can be obtained with such Time-Reversal-Mirrors.