Time reversal acoustics applied to rooms of various reverberation times

Abstract

Time Reversal (TR) is a technique that may be used to focus an acoustic signal at a particular point in space. While many variables contribute to the quality of TR focusing of sound in a particular room, the most important have been shown to be the number of sound sources, signal bandwidth, and absorption properties of the medium as noted by Ribay, de Rosny, and Fink [J. Acoust. Soc. Am. 117(5), 2866-2872 (2005)]. However, the effect of room size on TR focusing has not been explored. Using the image source method algorithm proposed by Allen and Berkley [J. Acoust. Soc. Am. 65(4), 943-950 (1979)], TR focusing was simulated in a variety of rooms with different absorption and volume properties. Experiments are also conducted in a couple rooms to verify the simulations. The peak focal amplitude, the temporal focus quality, and the spatial focus clarity are defined and calculated for each simulation. The results are used to determine the effects of absorption and room volume on TR. Less absorption increases the amplitude of the focusing and spatial clarity while decreasing temporal quality. Dissimilarly, larger volumes decrease focal amplitude and spatial clarity while increasing temporal quality. V

Condiciones acústicas en las aulas de clase: Una revisión de la literatura

“…En el estudio del tiempo de reverberación, la norma internacional BB93 establece que se debe definir un RTmid, que constituye un valor resultante del promedio de los tiempos de reverberación calculados en 500 Hz, 1 kHz y 2 kHz [11]. [12] aplicaron el método de fuente de imagen para simular un grupo de habitaciones con características de absorción y volumen distintas, encontrando que a menor absorción disminuye la calidad temporal mientras aumenta la amplitud focal máxima y la claridad de enfoque, y que este mismo efecto se tiene a mayor volumen. Los métodos y criterios para la estimación del tiempo de reverberación permiten su identificación y evaluación de tal forma que sea posible proponer medidas útiles para mejorar las condiciones de las aulas de clase.…”

The methods for the formation of optimal acoustic conditions for the transmission of speech content in small rooms

“…Постановка задачи. Основним завданням у роботі є розгляд методів корекції акустичних властивостей спеціальних приміщень малих обсягів з метою підвищення якості передачі мовного контенту [1][2][3][4]8]. Під час проведення акустичної експертизи необхідно вирішити низку завдань: 1) визначити роль та послідовність проведення етапів акустичної експертизи з урахуванням особливостей приміщень;…”

A comparison of impulse response modification techniques for time reversal with application to crack detection

“…Four primary metrics are used to quantify the relative merits of the focal signals generated by each of these impulse response modification techniques, three of which were introduced by Denison and Anderson. 41 The processing methods of deconvolution, one-bit, clipping, and decay compensation TR each result in changing more than just peak focal amplitude, and can often result in significant drawbacks along with their benefits. By applying quantitative measures to the focal signal, some of these drawbacks are identified, especially as related to adjustments in the threshold value used in each case.…”

“…where M x and M y are the number of spatial locations sampled in the x and y directions, respectively. 40,41 The velocity at each point, Aðm x ; m y ; tÞ, is measured as the TR process is repeated while the SLDV records the velocity at M x  M y spatial points both at and surrounding the focal location. At t 0 , n s represents how significant the peak amplitude is to the rest of the amplitude over the entire scan area.…”