Acoustical Study of a Lossy Gradient-Based Sonic Crystal Using Acoustic Beamforming

Sonic crystals (SCs) are unique periodic structures designed to attenuate acoustic waves in tunable frequency bands known as bandgaps. Though previous works on conventional uniform SCs show good insertion loss (IL) inside the bandgaps, this work is focused on widening their bandgaps and achieving better IL inside the bandgaps by using a gradient-based sonic crystal (GBSC). The GBSC applies property gradient to the conventional SC array by varying its basic properties, i.e., the distance between the scatterers/resonators (lattice constant), and resonator dimensions between the columns and hence the name GBSC. The design of the GBSC is backed by the results of acoustic beamforming experiments conducted over the uniform SCs of hollow scatterers and Helmholtz resonators (HRs) having two-dimensional (2D) periodicity prepared by using Polyvinyl chloride (PVC) pipes without any property gradient and their respective 2D finite element (FE) studies. The experimental and FE simulation results of the uniform SCs were found to be in good agreement and therefore, the GBSC was modeled and analyzed using FE method considering the viscothermal losses inside the resonators. The results indicated that the property gradient improves both Bragg scattering and Helmholtz resonance compared to that of the uniform SCs and therefore, the GBSC exhibits wider attenuation gaps and higher attenuation levels. An array of 30 microphones was used to conduct acoustic beamforming experiments on the uniform SCs. Beamforming was found to be an advanced and fast method to perform quick measurements on the SCs.

Acoustical study on spectral characteristics of teachers’ English vocalization

With the increase of English teaching courses, the specific vocal characteristics of teachers in English teaching are studied and used as the basic data for the design of teachers’ spatial acoustics. In order to study this problem, three different English voice materials were read in a anechoic room under three sound intensity levels: large, medium and small, respectively, so as to analyse the equivalent continuous sound pressure level (SPL) and frequency characteristic curves of male and female teachers at 0.3m. In the low frequency band, the SPL increases as the frequency increases. In the mid-frequency band, the SPL reaches the first peak, then decreases briefly as the frequency increases, then increases again to the second peak, and then decreases again briefly as the frequency increases. Then increase again to the third peak. In the high frequency band, the SPL decreases as the frequency increases.

Signal Enhancement of Acoustic Signature of Lutjanidae Family Species in Indian Waters

The present study is to carry out the enhancement of the acoustic signals of Lutjanidae species often found in abundance, in tropic shallow waters. Since most of the studies on Lutjanidae is about its physical structure both internal and external, and its population in sea ie., catches in tons per year. This research work is the first attempt on the acoustical study of Lutjanidae family species call signal. Five species of Lutjanidae family are considered for this study which includes L. analis, L. apodus, L. synagris, L. griseus, and L. jocu). The earlier literature which studied the acoustic toning of marine species vocalization using empirical mode decomposition method [1]. Here in this research, (i) signals with background noise and (ii) enhanced signals are considered for comparison. The enhancement of acoustic signals of Lutjanidae family species is useful as acoustic reference for those working in the field of biological signal processing. The enhancement of the signal is achieved by the logical applications and applying Short Time Fourier Transform (STFT), inverse STFT. From the above two cases considered, the frequency range of 50 to 2500 Hz approximately is clearly noticed in the spectrogram, power spectral density and it shows the frequency of all species looks similar. By listening the sound produced by the species, it is observed to be of type knocking sound.