Low-loss ultrasound transmission through glass assisted by resonance.

We have investigated transmission of ultrasound signals from a speaker in air through a 400 µm thick borosilicate glass plate, similar to those found in consumer electronics products such as mobile phones and tablets. In order to enhance transmission, we took advantage of resonances in the glass plate and a cavity, which is placed between the glass and the microphone. The results show that it is possible to achieve transmission of a signal with bandwidth of approximately 5 kHz with less than -10 dB attenuation, and only -2 dB attenuation at the resonance peak frequency. With more optimized assembly the attenuation can be further reduced. Finite element simulations and analytical considerations show that there are two main resonance peaks, attributed to the glass resonance and cavity resonance, respectively. The geometry can be tuned to exploit the synergy of these two resonances in order to tailor the peak frequency, the bandwidth and to optimize transmission.

Statistical tool to detect small hearing threshold shifts.

OBJECTIVE: The aim of this study is to present a new tool that can be used in the prevention of noise-induced hearing loss. Even in most countries where noise levels are well regulated, many workers are still exposed to high levels of noise and suffer from permanent threshold shifts. It is necessary to develop a new strategy to prevent such damage. METHOD: A statistical process control (SPC) scheme is presented that is able to detect both large and small hearing threshold shifts. Monte Carlo simulations were used to assess the performance of this hearing monitoring scheme. Different hearing threshold shifts were simulated to evaluate the performance of a variety of hearing development scenarios. RESULTS: It is possible to detect hearing threshold shifts smaller than the standard deviation of the hearing tests performed. This means that permanent hearing threshold shifts smaller than 5 dB can be detected and acted on. Outliers can also be automatically detected and treated, increasing the robustness of the monitoring scheme. CONCLUSION: The proposed statistical framework can be used as an early warning indicator of noise-induced hearing loss with the aim of improving workers' safety. Individual counteractions can be implemented, reducing the risk of further damage.

The efficacy of sound regulations on the listening levels of pop concerts.

This analysis of new and previously collected data was done to validate the efficacy of recommendations for limits regarding sound exposure levels at live pop concerts. After the World Health Organization (WHO) recommended limiting the sound levels at such concerts to avoid noise induced hearing damage among the audience, the actual levels at concerts where these recommendations are observed, have stabilized around 100 dBA. This is a level that is considered acceptable by WHO. At concerts where there are no limitations, however, the sound levels in the audience area are still increasing far beyond safe limits and thus the exposure may represent a serious threat to people's hearing.