A team of researchers from the Center for Audio, Acoustics and Vibration at Sydney University of Technology has developed a new type of virtual noise reduction system. In it components of active noise reduction are located not in earphones, and in a chair headrest. Details of the opening The team from Sydney has developed a system that works with both high and low frequencies. The researchers used a remote acoustic sounding system based on a laser Doppler vibrometer (LDV), which measures contactless vibrations over a wide range. They placed in the ear of a human model a tiny reflective membrane the size of a piece of jewelry as a sensor for LDV. How it works The amplitude and frequency of oscillations are extracted from the Doppler shift of the frequency of the reflected laser beam due to surface vibration.
The system demonstrated noise attenuation of several sources in the range up to 6 kHz with attenuation from 10 to 20 dB. The researchers tested their system on three typical types of noise: inside the plane, the noise of a flying plane and ordinary human speech. Commercial application The only limitation for mass production is the high cost, because the system uses LDV. However, researchers hope that developments in the near future will help make the system more cost-effective. Scientists also need to work on the accuracy of the head position tracking system, the membrane material placed in the ear, and the safety of the invisible lasers used. Previous developments Similar systems have been developed before, but their efficiency was lower than noise-absorbing headphones. Existing systems use microphones mounted in a specific position around the user’s head to pick up sounds. These units are best suited for low frequency noise up to 1 kHz. However, passive control for high-frequency noise is absent. And these frequencies include human speech, the range of which is from 4 to 6 kHz.