A group of researchers from the Center for Audio, Acoustics, and Vibration at the University of Technology in Sydney has developed a new type of virtual noise cancellation system. The active noise cancellation components in it are not located in the headphones, but the headrest of the chair.
Similar systems have been developed in the past, but their effectiveness was lower than the usual noise-canceling headphones. Current systems use microphones mounted in a specific position around the user’s head to pick up sounds. These settings are best suited for low-frequency noise down to 1 kHz. However, there is no passive control for high-frequency noise. And these frequencies include human speech, the range of which is from 4 to 6 kHz.
The Sydney team has developed a system that works with both high and low frequencies. The researchers used a remote acoustic sensing system based on a laser Doppler vibrometer (LDV) that measures non-contact vibrations over a wide range. They placed a tiny jewelry-sized reflective membrane in the ear of a human model as a sensor for the LDV.
The vibration amplitude and frequency are derived from the Doppler frequency shift of the reflected laser beam due to surface vibration.
The system has demonstrated noise reduction of several sources at once 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 an aircraft, the noise of the aircraft itself, and human speech.
The only limitation for mass production is the high cost as the system uses LDVs. However, the researchers hope that developments soon will help make the system more cost-effective.
Scientists will also have to work on the accuracy of the head tracking system, the material of the membrane placed in the ear, as well as on the safety of the invisible lasers used.
