Abstract
One enduring challenge for controlling high frequency sound in local active noise control (ANC) systems is to obtain the acoustic signal at the specific location to be controlled. In some applications such as in ANC headrest systems, it is not practical to install error microphones in a person’s ears to provide the user a quiet or optimally acoustically controlled environment. Many virtual error sensing approaches have been proposed to estimate the acoustic signal remotely with the current state-of-the-art method using an array of four microphones and a head tracking system to yield sound reduction up to 1 kHz for a single sound source. In the work reported in this paper, a novel approach of incorporating remote acoustic sensing using a laser Doppler vibrometer into an ANC headrest system is investigated. In this “virtual ANC headphone” system, a lightweight retro-reflective membrane pick-up is mounted in each synthetic ear of a head and torso simulator to determine the sound in the ear in real-time with minimal invasiveness. The membrane design and the effects of its location on the system performance are explored, the noise spectra in the ears without and with ANC for a variety of relevant primary sound fields are reported, and the performance of the system during head movements is demonstrated. The test results show that at least 10 dB sound attenuation can be realised in the ears over an extended frequency range (from 500 Hz to 6 kHz) under a complex sound field and for several common types of synthesised environmental noise, even in the presence of head motion.
Highlights
One enduring challenge for controlling high frequency sound in local active noise control (ANC) systems is to obtain the acoustic signal at the specific location to be controlled
ANC headphones are commonly used by passengers and aircrew in aircrafts, where the cabin noise during long haul flights is known to be detrimental to health and wellbeing[3,8]
Solutions that can deliver sound reduction performance on par with that of earmuffs-based ANC headphones, but without the need to wear anything, would have value in many scenarios such as for machinery or equipment operators, for drivers of vehicles and for people working in open plan offices
Summary
One enduring challenge for controlling high frequency sound in local active noise control (ANC) systems is to obtain the acoustic signal at the specific location to be controlled In some applications such as in ANC headrest systems, it is not practical to install error microphones in a person’s ears to provide the user a quiet or optimally acoustically controlled environment. Local ANC systems aim to reduce the sound only at specific (local) positions, often around a listener’s ears, with the most common example being increasingly ubiquitous personal ANC headphones In such solutions, the cushion and shell structure of the earcups provide passive sound attenuation in the mid to high frequency range (generally above 1 kHz) for auditory c omfort[6]. The fundamental principle of and motivation for an ANC headrest system is not to impose any disturbance on the user, whereas all of these alternative devices do
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