Active control of outgoing noise fields in rooms

Current active noise control systems can cancel noises in a duct effectively. However, they are insufficient for suppressing complex noise fields in time-varying rooms. This paper develops an active noise control system that can cancel tonal noise fields produced by a primary source in a room. The problem of tonal noise field control is formulated as estimating and canceling the outgoing field on a sphere surrounding the primary source. The proposed system limits the energy of the primary source radiating out of the sphere, thereby creating a global quiet zone inside the room. In addition, it removes the need for online secondary path estimation with reduced influence on desired sound fields in the room. A method for estimating the outgoing field on a sphere is presented, together with a wave-domain algorithm for controlling the outgoing field. Simulations and hardware demonstrations show the proposed system can reduce tonal noise fields in a room and over a wide frequency range.This work is sponsored by the Australian Research Council (ARC) Discovery Projects funding schemes with project Nos. DP140103412 and DP180102375. F.M. is supported by the China Scholarship Council—Australian National University Joint Funding Program

Real-time separation of non-stationary sound fields on spheres

The sound field separation methods can separate the target field from the interfering noises, facilitating the study of the acoustic characteristics of the target source, which is placed in a noisy environment. However, most of the existing sound field separation methods are derived in the frequency-domain, thus are best suited for separating stationary sound fields. In this paper, a time-domain sound field separation method is developed that can separate the non-stationary sound field generated by the target source over a sphere in real-time. A spherical array sets up a boundary between the target source and the interfering sources, such that the outgoing field on the array is only generated by the target source. The proposed method decomposes the pressure and the radial particle velocity measured by the array into spherical harmonics coefficients, and recoveries the target outgoing field based on the time-domain relationship between the decomposition coefficients and the theoretically derived spatial filter responses. Simulations show the proposed method can separate non-stationary sound fields both in free field and room environments, and over a longer duration with small errors. The proposed method could serve as a foundation for developing future time-domain spatial sound field manipulation algorithms.Comment: 34 pages, 15 figure

Active control of outgoing noise fields in rooms

Active noise control is a strategy to suppress a noise by superimposing it with a carefully designed secondary noise. The strategy has been under research over the past half century with active noise control aided devices surging on the market over the last decade. However, up to now, the most successful applications of active noise control are still limited to the single channel systems, where noises propagate in ducts or in the human ear canals. Many researchers attempted to extend the application of active noise control to spatial noise fields, such as controlling the tire rolling noise in cars, the ventilation noise in workplaces, or the pump engine noise outdoors, which account for the majority of noises we encounter in our everyday lives. They developed spatial active noise control systems based on room modes, spherical modes, or the Helmholtz integral equation. The attempts have found limited success in the real world because of two problems. The first is that a spatial noise field is the complicated interaction of a number of noise sources with the environment, both of which can be non-stationary and time-varying. This problem makes it extremely difficult to obtain clean reference signals for spatial active noise control systems. The second is that due to the lack of a time-domain spatial sound field control theory, the existing spatial active noise control systems process the acoustic quantities in the time-frequency domain. The time-frequency domain processing introduces the frame delay and thus probably makes the systems violate the causal control constraint. This thesis proposes an outgoing noise field control system based on the frequency-domain sound field separation method. The method decouples the outgoing field (due to the noise sources) from the incoming field (due to the environment) on a sphere surrounding the noise sources. By canceling the outgoing field only, the proposed system reduces the noise entirely in a room without estimating the secondary paths in real-time and with negligible influence on the desired sound field in the room. This thesis further derives a time-domain sound field separation method, based on which a low latency outgoing field control system with random noise field cancellation capacity is developed. Multiple circular arrays of vector sensors for three-dimensional sound field analysis are developed based on the time-domain method. The designed arrays have a compact geometry, and thus can be integrated with small sized wearable devices and provide them with real-time sound field analysis capacity

Predicting and auralizing acoustics in classrooms

Although classrooms have fairly simple geometries, this type of room is known to cause problems when trying to predict their acoustics using room acoustics computer modeling. Some typical features from a room acoustics point of view are: Parallel walls, low ceilings (the rooms are flat), uneven distribution of absorption, and most of the floor being covered with furniture which at long distances act as scattering elements, and at short distance provide strong specular components. The importance of diffraction and scattering is illustrated in numbers and by means of auralization, using ODEON 8 Beta

An Active Noise Control System Based on Soundfield Interpolation Using a Physics-informed Neural Network

Conventional multiple-point active noise control (ANC) systems require placing error microphones within the region of interest (ROI), inconveniencing users. This paper designs a feasible monitoring microphone arrangement placed outside the ROI, providing a user with more freedom of movement. The soundfield within the ROI is interpolated from the microphone signals using a physics-informed neural network (PINN). PINN exploits the acoustic wave equation to assist soundfield interpolation under a limited number of monitoring microphones, and demonstrates better interpolation performance than the spherical harmonic method in simulations. An ANC system is designed to take advantage of the interpolated signal to reduce noise signal within the ROI. The PINN-assisted ANC system reduces noise more than that of the multiple-point ANC system in simulations

Spatial Acoustic Vector Based Sound Field Reproduction

Spatial sound field reproduction aims to recreate an immersive sound field over a spatial region. The existing sound pressure based approaches to spatial sound field reproduction focus on the accurate approximation of original sound pressure over space, which ignores the perceptual accuracy of the reproduced sound field. The acoustic vectors of particle velocity and sound intensity appear to be closely linked with human perception of sound localization in literature. Therefore, in this thesis, we explore the spatial distributions of the acoustic vectors, and seek to develop algorithms to perceptually reproduce the original sound field over a continuous spatial region based on the vectors. A theory of spatial acoustic vectors is first developed, where the spatial distributions of particle velocity and sound intensity are derived from sound pressure. To extract the desired sound pressure from a mixed sound field environment, a 3D sound field separation technique is also formulated. Based on this theory, a series of reproduction techniques are proposed to improve the perceptual performance. The outcomes resulting from this theory are: (i) derivation of a particle velocity assisted 3D sound field reproduction technique which allows for non-uniform loudspeaker geometry with a limited number of loudspeakers, (ii) design of particle velocity based mixed-source sound field translation technique for binaural reproduction that can provide sound field translation with good perceptual experience over a large space, (iii) derivation of an intensity matching technique that can reproduce the desired sound field in a spherical region by controlling the sound intensity on the surface of the region, and (iv) two intensity based multizone sound field reproduction algorithms that can reproduce the desired sound field over multiple spatial zones. Finally, these techniques are evaluated by comparing to the conventional approaches through numerical simulations and real-world experiments

Room transfer function measurement from directional loudspeaker

Room transfer function (RTF) is the room response observed at a particular listening point due to an impulse generated from an omnidirectional point source. Typically, measured RTFs in practice are often erroneous due to the directivity of the measurement loudspeaker. This paper formulates a spherical harmonic based parameterization of the room response for a directional loudspeaker, and provides a direct approach to derive the point to point RTF using measurements from a directional loudspeaker. Simulation results are presented for 2 directional loudspeakers with an active frequency bandwidth of 200 - 4000 Hz.This work is supported by Australian Research Council (ARC) Discovery Projects funding scheme (project no. DP140103412)