Sound Field Model Research Articles

Optimization of a point-in-polygon algorithm for computer models of sound field in rooms

Testing inclusions of a point in a polygon is an important element of various computer models used in architectural acoustics. In this paper, an algorithmic representation of such a test is presented. Different forms of the algorithm are discussed and the form suitable for convex polygons is optimized from a viewpoint of execution time. A room shape analysis is employed to obtain an additional improvement of the algorithm efficiency. The concept of a preliminary checking of a point position prior to the main test execution is also discussed. Altogether, c. 60% reduction of execution time is obtained. Though the algorithms discussed are the ray method oriented, they can also be applied to other methods of sound field modelling in bounded spaces.

Principles of binaural room simulation

Binaural room simulation is a method of allowing for listening into non-existing spaces by means of a computer model that takes all acoustical relevant parameters of the environment into account. It is based on a combination of traditional sound-field modelling techniques and binaural technology. An introduction into the underlying principles is given. Special attention is paid to the treatment of physical data, optimisation methods and aspects of auralisation and real-time performance.

A study on designing the amplitude gain of the feedback loop of an electroacoustic system.

The acoustic feedback from a loudspeaker to a microphone forms a closed loop and is the cause of instability (howling). When the electrical amplifier gain is fixed on maximum within a designed range, it is the excess amplitude of the open-loop gain over the unity (0 dB) that should be minimized by a howling suppression technique. It can be designed using a diffuse sound field model [Diestel, J. Acoust. Soc. Am. 35, 2019–2022 (1963)]. According to this method, the designed value was 18–24 dB in the case of a single loudspeaker and single microphone system located in a room with dimensions of 10×20×6 m and sound absorption coefficient of 0.05–0.5 and the gain of the electrical amplifier being fixed so that the farthest located attendant from the loudspeaker could perceive 62.9 dB (SPL). In order to evaluate the result, measurements were carried out in a conference room.

Separation of mixed voices by acoustic parameter optimization

AbstractThe human auditory response is highly adaptable to the environment, enabling voices to be recognized even in a noisy environment. This ability is due primarily to the language processing function in the central auditory nervous system, but the binaural sound locating function also seems to play an important role. From such a viewpoint, the author has presented a method which estimates the sound source locations and separates the voices from more than one speaker using the position information.A problem in this method is that the acoustic space is assumed as a free space, and the voice is separated based on the sound field model. Consequently, in the actual sound space, the estimation of the source location may be incorrect, thereby making the voice separation inaccurate.This study proposes a method whereby the separation index is estimated using the evaluation function based on the cross correlation of the separated voices, and the sound parameters are sought in the direction to minimize the evaluation function to improve the voice separation. The effectiveness of the method is verified by an experiment.

Sound field modeling and simulation of a concert hall

A sound field simulator has been developed in order to subjectively evaluate hall acoustics in the laboratory. This process consists of three parts: (1) a computer program for deriving the impulse response of the room from the architectural drawings using the ray tracing technique; the program is written mainly in FORTRAN and the calculation is implemented using a maximum of 1500 plane surfaces and 1 000 000 rays at most; (2) a new source of orchestral music that is digitally recorded in a temporarily constructed anechoic room for this purpose, and (3) hardware to synthesize the calculated sound field, which convolutes impulse response with input signal by digital signal processing and outputs from 24 speakers set up in an anechoic room in real time. In order to apply this simulator, subjective experience by means of audition for comparison of six concert halls is made and its ability and accuracy are investigated.

The influence of vegetation on acoustic properties of soils

Possible influences of vegetation on acoustically relevant soil parameters, such as porosity and soil structure, were considered. In situ measurements of sound interference patterns were performed in seven plant communities by means of an inclined track method. Normal acoustical specific impedances were calculated with a plane wave outdoor sound propagation model. The impedances found generally showed a real part constant with frequency, and an imaginary part decreasing with frequency. It is concluded that forest floors have an acoustically detectable layer structure and that, for purposes of modelling of outdoor sound fields, much lower impedances have to be used than for institutional grass.

Influence of vegetation on acoustic properties of soils

Possible influences of vegetation on acoustically relevant soil parameters, such as porosity and soil structure, were considered. In situ measurements of sound interference patterns were performed in seven plant communities by means of an inclined track method. Normal acoustical specific impedances were calculated with a plane wave outdoor sound propagation model. The impedances found generally showed a real part constant with frequency, and an imaginary part decreasing with frequency. It is concluded that forest floors have an acoustically detectable layer structure and that, for purposes of modelling of outdoor sound fields, much lower impedances have to be used than for institutional grass.

Approximate Ray Tracing in Inhomogeneous Media

A method of approximate ray tracing is developed that can be applied to media that are inhomogeneous in two or three dimensions. The medium is subdivided into regions in each of which the velocity is approximated by a linear function of the space coordinates. The approximation results in a constant-velocity gradient in each region and a continuous velocity across the boundary between any two regions. A ray trace through the regions consists of a sequence of circular arcs that are tangent to one another at each boundary between regions. The technique may be applied to study the effects of inhomogeneity in more than one dimension in the construction of soundfield models, using geometric acoustics.