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Sound field, spatial hearing, and sound reproduction
Published in Bosun Xie, Spatial Sound, 2023
A sound field is defined as a region in a medium in which sound waves are being propagated. A sound field in air is physically characterized by the temporal and spatial distribution of sound pressure in the time domain or equally characterized by the frequency and spatial distribution of sound pressure in the frequency domain. The free field refers to a special sound field in a uniform and isotropic medium in which the influences of boundary are completely negligible (absence of reflections from boundaries). The sound field generated by a point source in the free field is a spherical wave in which the magnitude of sound pressure is inversely proportional to the distance between the receiver position and the source. The sound field generated by a straight-line source with an infinite length in the free field is a cylindrical wave. In a local region of a far field where the distance between the receiver position and the sound source is large enough, spherical and cylindrical waves can be approximated as a plane wave. In general cases, the sound pressure generated by a sound source depends on the direction of the receiver position with respect to the source. This directional characteristic is described by the directivity of sound source radiation.
Sound Measurement and Analysis
Published in Lewis H. Bell, Douglas H. Bell, Industrial Noise Control, 2017
Lewis H. Bell, Douglas H. Bell
This implies that to measure sound intensity in a free field, only sound pressure measurements are required. These can be performed with a sound level meter and appropriate calculations can be applied. However, in sound fields that are not free fields, this relationship between sound pressure and sound intensity does not apply. A more general equation for sound intensity is given by [3]: () I→=p×u→[W/m2]
Hearing, Sound, Noise, and Vibration
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
Sound attenuates in a free field according to the inverse square law. The sound pressure drops according to the square of the distance from the source. So, if the distance from the source doubles, the reduction in SL is 10log10(2/1)2=10log104(since20log10(p/pr)=10log10(p/pr)2)10log104=6dB
Response of an isosceles trapezoidal hill with a semicircular canyon to plane SH waves
Published in Waves in Random and Complex Media, 2022
Xia An, Yunqiu Song, Zailin Yang, Zhiyong Zhang
The free field is the sum of the incident wave field and the reflected wave field . Employing the Jacobi-Anger formula which is an expansion of the exponential in terms of Bessel functions, the can be expressed in the complex plane as where is the Neumann factor (;), and the means the Bessel function of the first kind of order .
Prediction of cutting tool wear during milling process using artificial intelligence techniques
Published in International Journal of Computer Integrated Manufacturing, 2019
S. Shankar, T. Mohanraj, R. Rajasekar
This present work uses a microphone and milling tool dynamometer to acquire the sound pressure and cutting force signals. The sound pressure signal was measured at 30 cm distance from cutting zone with a sensitive free field microphone. Milling tool dynamometer and microphone were connected with BNC noise-free cable and the raw signals were conditioned with signal conditioning unit. The electrical noise signals were removed with a proper filter circuit, which was designed through the LabVIEW Virtual Instrumentation software during the data acquisition process. The cutting condition was maintained as external noise free environment to eliminate the noise, and the same environment was used for entire experiments. The microphone used to measure the sound pressure was the GRAS 46 AE CCP free field microphone which has 12.7 mm diameter with a frequency range of 3.15 Hz to 20 kHz, and a sensitivity of 50 mV.Pa−1. The milling tool dynamometer has the accuracy of ±1 % of full-scale voltage and force range of 0–5000 N.