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Sound in Enclosed Spaces
Published in David A. Bies, Colin H. Hansen, Carl Q. Howard, Engineering Noise Control, 2018
David A. Bies, Colin H. Hansen, Carl Q. Howard
Sabine introduced the reverberation time, T60 (seconds), as the time required for the sound energy density level to decay by 60 dB from its initial value. He showed that the reverberation time, T60, was related to the room volume, V, the total wall area including floor and ceiling, S, the speed of sound, c, and an absorption coefficient, ᾱ, which was characteristic of the room and generally a property of the bounding surfaces. Sabine’s reverberation time equation, which follows from Equations (6.50) and (6.51) with Lp0 − Lp = 60, may be written as: () T60=55.25VScα¯
Sound In Enclosed Spaces
Published in David A. Bies, Colin H. Hansen, Engineering Noise Control, 2017
David A. Bies, Colin H. Hansen
Sabine introduced the reverberation time, T60 (seconds), as the time required for the sound energy density level to decay by 60 dB from its initial value. He showed that the reverberation time, T60, was related to the room volume, V, the total wall area including floor and ceiling, S, the speed of sound, c, and an absorption coefficient, α¯, which was characteristic of the room and generally a property of the bounding surfaces. Sabine's reverberation time equation, which follows from Equations (7.50) and (7.51) with Lp0 - Lp = 60, may be written as follows: T60=55.25VScα¯
Room Acoustics
Published in Dhanesh N. Manik, Vibro-Acoustics, 2017
The machine may be operated under its normal load in a corner of the room, and the sound pressure levels can be measured at any point away from the machine. In this method, the directivity of the source cannot be determined. On the other hand, the diffuseness of the field allows a relatively easy estimation of the sound energy density in the room, because the sound energy density in the room is directly related to the difference between the sound energy emitted by the machine and that absorbed by the room boundaries. A measure of absorption is obtained by determining the room reverberation time T. Reverberation time is the time taken by sound to decay by 60 dB and it depends on the acoustic absorbing environment. When the volume V of the room and its reverberation time are known, the sound power level can be derived as follows.
Identification of acoustic wave transmission mechanism to efficiently harvest the acoustic energy from gaseous flow in a pipeline
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Xuewen Zhang, Junyoung Lee, Jongwon Seok
During the past few years, many researchers have investigated the extraction and use of acoustic energy from various sound sources and transmission media using Helmholtz (Yuan et al. 2021), quarter-wavelength (Guo et al. 2018), or half-wavelength resonators. The harvested acoustic energy is converted into electricity using electromagnetic (Ahmad et al. 2022) or piezoelectric (Li et al. 2021) transducers. Yuan et al (Yuan et al. 2021). developed a quarter-wavelength acoustic resonator system and combined it with an acoustic triboelectric nanogenerator to achieve high-performance acoustic energy harvesting. The system produced a power output of 4.33 mW under excitation with a sound pressure level of 100 dB. Ma et al (Ma et al. 2021). presented an acoustic energy harvester based on an acoustic metamaterial coupled with a Helmholtz resonator to enhance the sound energy density through energy focusing and pressure amplification. Cao et al (Cao et al. 2020). introduced an enhanced pressure-fluctuation energy harvester for harvesting energy from a hydraulic-pressure pipeline system. It was installed on the pipeline in a side pocket, and an interface film was used to separate the fluid flow from the force amplifier where the piezoelectric stack was fixed to realize electromechanical transformation. Horowitz et al (Horowitz et al. 2006). proposed a silicon-micromachined acoustic energy harvester based on a Helmholtz resonator; they revealed a maximum power density of 0.34 μW/cm2 at 13.6 kHz at an incident sound pressure of 149 dB (564 Pa). Natural gas is often the working fluid in an energy supply pipeline system. Su et al (Su et al. 2019). numerically studied the manifold system to uncover the spectral characteristics of the noise in natural gas pipelines and found that the sound level can go up to 94 dB with frequencies near 850 and 1800 Hz.