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Acoustic Signal Processing
Published in Richard C. Dorf, Circuits, Signals, and Speech and Image Processing, 2018
Juergen Schroeter, Gary W. Elko, M. Mohan Sondhi, Vyacheslav Tuzlukov, Won-Sik Yoon, Yong Deak Kim
The principal areas of interest to humans have been acoustic pressure threshold for hearing; acoustic threshold of damage to hearing; threshold for speech communication in the presence of noise; and community response to annoying sounds. The vast amount of data required to evaluate human responses, and then to communicate the recommendations to laymen, forced psychoacousticians and noise-control engineers to adopt simple instrumentation and a simple vocabulary that would provide simple numbers for complex problems. Originally this was appropriate to the analog instrumentation. But even now digital measurements are reported according to former constraints. For example, the octave band, which is named for the eight notes of musical notation that corresponds to the 2:1 ratio of the top of the frequency band to the bottom, remains common in noise-control work. For finer analysis, one-third octave band instruments are used; they have an upper-to-lower-band frequency ratio of 20.33, so that three bands span one octave.
Fundamentals and Basic Terminology
Published in David A. Bies, Colin H. Hansen, Carl Q. Howard, Engineering Noise Control, 2018
David A. Bies, Colin H. Hansen, Carl Q. Howard
To facilitate comparison of measurements between instruments, frequency analysis bands have been standardised. The International Standards Organisation has agreed on ‘preferred’ frequency bands for sound measurement and by agreement, the octave band is the widest band usually considered for frequency analysis. The upper-frequency limit of each octave band is approximately twice its lower-frequency limit and each band is identified by its geometric mean called the band centre frequency. When more detailed information about a noise is required, standardised 1/3-octave band analysis may be used. The preferred frequency bands for octave and 1/3-octave band analysis are summarised in Table 1.2. Reference to the table shows that all information is associated with a band number, BN, listed in column one on the left. In turn the band number is related to the centre band frequencies, f, of either the octaves or the 1/3-octaves listed in the columns two and three. The respective band limits are listed in columns four and five as the lower- and upper-frequency limits, fℓ and fu. These observations may be summarised as: () BN=10log10fandf=fℓfu
Basic Concepts and Acoustic Fundamentals
Published in Colin H. Hansen, Foundations of Vibroacoustics, 2018
To facilitate comparison of measurements between instruments, frequency analysis bands have been standardised. The International Standards Organisation has agreed on ‘preferred’ frequency bands for sound measurement and by agreement, the octave band is the widest band usually considered for frequency analysis. The upper-frequency limit of each octave band is approximately twice its lower-frequency limit and each band is identified by its geometric mean called the band centre frequency. When more detailed information about a noise is required, standardised 1/3-octave band analysis may be used. The preferred frequency bands for octave and 1/3-octave band analysis are summarised in Table 1.1. Reference to the table shows that all information is associated with a band number, BN, listed in column one on the left. In turn, the band number is related to the centre band frequencies, f, of either the octaves or the 1/3-octaves listed in columns two and three. The respective band limits are listed in columns four and five as the lower- and upper-frequency limits, fℓ and fu. These observations may be summarised as: () BN=10log10fand f=fℓfu
Effect of ternary blends on the noise, vibration, and emission characteristics of an automotive spark ignition engine
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Bhavin K Bharath, Arul Mozhi Selvan V
Figure 4(a-b) represents the 1/3 octave band spectrum for different test fuels at various rpm. The octave analysis used for noise control and machine testing. There are mainly two types of study for the frequency composition of a sound field; 1/1 Octave band and 1/3 Octave band. Generally, the octave frequency band composition consists of a Lower Band Limit, Center Frequency, and an Upper Band Limit. The 1/3 Octave Bands are formed by dividing 1/1 octave band into three for providing an in-depth view of noise levels across the frequency composition. In this study, the 1/3 Octave band spectrum was analyzed for engine noise. All the test fuels showed a higher noise level at 6300 Hz, and the noise level again decreased as the band frequency increased to 20000 Hz. The fuel blend M15 showed a higher noise level at engine speeds of 1500 rpm and 2500 rpm; the result is consistent with the previous finding of the overall noise level.
Implementation and evaluation of ASHRAE’s acoustic Performance Measurement Protocols
Published in Science and Technology for the Built Environment, 2019
Gabrielle McMorrow, Liping Wang
During intermediate-level measurement, background noise and reverberation time of selected spaces are evaluated. These measurements are then compared to recommended criteria for rooms of the same space type. Background noise measurements are taken simultaneously on a range of frequencies (⅓-octave bands) using a sound-level meter. Sound pressure levels at each octave band are then used to find Noise Criteria or Room Criterion ratings. The PMP requires that background noise measurements be taken for at least four locations within a selected room. Reverberation time, the time (in seconds) that it takes for a loud noise to decay 60 dB, should also be measured at the intermediate level. A loud noise is generated, either through a loudspeaker or a hand-generated noise, such as the popping of a balloon. A sound pressure-level meter can be used to measure and calculate the reverberation time across frequencies.
Acoustics and Heat Transfer Characteristics of Piezoelectric Driven Central Orifice Synthetic Jet Actuators
Published in Experimental Heat Transfer, 2022
Muhammad Ikhlaq, Muhammad Yasir, Omidreza Ghaffari, Mehmet Arik
Acoustic measurements in terms of time series of pressures were acquired using PLUSE Labshop software version 18.1.1.9 [42]. The is the reference pressure of the anechoic chamber, which is also stored with the each data point within the PLUSE Labshop software, which is later used to estimate the sound pressure levels. Fast Fourier Transform (FFT) was used to convert the time series data into constituent frequencies and amplitudes of the measured signal in order to conveniently post-process the data. FFT data has a linear frequency scale but the human ear perceives sound in a logarithmic-like scale. Therefore, octave band analysis is usually employed for noise and sensory analysis in which Sound Pressure Levels (SPL) are represented in discrete frequency bands on a log scale.2https://rion-sv.com/support/st_frequency_en.aspx; https://www.evaluationengineering.com/home/article/13003909/octave-analysis-explored The ratio of upper to lower frequency bands is constant for each band, where the bandwidth is specified as a fixed percentage of the mid-band frequency [43]. This is also called Constant Percentage Bandwidth (CPB) analysis and was used to analyze the noise spectrum of SJAs. A band resolution of 1/3 octave and a CPB percentage of 23% was used [1/1 is 70% according to standards and 1/3 is 70/3%]. MATLAB 2015b was used to perform all evaluations including FFT and CPB. Figure 7 to Figure 10 present the acoustic findings for both jets examined in this study.