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Principles of Energy Conversion
Published in Hamid A. Toliyat, Gerald B. Kliman, Handbook of Electric Motors, 2018
Hamid A. Toliyat, Gerald B. Kliman
The electrical signal proportional to the sound pressure at the capacitor microphone is amplified and passes through a weighting filter. The weighting filter is actually a bandpass filter with defined frequency-response characteristics. It is used so that the measuring system will produce a result that conforms to the subjective noise-sensing ability of the human ear. The most frequently used weighting filter is the A-weighting filter, which simulates the average sound sensing ability of the human ear in the 60-90dB range of sound pressure levels. The damping curve of this filter is shown in Fig. 11.6. The cutoff frequencies of the A-weighting filter are around 700Hz at the low end of the frequency spectrum and around 10,000Hz at the high end.
Emissions Formation and Control
Published in John B. Heywood, Eran Sher, The Two-Stroke Cycle Engine, 2017
In the frequency range 500–5000 Hz, the ear responds almost logarithmically to sound intensity, so this logarithmic decibel scale is appropriate. However, sounds of different pitch or frequency perceived as equally loud do not have the same intensity. To provide a quantitative measure of subjective loudness, sound is said to have a loudness in phons equal to the intensity level of a pure tone of frequency 1 kHz that appears equally loud.44Figure 7-42 shows how the actual intensity required to produce a certain sensation of loudness for an average listener varies with frequency. The weighting shown is known as the A-weighting and corresponds to the ear’s response at 40 phon. An A-weighting filter is normally applied automatically to noisemeter (a microphone that converts variations in pressure to variations in voltage) measurements and is designated dB(A). Note that the most irritating frequencies are between about 1 and 5 kHz, with increasingly higher sound pressure levels sounding equally loud as frequencies decrease and increase below and above this band, respectively.
Audio basics
Published in John Watkinson, The Art of Sound Reproduction, 2012
In acoustic measurements, the sound pressure level (SPL) is measured in deciBels relative to a reference pressure of 2 × 10–5 Pascals (Pa) rms. In order to make the reference clear the units are dB(SPL). In measurements which are intended to convey an impression of subjective loudness, a weighting filter is used prior to the level measurement which reproduces the frequency response of human hearing which is most sensitive in the mid-range. The most common standard frequency response is the so-called A-weighting filter, hence the term dB(A) used when a weighted level is being measured. At high or low frequencies, a lower reading will be obtained in dB(A) than in dB(SPL).
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
The initial and final weight of the fuel tank was taken for every 10 g fuel consumed for different blends at different speeds. The average emission and fuel consumption values were taken by repeating the tests to reduce the experimental error. Engine noise level is calculated as a sound pressure level (SPL) in hertz. Generally, two different weighting filters (A & C) are used to check compliance with safety regulations and acoustic analysis. The A-weighting is for the general noise sound level, and the C weighting is for measuring sound level of acoustic material control in various environments (i.e., 94 dB 1 kHz). Here we used ‘A’ weighing for the engine noise measurement. The data for noise characteristics were collected and stored using a microphone and a noise level meter, which was positioned 1 m away from the engine, as per the standard practice. The engine vibrations were measured as accelerations in vertical, longitudinal, and lateral directions, and were expressed in terms of root mean square (RMS) value of acceleration in m/s2 since, RMS value gives an amplitude value by considering time history of the wave (Uludamar, Tosun, and AydIn 2016).
Modelling, simulation and evaluation of ground vibration caused by rail vehicles*
Published in Vehicle System Dynamics, 2019
David J. Thompson, Georges Kouroussis, Evangelos Ntotsios
In common with environmental noise, it is usual to assess ground-borne noise in terms of the A-weighted sound pressure level in decibels. The A-weighting filter attempts to mimic human sensitivity to sound at relatively low amplitudes but is widely used in assessing noise at all amplitudes. This filter attenuates the sound pressure levels below 100 Hz by more than 20 dB and the level at 20 Hz by as much as 50 dB.