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Sound fields
Published in Carl Hopkins, Sound Insulation, 2020
A-weighting is used to combine sound pressure levels from a range of frequencies into a single value. This is the A-weighted sound pressure level, Lp,A. It is intended to represent the frequency response of human hearing and is often used to try and make a simple link between the objective and subjective assessment of a sound. A-weighting accounts for the fact that with the same sound pressure level, we do not perceive all frequencies as being equally loud. In terms of the building acoustics frequency range it weights the low-frequency range as being less significant than the mid- and high-frequency range. This does not mean that the low-frequency range is unimportant for sound insulation, usually quite the opposite is true; the A-weighted level depends upon the spectrum of the sound pressure level. Although it is common to measure and predict sound insulation in frequency bands, assessment of the sound pressure level in the receiving room is often made in terms of the A-weighted level.
Basic Concepts and Quantities Characterizing Sound
Published in Dariusz Pleban, Occupational Noise and Workplace Acoustics, 2020
The sound pressure defined by Equation 1.1 is the fundamental quantity adopted commonly to characterize the strength or intensity of sound waves. The organ of hearing responds differently to sounds characterized by the same sound pressure amplitude and level but differing in frequency. This dependence of the subjective sensation of sound intensity (loudness) on the frequency of sounds was taken into account when developing experimentally the so-called loudness curves corresponding to different frequency weighting characteristics denoted as A, C, and Z (characteristics B and D have fallen into disuse). The A-weighting reflects the sensitivity of the human ear, whereas C-weighting follows the frequency sensitivity of the ear at much higher noise levels and is used to take peak level measurements. Z-weighting is just a flat frequency response within the range of audible frequencies. The corresponding characteristics are implemented in the form of suitable filters integrated into sound level meters commonly used for the purpose of noise assessment. Both filters and sound level meters must meet the requirements of the standard IEC/EN 61672-1:2013. Table 1.1 is a list of A, C, and Z frequency correction characteristic values.
Frequency Weighting and Filters
Published in Eddy B. Brixen, Audio Metering, 2020
A-weighting applies, in particular, to the measurement of acoustic noise at the workplace and in the environment. However, it also applies to electrical measurements. It is developed from the inverse of the 30 phon equal loudness curve.
A feedback-feed-forward steering control strategy for improving lateral dynamics stability of an A-double vehicle at high speeds
Published in Vehicle System Dynamics, 2022
Maliheh Sadeghi Kati, Jonas Fredriksson, Bengt Jacobson, Leo Laine
The measurable disturbance in the system is the driver steering input. In order to model the driver behaviour, the measurable disturbance is assumed to be generated by an input weighting filter of the form where is the input filter state vector and represents an artificial signal of finite-energy. With this filter, it is assumed that the frequency content of the driver steering is concentrated in a particular range of frequency. In fact, the use of a weighting filter is motivated by the fact that drivers will not provide arbitrary steering inputs. Indeed the manoeuvres will typically be initiated by smooth steering inputs as in real life, whose frequency contents would be limited to a certain frequency band.
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 order to quantify the magnitude of a fluctuating sound pressure p, it is conventional to use the mean-square value over a time T in which is an arbitrary time. The sound pressure level in decibels is defined by where is the reference pressure which usually takes the value of 20 Pa. In practice, in a sound level meter, an exponential time weighting is used to allow a continuous reading of the sound pressure level in which τ is the time constant. This is usually set to 0.125 s for fast (F) weighting or 1 s for slow (S) weighting. In practice, the infinite limit can be truncated to a suitable finite time.
A frequency-shaping methodology for discrete-time sliding mode control
Published in International Journal of Control, 2019
Minghui Zheng, Masayoshi Tomizuka
In general, the suitable weighting filter differs among various disturbance sources. It is not efficient to solve the optimisation problem (21) every time when the disturbance sources change. This motivates a shaping filter which is explicitly dependent on wd's. One approach of obtaining the parameter-dependent sub-optimal filter was proposed in Apkarian, Gahinet, and Becker (1995) and Apkarian and Adams (1998). This approach requires that the state-space matrices of Pf(z) are affine in the parameters of wd's, which may not always be satisfied and limits the flexibilities in the design of We. Furthermore, the constructed solutions through this approach are usually conservative by taking linear parameter-varying systems into consideration. This motivates an interesting question: is it possible to design an optimal/sub-optimal shaping filter that is explicitly dependent on the weighting filter? Within this motivation, the optimisation problem (21) is modified as follows: