Some Considerations Regarding the Use of Overall Noise Weighting Functions 2007-01-2601
Since the Weber-Fechner Law (1860) until 1950 there was no trustful method to calculate Loudness of complex sounds. At that time, ISO proposed three weighting curves, A, B and C based on rough approximations of the isophonic curves, 40, 70 and 100 phons. It was supposed to be a temporary suggestion. Curves B and C were abandoned, but A weighting survives until today! In 1957, Stevens and Zwicker presented two independent methods to obtain Loudness in sones, based on the new Stevens' Power Law. In 1965, Kryter introduced Noisiness in noys. Stevens in 1975 presented Perceived Magnitude as an improvement of Loudness calculation. In these acoustic parameters, the sound pressure levels per frequency band are transformed into acoustic sensation levels, and through the sensation spectrum the magnitude of the overall sensation is calculated. The A, B and C curves, for low, moderate and high levels do not follow this concept. If we choose A weighting, we apply the same attenuation per frequency band for any level… Nowadays curve A is used without considering the values of the sound pressure levels. In this paper, we adopt limits and boudaries for the existing curves, concerning the sound pressure levels per frequency bands, and apply them to the interior noise spectra of two sets: passenger cars and commercial vehicles. We are able to obtain overall noise in dB(H), a hybrid process, using the appropriate attenuation for each band, and compare with the usual dB(A) and other acoustic parameter like Loudness in sones. We look for the degree of linear correlation of these parameters, applying to the experimental data a least-squares curve fitting. We establish a ranking inside a vehicle set and discuss the results obtained.