B&K 2250 Light Manual de usuario descargar pdf (Pagina 182)

170

Hand-held Analyzer Types 2250 and 2270 – User Manual

15.3 Tone Assessment According to Italian Law

Tone Assessment in Italy is performed on normal 1/3-octave spectra but with an option to use

narrow bands (such as FFT), in case of doubt.

The method described in the Italian “Decreto 16 marzo 1998” states that the 1/3-octave L

ZFmin

spectrum is used for evaluation of tones in noise. The analysis must be performed in the

frequency range from 20 Hz to 20 kHz and a tone is present if the level of a band is more than

5 dB higher than the levels in the adjacent bands. The adjustment K

, which should be added to

the measured L

Aeq

, will only be applied if the band with the tone touches or exceeds a loudness

level contour touched by another frequency value of the spectrum. (Examples of loudness level

contours from Evaluator Type 7820 are shown in Fig.15.2.) The size of the adjustment K

defined as 3 dB.

Fig.15.2

Example display from

Evaluator Type 7820

showing an L

LFmin

spectrum and loudness

level contours

An equal loudness curve is a frequency response curve. Equal loudness curves are the

experimental results of presenting pure tones and levels at different frequencies to young

people with no hearing impairment. Along a contour line the young, average, normal listener

will judge tones presented with different combinations of frequency and dB to be equally loud.

Equal loudness level curves are defined by ISO 226 “Acoustics – Normal equal-loudness-level

contours”. The Italian “Decreto 16 marzo 1998” refers to ISO 226 (1987), but the ISO 226

standard has been thoroughly revised in the latest version from 2003. Your analyzer, with

BZ-7231 software installed, uses by default the free-field curves from the 1987 version. But the

diffuse-field contours from the ISO 226 (1987), as well as the free-field curves from

ISO 226(2003) have been implemented and may be selected.

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B&K 2250 Light Manual de usuario Pagina 182