B&K 2250 Light Manual do Utilizador descarregar pdf (Página 181)

CHAPTER 15

Tone Assessment Option BZ-7231 – 1/3-octave Method

169

Fig.15.1 Definition of frequency ranges and level differences

The proposed frequency ranges and level differences between adjacent bands are:

• Low frequency range: includes the 1/3-octave bands from 25 Hz to 125 Hz with a level

difference for a detected tone greater than 15 dB

• Middle frequency range: includes the 1/3-octave bands from 160 Hz to 400 Hz with a

level difference for a detected tone greater than 8 dB

• High frequency range: includes the 1/3-octave bands from 500 Hz to 10 kHz with a level

difference for a detected tone greater than 5 dB

With BZ-7231 software, frequency ranges and the limit for the level differences in low, middle

and high range can be set by the user.

Tone assessment is carried out for all the measured frequency bands (including those below

25 Hz and above 10 kHz). The level difference limit is extrapolated from the low and high

range to cover the complete measurement range.

If tones are detected outside the range from 25 Hz to 10 kHz the quality indicator (yellow

smiley) indicates “Tone out of ISO range detected”.

ISO 1996-2, Annex D does not specify the size of the adjustment. In the default setting of the

BZ-7231, Brüel & Kjær has chosen to set the value to 5 dB.

Calculating the Level Difference Between One Band and the Adjacent Bands

BZ-7231 software calculates the level difference between a 1/3-octave band and two adjacent

1/3-octave bands with lower levels. The difference is calculated between the band in the middle

and the highest of the adjacent bands.

25 Hz

Low

Middle

High

125 160 400 500 10 kHz

1/3 - octave bands [Hz]

Proposed level

difference limits

for adjacent

bands [dB]

Level differences can be defined in Low, Middle

and High frequency range:

080160

1 2 ... 176 177 178 179 180 181 182 183 184 185 186 ... 331 332

Sem comentários

B&K 2250 Light Manual do Utilizador Página 181