B&K 2250 Light Manual de usuario descargar pdf (Pagina 164)

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Hand-held Analyzer Types 2250 and 2270 – User Manual

14.2.1 Interrupted Noise Method

8) Set the number of decays you want to measure per position – the analyzer automatically

controls the generator, measurement of the decays and averaging the decays.

9) Set the Generator as required – set Generator Type = External if you want to control an

external generator (details in Appendix A) – otherwise leave it at Internal to use the

internal generator.

10) Select Noise Type for the internal generator. Pink noise is typically used.

11) Adjust the level of the internal generator output to match the input of the power amplifier

used by setting Level [re. 1 V].

Note: You can manually turn the generator on and off by tapping on the Loudspeaker

icon in the Status Field.

12) Set the Escape Time allowing you to leave the room before the generator is turned on

during the measurement – see Fig.14.3.

13) Set Build-up Time to allow the excitation noise to reach a steady level before the

measurement starts. 1 s is adequate in most ordinary rooms, but should be increased for

larger halls or reverberation rooms.

14) Select the Sound Source used, to optimise the frequency response of the internal generator

output for either a flat power response or optimum power difference between adjacent

1/1- or 1/3-octave bands – thereby eliminating the need for an equalizer to smooth the

response in most cases. Select a type matching your sound source – select Unknown if you

are using a non Brüel & Kjær sound source, or do not want to make a correction to the

frequency response. Go to step 16.

14.2.2 Impulsive Method

15) Set Trigger Level low enough to be sure the impulse will be triggered, but high enough to

avoid triggering on the background noise. A level between 80 and 100 dB is normally

adequate.

16) If you have selected Automatic Save = Yes, then Trigger Repeat can be set to Yes to

automatically start a new measurement when a measurement has been saved. This allows

you to go to another position and make a new impulse, without the need for controlling the

analyzer between the measurements. Observe how the “traffic light” indicates the status of

the measurement (see Table 4.2 and Fig.14.4) making it easy for you to change position

and generate the impulse synchronised with the measurement procedure. Press the

Start/Pause pushbutton to stop the measurement when the last measurement has been

saved.

14.2.3 Signal Recording

17) Set Recording Control = Automatic if you want to record the signal during the measurement.

The recordings can be played back afterwards for identifying the cause of measurements

differing from each other – or (if Excitation = Impulse) for further analysis of the measured

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B&K 2250 Light Manual de usuario Pagina 164