B&K 2250 Light Manual do Utilizador descarregar pdf (Página 163)

CHAPTER 14

Reverberation Time Software (Optional Module)

151

4) The impulse measurement stops after the analyzer detects the background noise level

again (automatically measured by the analyzer).

5) The analyzer performs backward integration of the impulse measurement.

6) The reverberation time spectra EDT, T20 and T30 are calculated and displayed on the screen.

The measurement can be in octaves or 1/3-octaves in parallel over a selectable frequency

range. In each frequency band, the decay is sampled 200 times each second.

The impulse response is backward integrated (according to the Schroeder method). In theory,

the resulting decay will be equivalent to the average of a large number of decays made with the

interrupted noise method. Therefore, the decays will be smooth using just one single shot.

14.2 Setting up the Analyzer

1) Select the Reverberation Time project template. (see section 3.3.1 for more details on

templates.) The project template is displayed at the top of the screen, if it does not display

Reverberation Time, tap the black bar at the top of the screen and select Reverberation

Time from the drop-down menu that appears.

2) Tap the Main Menu icon and select Setup from the list of options. Set the Bandwidth

and Bottom and Top Frequency of the measurement as required.

3) Set Map Based Measurement = No in the Measurement Control setup – the reverberation

decays will then be numbered from Pos. 1 to N. See how to measure with position

management in section 14.2.1.

4) Set Automatic Save = No, if you want to inspect the reverberation time and decays before

manually saving the measurement – otherwise select Yes to automatically save the decays

after each measurement.

5) Set Measurement Mode to:

– Parallel, for measuring all bands in a spectrum simultaneously

– Serial, for measuring selected bands only (to be saved and merged with a previously

measured Parallel spectrum)

– Combined, for measuring Parallel and then Serial in an automated sequence

When doing the Serial measurement, the bandwidth of the generator will match the

selected band, thus increasing the output power for the band and increasing the signal to

noise ratio for the band.

6) The analyzer automatically detects the decay time and stops the measurement at the end of

the decay – however, under special conditions (for example, when measuring with high

background noise) the decay time cannot be detected and the measurement will run up to

20 s. To minimise the measurement time and memory requirement for the measurement,

you can limit the measurement by setting the Max Decay Time. 3 s is adequate for most

ordinary rooms, but should be increased for larger halls or reverberation rooms.

7) Set Excitation to Impulse if you want to measure using the impulse method (go to step 15)

– otherwise select Interrupted Noise.

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B&K 2250 Light Manual do Utilizador Página 163