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148

Hand-held Analyzer Types 2250 and 2270 – User Manual

Fig.14.1 Definition of Reverberation Time (RT). Evaluation range of 30 dB for calculation of

T30 indicated

RT varies between positions in a room, so it is usually measured at several positions. The

spatial average (Room average) for all positions gives an overall assessment, and the position

results may be used to indicate the acoustic quality as a function of location.

The Room average can either be made as an average of the RT spectra, or calculated for the

averaged decays (ensemble average), that is: the decays for each frequency band are averaged

over all positions and the RT spectrum is then calculated for the averaged decays.

14.1.2 How Do We Measure Reverberation Time?

RT can be measured using either Interrupted Noise, with the built-in noise generator, or by

using Impulsive Excitation (Schroeder Method), such as from a pistol or balloon burst.

Interrupted Noise Method

When using a power amplifier and loudspeaker sound source (Fig.14.2), the analyzer will turn its

noise generator on and off, then measure and display the RT spectrum and decays.

Reverberation Time

–35 dB

Background

Noise Level

Time

–5 dB

0dB

Regression Line

Excitation

Level

Evaluation Range

060210

–60dB

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B&K 2250 Light Manual de usuario Pagina 160