ISO 9614-1 Temporal Variability

The Temporal Variability measurement for ISO 9614-1 is described below.

Temporal Variability

To evaluate the stationarity of the sound field to be measured, a separate measurement must be conducted and special field indicator must be calculated.

The Temporal Variability indicator F₁ measures the variability of the sound field in time by measuring a set of intensity values and evaluating the deviation from the mean value.

F₁ = 1/I · (1/(M-1) Σ (I_k - I)²)^1/2

where k represents the period index and M is the total number of periods.

The indicator should be less than 0.6 in all applicable bands for the measurement to be compliant to ISO 9614-1.

To perform a measurement according to the standard, set up the parameters in the Measurment menu. The relevant parameters are:

Averaging time:
The number of seconds per period of measurement.
Number of averages:
The number of periods to evaluate.

ISO 9614-1 recommends an averaging time of 8 to 12 seconds and 10 periods. Consult the standard for further information about stationarity.

To make a measurement, find a typical and representative position on the hypothetical surface and position the probe there. On the instrument, navigate into the corresponding surface and press and hold on the selected segment to bring up the context menu. Then select Temporal Variability. A special mode is now activated with the current settings. Press the Start button to make the measurment. The instrument will stop automatically when the predefined number of periods have been measured.

Evaluate the measurement by pressing WIEW, the F₁ is displayed. Warnings will be given if the measurement is not within the requirement of the standard.

Press accept to store the measurement in the project and populate the F₁ indicator for the project.

Additional info

Temporal variability measurements should be made before and after the individual segments have been measured according to ISO 9614-1. Several temporal variability measurements may be made by following the procedure above.

To inspect and access the temporal variability measurements, go to the Measurement menu and select temporal variability.