NTi Audio XL2 Sound Level Meter - Manual (Page 129)

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STIPA
STIPA Measurement Hints
Hints: Ambient Noise
The ambient noise has to be sufficiently static during the •
measurement. A signal-noise ratio of 15 dB or higher is rec-
ommended to achieve best speech intelligibility. Impulsive
ambient noise during the measurement, such as speech,
causes severe measurement errors. The STIPA result is usu-
ally too high.
Fluctuating noise is detected by measuring the direct STI •
in the absence of the test signal. Carry out these measure-
ments at least at a representative set of locations. If the STI
is too high (e.g. STI > 0,2), the measurement results are
likely to be erroneous. Then the STIPA measurement should
be carried out without this noise being present. Utilize the
ambient noise correction for such instances.
At locations with varying conditions (e.g., some public areas •
with few people and other areas with crowds) the worst-
case STIPA results should be measured. Consult the local
regulations (e.g., the NFPA code in the U.S.) for directives
concerning measurement locations and number of required
STIPA measurements under which circumstances.
Hints: German Standard VDE 0833-4 Requirements
STI > 0.63 One single measurement is sufficient.
STI < 0.63 Perform three subsequent measurements for this
measurement position.
If the maximum result deviation of these three •
measurements is > 0.03 then further three
measurements shall be performed.
If the maximum result deviation of these mea-
•
surements is > 0.05 then the cause of this in-
stability shall be evaluated and removed.
The arithmetic average of the performed three
•
or six measurements has to be reported.
Utilize the STIPA Reporting Tool for the documentation of your
measurements according the standard.
An STI > 0.63 ensures, that the speech intelligibility is higher
than 0.5 with a confidence level of 95%.