54
Chapter 10
Reverberation time measurements
55
Norsonic Nor118
User Guide
Making reverberation measurements
Setup of the Nor118 for reverberation time measurements
is really simple. ere is no range or duration setting, all
you need to do is to set the trigger level.
To set up for reverberation time measurements:
1
Press > 2 (Rev) to enter reverberation time mode.
e display will now look as shown above.
2
If needed, set the filter bandwidth to ⁄ or 1⁄3 octave
(requires that filters are installed – see the chapter
Frequency analysis
for details).
e
R
in the
upper left corner
of the display indicates that
the instrument now is in reverberation time mode. By
default, the cursor is located on the 1 kHz frequency band.
e cursor position determines the frequency band used
to trigger the measurement.
3
If 1 kHz is not suitable as trigger band (which may
well be the case when using a paper bag as excitation
source) use the keys to move the cursor in the
usual manner.
What is trigger?
To start a measurement
the instrument will need to have a trigger
condition fulfilled. Sound analyseres designed to be
used for a broad variety of applications need a set of
trigger conditions to be versatile enough. Such con-
ditions may include trigger by clock (start measuring
at a predefined time of day), trigger when the level
exceeds a certain predefined threshold, trigger on an
external trigger signal occurring (e.g. a car passing
a light barrier) etc.
A sound level meter albeit as sophisticated as the
Nor118, normally provides only one trigger condi-
tion – the trigger on pressing , often referred
to as unconditional triggering.
However, reverberation time using external exci-
tation sources will require a
trigger on level exceeds
a predefined threshold
function so that the instru-
ment knows when to start capturing the impulse
and its decay. You will then have to define the level
threshold above which the impulse is considered to
be present and the frequency band in which to look
for the impulse.
The level above which trigger will take place (provided that
a level transition takes place) is shown as a horizontal line.
This line is always located 30 dB below the display top scale.
To “move” the line up and down (what you do is to change
the display top scale) use the + and – keys. The position
of the graph cursor (the frequency cursor) determines the
frequency band to be used as trigger band.
The
instrument is in
Reverberation
time mode
Display top
scale
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