PART 1
English
23
Selecting the Sound Level Parameter
Selecting the right sound level parameter to display and report is dependent on the regulations
and standards to which you must comply.
Selecting the Sound Level Range
Sound Level Meter Type 2240 can measure sound pressure levels spanning from 30dB to
140 dB, separated in two ranges: 30 to 110dB, and 60 to 140 dB. For any measurement task,
you have to select one of the ranges by pressing .
The L
AF
parameter (L
A
) and the quasi-analogue bar are useful tools to help you decide which
range to choose. Switch between the two ranges as you read the bar graph. Ideally your signal
should fluctuate around the middle graph without indications of under-range or overload
. If there are very large fluctuations in the sound pressure, for example, because impul-
sive sounds are present, you may find it difficult to completely avoid at least one of these
indicators. If you have to choose between seeing under-range or overload conditions, select the
higher measurement range in order to avoid the overloads.
1
This type of situation indicates that
the signal fluctuates heavily, so be sure to use a sufficiently long averaging time to obtain a
stable level of L
Aeq
.
Measuring L
Aeq
L
Aeq
is always calculated for a specific duration, often due to standardised requirements, which
demands a report of the measurement duration. L
Aeq
durations are recorded as: L
Aeq,10min
or in
elongated form as “the 10 minute L
Aeq
was xx.x dB”.
Type 2240 can calculate L
Aeq
over durations ranging from 1 second to 60 minutes (in 1 second
steps), with a built-in timer for accuracy. The current measurement time is displayed in the
upper right-hand corner of the display. If regulations require measurements of a specific dura-
tion, follow this regulation and pay attention to the instrument's timer. If no specific measure-
ment time is required by regulation, you can determine the length of time on your own. Below
are some practical guidelines on how to make a proper L
Aeq
measurement:
• After a significant amount of time, even considerable fluctuations in sound pressure will aver-
age out and L
Aeq
will stabilise around a value. If you start a measurement and press until
L
Aeq
is displayed, you can easily observe this effect. Continue measuring until the value of
L
Aeq
becomes stable.
• All measurement subjects exhibit some fluctuation. Depending on the fluctuation, you should
select a measurement time that can limit the short variations of L
Aeq
to one or a few tenths of a
dB. The time required for this to happen depends on the amount of fluctuation. Remember that
the L
Aeq
averaging (measurement) time should always be reported.
1This is because you will then have values for L
Amax
and L
Cpeak
that are not affected by an overload. With
sufficient averaging time, the under-range conditions have only a negligible influence on the L
Aeq
value.
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