Brüel & Kjær 2240 Guide De L'utilisateur page 29

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 30 dB to
140 dB, separated in two ranges: 30 to 110 dB, and 60 to 140 dB. For any measurement task,
you have to select one of the ranges by pressing
The L parameter (L
AF
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
. 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.
the signal fluctuates heavily, so be sure to use a sufficiently long averaging time to obtain a
stable level of L
Aeq
Measuring L
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L is always calculated for a specific duration, often due to standardised requirements, which
Aeq
demands a report of the measurement duration. L
elongated form as "the 10 minute L
Type 2240 can calculate L
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
• After a significant amount of time, even considerable fluctuations in sound pressure will aver-
age out and L
Aeq
L is displayed, you can easily observe this effect. Continue measuring until the value of
Aeq
L becomes stable.
Aeq
• All measurement subjects exhibit some fluctuation. Depending on the fluctuation, you should
select a measurement time that can limit the short variations of L
dB. The time required for this to happen depends on the amount of fluctuation. Remember that
the L averaging (measurement) time should always be reported.
Aeq
1This is because you will then have values for L
sufficient averaging time, the under-range conditions have only a negligible influence on the L
) and the quasi-analogue bar are useful tools to help you decide which
A
.
was xx.x dB".
Aeq
over durations ranging from 1 second to 60 minutes (in 1 second
Aeq
will stabilise around a value. If you start a measurement and press
Amax
.
1
This type of situation indicates that
durations are recorded as: L
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measurement:
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to one or a few tenths of a
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and L that are not affected by an overload. With
Cpeak
PART 1
23
English
or overload
or in
Aeq,10min
until
value.
Aeq