Larson Davis SoundAdvisor 831C Reference Manual page 206

L
eq
Level (dB)
Linear Integration
Ln Value
Measurement Duration (T)
Microphone Guidelines
SoundAdvisor Model 831C
See "Energy Equivalent Sound Level (Leq)", "Sound", and "Time Weighting"
A descriptor of a measured physical quantity, typically used in sound and vibration measure-
ments. It is attached to the name of the physical quantity to denote that it is a logarithmic mea-
sure of the quantity and not the quantity itself. The word decibel is often added after the number
to express the same thing. When frequency weighting is used the annotation is often expressed as
dB(A) or dB(B).
One of 2 integration methods used on the 831C SLM.
This is the default and most commonly used integration method for measuring sound. Linear inte-
grates only the energy during a given period. It does not show a decay slope of a Fast, Slow, or
Impulse exponential detector. For additional information, see "Exponential Integration".
You can locate this setting by selecting any menu Setup Manager General.
The Ln value is the sound level that has exceeded n% over the total measurement time. For exam-
ple, if n=90%, a displayed value of 35dB for L90 means that for 90% of the measurement period
the dB level was at or above 35dB. These statistical values are commonly used to describe the
characteristics of non-steady sound such as environmental noise.
To calculate Ln values, the 831C creates an amplitude distribution table over the range 0 to 200
dB, in amplitude increments of 0.1 dB. This data permits the calculation of Ln values for any value
of n in the range 00.01 to 99.99%.
Locate the Ln values on the 831C by going to Setup Manager Ln Page.
The time period of measurement. It applies to hearing damage risk and is generally expressed in
hours.
Standard: ANSI S12.19
Microphone - Types: A device for detecting the presence of sound. Most often it converts the
changing pressure associated with sound into an electrical voltage that duplicates the changes. It
can be composed of one of the following types:
Capacitor (Condenser): A microphone that uses the motion of a thin diaphragm caused by the
sound to change the capacitance of an electrical circuit and thereby to create a signal. For high
sensitivity, this device has a voltage applied across the diaphragm from an internal source.
Electret: A microphone that uses the motion of a thin diaphragm caused by the sound to change
the capacitance of an electrical circuit and thereby to create a signal. The voltage across the dia-
phragm is caused by the charge embedded in the electret material so no internal source is
needed.
Microphone - Uses: The frequency response of microphones can be adjusted to be used in spe-
cific applications. Among those used are:
C-9