Wörterbuch
-
L
Suchen Sie in unserem Wörterbuch nach Schlagworten aus dem Bereich Schall und Schwingungen.
L-weighting
Linear weighting. All values are weighted equally in the specified range.Lateral Location
The physical location of a rotor relative to the fixed, or non- rotating parts of the machine.Law of the First Wavefront
The first wavefront falling on the ear determines the perceived direction of the sound.Ldn
A 24-hour Leq, except 10 dB is added to all levels measured between 2200 and 0700 hrs.Leading Edge
The part of the signal near the start of the time window.Leakage
In an FFT analyzer, the input signal is recorded in time blocks, called time records, and individual spectra are computed from each block of data. Because the input signal period is not synchronised with the duration of the time block, the signal will be truncated at the beginning and end of the block. This truncation causes an error in the calculation, which effectively spreads out, or “smears”, the spectrum in the frequency domain. This phenomenon is called leakage; the signal energy essentially “leaks” from a single FFT line to adjacent lines. Leakage reduces the accuracy of the measured levels of peaks in the spectrum, and reduces the effective frequency resolution of the analysis. Leakage is worst for continuous signals and rectangular window, and it is greatly reduced by use of the Hanning Window, which forces the signal level to zero at the ends of the data block.LED
Light emitting diode.LEPN
Effective Perceived Noise Level. A complex rating used to certify aircraft types for Flyover Noise. Includes corrections for pure tones and for duration of the noise.Level
A sound pressure level in dB means that it is calculated relative to the standard reference level of 20 µPa for airborne sound. The word “level” associates that figure with the appropriate standard reference level. In common usage the level of a signal is its amplitude, but strictly speaking the term should be reserved for the amplitude expressed on a decibel scale relative to a reference value.LFD
Low-frequency diffusion.Liftering
A technique to separate harmonic vibration families. The main application for Cepstrum analysis is analysis of gearboxes. Liftering is used to separate the different harmonic vibration families from the various rotating shafts.Line Amplifier
An amplifier designed to operate at intermediate levels. Its output is usually on the order of one volt.Line Drive
An input socket that can also provide power to drive a transducer.Line Source
A sound source composed of many point sources in a defined line, such as a train, flow of traffic on a motorway, or constant aircraft take-offs and landings.Line Spacing
In an FFT spectrum, the frequency difference between two adjacent bin centres or lines.Line Spectrum
A line spectrum is a spectrum where the energy is concentrated at specific frequencies (lines or bins), as opposed to a continuous spectrum where the energy is smeared out over a band of frequencies. A periodic deterministic signal will have a line spectrum, and a random signal will have a continuous spectrum. Spectra generated by machine vibration signatures are always a combination of these two types.Linear
A device or circuit with a linear characteristic means that a signal passing through it is not distorted.Linear Taper
Attenuation by a numerical factor that increases or decreases linearly with time.Live End-Dead End
An acoustical treatment plan for rooms in which one end is highly absorbent and the other end reflective and diffusive.LN
The dB(A) level exceeded N % of the time, for example, L90, the dB(A) level exceeded 90% of the time, is commonly used to estimate ambient noise level.LNP
Noise Pollution Level. A variation of Leq which accounts for short-term variability in noise level.Logarithm
The exponent required (power to which a number must be raised) to produce a given number. For example, used in acoustics, 10 to the exponent 2 = 100; the log of 100 = 2.Logarithmic Amplitude Scale
Critical vibration components usually occur at low amplitudes compared to the rotational frequency vibration. These components are not revealed on a linear amplitude scale because low amplitudes are compressed at the bottom of the scale. But a logarithmic scale shows prominent vibration components equally well at any amplitude. Moreover, percent change in amplitude may be read directly as dB change. Therefore, noise and vibration frequency analyses are usually plotted on a logarithmic amplitude scale.
Loudness
An observer’s auditory impression of the strength of a Loudness: The subjective judgement of intensity of a sound by humans. Loudness depends upon the sound pressure and frequency of the stimulus. Over much of the frequency range it takes about a threefold increase in sound pressure (a tenfold increase in acoustical energy, or, 10 dB) to produce a doubling of loudness. The unit is the Sone. The Zwicker method of calculation of stationary loudness is described in ISO 532 B and DIN 45631.Loudness Level
Measured in phons it is numerically equal to the median sound pressure level (dB) of a free progressive 1000 Hz wave presented to listeners facing the source, which in a number of trials is judged by the listeners to be equally loud. Loudness level can be calculated according to ISO 532B.Loudspeaker
An electro-acoustical transducer that changes electrical energy to acoustical energy.Low-pass Filter
A filter that passes signals with less than 3 dB attenuation up to its cut-off frequency, and attenuates the signal above that frequency. The attenuation slope is called the Roll Off. An Anti-aliasing Filter is an example of a low-pass filter.LSEL
Single Event Noise Exposure Level. The dB(A) level which, if it lasted for one second, would produce the same A-weighted sound energy as the actual event.Brüel & Kjær Sound & Vibration Dictionary End User Agreement
