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p-I index
The p-I index is equivalent to the mean pressure level minus the sound intensity level.Paired Comparison Test
A test method in which recorded sounds are compared in pairs.Parameter
An attribute with a value (for example, weighting).Parameter Estimation
The process of evaluating and curve fitting frequency response functions in order to estimate modal parameters.Parametric Model
A model with structure, that is, one that includes geometry and material properties.Partial
One of a group of frequencies, not necessarily harmonically related to the fundamental, which appear in a complex tone. Bells, xylophone blocks, and many other percussion instruments produce harmonically unrelated partials.Partial Fields
In STSF applications one of the basic assumptions is that the total sound field consists of a small number of independent, or partial sound fields.Partial source
An input in airborne contribution analysis (for example, top engine face).Particle Velocity (Acoustics)
The instantaneous value of the distance travelled by a particle per unit time in a medium that is displaced from its equilibrium state by the passage of a sound wave.Pascal (Pa)
The unit in which pressure is measured. 1 Pa = 1 N/m2.Passband
The range of frequencies between filter cut-off frequencies defining the frequency band that is not attenuated.Passive Absorber
A sound absorber that dissipates sound energy as heat.Passive side
In structure-borne contribution analysis, the side which receives or transfers energy, and is thus passive. Also referred to as body side. Note: There may be sub-frames in a measurement setup, which could be considered both part of the vehicle’s body and engine – it is up to the user to determine what to classify these in his SPR modelPath
An input in structure-borne contribution analysis.Path-to-receiver FRF
A noise FRF for structure-borne contributions, and an acoustic FRF for airborne contributions. Other names and variants include: Body sensitivities, Path sensitivities, Path-to-receiver transfer function, FRF, P/F, Path sensitivities, Vibroacoustic sensitivity.Peak
The maximum positive or negative dynamic excursion from zero (for an AC coupled signal) or from the offset level (for a DC coupled) of any time waveform. Sometimes referred to as “true peak” or “waveform peak”.Peak Pick
A parameter estimation technique where the peak value of the imaginary part of the frequency response function is used to estimate the mode shape value at that point. The phase is given by its sense (positive or negative). This method is also known as quad picking since the value is being picked off the imaginary or quadrature part of the frequency response function.Peak Sound Pressure
The maximum absolute value of the instantaneous sound pressure in a specific time interval. Note that in the case of a periodic wave, if the time interval considered is a complete period, the peak sound pressure becomes identical with the maximum sound pressure.Peak-to-peak
The amplitude difference between the most positive and most negative value in a time waveform, that is, the total amplitude.Period
A signal that repeats the same pattern over time is called periodic, and the period is defined as the length of time encompassed by one cycle, or repetition. The period of a periodic waveform is the inverse of its fundamental frequency.Periodic Random Noise
Sequences of different pseudo-random signals of the same power. The first periods of each sequence give the system time to respond to the change. The last period is used for the analysis.Periodic Signal
A signal is periodic if it repeats the same pattern over time. The spectrum of a periodic signal always contains a series of harmonics.Periodic Vibration
An oscillatory motion whose amplitude pattern repeats after fixed increments of time.Permanent Threshold Shift (PTS)
The component of threshold shift that shows no progressive recovery with the passage of time when the apparent cause has been removed. Noise-induced permanent threshold shift (NIPTS) is the component of PTS associated with a noise exposure. Age-related threshold shift (ARTS) is the component of PTS related to age. It is usually assumed that these components are additive, at least for small values of the components. A permanent decrease of the acuity of the ear at a specified frequency as compared to a previously established reference level. The amount of permanent threshold shift is customarily expressed in decibels.PFC
Phase-frequency curve.Phase
Time lag or lead. The difference in time between two events such as the zero crossing of two waveforms, or the time between a reference and the peak of a waveform. The phase is expressed in degrees as the time between two events divided by the period (also a time), times 360 degrees. The phase of the cross spectrum reflects the time relation between the two signals.Phase Demodulation
Angular (or torsional) vibration from rotating shafts can be measured using phase demodulation of the signal from shaft encoders mounted on the end of the shaft.Phase Mismatch
The relative phase mismatch between the two channels in an Intensity Measuring System.Phase Shift
The angular difference between two signals, which reflects the time difference.Phon
Unit of measurement for Loudness Level of a sound. It Is numerically equal to the sound pressure level of a 1 kHz free progressive wave which is judged by reliable listeners to be as loud as the unknown sound.Picket Fence Effect
The FFT spectrum is a discrete spectrum, containing information only at the specific frequencies that are decided upon by setting the FFT analyzer analysis parameters. The true spectrum of the signal being analysed may have peaks at frequencies between the lines of the FFT spectrum, and the peaks in the FFT spectrum will not be at exactly the correct frequencies. This is called Resolution Bias Error, or the Picket Fence Effect. The name arises because looking at an FFT spectrum is something like looking at a mountain range through a picket fence. By a process of interpolation, it is possible to increase the apparent resolution and amplitude accuracy of the FFT spectrum by a factor of ten. Note: The Flat Top Window provides the best weighting function for reducing picket fence error.Piezoelectric Accelerometers
Piezoelectric (PE) accelerometers use a spring-mass system to generate a force proportional to the amplitude and frequency of vibration. The force is applied to a PE element, which produces a charge on its terminals that is proportional to the mechanical motion. An advantage of PE materials is that they are self-generating and do not require an external power source. They are also capable of operating at very high and very low temperatures, and are known for their ruggedness. A variety of designs are available.Piezoresistive Accelerometers
PR accelerometers offer the advantage of dc response. This suits them to measurements of long duration pulses found in transportation vibration, automotive crash studies and blast testing. Because they utilise an external source of electrical energy, they have inherently low output impedance. For many applications, sensitivity is high enough that preamplification of the output is unnecessary. Standard and miniature sizes are available. System calibration checks can be performed using the turnover technique, or by shunt calibration.Piezoresistivity
Piezoresistive (PR) strain gauge elements are solid state silicon resistors that change electrical resistance in proportion to applied mechanical stress. In the traditional design, discrete strain gauges are mechanically attached to cantilever beams and electrically connected in a Wheatstone bridge to produce an electrical signal proportional to vibratory motion. Compared to wire gauges, PR gauges are virtually free of mechanical hysteresis and have several orders of magnitude greater sensitivity. Monolithic sensors are microfabricated mechanisms that include diffused silicon strain gauges as well as the mechanical components of an accelerometer in a common silicon chip. This eliminates the epoxy joints and reduces the problem of matching gauge elements. Monolithic micromachined silicon microsensors offer outstanding reliability, high sensitivity and excellent linearity. Because of silicon’s excellent yield strength and relatively high piezoresistive coefficient, sensor design stress levels can be kept low for outstanding ruggedness, while still maintaining an excellent signal-to-noise ratio.Pink Noise
Broadband noise whose energy content is inversely proportional to frequency (-3 dB per octave or -10 dB per decade).Pinna
The cartilaginous structure of the external ear.Pitch
The attribute of auditory sensation that orders sounds on a scale extending from low to high. Pitch depends primarily upon the frequency of the sound stimulus, but it also depends upon the sound pressure and waveform of the stimulus.Place Effect
The theory that pitch perception is related to the pattern of excitation on the basilar membrane of the cochlea.Plane Wave
A wave whose wave fronts are parallel planes perpendicular to the direction in which the wave is travelling.Plenum
An absorbent-lined cavity through which conditioned air is routed to reduce noise.Point Source
A source whose dimensions are small compared to the propagation distances described in reference to it.Polar Pattern
A graph of the directional characteristics of a microphone or loudspeaker.Polarization Voltage
The polarization voltage used to drive a condenser microphone.Post-averaging
The averaging of a signal after a measurement has been made on it.Post-processing
The application of a mathematical function to a signal after measurement to further improve the information that can be obtained from the analysis.Power over Ethernet
Power over Ethernet (PoE) described in the IEEE 802.3af standard, is a technology that integrates power into a standard LAN infrastructure. It provides the network device, in this case the module, with up to 15 W of power using the same cable as that used for network connection.Power (PWR)
A scaling unit. The power of a signal is the mean value of a signal squared.Power Spectral Density (PSD)
A scaling unit. Power spectral density is a method of scaling the amplitude axis of spectra of random rather than deterministic signals. Because a random signal has energy spread out over a frequency band rather than having energy concentrated at specific frequencies, it is not meaningful to speak of its RMS value at any specific frequency. It only makes sense to consider its amplitude within a fixed frequency band, usually 1 Hz. PSD is defined in terms of amplitude squared per Hz, and is thus proportional to the power delivered by the signal in a one-Hz band.Power Spectrum
The average squared magnitude of multiple frequency spectra.Power Spectrum Level
The level of the power in a band one hertz wide referred to a given reference power.PRD
Primitive root diffuser.Preamplifier
An amplifier used to boost the physical input signal detected at the transducer before it is sent to an input module and down the measurement chain for measurement and analysis.Precision Time Protocol
The IEEE 1588 Precision Time Protocol provides a protocol for synchronising the clocks of modules in a distributed measurement system, thus providing correlated data acquisition across the measurement transducers.
Under the protocol, the “best” clock in the system becomes the master clock, and all the rest become “slave” clocks. The master clock sends a “sync” packet that contains the time of packet’s departure. When this packet is received by a slave clock, it notes the arrival time according to its own clock. The difference between the two is equal to the network propagation time plus the offset between the master and slave clocks. The slave adjusts its clock, thereby reducing the difference between the two clocks to the network propagation time.
IEEE 1588 assumes that network propagation time is the same from slave to master as from master to slave. Using this assumption, the slave sends a time-stamped “delay request” to the master. The master promptly returns a “delay response” stamped with the time at which it received the request. The difference between these two time stamps is the network propagation delay and the slaves can thus adjust their clocks to match the master clock.Predicting Sound Pressure level from Sound Power Level
- In free field: Lp = Lw + log Q - 20 log r – 10.8 dB
- Over hard reflecting plane: Lp = Lw + log Q - 20 log r – 7.8 dB
- In Reverberant Room: Lp = Lw - 10 log R + 6.2 dB
where:
- r is distance in metres
- Q is Directivity Factor of the sound source
- R is the room constant in square metres
Preferred Frequencies
A set of standardised octave and third-octave centre frequencies defined by ISO R266, DIN 45401 and ANSI S1.6-1967. Octave and 1/3-octave filters are centred at preferred frequencies defined in ISO R 266. Although nominal frequencies are used to identify the filters, the true centre frequencies of 1/3-octave filters are calculated from 10n/10 where n is the band number.
|
Band
Number |
Exact
Frequency
(Hz) |
Band
Number |
Exact
Frequency
(Hz) |
|
0 |
1 |
6 |
3.9811 |
|
1 |
1.2589 |
7 |
5.0119 |
|
2 |
1.5849 |
8 |
6.3096 |
|
3 |
1.9953 |
9 |
7.9433 |
|
4 |
2.5119 |
10 |
10 |
|
5 |
3.1623 |
11 |
12.589 |
Because of the way their centre frequencies are generated, 1/3-octave filters are often referred to as 1/10-decade filters. Crossover frequencies are calculated from 10n/10 ± 0,5. Octave filters are successive sets of three third-octave filters, starting with Bands 2 — 4.
Presbycusis
Hearing loss mainly for high tones that is attributed to the ageing process.Pressure Conversion Chart
|
From
To |
PSI |
pascal |
bar |
millibar |
in. Hg |
IN. H2O |
mm Hg |
mm H2O |
atm |
*kg/cm2 |
|
PSI |
1 |
0.00014504 |
14.504 |
0.014504 |
0.49118 |
0.036127 |
0.019337 |
0.0014223 |
14.696 |
14.223 |
|
pascal |
6894.6 |
1 |
1.00000 |
100 |
3386.5 |
249.08 |
133.32 |
9.8068 |
101320 |
98067 |
|
bar |
0.068946 |
0.00001 |
1 |
0.001 |
0.033865 |
0.0024908 |
0.0013332 |
9.8068E-05 |
1.0132 |
0.98068 |
|
millibar |
68.946 |
0.01 |
1000 |
1 |
33.865 |
2.4908 |
1.3332 |
0.98068 |
1031.2 |
980.68 |
|
in. Hg |
2.0359 |
0.00029529 |
29.529 |
0.029529 |
1 |
0.073552 |
0.039368 |
0.0028959 |
29.92 |
28.959 |
|
IN. H2O |
27.68 |
0.0040147 |
401.47 |
0.40147 |
13.596 |
1 |
0.53525 |
0.039372 |
406.78 |
393.72 |
|
mm Hg |
51.714 |
0.0075006 |
750.06 |
0.75006 |
25.401 |
1.8683 |
1 |
0.073558 |
760 |
735.59 |
|
mm H2O |
703.05 |
0.10197 |
10197 |
10.197 |
345.32 |
25.399 |
13.595 |
1 |
10332 |
1.0000 |
|
atm |
0.068045 |
9.8692E-06 |
0.98692 |
0.00098692 |
0.033422 |
0.0024583 |
0.00131558 |
9.6788E-05 |
1 |
0.9678 |
|
kg/cm2 |
0.070305 |
1.0197E-05 |
1.0197 |
0.0010197 |
0.034531 |
0.0025399 |
0.0013595 |
0.0001 |
1.0332 |
1 |
Pressure Gradient
The change in pressure with distance, from lower to higher pressure, or vice versa. Used in the determination of sound intensity, the pressure gradient enables particle velocity to be measured.Pressure-Intensity Index, LK
The reactivity index in a given direction at a point is defined as the difference between the sound intensity level and the sound pressure level measured in the given direction at that point. In practice LK is normally negative.Pressure-Residual Intensity Index, LK,0
The residual intensity index for a given measurement system is defined as the difference between the indicated intensity level and the measured sound pressure level when exactly the same signal is fed into the two channels of an intensity analysing system. This index will normally be negative.Pressure Zone
As sound waves strike a solid surface, the particle velocity is zero at the surface and the pressure is high, thus creating a high-pressure layer near the surface.Probability Density
In analysing signals, the probability density is the probability that the signal level at some point in time lies within a defined area.Prominence Ratio
The difference between the total power in a critical band and the average power in the adjacent critical bands. If the difference is greater than 7 dB, the component is "prominent".Pseudo-random Noise
A periodic signal where one period is a segment of a random signal. The period is determined by the generator span and the number of generator lines.Psychoacoustic Test Bench
Brüel & Kjær’s sound quality tool used to carry out subjective and objective sound tests, and statistical regression analysis.Psychoacoustics
The study of the interaction of the human auditory system and acoustics.Pulse
A single or a series of pulses. The pulse shape, the width and the interval between pulses are selectable.Pure Tone
A sound having a single frequency whose sound pressure varies sinusoidally with time. A tone with no harmonics. All energy is concentrated at a single frequency. The sound pressure is a simple sinusoidal function of the time, and characterised by its singleness of pitch.Brüel & Kjær Sound & Vibration Dictionary End User Agreement
