*Pac •* sound power.

**Partial Definition** IEC 801-30-02, sinusoidal component of a complex sound wave

On the other hand an object, like a cricket ball experiences **acceleration, velocity and displacement** literally so the general acceleration, displacement and velocity terms are more apt.

**Particle Definition** IEC 801-21-24, portion of a medium whose volume has dimensions which are small compared to the wavelength of the sound.

See also • instantaneous particle acceleration

**Particle Displacement Definition** IEC 801-21-26, RMS of the instantaneous particle displacement, over a given time interval, unless otherwise specified

See also • peak particle displacement

**Particle Velocity (v)** is the *speed of a particle* and should not to be confused with the speed of sound (c).

**Particle Velocity Definition** IEC 801-21-29 is the RMS of the instantaneous particle velocity, unless otherwise specified

*Particle velocity relationships* :

Particle velocity × sound pressure = sound intensity.

Particle velocity = sound pressure ÷ acoustic impedance

Particle velocity = sound intensity ÷ sound pressure

Particle velocity = **√**(sound intensity ÷ acoustic impedance)

See also • peak particle velocity

**Particle Velocity Level (Lv)** = 20 lg (v/vo) dB

where

v is the effective *particle velocity* and

vo is the reference particle velocity = 5 x 10^{-8} m/s ≡ 0 dB

The following notations : dB SVL, dB(SVL), dBSVL or dBSVL are often seen but are not strictly correct

1 Pa = 1 N/m^{2} = 1 J/m^{3} = 10^{-5} bar : kg·m^{-1}·s^{-2}

Sound pressure is measured in *pascals*.

Passive Sound Absorber

See also time weightings

Peak Frequency-weighted Sound Pressure Level

See also • particle displacement

If measurements are made in 3-axis then the resultant *PPV (peak particle velocity)* is the vector sum i.e. the square root of the summed squares of the maximum velocities, regardless of when in the time history those occur.

See also • particle velocity • PPV measurements.

Peak Sound Level

Peak Sound Pressure

Peak Speech Power

Peak-to-Peak Sound

**Perceived Noise Level (PNL)**, jet engines are perceived to be noisier than propeller aircraft and led to the development in the 1960's of a scale based on equal loudness contours called Noys.

**Perceived Noise Level Definition** IEC 801-29-11, the frequency-weighted sound pressure level in decibels, obtained by a stated procedure that combines the sound pressure levels in the 24 one-third octave bands centred on 50 Hz to 10 kHz

● Note 2 : Perceived noise level is intended to approximate judged perceived noise level.

See also • effective perceived noise level • judged perceived noise level • maximum perceived noise level • noise exposure forecast • noise and number index • tone-corrected perceived noise level

Permanent Threshold Shift (PTS)

Personal Hearing Protectors

Personal Sound Exposure Meter

This is the basis for the measurement of loudness in phons. If a given sound is perceived to be as loud as a 40 dB sound at 1000 Hz, then it is said to have a loudness of 40 phons.

**Phon Definition** IEC 801-29-07, unit of loudness level, judged or calculated as specified in definition of "loudness level" or definition of "calculated loudness level"

See also • sones

**Picket Fence Effect** information between samples in FFT spectrum analysis may be missing. hanning windows may help

The piezoelectric property of materials is used in transducers that convert acceleration (or force) into electrical signals, and vice versa.

This is useful when using sound analysers with constant percentage bandwidth octave or third-octave filters, the net result is a flat spectrum

**Pink Noise Definition** IEC 801-21-11, noise whose power spectral density is inversely proportional to frequency

Other noise descriptors • ambient noise • background noise • broadband noise • gaussian noise • narrowband noise • periodic • pseudo random noise • random noise • residual noise • specific noise • white noise • wideband noise

They are single frequency devices, usually 250 Hz and include a calibrated barometer to correct for local changes in atmospheric pressure.

**Pistonphone Definition** IEC 801-28-11, apparatus having a rigid piston which can be given a reciprocating motion of known frequency and amplitude so permitting the establishment of a known sound pressure in a closed cavity of small dimensions

**Pitch Definition** IEC 801-29-01 that attribute of auditory sensation in terms of which sounds may be ordered on a scale extending from low to high

● Note 2 : the pitch of a sound may be described by the frequency of that pure tone having a specified sound pressure level that is judged by subjects to produce the same pitch.

Plane Wave or Planewave

**Planning and Noise** the Planning Policy Guidance PPG24 sets out the UK Government's policies on different aspects of planning. Local authorities must take their content into account in preparing their development plans.

*PNL •* perceived noise level

*PNLmax •* maximum perceived noise level

**Point Source**, a noise source whose dimensions are small compared to the propagation distances involved.

We know from the inverse square law that the sound energy level decreases by 6 dB every time the distance between the measurement point and the source is doubled.

See also • line source

**Polar Pattern or Polar Response**, microphones respond to sound coming from different directions with varying degrees of sensitivity. A plot or graph of this response is called a polar pattern (sometimes polar response curve). Similarly loudspeakers and other sound sources have Polar Responses.

*Polar Patterns* are frequency dependent, the low frequency response may be almost omnidirectional but the polar pattern will be come more directional as the frequency rises up the audio range.

Potential Sound Energy Density.

W = J/s joule per second = N m/s newton metre per second : base unit m^{2} kg s^{-3}

See also • our full page on sound power and related parameters.

A root-power quantity is a quantity such as sound pressure, which when squared is proportional to the sound power.

See also our sound level calculation article and the IEC decibel definition.

Power Reference Levels

**Power Spectral Density Definition** IEC 801-21-44, limit as the bandwidth approaches zero, of sound power divided by Bandwidth

**Power Spectrum Averaging** also called **rms averaging**, calculates the weighted average of the sum of the squared levels. The weighting is either linear or exponential. **Power Spectrum Averaging** reduces random fluctuations in the levels but does not reduce the noise floor.

See also other types of averaging

**Power Spectrum Density Definition** under power spectral density definition

**Power Spectrum Level** the level of the power in a band one hertz wide referred to a given reference power.

**Predicted Noise Level Reduction (PNR)** is the calculated noise level reduction at the ear when using ear protectors, based on the manufacturers' HML figures and the measured noise levels at the operators position.

*Preferred frequency* is also known as nominal frequency.

Frequency | Octave | 1/3 octave | Frequency | Octave | 1/3 octave | Frequency | Octave | 1/3 octave | ||
---|---|---|---|---|---|---|---|---|---|---|

16 Hz | x | x | ||||||||

20 Hz | x | 200 Hz | x | 2000 Hz | x | x | ||||

25 Hz | x | 250 Hz | x | x | 2500 Hz | x | ||||

3.15 Hz | x | x | 315 Hz | x | 3150 Hz | x | ||||

40 Hz | x | 400 Hz | x | 4000 Hz | x | x | ||||

50 Hz | x | 500 Hz | x | x | 5000 Hz | x | ||||

63 Hz | x | x | 630 Hz | x | 6300 Hz | x | ||||

80 Hz | x | 800 Hz | x | 8000 Hz | x | x | ||||

100 Hz | x | 1000 Hz | x | x | 10000 Hz | x | ||||

125 Hz | x | x | 1250 Hz | x | 12500 Hz | x | ||||

160 Hz | x | 1600 Hz | x | 16000 Hz | x | x |

**Preferred Noise Criterion (PNC)** a noise measurement system for continuous or ambient noise in indoor environments proposed by Leo Beranek in 1971.

Preferred Speech Interference Level (PSIL)

See also • atmospheric pressure • static pressure • sound pressure and related parameters

The presence of the microphone should not to effect the measurement.

Because of their importance in acoustics we have a full page on measurement microphones

See also • free-field microphones • random incidence microphones

Pressure Residual Sound Intensity Index

Privacy Index

Progressive Waves

Also known as transmission loss, but should not to be confused with sound insulation transmission loss

**Proportionality**, two variables are proportional if there is always a constant ratio between them

*Direct Proportion*, as one value increases, another value increases at the same rate.

*Inverse Proportionality,* when one value decreases at the same rate that the other value increases.

Other noise descriptors • ambient noise • background noise • broadband noise • gaussian noise • narrowband noise • periodic • pink noise • random noise • residual noise • specific noise • white noise • wideband noise

**Psychoacoustics** the interaction of the human auditory system and acoustics.

**Pulse Code Modulation** and **Adaptive Delta Pulse Code Modulation**, subclasses of the WAV : waveform audio file format

**Pulse Code Modulation,** works by taking discrete samples at even intervals (called the sampling rate). Common intervals are 11 kHz, 22 kHz, and 44 kHz. The higher the sampling rate, the better the representation of the original analogue wave and the better the sound quality.

**Adaptive Delta Pulse Code Modulation (ADPCM),** is a form of compression, is a more efficient way of storing waveforms than 16-bit or 8-bit PCM

**Pure Tone**, a tone with a single frequency, no harmonics, for example a sine wave.

**Pure Tone Definition** IEC 801-21-05, sinusoidal acoustic oscillation, also known as *pure sound*

See also • complex sound • tone

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