Throughout this Glossary we include IEC Definitions where appropriate

The built-in electronic preamplifier transforms the high impedance charge output of the sensor into a low impedance voltage signal that can be transmitted over longer distances.

This technique is widely used under other trade names: ICP ®, Deltatron ®, Piezotron ®, etc.See also piezoelectric

See also real

See also impact noise rating • impact sound • impact testing

● Note 1 : the term impedance is generally applied to a linear system and to steady sinusoidal signals.

● Note 2 : in the case of a transient, impedance as a function of frequency is the quotient of the respective Fourier or Laplace transforms.

● Note 3 : an impedance is the quotient of two quantities the product of which has the dimensions of power or power per unit area.

See also acoustic admittance • acoustic impedance • acoustic ohm • acoustic reactance • acoustic resistance • admittance • characteristic acoustic impedance • characteristic impedance of a medium • complex acoustic impedance • conjugate impedances • driving point impedance • specific acoustic impedance • specific acoustic reactance • specific acoustic resistance • specific wall admittance • specific wall impedance • transfer impedance • transmission impedance and radiation

Impedance Tube

**Impulse** in acoustics, events with a very short duration, see the formal definition and other terms in common use below.

**Impulse Definition** IEC 801-24-26, time integral of a force over the time during which the force is applied.

The frequency response, phase response, and transient response are all tied to this specification.

1 ) a single or multiple sound pressure peak(s) with a rise time less than 200 milliseconds or total duration less than 200 milliseconds.

2 ) or generally speaking, a noise which manifests itself as a succession of distinct pulses or transients.

See also impulsive time weightings

See also direct sound field

Incident Sound Wave

Indicators : LAeq,16h • Lday • Levening.

See also aircraft noise • railway noise • road traffic noise

● Note :

See also other oscillation terms

See also decay and reverberation.

INR (impact noise rating)

See also instantaneous sound pressure

Instantaneous Sound Intensity

Instantaneous Kinetic Sound Energy Density

See also particle acceleration

See also particle displacement

See also particle velocity • peak particle velocity

Instantaneous Potential Sound Energy Density

Instantaneous Sound Energy Density

Instantaneous Sound Pressure

Instantaneous Speech Power

Institute of Acoustics

*Integrated Circuit Piezoelectric and Integrated Electronic Piezoelectric* under IEPE.

**Integration in mathematics** an integral assigns numbers to functions in a way that can describe displacement, area, volume and other concepts that arise by combining data.

A vibration integrator is basically a low-pass filter with 6 dB or 12 dB per octave attenuation. Analogue integrators are only accurate over a discrete frequency range.

Intelligibility

Intensity

International Electrotechnical Commission

International System of Units

International Standards Organisation

● Note 1 : the International System of Quantities is published in the International Standard ISO/IEC 80000, Quantities and units.

● Note 2 : the International System of Units (SI) is based on the ISQ.

For example at 16 metres from a point sound source the sound pressure level will be reduced by 20 log (16) = 24 dB, relative to the level at 1 metre, to check this example type 20 log (16) into Google.

Since the surface area of a sphere is 4·π·r², then the surface area **increases by a factor of 4** each time r (the distance from the source) is doubled

Measuring sound pressure levels is more common in the practical world and the sound pressure decreases by a factor of 2 every time the distances is doubled. In decibels this is 20·log (2) = 6 dB *. However we know that sound intensity ∝ p² so the 'general' 6 dB rule still applies. Strictly speaking this is not *inverse square* but inverse proportionality, also known as inverse distance law.

See also point source • line source • sound level calculations article

IOA : Institute of Acoustics

Isotron ®

ISQ : International System of Quantities

ITD (initial time delay)

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