**ICP ®** Integrated Circuit Piezoelectric, see IEPE below.

**IEC : International Electrotechnical Commission,** founded in 1906, the IEC is the world’s leading organization for the preparation and publication of International Standards for all electrical, electronic and related technologies. These are known collectively as "electrotechnology

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 • various impulse definitions.

**Impact Sound Insulation** see
normalized impact sound pressure level (Ln & L'n) and also
impact sound pressure level (Li)

**Impedance Definition** IEC 801-25-13, at a given frequency, quotient of a dynamic field quantity (such as force, sound pressure) by a kinematic field quantity (such as vibration velocity, particle velocity), or quotient of a voltage by a current

● 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 • 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

**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

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.

● Note : *inertance* has dimensions of mass divided by the square of area

See also other oscillation terms

See also • decay and reverberation.

Also known as the 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.

**Integrating** (of an instrument), indicating the mean value or total sum of a measured quantity.

Integrating Sound Level Meter, more correctly known as the *Integrating-averaging Sound Level Meter* and commonly known as the *Leq Meter*

**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.

**Integration in vibration,** will convert an acceleration signal into a velocity signal, or a velocity signal into a displacement signal. For this reason, an accelerometer is the transducer of choice because velocity and displacement can be so easily derived from its output.

An 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.

See also • differentiation

**Integrator,** an electrical frequency filter used to convert a vibratory acceleration signal to one whose amplitude is proportional to velocity or displacement.

*International Electrotechnical Commission* under IEC

*International System of Units* under SI units

*International Standards Organisation* under ISO

● 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.

Since the surface area of a sphere is 4·π·r^{2}, then the surface area **increases by a factor of 4** each time r (the distance from the source) is doubled

Therefore the sound intensity (Watts/m^{2}) **decreases by a factor of 4** each time the distance from the source is doubled. In decibels this is 10·Log(4) = 6dB.

Measuring sound pressure levels is more common in the practical world and the sound pressure decreases by 50% every time the distances is doubled. However we know that intensity I ∝ p^{2} so the 6 dB rule still applies. Strictly speaking this is not inverse square but inverse proportional, also known as *inverse direct law*.

See also • point source

**Isotron ®** trade name for IEPE : integrated electronic piezoelectric.

**Isotropic,** is derived from Isotropy i.e. an object or substance which is uniform in all directions. In acoustics it is sometimes used to describe noise sources like loudspeakers arrange in a dodecahedron format to give uniform sound output levels in all directions.

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