C-weighting

C and Ctr (spectrum adaption terms) - sound insulation

**Calculated Loudness Level Definition** IEC 801-29-06, loudness level calculated by a specified procedure.

Note 1 : such procedures are given in BS ISO 532-1:2017 methods for calculating loudness

See also equal loudness contours • loudness level

Hand-held calibrators available for this purpose.

See also • hand arm vibration syndrome

CB (critical band)

CCLD (constant current line drive)

**Characteristic Acoustic Impedance Definition** ASA 6.35, at a point in a medium, the complex ratio of sound pressure to particle velocity in the direction of the wave propagation. SI Unit = Pa·s/m (pascal second per metre), also known as the *specific acoustic impedance*.

See other acoustic impedance topics

**Characteristic Impedance of a Medium Definition** IEC 801-25-39, product of the equilibrium, the density and the speed of sound in a medium.

Note : for a plane acoustic wave propagating in a non-dissipative medium, the specific acoustic impedance relative to this wave is equal to the *characteristic impedance of the medium*.

To take into account different cable lengths or to convert from charge sensitivity to voltage sensitivity, divide the *charge sensitivity* by the total capacitance of the accelerometer and the cable. For example a 1 pC/ms^{-2} and 9.8 pC/g accelerometer with a capacitance of 900 pF and a 1.2 m cable (100 pF), would give 1 pC / (900+100) pF = 1 mV/ms^{-2} or 9.8 pC / (900+100) pF = 9.8 mV/g. By definition 1 g = 9.807 ms^{-2} and conversely 10 ms^{-2} = 1.01 g

See also IEPE, integrated electronics piezoelectric

CIS : common intelligibility scale

Clarity

**Class 0** precision grade sound instrumentation, laboratory measurements, also known as *Type 0*

**Class 1** precision grade sound instrumentation, laboratory and field use, also known as *Type 1*.

**Class 2** general grade sound level meters for field use, also known as *Type 2*.

CNEL : community noise equivalent level

**Coherent Output Power Spectrum ** a measure of what part of the (output) power spectrum is fully coherent with the input signal.

**Coherent Sources** a sound arriving directly from a source and a sound arriving at the same point from the same source but modified by the reverberant field are said to be coherent. Changes in level, phase or time do not change the fact that the sound is coherent.

Coincidence Effect

Common Intelligibility Scale

See also the IEC Definition of Level

See related acoustic impedance topics

**Complex Sound Definition** IEC 801-21-06, sound that is not a simple oscillation

Complex Sound Source

**Compliance**, conforming to environmental laws, regulations, standards and other requirements.

Compression Wave

**Conjugate Impedances Definition** IEC 801-25-14, impedances whose real components (resistances) are equal and whose imaginary components (reactances) are equal but opposite in sign.

Note : conjugate impedances are expressed by conjugate complex quantities.

*Constant Bandwidth Filter* with fixed frequency
bandwidth, expressed in Hertz (Hz), regardless of centre frequency.

*Constant Percentage Bandwidth Filter* the bandwidth is a fixed percentage of centre frequency. The width of the individual filters is defined relative to their position in the range of interest. The higher the centre frequency of the filter, the wider the bandwidth. The bandwidth is usually defined in octaves, 1/3 octaves or as a fixed percentage of the centre frequency of the filter.

**Continuous Spectrum Definition** IEC 801-21-17, sound spectrum whose components are continuously distributed over a given frequency range.

See also noise dose

*Correlation Coefficient* when the correlation is 1 then *perfect positive correlation* exists and -1 equates to a *perfect negative correlation*. When the correlation is 0, there is no relationship between the two sets of data.

**Coulomb (C)** a coulomb is a unit of electrical charge, defined as the quantity of electrical charge transferred by 1 ampere in 1 second. Symbol C.

1 picocoulomb = 1 x 10

**Coupled Modes Definition** IEC 801-24-17, modes of oscillation which are not independent but influenced by the transfer of energy from one mode to the other.

See also uncoupled mode

CPB : constant percentage bandwidth filter

Sound levels often have high **Crest Factors**, so hearing damage risk assessments require both the LAeq and the Peak values to be reported.

Criterion Level

Criterion Time

The notion of critical bands explains the auditory masking of a narrow band (sinusoidal) signal by a wideband noise source. Critical Band Frequencies.

See also loudness.

**Critical Damping Definition** IEC 801-24-20, minimum damping that will allow a displaced system to return to its initial state without oscillation.

See also other acoustic damping topics

Critical Distance

Critical Frequency

See also autocorrelation

*Cross Power Spectrum* measurement of two signals with an amplitude that is the product of the two signal amplitudes and a phase that is the difference of the two phases.

Ctr : spectrum adaption terms - sound insulation

Cylindrical Wave

Home • Glossary Search • Certified Instrumentation for Hire