What are A, C & Z Frequency Weightings?

On your sound level meter or noise meter you will often see references to Frequency Weightings such as ‘A’, ‘C’ or ‘Z’. But what do these mean?

Your ears are most sensitive to frequencies between about 500Hz and 6kHz and less sensitive to frequencies above and below these. To allow the sound level meter or noise dosimeter to measure and report noise levels that represent what we hear, Frequency Weightings are used. These are electronic filters within the the instrument that are used to adjust the way in which the instrument measures the noise.

The most commonly used Frequency Weightings that you will see on a modern sound level meter or noise dosimeter are ‘A’, ‘C’ and ‘Z’ and below is a brief explanation of each of these.

It is very important that you measure the noise levels using the correct frequency weighting as it is not possible to convert from one to another after the measurement has been made. This is why a the Cirrus Optimus® Sound Level Meters will measure all three Frequency Weightings at the same time, saving you time and removing the risk of measuring the wrong parameter.

‘A’ Frequency Weighting

‘A’ Weighting is standard weighting of the audible frequencies designed to reflect the response of the human ear to noise. At low and high frequencies, the human ear is not very sensitive, but between 500 Hz and 6 kHz the ear is much more sensitive.

The ‘A’ weighting filter covers the full frequency range of 20 Hz to 20 kHz, but the shape approximates to the frequency sensitivity of the human ear. So the A-weighted value of a noise source is an approximation to how the human ear perceives the noise.

Measurements made using A-weighting are usually shown with dB(A) to show that the information is ‘A’ weighted decibels or, for example, as LAeq, LAFmax, LAE etc where the A shows the use of A-Weighting.

‘C’ Frequency Weighting

‘C’ Weighting is a standard weighting of the audible frequencies commonly used for the measurement of Peak Sound Pressure level.

Measurements made using ‘C’ weighting are usually shown with dB(C) to show that the information is ‘€˜C’€™ weighted decibels or, for example, as LCeq, LCPeak, LCE etc where the C shows the use of ‘C’ Weighting.

‘Z’ Frequency Weighting

Z weighting is a flat frequency response between 10Hz and 20kHz ±1.5dB excluding microphone response.

Measurements made using ‘Z’ weighting are usually shown with dB(Z) to show that the information is ‘Z’€™ weighted decibels or, for example, as LZeq, LZFmax, LZE etc where the Z shows the use of ‘Z’ Weighting.

Frequency Weighting Curves used on Sound Level Meters

Frequency Weighting Curves – ‘A’, ‘C’ & ‘Z’

Where these Frequency Weightings are defined

All of these frequency weightings are defined in the standards to which a noise measurement instrument is designed. For example, the frequency weightings used on a sound level meter will be defined in IEC 61672:2003 (BS EN 61672-1:2003 ).

This standard specifies the performance and tolerances for the frequency weighting curves to be used.

Frequency (Hz)

63

125

250

500

1k

2k

4k

8k

16k

A-weighting (dB)

– 26.2

– 16.1

– 8.6

– 3.2

0

+ 1.2

+ 1.0

-1.1

– 6.6

C-weighting (dB)

– 0.8

– 0.2

0

0

0

– 0.2

– 0.8

– 3.0

– 8.5

Z-weighting (dB)

0

0

0

0

0

0

0

0

0

The A, C & Z Frequency Weighting is measured simultaneously by all our Optimus® Sound Level Meters. To find the right sound level meter for you, use our online Optimus® Selector. Simply select the applications, features and functions you require and we’ll tell you the best sound level meter for your requirements.


Download the Noise Measurement Terminology Guide to expand your noise knowledge and make measuring noise simpler.

download a Guide to Noise Measurement Terminology

James Tingay

James Tingay

Marketing Manager at Cirrus Research plc
Marketing Manager at Cirrus Research plc, the leading manufacturer of noise measurement instruments.
James Tingay

Expand your Noise Knowledge!

Signup to the NoiseNews blog for the latest article updates straight to your inbox.