ISO 7196 pdf download.Acoustics – Frequency-weighting characteristic for infrasound measurements
1 Scope
This In4emtioml Standard specifies a frequency- weighting cha~ad-tjc, designated G. for the deter- rniriardion OB weighted sound pressure levels of sound or noise wkme spemurn hex+ port& or wholly within the frequency bard tiram: t Ht ta 2Ci Hz. 1′ In; the w e af wideband noises whose spectrum em- braces- both, the infiramnic and audio-frequency ranges, use of, this International. Standard to determine the infrasonic w e i g h t sound’ pesure level is supplementary to the de- scription of sime noise by methods already standard- ized which cover the audio-frequency range only, for example the descriptkm in terms of A-weighted sound pressure level. The numerical value of the results will, in general, differ from the G-weighted result. No significance should be attached to this difference. since the respective results relate to different parts of The noise spectrum with little overlap. 2 The G-weighting can also be used in connection with the determination of sound power levels and sound intensity levels. When measured with the G-curve, these are sym- bolized respectively as kG and L,G.
2 Normative reference
The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publi- cation, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate: the possibility of applying the most re- cent edition of the standard indicated below. Mem- b s of IEC and I S0 maintain registers of currently valid International Standards. I EC 651 :I 979, Sound level meters.
3 Definitions
For the purposes of this International Standard, the following definitions apply. 3.1 infrasound: Sound or noise whose frequency spectrum lies mainly in the band from 1 Hz to 20 Hz. 3.2 audio-frequency sound: Sound or noise whose frequency spectrum lies mainly in the band from 20 Hz to 20 O00 Hz.
4 Specification of frequency-weighting characteristic G
The G frequency response is obtained with a combi- nation of poles and zeros in the complex frequency plane, as given in table 1 . The relative frequency re- sponse corresponding to this pole-zero configuration is given in table2 and shown graphically in figure 1. The G-weighting curve is so defined that it has a gain of O dB at 1 0 Hz, that is, the G-weighted sound pres- sure level of a pure tone at 1 0 Hz is equal to the un- weighted sound pressure level. Between 1 Hz and 20 Hz the curve approximates a straight line with a slope of 12 dB per octave. In this way, each fre- quency is weighted in accordance with its relative contribution to the perception. Below 1 Hz and above 20 Hz, the curve has cut-Offs with rates of 24 dB per octave.
The frequency weighting is designed to be introduced into an instrumentation system having an otherwise constant frequency response. Alternatively, part of the frequency weighting can be omitted from the weighting filter and included elsewhere in the instru- mentation system, so that the entire system exhibits the same performance. The system should be de- signed to indicate the level of the root-mean-square sound pressure in decibels relative to 20 UPa.
The amplifier and frequency-weighting circuit of the instrumentation system should be designed to avoid overload and, bari conjunction with the microphone, to produce the overaft frequency-weighting characteristic G. Relative to the gain at IO Hz, the response of the system should conform as as possible Q the characteristic specified in c b ~ 4, b u s @ o;f the steep rise in sensation with cour^$! pressure Iwefli s- curacy is cmcial and more importan? 1Rm a$ aw$~ frequencies. For the frequency range 1 Hz to 20″k,, the tolerance range should not exceed f 1 dB, and for frequencies below 1 Hz and above 20 Hz, a toler- ance range of – 00′ ta + 1 dB can be applied to the nominal values.