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ISO 31-7 is the part ofinternational standardISO 31 that defines names and symbols forquantities andunits related toacoustics. It is superseded byISO 80000-8.[1]
Its definitions include:
| Quantity | Unit | Remarks | |||
|---|---|---|---|---|---|
| Name | Symbol | Definition | Name | Symbol | |
| period, periodic time | T | time of one cycle | second | s | |
| frequency | f,ν | f = 1/T | hertz | Hz | 1 Hz = 1 s−1 |
| . . . | |||||
| loudness level | LN | LN = ln(peff/p0)1 kHz wherepeff is theroot-mean-square value of thesound pressure of apure tone of 1 kHz, which is judged by a normal observer under standardized listening conditions as being as loud as the sound under investigation, and wherep0 = 20μPa | phon | The loudness level is 1 phon if 20 log10(peff/p0)1 kHz=1, that is for a pure tone of frequency 1 kHz, 1 phon = 1 dBsound pressure level. This is not a purely physical quantity and unit, as it involves the subjective evaluation by humans. | |
| loudness | N | A normal observer's auditory estimate of the ratio between the strength of the sound considered and that of a reference sound having a loudness level of 40 phons | sone | A standard relation between loudness in sones and loudness level in phons has been adopted for practical use in ISO 131. | |
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