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ISO 226:2023 Phon (Loudness Level) Conversions

iso226_phon.Rd

Functions for converting between sound pressure level (dB) and loudness level (phon) according to ISO 226:2023 "Acoustics - Normal equal-loudness-level contours".

Details

The phon scale represents loudness level - the perceived loudness of a sound compared to a 1000 Hz reference tone. Unlike other psychoacoustic scales (Bark, ERB, Mel), phon is a bivariate measure requiring both frequency and sound pressure level.

Key concept: A sound at 40 phon sounds as loud as a 1000 Hz tone at 40 dB SPL, but different frequencies require different SPLs to achieve the same loudness.

Valid ranges (per ISO 226:2023):

  • Frequency: 20 Hz to 12,500 Hz

  • Loudness level: 20 phon to 90 phon (20-4000 Hz), 20-80 phon (5000-12500 Hz)

  • Below 20 phon: Informative only (near hearing threshold)

  • Above 90/80 phon: Limited experimental data

Implementation notes:

  • Based on ISO 226:2023 Formulas (1) and (2)

  • Parameters from ISO 226:2023 Table 1

  • Interpolation used for frequencies between standard 1/3-octave values

  • Free-field listening conditions (frontal incidence, binaural)

References

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