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ISO 532 Sone (Loudness) Conversions

iso532-sone.Rd

Functions for converting between phon (loudness level) and sone (loudness) according to ISO 532 standards. Sone is a linear unit of perceived loudness, where 1 sone = 40 phons by definition.

Details

Standards

Two ISO 532 methods are supported:

  • ISO 532-1 (Zwicker method): Uses piecewise mathematical formulas

  • ISO 532-2 (Moore-Glasberg method): Uses lookup table with interpolation

Zwicker Method (ISO 532-1)

The Zwicker method uses different formulas depending on loudness level:

For sone < 1 (phon < 40): $$L_N = 40 \times S^{0.35}$$

For sone >= 1 (phon >= 40): $$L_N = 40 + 10 \times \log_2(S)$$

Inverse formulas:

For phon < 40: $$S = (L_N / 40)^{1/0.35} = (L_N / 40)^{2.857}$$

For phon >= 40: $$S = 2^{(L_N - 40) / 10}$$

Moore-Glasberg Method (ISO 532-2)

Uses a lookup table with 23 reference points from 0.001 sone (0 phon) to 337.6 sone (120 phon), with log-linear interpolation.

Key Properties

  • Reference: 1 sone = 40 phons = 40 dB SPL at 1 kHz

  • Doubling: Each 10 phon increase ~= doubles loudness in sones

  • Linear perception: Sones represent linear loudness (2 sones = 2x louder)

  • Stevens' power law: Loudness is proportional to intensity^0.3

References

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(Stevens 1936)