ToolsSound, propagation & hearing
Speech intelligibility: STI ↔ ALcons
Convert Speech Transmission Index and articulation loss of consonants, with ratings.
STI
% ALcons
Rating (IEC 60268-16)
Good
| Rating | STI | ≈ ALcons |
|---|---|---|
| Bad | 0 – 0.3 | 33.6 – 171 % |
| Poor | 0.3 – 0.45 | 14.9 – 33.6 % |
| Fair | 0.45 – 0.6 | 6.6 – 14.9 % |
| Good | 0.6 – 0.75 | 2.93 – 6.6 % |
| Excellent | 0.75 – 1 | 0.756 – 2.93 % |
The STI ↔ ALcons relation is an empirical approximation (Farrel Becker). Use it to compare figures from different sources, not as a replacement for measurement.
How it works
STI (0 to 1) and %ALcons both describe how well speech is understood through a system and room. Higher STI and lower ALcons are better. Voice alarm systems commonly require STI ≥ 0.5.
Formulas
- ALcons ≈ 170.5405 · e^(−5.419 · STI)
Read more
Found a mistake or have an idea for this tool?
Suggest a change