ToolsSound, propagation & hearing
Air absorption
High-frequency loss in air over distance, by frequency, temperature and humidity (ISO 9613-1).
°C
%
kPa
m
| Frequency | Absorption (dB/100 m) | Loss over 100 m (dB) |
|---|---|---|
| 63 Hz | 0.0122 | 0.0122 |
| 125 Hz | 0.044 | 0.044 |
| 250 Hz | 0.131 | 0.131 |
| 500 Hz | 0.273 | 0.273 |
| 1k Hz | 0.466 | 0.466 |
| 2k Hz | 0.989 | 0.989 |
| 4k Hz | 2.97 | 2.97 |
| 8k Hz | 10.5 | 10.5 |
| 16k Hz | 36.5 | 36.5 |
ISO 9613-1 pure-tone absorption, added on top of the 6 dB per doubling of distance. Dry air absorbs high frequencies most; this is why distant delay speakers and outdoor PAs need high-frequency boost.
How it works
Air converts sound into heat, mostly at high frequencies. Over 100 m at 20 °C and 50 % humidity, 8 kHz loses roughly 10 dB more than 1 kHz. Dry and cold air can make it worse.
Formulas
- α(f, T, h, p) from ISO 9613-1, in dB/m
- loss = α · distance
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