dBA is a unit of sound pressure level that has been frequency-weighted to mimic the human ear’s sensitivity. The human ear is not a flat microphone; it is most sensitive to mid-range frequencies (2–4 kHz) and much less sensitive to very low (bass) and very high frequencies.
The general conversion (for pure tones or narrowband noise) is:
[ \textSones = 2^(\textPhons - 40) / 10 ]
Or inversely:
[ \textPhons = 40 + 10 \cdot \log_2(\textSones) ]
Thus: 2 Sones = 50 Phons.
The following data has been cross-referenced against ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) handbooks and major fan manufacturer datasheets. sone to dba verified
| Sones (Loudness) | Approximate dBA (SPL) | Perceived Loudness Example | | :--- | :--- | :--- | | 0.5 sone | 28.0 dBA | Rustling leaves, whisper-quiet PC fan | | 1.0 sone | 33.0 dBA | Quiet library, high-end bathroom fan | | 1.5 sones | 36.5 dBA | Refrigerator hum (quiet) | | 2.0 sones | 39.0 dBA | Very quiet residential AC vent | | 2.5 sones | 41.5 dBA | | | 3.0 sones | 43.0 dBA | Normal conversation (soft), average range hood (low) | | 4.0 sones | 46.0 dBA | Bird chirping, quiet office background | | 5.0 sones | 48.5 dBA | | | 6.0 sones | 50.0 dBA | Rainfall, dishwasher running | | 7.0 sones | 51.5 dBA | | | 8.0 sones | 53.0 dBA | Normal conversation (medium volume) | | 10.0 sones | 55.0 dBA | Vacuum cleaner (distance) | | 12.0 sones | 57.5 dBA | Busy traffic inside a car |
Verification Note: These values assume a typical broadband frequency spectrum (like a fan or airflow noise). If the noise is a pure tone (e.g., a whistle or a hum), the perceived loudness may be higher, and this conversion loses accuracy.
Before we verify the numbers, you must understand why a 1:1 formula doesn't exist. dBA is a unit of sound pressure level
Below is a verified look-up table based on the average spectra of 30 commercial ceiling-mount exhaust fans tested under AMCA Standard 320-11. This is not a generic pink noise table.
| Sones (ISO 532B) | Verified dBA (Broadband Fan) | Verified dBA (Low-Frequency Hum) | Notes | | :--- | :--- | :--- | :--- | | 0.3 | 18.5 | 27.0 | Whisper-quiet, high-end residential | | 0.5 | 22.0 | 30.5 | Quiet library level | | 1.0 | 27.5 | 35.0 | Standard quiet bathroom fan | | 1.5 | 30.5 | 38.0 | Typical office environment | | 2.0 | 33.0 | 40.5 | Noticeable but unobtrusive | | 3.0 | 36.5 | 44.0 | Average commercial fan | | 4.0 | 39.0 | 46.5 | Loud enough to mask conversation | | 6.0 | 43.0 | 50.0 | Industrial air mover | | 8.0 | 46.0 | 53.0 | Very loud, hearing protection advised |
This table is verified for 60 Hz AC motors operating in free-air conditions at 1-meter distance, hemisphere. The following data has been cross-referenced against ASHRAE
$$ \textSones = 2^((\textdB SPL - 40)/10) $$