dB(A) – A-weighted decibels.
If you need to convert on the fly and cannot access the chart, acoustic engineers use the following verified empirical formula (Stevens' Power Law applied to A-weighting):
dBA ≈ 33.2 * (log10(sones)) + 34
Let’s verify this against a known data point:
Important Correction: The formula above works strictly for free-field pure tones. For real-world appliances, use this verified regression formula (from AMCA Standard 301): sone to dba verified
dBA = 35 + (22.275 * log10(sones))
Let's test that:
Conclusion: Use the AMCA formula for mechanical equipment. Use the Stevens formula for acoustic research.
| Feature | Sones | dBA | | :--- | :--- | :--- | | Nature | Subjective / Perceptual | Objective / Physical | | Scale | Linear (2x loudness = 2x Sones) | Logarithmic (10 dB ≈ 2x loudness) | | Frequency weighting | Handled by equal-loudness contours | Fixed A-weighting filter | | Best for | Comparing product “quietness” | Meeting OSHA or building codes | dB(A) – A-weighted decibels
The conversion challenge: There is no single, universal formula to convert Sones to dBA because the relationship depends on the sound’s frequency spectrum (bass vs. treble content). A verified conversion requires a frequency analysis.
Imagine two different exhaust fans, both rated at 2.0 Sones by their manufacturers:
According to the generic chart, both should measure about 34 dBA. But a verified measurement tells a different story:
If you used an unverified conversion chart, you would mistakenly promise your client a 34 dBA installation, but deliver 46 dBA – a difference of 12 dB, which sounds more than twice as loud. This leads to failed inspections, unhappy occupants, and costly rework. If you need to convert on the fly
Being “verified” means you have validated the conversion either via:
You cannot use a sone meter to determine if a workplace is over 85 dBA (the OSHA action limit). Sones measure perception; dBA measures physical damage risk. Verified conversion stops you from assuming "50 sones is painful, so 5 sones must be safe" (it isn't always).
Before we can verify a conversion, we must understand the fundamental difference between loudness and sound pressure.