Decibels don't add up.
Every +10 dB is a ×10 jump in actual sound intensity — not “10% more,” not additive. Yet your ear hears that same +10 dB as roughly a doubling in loudness — a widely cited rule of thumb, not a physical law. Those two curves pull apart fast: drag the slider and watch how far.
intensity, I / I₀ (log scale)
perceived loudness (≈)
Level dB
+10 dB → ×10 intensity
0 dBthreshold of hearing → jet at takeoff140 dB
Sound level
dB
85 dB — prolonged exposure risk
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The decibel scale is logarithmic: dB = 10·log₁₀(I/I₀), where I₀ = 10⁻¹² W/m² is the standard reference intensity, roughly the threshold of human hearing. “Loudness doubles every +10 dB” is a widely cited psychoacoustic approximation (2^(ΔdB/10)) — useful for intuition, but itself a rough empirical rule, not an exact law; some sources fit a different exponent, and perceived loudness also depends on frequency and individual hearing. The named source levels (whisper, traffic, lawnmower, and so on) are commonly cited approximate figures — real measurements vary with distance from the source and recording conditions. The 85 dB and 120 dB hearing-damage markers are likewise commonly cited guidelines for sustained and acute exposure, not precise medical thresholds.