Decibel (dB)

The decibel is the fundamental unit of virtually every audio measurement. Unlike linear units, the logarithmic scale mirrors human perception: a 10 dB increase sounds roughly twice as loud, even though it represents a tenfold increase in acoustic power. This compression is what makes the dB scale so useful — the ratio between the quietest audible sound and the threshold of pain spans a factor of over one million in pressure, but only 120 dB on the logarithmic scale. In sound pressure level measurements, the reference value is 20 micropascals (μPa), the nominal threshold of human hearing at 1 kHz. In electrical or power measurements, the reference depends on context: dBV uses 1 volt, dBu uses 0.775 volts, and dBW uses 1 watt. Confusing these references is a common source of error. A critical distinction is whether you are measuring a field quantity (pressure, voltage) or a power quantity. For field quantities, dB = 20 × log₁₀(V₁/V₂), because power is proportional to voltage squared. For power quantities, dB = 10 × log₁₀(P₁/P₂). Mixing up the 20× and 10× multipliers is one of the most frequent mistakes in audio engineering. Practical rules of thumb: +3 dB doubles acoustic power, +6 dB doubles sound pressure, +10 dB sounds approximately twice as loud. Combining two identical incoherent sources yields +3 dB, not +6 dB, because their powers add but not their pressures. Understanding these relationships is essential for system design, gain staging, and predicting the effect of adding speakers to a system. SonaVyx displays all measurements in dB with appropriate references, and the SPL meter provides real-time A/C/Z-weighted readings on a calibrated decibel scale.