Two speakers rated at 90 dB may need different power to produce the same listening level. The explanation often lies in the small print: 1 W/1 m or 2.83 V/1 m.
Voltage and power are different conditions
For a simple resistive load, power equals voltage squared divided by resistance. At 2.83 V, an 8-ohm load receives about 1 W, while a 4-ohm load receives about 2 W. Equal measurement voltage does not necessarily mean equal input power.
A conversion example
Suppose a 4-ohm speaker produces 90 dB at 2.83 V and one metre. In a simplified calculation, reducing power from two watts to one reduces output by about 3 dB, giving approximately 87 dB/1 W/1 m. This does not mean the manufacturer exaggerated the rating; the conditions differ.
Why this is approximate
Real speaker impedance changes with frequency and includes reactance. A nominal 4 or 8 ohms does not describe the entire curve. Averaging bandwidth, room conditions and measurement method also matter. Conversion using nominal impedance explains the scale of the difference but cannot replace comparable measurements.
What to check before choosing an amplifier
- Find the sensitivity units and measurement distance.
- Check nominal and minimum impedance where provided.
- Compare results obtained using the same method.
- Consider the required level and listening distance.
Sensitivity does not establish sound quality. A larger number alone promises neither lower distortion nor an easier load for the amplifier.