Subwoofer tools.
DRIVERS & OUTPUT / THE TOOLKIT

Reference efficiency.

Calculate one-sided reference efficiency and a stated-condition, mass-controlled sensitivity estimate. A nominal 1 W reference is not the power consumed by a real loudspeaker.

01 / THE INPUTS
Driver parameters
Hz
Ω
Sensitivity conditions
V
Air & conventions
m/s
kg/m3
Optional driver overrides

Blank derives mass from fs, Vas, and Sd. A conflicting entered value is flagged.

T m

Blank derives Bl from the moving mass, fs, Re, and Qes.

02 / THE RESULTS
One-sided reference efficiency
0.587%
Stated-condition sensitivity
93.55dB SPL
RMS reference voltage
2.830V
Mass-controlled RMS pressure
0.9517Pa

Read this result with its assumptions.

Efficiency counts one side radiating into an infinite-baffle half-space. A two-sided acoustic-power convention doubles that number.

Sensitivity: 2.830 V RMS, 1 m, ideal half-space, negligible inductance and source resistance.

Sensitivity uses Mms = 99.336 g and Bl = 11.894 T m, derived unless overridden.

Voltage sensitivity is not automatically 1 W sensitivity. Actual loudspeaker power is frequency-dependent.

Units & assumptions

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03 / UNDER THE HOOD

The math, in plain sight.

Efficiency is not the same as sensitivity.

One-sided reference efficiency

The convention here counts one side radiating into an ideal infinite-baffle half-space. A convention that counts both sides of an ideal infinite baffle gives twice the acoustic power.

η0≈4π2fs3Vasc3Qes\eta_0\approx\frac{4\pi^2 f_s^3V_{as}}{c^3Q_{es}}

Efficiency is a dimensionless fraction; multiply by 100 for percent. With fs = 30 Hz, Vas = 100 L, and Qes = 0.45, this convention gives approximately 0.59%.

Sensitivity under stated conditions

For a specified RMS voltage in a mass-controlled, approximately flat on-axis range, neglecting voice-coil inductance and source resistance:

pRMS(r)≈ρSdBlE2πrReMms(ideal half-space)p_{\mathrm{RMS}}(r)\approx\frac{\rho S_dBlE}{2\pi rR_eM_{ms}}\quad\text{(ideal half-space)}
Lp=20log⁡10(pRMS20 μPa)L_p=20\log_{10}\left(\frac{p_{\mathrm{RMS}}}{20\ \mu\mathrm{Pa}}\right)

The ideal free-space comparison uses 4 pi instead of 2 pi in the pressure denominator. Sensitivity is always labeled with voltage, distance, and radiation condition.

What nominal 1 W means

Enominal=PnominalZnominalE_{\mathrm{nominal}}=\sqrt{P_{\mathrm{nominal}}Z_{\mathrm{nominal}}}
Pelectrical(f)=∣E∣2Re⁡{1Zin(f)}P_{\mathrm{electrical}}(f)=|E|^2\operatorname{Re}\left\{\frac1{Z_{\mathrm{in}}(f)}\right\}

2.83 V RMS corresponds to 1 W into an 8 ohm resistive reference, not automatically 1 W into a real driver or a 4 ohm nominal load. Reference efficiency does not predict maximum output or thermal compression.