Loudspeaker Impedance Sweep Fixtures And Calibration

An impedance analyzer does not remove the need to verify its reference, leads, drive level, mechanical environment, and measurement state.

What the sweep measures

Z(f) = Vdriver(f) / Idriver(f)

Save magnitude and phase. The nominal-ohm label and DC resistance are not substitutes for the complex curve.

DATS workflow

inspect and zero the fixture
run the platform calibration using the known reference
verify with an independent resistor
record lead set and contact method
measure at a declared low terminal voltage
repeat at a second low level to check linearity

Dual-channel fixture

Use a measured non-inductive sense resistor, matched input channels, open-circuit calibration, short-circuit lead compensation, and known-reference calibration. Protect soundcard inputs if an external amplifier is used.

Mechanical quiet matters

A loudspeaker is also a microphone. Room noise, bench vibration, a flexible frame support, moving leads, and nearby boundaries can corrupt the resonance region. Use long enough sweeps, quiet conditions, rigid support, and vibration isolation.

Validity checks

known resistor measures correctly
channels are not swapped
no input or output clipping
lead or contact resistance is stable
curve repeats after disconnect and reconnect
temperature and orientation are unchanged