Apparatus and method for measuring speaker transducer impedance versus frequency with ultralow inaudible signal

An apparatus for measuring an impedance of a speaker, comprising:

• a digital-to-analog converter that converts a known digital input signal to a first analog voltage signal in an audio frequency band;
• resistors having a known resistance that attenuate the first analog voltage signal to generate a current, wherein the known resistance is high relative to the speaker impedance so that the known resistance effectively determines the current;
• wherein the apparatus is operable to generate a second analog voltage signal when the current is sourced into the speaker, wherein the known resistance is sufficiently high to cause the second analog voltage signal to be inaudible as transduced by the speaker;
• an amplifier that amplifies the second analog voltage signal with a known gain to generate a third analog voltage signal;
• an analog-to-digital converter that converts the third analog voltage signal to a digital output signal;
• and
• a processing element that calculates the impedance of the speaker proportional to the digital output signal based on the known digital input signal, the known resistance, and the known gain.