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Measure loudspeaker impedance at any power level from milliWatts to kiloWatts!

Precision measurement of loudspeaker impedance has always presented a unique set of problems. While the commonly used constant current source (CCS) method provides easy and quick impedance measurement, it sacrifices the quality and accuracy of the data.

Loudspeakers are normally operated in a constant voltage source (CVS) mode, by direct connection to a power amplifier. For accurate impedance measurements CVS operation must be maintained during impedance measurement as well.

VI Box Photo
The VI Box is a device which provides all of the components, circuitry, and interface connectors necessary to make precision impedance measurement using the CVS method a snap. The VI Box provides binding post connectors for the amplifier and speaker cables, as well as two XLR signal line outputs for the load current (I) and load voltage (V). The VI Box is built entirely with 1% precision low TC components and features selectable 4-wire Kelvin shunts, a precision voltage divider, and balanced line output impedance.
Once the current flow through the load and the voltage across the load are measured, the true load impedance can be calculated using basic Ohmís law as Z=V/I and the true power calculated as P=V*I. The VI Box can be used with almost any audio analyzer or meter including the LMS, TEF-20, AP System-1, and any other analyzer which provides a balanced line input. Dual channel analyzers are ideal for use with the VI Box since both current and voltage can be measured simultaneously.

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