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Impedance Analyzer Menu
The Impedance Analyzer Menu contains commands for running measurements and for performing
calibration of the test lead resistance and master calibration as follows:
Measure Free Air Parameters
This command causes WT3 to run an impedance sweep and then extract the driver's free air
parameters. You can also use this command to measure resistor and inductor values. Measuring a
resistor should result in a flat impedance plot indicating the resistance is the same across the audio
frequency band. R(e) is the measured resistance value. The measured resistance can also be read
directly from the plot. When measuring an inductor, the plot will rise at high frequencies and L(e)
indicates the measured inductance value. You can also execute the Free Air Parameters command by
clicking the same named button at the Impedance Bar at the left side of the main window.
Measure V(as) by the Selected Method
Before any measurements are made this command is disabled (grayed out). After making a free air
measurement this command becomes enabled and can be used to measure the V(as) of a driver by any
of three methods. The V(as) test method is selected at the Parameters Bar at the right side of the main
window. You can also Measure V(as) by clicking the same named button at the Impedance Bar at the
left side of the main window. The three methods are: Test Box, Added Mass and Specified SPL.
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Test Box: This method is probably the most widely used and trusted. For this method
you will need a test speaker enclosure of suitable size for the driver being tested
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Added Mass: Although the added mass method can employ added mass in the simple
form of coins added to the cone it is best to make sure the added mass actually adheres
to the cone so that it moves with the cone at all times. If the mass "decouples" as the
cone moves then accuracy will be compromised. Use an added mass that will shift the
F(s) lower by about 25-50%. An added mass equal to the driver's Mms is just about
right. WT3 will warn you if the shift in the measured F(s) is not within the above
recommended range.
Some items used for added mass include: coins, modeling clay, carpenters putty, rope caulk, tape rolls.
In general you should measure the weight of the added mass accurate to 1/10th of a gram. In a pinch,
US coins can provide an easy source of standard weights. One US nickel ($.05) weighs 5.0 grams.
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Specified SPL: This is the simplest V(as) method as it requires no test box or added
masses. It is also probably the least accurate as it depends strongly on the accuracy of
the SPL you specify.