Dayton Audio OmniMic V2 Precision Measurement System - Manual (Page 19)

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How to use the Z-Offset Calculator :
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1). Position your microphone at the design center point (often on-axis with driver "A", usually the higher
frequency driver, such as the tweeter if measuring a tweeter/midrange pair).
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2). Make sure that "show phase" is checked on the Frequency Response screen. Measure the response of
driver "B" playing at moderately low level alone with the microphone at this position. Save this file to disk.
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3). Connect so that both drivers "A" and "B" play simultaneously (use a blocking capacitor to protect tweeters, of
course, and be careful of levels -- these measurements need not be done at high level!) and save that to file also.

4). Use the "Added Curves">"Add" menu to add the newly saved file (of both drivers together) to the display.
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5) Now go to the "Main Math">"Sum" menu and select the first curve (of driver "B" playing alone). Then click
"Main Math">"Adjust Delay" to bering up the form shown above. Put a check in its "Show Z-Axis Calculator"
checkbox.
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6) Get out a tape measure and measure the distances shown in the figure (in either meters or inches), enter
them in the boxes. Enter an estimate for the distance from the baffle to the voice coil of driver B (this need not be
highly accurate, within several inches should be fine).

7) Uncheck the "show phase" box on the Frequency Response screen. Now, while measuring driver "A" alone
(the display of which is now summed with driver "B''s curve), adjust the control (in seconds) at the top of the new
form until the measured response curve best matches the magnitude (not necessarily phase!) of the Added Curve
that shows the actual measurement of both drivers together. When this is correct, then the value of Z axis offset
will be shown at the bottom right of the form. THIS (IN METERS) IS THE Z VALUE YOU WOULD ENTER FOR
DRIVER B in PCD, if driver A uses a Z axis position of 0.
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8) Turn off the "Sum" function for Main Math, and measure (and save) the data from driver A playing alone for
use in PCD with driver B's curve taken initially.