Winding your own inductors
Using the formulas in Vance Dickason's Loudspeaker Cookbook, I created the following basic Excel spreadsheet:
inductors.xls
My students use the Excel table to locate the value of inductance needed for a particular crossover, assuming we don't have a suitably close value inductor on hand.  The spreadsheet shows them the number of turns of 16 gauge magnet wire needed and the radius and height (they're equal in this sheet which is written for type A air core inductors).  The nearest fit to the required diameter of "air core" is chosen from the various PVC jigs I constructed for this purpose.  The students assemble the corresponding end plate (made from 1/4 inch masonite hardboard) to the PVC pipe and adjust the spacing between it and the fixed plate, anchoring it with masking tape.  The plates were cut out with a fine scroll jig saw blade and then enlarged slightly by use of a curved file until they fit snuggly on the pipe.  The end plate has a groove to keep the starting wire  out of the way of the windings.  Depending on how carefully the students avoid unnecessary air gaps in the winding, the required number of turns is close to the predicted number.  I advise the students to wind  at least 3 to 5 additional turns before cutting the wire and measuring inductance.  That way they can remove turns if needed.  We use the Woofer Tester to measure inductance.  You can also use a signal generator and an  AC voltmeter with an impedance bridge if you don't have the Woofer Tester.  We have done it both ways.  The same inductors test within about 1% to 2% by each method. 
Type A
Type B
used for smaller values
<--- Mounted handmade inductors ---------------------->
Crude prototype of a more sophistocated student crossover network.(using 4 inductors; the large vertical inductor is commercial, but its opposite speaker handmade counterpart is visible on the counter in the background).  By the way, this is the crossover we found most successful with the Dayton 8 inch, #295-310, and the Dayton silk dome tweeter, #275-070, a combo much discussed on the PE Tech Talk board in early February.
Ashley
Kin
Lindsey
Ratch Higgins, Ph.D.
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