Is the TDI DF coil just a compromise? A 12" and a 5" (5 + 12= 17 / 2 = 8 1/2). Wouldn't a 8 or 9 inch coil give approximately the same performance? It doesn't seem to have the depth of a 12" mono or the sensitivity of a 5". Inquiring minds want to know. Thanx,
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