Carlspeak Posted February 21, 2012 Report Share Posted February 21, 2012 Below is a 10-20kHz scan of the infamous later model AR3a woofer's No. 9 coil. The same measurement techneque was used here as in the 'good, bad & ugly cap' measurement thread. Only with this measurement, the red impedance line curves upwared from left to right and phase starts at about 0 deg and end close to +90 Deg. What's of most interest here is the Z-impedance column. Note how impedance varies with frequency and how impedance climbs rapidly above the 500 hz roll off point of the woofer. Also note the far right column showing true inductance at each freq. For most of the scan it's 2.81 mH - close to the target of 2.85 mH for a #9 coil. Link to comment Share on other sites More sharing options...
rrcrain Posted February 21, 2012 Report Share Posted February 21, 2012 I'd find it interesting to see how this compares to modern coils of the same value. The "perfect lay" and the litz coils come to mind. Link to comment Share on other sites More sharing options...
ligs Posted February 21, 2012 Report Share Posted February 21, 2012 I had a pair AR3a's. Each of the nominally 2.85 mH 17 gauge coils had a metal clip to fasten to the XO board. I wondered about the effect on inductance.I also have the same coils used in Heathkits' version of 3a. However, Heathkits used a wooden dowel with a hole in the center and a brass wood screw to fasten each coil to the XO board.Carl, can you measure the frequency response (especially the low end) of the AR3a crossover. 17 gauge 2.85 mH has DCR about 0.8 ohm. I wonder what would happen if one substitutes this with a lower DCR coil like 0.2 ohm. I seem to remember seeing the frequency response of a low pass XO has roll-off on both the high and low end. Zilch showed a graph of voltage drives of just the crossover for Pioneer HPM 100, but I don't have the original reference anymore. Link to comment Share on other sites More sharing options...
Carlspeak Posted February 21, 2012 Author Report Share Posted February 21, 2012 I don't have two different type coils that measure around 2.8 mH. However, I do have two, a Madisound 0.15 mH 16 ga. Sidewinder air coil and a Jantzen also labeled 0.15 mH 14 ga. copper foil coil favored by audiophiles. I took scans of each which are shown below.The biggest difference I see is in the 7 kHz to 20 kHz range of phase and R-real (ESR) columnar data. The mad. coil phase starts to decline after peaking about 86 deg. whereas the Jantzen foil coil stay relatively flat. The ESR started climbing in the Mad. coil in that same freq. range, whereas it increased only slightly in the foil coil. This difference may be significant at this low mH range. The difference seen may be solely attributable to the difference in wire gage rather than a difference in construction. I'd have to get two coils with both the mH and wire gage specs the same to answer that question. Maybe someday. Link to comment Share on other sites More sharing options...
Carlspeak Posted February 21, 2012 Author Report Share Posted February 21, 2012 Quote: "I had a pair AR3a's. Each of the nominally 2.85 mH 17 gauge coils had a metal clip to fasten to the XO board. I wondered about the effect on inductance. I also have the same coils used in Heathkits' version of 3a. However, Heathkits used a wooden dowel with a hole in the center and a brass wood screw to fasten each coil to the XO board." I believe that metal clip's effect is insignificant because it is pressed onto an aluminum nail that goes up thru the center of the coil. Wood, brass, aluminum - all non-ferrous. Quote: "Carl, can you measure the frequency response (especially the low end) of the AR3a crossover. 17 gauge 2.85 mH has DCR about 0.8 ohm. I wonder what would happen if one substitutes this with a lower DCR coil like 0.2 ohm. I seem to remember seeing the frequency response of a low pass XO has roll-off on both the high and low end. Zilch showed a graph of voltage drives of just the crossover for Pioneer HPM 100, but I don't have the original reference anymore." A 0.2 ohm 1.8 mH coil would necessitate a very expensive 12 ga. air coil. Perhaps one could model an electrical response using p-spice or something similar to see what happens electrically (in theory). I don't have that capability. Buy me one of those 12 ga coils and I'll be glad to measure it! Link to comment Share on other sites More sharing options...
rrcrain Posted February 21, 2012 Report Share Posted February 21, 2012 Carl,Your latest set of graphs answer one question. Yes, there is possibly a measurable electrical difference with differing types of inductors. And you raise a new one in the same breath.Doew wire gauge have an effect on inductor performance beyond simple resistance?The ultimate question of course is if any of this actually audible to simple humans such as myself? Link to comment Share on other sites More sharing options...
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