Ethyl Merman Crossover Schematic
After much listening, tweaking, changing, and even an unintentional mistake that led to the final product, this is the current crossover schematic for the 2241H/2251J/Heil AMT.
The unintentional mistake that led to an unconventional wiring arrangement lets the 2251H sing so clearly that the detail is unreal, probably about the best I've heard, certainly in my home at concert levels. (Perhaps the Harbeths that were here for a day or my LS3/5s sound better at lower volumes, but I've not done a head-to-head comparison.)
If you look at the schematic you see that the 6.8 mfd cap for the 2251 actually attaches to the woofer's positive lead rather than directly to ground. The connection was supposed to go to ground (the other side of the 47 mfd cap), and did in one crossover. But I accidently put the wire on the wrong side of the cap in the other crossover, and in head-to-head comparisons, one was head-over-heels better. (Had to figure out why.) This works with the wedgie in the AMT and the UHF control brings the "air" back in, not that there's not plenty without it. But when I would listen to the 2405 I could hear more "top end sizzle." This takes care of that top end without adding sibilence, and the 2405 looses its advantage here.
http://www.audioheritage.org/photopo...y_01_16_51.jpg
Truely Interesting Situation
Truely an interesting situation.
The inductance/impedience of the 2241H woofer is creating a second order filter for the 2251J mid. When the 2241 woofer is disconnected, the slope on the mid appears as a 1st order (on the 61-band RTA) letting the speaker play to <100 Hz petering as it goes down, with some peaks, from ~1kHz. But there is a suck-out/drop-out at ~350 Hz.
When the 2241H is connected, the mid goes to a second (or more) order filter falling like a stone at ~350Hz. But the entire band above this is pushed up flattening it out up to the ~1kHz peak. If the 2241 is replaced by an 8-ohm non-inductive resistor, the mid does not fall like a stone at ~350Hz and largely resembles the curve without the 2241 connected, just falling a bit more at toward bottom end of <100 Hz. The size of the cap (i.e., 6.8 mfd) controls the top end of the 2251J up to its upper crossover point. A bigger cap rolls off the high end sooner. The 6.8 mfd looks about right to get the flattest spectrum and best detail.
The arrangement seems to have little measureable effects on the 2241H and its spectrum looks pretty much the same with or without the additional connection to the 6.8 mfd cap. Perhaps there is a bit more roll-off above the 350 Hz crossover frequency (notable at ~500Hz and up) which is a welcome trait.
Recognize that unlike the 2241H, the 2251J has no inductance (differential drive with a neodynium magnet) and any loss to the upper frequencies of the 2241 is from the combination of the 6.8 mfd through the 16 ohm load (of the L-pad/2251J) to ground which is very minor when compared to the 47 mfd dumping to ground directly.
