The scale is as you see it. Each horizontal line represents a span of 5 dB.
So what you see is the minimum of ~-75 dB @~420Hz to ~-61 @ ~3,800 Hz for a total span over the usable range of ~14 dB.
A 0.5 mH coil in series with the woofer reduces the 3,800 Hz peak/hump to a bit below that at ~600Hz also reducing this span. I've actually taken to winding my own coils for experimentation now that I have a meter that can read Henrys. When I do this, the crossover point works almost perfectly to the Heil on a 1st order 3.3 mfd cap with a bit of a dip between ~1 - 2.5 KHz.
It's amazing that with some of the chokes I have on hand, each wind of the coil will change the inductance by ~0.05 mH and I can wind/unwind the coil and see the results on the 61-band RTA in real time.
When I got my woofers, there was a vendor on the 'bay who had a bunch of these at this price. My pair have matching DCRs. I guess they're gone now.
Actually, another vendor on the bay had a shiite load of 2123s that he was selling for $150/pr in excellent shape.
If anyone is looking for a nice pair of 2123s, there is a pair on C/L new in the boxes for $299/pr that have been listed off and on for a dog's age.
No affiliation.
https://losangeles.craigslist.org/ws...413973578.html
I ported the cabinet and designed parallel passive bandpass filters and have the 2251J +- ~3 dB from <120Hz - >4,000Hz. Should do a beautiful rendition of vocals! I can't think of any JBL designs using a single driver that can achieve this.
Note the nice smooth "1st order" slope on top to the Heil, and smooth "quasi-2nd order" slope at the bottom to the 2241.
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