The compensation network is impedance sensitive. Any fixed L-Pad attenuation should be precise; I'm using 8-Ohms nominal for calculating. It should go before any final adjustable, as those are not very constant impedance, despite the hype.
I'll work on the lowpass tomorrow; still using Model 19 crossover for that here.
[OH, and yeah, these sound damn good.... :yes: ]
They really do sound damn good. My wife asked if I could replace the JBL 2431's in my DIY 4430s with the Seleniums and sell the JBL's. I said "No, dear, it don't work that way."
I haven't messed with the resistor values in the compensation network yet, cause I thought they had to be exact to match the driver impedance to the crossover. Then it dawned on me that introducing the HF comp capacitor changes the impedance depending upon frequency. Thats how it works. Well then, why not look at some other ways to skin the cat. The way the final L-Pad is configured in my previous schematics allows the compensation cap to drive it's correction into the resulting impedance sum of the tweeter plus the resistance between pins 2 and 3 of the L-Pad. That resistance is big compared to the other values in the circuit, so it's share of the correction voltage is fairly large. Plus it is wasted due to the fact that the tweeter drive doesn't include that part of the correction voltage.
Flipping both ends of the connection between the HF section of the crossover to the tweeter gives the circuit labeled modded HF as shown here. Now although the L-Pad works exactly the same as before, the resistance between pins two and three can be bipassed, with the compensation capacitor hooked to the tweeter instead of to the L-Pad. Having all of the correction voltage drive available to the tweeter regardless of the L-Pad setting, allows the reduction of the cap to 1 microfarad while providing more HF correction than the previous circuits 2 Microfarads. The trail off in response at 20 KHz is less with this connection. as shown in the FR pix.
The first FR shows the response with max L-Pad setting. The second shows min L-Pad setting, while the third shows what would probably be ideal for me. Actually, the L-Pad will reduce the volume even lower than my min FR shows, but it is probably about as low as it would be adjusted if you wanted some HF sound, and had a very inefficient woofer.
Zilch, there are some real possibilities that by juggling the values of the compensation resistors and capacitor we can achieve something as close as could be had with tuned circuits. JackLab is about at the end of it's rope, as far as doing this. My selection of power resistors is skimpy at best, and caps are not much better, since most of my stock is larger values. Maybe you can finalize this if you think it is worth pursuing.
Obviously, once frequency falls in to 1.25 KHz or below range, that becomes a woofer effect, so don't consider any FR except from 1.6 KHz and up. And perhaps a final juggle with xover frequencies will yield a smoother cross into the tweeters range. Obviously the slight rising response in the HF band indicates the 1 microfarad is probably a little large.
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