Dahlquist DQ-10 Passive Crossover

I'm a new forum member. Do we have an electrical engineer or crossover guru in our midst who has done an exhaustive analysis of the DQ-10 passive crossover and would like to share this information? It's certainly not a textbook series layout and quite frankly some of it baffles me. Is it brilliantly laid out or just a compromise to get it to market? I've mirror-imaged my DQ-10s, changed out the midbass, bypassed the poly caps and replaced the 80 mfd electrolytic with a metallized poly, and I'm a speaker diy'er, so I'm not a passive listener. I'm sure that I'm not the only one who'd like a definitive explanation of the crossover design.

Thorens TD125LB Turntable
SME 3012 Tonearm
Shure M97XE
Denon DL110
Yamaha CDC-585 CD Player
Adcom GFT-555II Tuner
Hafler DH-110 Preamp
Phase Linear 400
Adcom 5400
At present mirror imaged Dahlquist DQ-10s
http://www.syer.net/dahlquist.htm (has x-over schematic)

http://www.regnar.com/ (offers rebuilt parts etc, think they used to sell an alternative x-over)

I eventually warped the woofer voice coils in my dq-10's (after I melted the wax off the x-over boards & toasted the tweeter level control)
DQ-20's well regarded & much simpler x-over & driver complement
Burning out your speakers is hardly relevant to my request for DQ-10 crossover information. Maybe you should get Voice of the Theatres.
Sorry to bother you....
Hi Clyde -

I knew someone who did that exact thing. Jim Austin, who owned "Pro-Sonics" which made what was at the time one of the best sounding electronic crossovers you could buy. He was highly motivated because he wanted to design an electronic crossover for the DQ-10, and dump the passives. He failed in making them sound better, although simple bi-amping did improve them. His conclusion, IIRC was that the DQ-10 was designed from in front of the speaker, not behind. A series topology was selected,for the bass and lower midrange, then modified until it was right.
The the second series leg was designed and modified until it too was right. Finally both legs were combined in parallel, then tweaked some more.
Personally, I think both brilliance and luck were involved in the success of the final product.
I'd ask Jim for his notes, but he passed away long ago now.
In short though and pertinent to your question, being designed the way this was, you are not going to find a definitive explanation. I'm quite certain that if a top flight speaker designer today were given those exact parts to design a system around, you'd have something very different as a result. Would it be better? You'd have to conclude it would have to be with today's design tools.However, no designer would wish to start with those drivers, so the DQ-10 which we know and love would not even exist. That would certainly have been a shame since the darn things continue to pump out some great sounds all of these years later, flawed by today's standards as they are.
Good luck in your quest!
Yeah, thanks. I'm convinced that the concern for bass boost is why Jon separated the legs because the topology he used there would have messed up the rest of the series circuit. The resistors across the woofer, where a cap should be, bring the woofer Re below 3 ohms, and the midbass crosses over way under the published 400 hz. The cap in series with the midbass appears to be the only place he could put one in order to roll it off but he could have put it ahead of the bass resistors too. Maybe that didn't pan out. As an experiment I replaced the 80uf cap, which rolls the midbass off at approx 180hz (too low for the stock driver's capabilities IMO and the reason that replacing it improves the midbass), with a 36uf cap for a 400hz rolloff and the upper bass disappears. The lack of bass was a criticism of the prototypes, and according to J. Gordon Holt, Jon scrambled to correct it. A pretty imaginative change to the layout, I have to say. A desire to have the cosmetic appearance of a Quad and a reasonably sized bass enclosure really painted the DQ-10 into a corner.