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In the Forum: Audio Discussions
In the Thread: Crossover Design
Post Subject: Crossover DesignPosted by drdna on: 10/29/2005
Hi Roman et al!
Allow me to introduce myself. I have followed with amusement Romy the Cat for many years. He is ascerbic and ultracritical, but he does know audio. We share many tastes, like the Koetsu Onyx Platinum foir instance, only Romy can afford such things and I cannot. I try hard not to do things to label me as an audio-moron, but I will be the first to admit I know only very little about audio or design, despite having built or modified nearly every part of my stereo.
I am considering the crossover design for a multi-driver horn system. I am not a wealthy man, or surely I would have done as Romy and built speakers to my specification. I have had designs, actually quite similar to the Macondo with some baffle changes, in my head for many years, but I don't have the money to afford such a project. Recently however, I got the opportunity to acquire some EdgarHorns for a really good price, much less than it would cost me for even the drivers I wanted for my DIY horns, so I said: WTF! I know all the compromises involved with the EdgarHorns, I have heard them when I visited Bruce Edgar in Gardena, and they were pretty good compared to most of what is out there. I realized that I would likely never be able to do much better, especially at that price.
So I did it and I am getting these EdgarHorns, but now what? Ultimately it is best to use (I think) a minimum of three, or better four, drivers to cover the audio spectrum, since the drivers can the function optimally. This results in certain compromises, however. Many people are drawn to the single-cone "point-source" speakers like the Lowthers, the Cain & Cain, etc. with the idea that a point source is critical for good sound. I am not so sure about this since the other thing that happens is that the crossover is eliminated, and this is BIG for sound quality.
Ultimately it doesn't even matter, because all the so-called single-driver speaker designs eventually start adding a tweeter here, a subwoofer there, because the listeners, although initially enamored with the great crossover-less midrange, now crave highs and lows as well. Worse, the new drivers are usually not time-aligned or even vertically aligned, in part due to the large size of the horn enclosures. So one ends up with non-spherical horns and folded horns and all these things that don't follow the theory well and don't sound as good, but it is a compromise some of us must live with.
I like the EdgarHorns because they are at least aligned and they were designed from the first as a multi-driver system. However, to get the best out of them, I believe the crossovers must go! This means a line-level crossover must be employed. Options include a Marchand tubed unit, a DEQX digital crossover, or a passive line-level unit. The Marchand unit might be okay if modified aggressively, but it is like adding Coca-Cola to a fine Burgundy, as you are adding a decent (but not great) amplification stage and assorted components to a system of better components. The DEQX is expensive and it trades off good control of time and phase alignment and very good filtering and adjustment for flat response FOR digitalizing and destroying the signal. It may improve the sound of some systems but not others, depending on what is wrong to start with.
Because I already use only a passive preamplifier of my own design, I may be limited by the "lossy" nature of a line level crossover network and the problems with impedence mismatching. And I only have a single set of heavily modifed Welborne Moondog 2A3 monoblocks that I built, so I will need more amplifiers -- at least two more sets. The Moondog is no longer made available (the kits are easiest for me) so I can't make Moondogs for all drivers, so I thought to try the Welborne 45 and 300B designs (based on Jack Eliano's Ultrapath circuit) on the tweeter and mid-bass drivers, mixing and matching designs based on what wourks best for a particular frequency range.
Then I read about the Melaquiades. Very interesting schematic. I don't understand all of it, not being an engineer. The cost is about what Welborne's kits would be, and the sound might be better (won't know until I give it a listen of course). Hopefully, I will not blow myself up during building such a project. My thought was that the optimal soultion would be to built a Super Melaquiades amplifier with a crossover incorporated to deal with the EdgarHorns at line level. I think this would be the best solution, but I have not listened to the options to knowledgably compare the passive speaker-level crossover to the active Marchand to the passive line-level for the EdgarHorn application.
Does this make sense? If anyone has had experience comparing these different types of crossover networks, to be able to speak to the superiority of one design versus another, I would appreciate the advice. Does this plan sound reasonable? And to Romy, thanks for allowing access to the Melquiades design; if I have specific questions about the design implementation, may I ask you about it?
Best wishes to all!
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