First Order Crossovers: Pros and Cons
In honor of the impending release of a diy version of the Nelson Pass designed First Watt active crossover, I thought I’d bump this amazingly informative thread on crossover design... looking forward to building the FW crossover and using it to facilitate bi-amping of my Coincident PREs. https://www.diyaudio.com/forums/pass-labs/165756-pass-labs-b4-crossover-questions-58.html |
@murphythecat That is exactly what my Coincidents due with the midrange and tweeter. Midrange is connected directly to amp and the tweeter just has a single 4.7uF cap in front of it. But then they've got an additional two 12" woofers after an inductor on each channel... I'll be using Nelson's crossover to skip the inductor and play a bit with the crossover frequency (they don't fall away until 2000hz and I'm getting some resonance up there with my current sub amps). |
Transducers are not flat though there operating range they roll off the 1st order utilizes the reduced levels and since it overlaps do to its slight -6db per octave roll-off you can fill in these dips in response by allowing other driver to gently roll off overlapping and filling in. A 1st order is not for every loudspeaker type and I would say 1st orders require more costly drivers without peaks and severe breakup modes as well as smooth gentle roll-off. I find horns can take advantage of 1st orders since the horn itself has a fairly severe drop off at its operating range you can use a 1st order without worrying about to much overlap. A 1st order can reduce power handling and peak SPL but its advantages in-phase and lower parts count can have sonic benefits. |
Absolutely wonderful read! Glad this thread was bumped recently back from 2005 or I would never have found it. I am an electrical engineer myself with significant signal processing background, and I truly appreciate the clarity of Roy’s and Karls explanations here. They are absolutely correct. At the same time, it is easy to see how without formal study of electrical signal mathematics it might be difficult to follow or even counterintuitive. Nowhere is this as obvious as the discussions relating to Phase coherency vs Time coherency (i.e. simultaneity). Time coherency is clearly the stricter condition as Roy points out. I also really liked Karls explanation of the sum of the high and low frequency drivers output after first order crossover as the sum of two phasors separated by 90 degrees at all frequencies. I think I would have further reinforced the fact that it is *perfectly fine* to add these "out of phase" signals because the result is always a constant phase at the average of the two individual phases, which is actually ideal. Without some background in signal processing it might be easy to think these two drivers were fighting each other and causing distortion. Karls post really helped clear this up. Finally, it was good to see it pointed out correctly that the spatial lobing problem is a multiple emitter issue, and not a crossover issue. Steep crossovers merely narrow the region over which multiple emitters "exist" for that frequency. Thanks for the great read. I hope there is more discussion on this. I have a pair of speakers with a first order crossover now myself (Dynaudio Special 40), and they really do have a very special sound. Yes, I hear the lobing, but yes, I also hear the outstanding clarity which I assume is the phase and/or time coherency of the drivers in the sweet spot. Still trying to decide what I think of them overall, but so far very impressed. Btw, there are a lot of other LC components on the crossover boards (presumably used for impedance correction of the drivers?). Would like to learn more. |
