also does the quality of the active x-over matter? I worry about having a tube amp and preamp hand built from boutique parts then running the signal through an $150 ss active cross (I am not trying to disparage SS directly, just am a tube guy) I have bought a couple circuit boards to build steve benches tube active x-over, which he describes as "The Tube (valve) crossover shown here is a 3 pole lowpass and highpass used for a 2 way crossover design. The circuit needs +150VDC and 6.3V filament power for its operation. The circuit is a modification of a unity gain non-inverting Sallen-Key circuit that provides 18 dB per octave rolloff characteristics."

the schematic is here: http://members.aol.com/sbench101/Crossover/xover.gif

the circuit boards here:
http://www.the-planet.org/active.htm

does anyone have an opinion on this x-over and/or can anyone explain the pros and cons of active before the amps vs. passive before the amps?

thanks, Kevin

• my whacky no x-over speakers

Generally speaking, what reactive components do is to act as filters. Capacitance passes current before developing voltage across itself. This also has the characteristic of presenting less impedance to high frequencies than to low frequencies. Inductance is the opposite, developing voltage across itself before allowing current to pass, and posing less impedance for low frequencies than to high. Resistance is neutral, having current and voltage rise at the same rate, and having the same impedance regardless of frequency.

Amplifiers are essentially just signal multipliers. You can put them in front of a filter or behind one, and the situation is basically the same. Of course, in the case of loudspeakers, the load is reactive too so the reactive components in the crossover interact with it. This is a situation that merits some investigation, and it is one of the main reasons that having the crossover before the amp is attractive.

There is also several cases where reactive components are used within signal multiplier circuits, and more complicated response curves can be formed. A passive filter can only form a fairly simple response curve, but using feedback within an active circuit allows for more variations. This is why there are a lot of configurations that are possible, all of which are grouped together as "active filters."

The Sallen-key filter is very versatile, and is worth studying:

• Discussions about Sallen-Key filters and crossovers

kevin

About your crossover, maybe we'll look at your crossover with a signal generator and scope and set it up with that. I think there's lots of people here that would be thrilled to have an active crossover using tubes, and to know the component values that should be used to provide the appropriate response curve for their horns.

By the way, Mitch left for Norman this weekend, bringing his Theater Series four π's with him. They're the same size as your Altec 416 π's and are tuned similarly too. The port isn't as long or have as much cross-section area, but the Helmholtz frequency of the Theater four π Speaker is 25Hz, and the Helmholtz frequency of your 416 π Speaker is 30Hz, so they're pretty close. I'd say the two woofer motors would be interchangeable in either cabinet.

I don't know if Mitch will be one of your students this semester, but we'll all get together sometime soon, in any event.