Capacitor as Crossover for High Pass?

Not sure why I've read comments that running the satellites through an electronic crossover has a detrimental effect, while it is OK on the woofers/subs? I guess it would be not having to use an additional cable and the cross-over?

I would imagine so, particularly with respect to the electronic crossover. Any sonic degradation or artifacts it might introduce would figure to be more significant if they affected the mid-range (and adjacent) frequencies, as opposed to just the low bass.

Would the capacitor have a 6db slope?

Yes. If placed between preamp and SET amp, the high pass filter would be comprised of the capacitor and the input impedance of the SET amp, which presumably is essentially resistive at audio frequencies. An RC filter has a slope of 6db/octave once you get beyond the point at which it is 3db down (that point being referred to as the 3db bandwidth). So if you set the 3db bandwidth (which in this context is the same as the "crossover frequency") to 150Hz, then at 75Hz it would be down 9db relative to the upper bass, the mid-range, and the treble, and at 37.5Hz it would be down 15db.

You would calculate the required capacitance by using the formula for capacitive reactance (impedance), Xc = 1/(2 x pi x F x C). The 3db bandwidth point would occur when Xc equals the input impedance of the amp. So you would substitute the value of that impedance (which might be perhaps 50,000 or 100,000 ohms) for Xc, set F equal to the desired crossover frequency, and re-arrange the equation to calculate C. If you use units of ohms and Hertz, the calculated C will be in Farads, so multiply the answer by a million to get microFarads (uF).

The specs you provided for the amps and speakers seem generally reasonable, but I still have a concern about the disparity in power between the two amps. A 400W amp driving 87db panels will be able to play about 8db louder than a 24W amp driving 91db speakers, which is a substantial difference. Even with an electronic crossover and a sharp rolloff, I think you might find yourself unable to use perhaps 1/2 or more of those 400 watts without clipping the SET amp. (I'm assuming the 87 db figure is for 1W input and at 1m, not 2.83V input and at 1m. Given the 4 ohm impedance, if the 87db is based on 2.83V, that corresponds to 2 watts, or 84db/1W/1m, which would reduce the concern).

Together with the fact that the satellites are reasonably sensitive, and the room is not large, that would seem to suggest (assuming 87db/1W/1m) that perhaps a 200 or 250W SS amp (into 4 ohms) would be a more appropriate choice.

I have no particular knowledge of the quality of the Behringer or Marchand (or other) electronic crossovers. But having the flexibility to adjust the crossover slopes over a wide range, as you mentioned, would certainly seem to be desirable.

Best regards,
-- Al

All of your points sound reasonable.

What do you think of running the monitors "full range" and then just using the electronic crossover for the lower frequencies? I could always experiment with a capacitor as I go along here. I'll also take your advice on the bass amp.

Also want to say that being new to this audio, (I wouldn't call it a hobby as it's become a passion) experience, how really supportive everyone one is and how willing they are to share their knowledge. It is a great help.

Thanks again.

Lee V.

Lee, the one issue I see with that (aside from the fact that the monitors might sound better if the deep bass were kept out of them, which as you say can be evaluated later) is along the lines of my earlier comments. The power capability of the tube amp will constrain how much of the SS amp's power can be utilized.

If the bass panels are 4db less efficient than the monitors, and the monitors are run full-range from the 24W tube amp, and you gain-match properly, then the maximum amount of SS power that can be utilized without clipping or overdriving the tube amp (which would result in a highly distorted signal being supplied to the monitors) is:

24W + 4db + whatever amount of headroom the tube amp can provide above its 24W continuous power rating.

4db above 24W is 60 watts. So on a sustained basis you would not be able to supply much more than 60W to the bass panels, or perhaps (just guessing) 75 to 100W on brief transients, regardless of how powerful the SS amp may be.

And those numbers are based on the optimistic assumption that when high volume bass notes occur, there is no significant musical energy present at higher frequencies. If there were, that would add further to the burden on the tube amp, and thereby further reduce the amount of power from the low-pass filtered SS amp that could be utilized without clipping the tube amp.

Best regards,
-- Al

Got it. I'll plan on rolling the lower frequencies off the monitors. If its OK, once I find the panels and start working through the process I'll send an update.

Lee

Next crossover Slopes?

Could I get some thoughts on slopes to use on both active (for the low pass) and passive (for the high pass)?

Is there a reason you wouldn't want to use 8th order slopes? Complexity, noise? It would seem that one would want to use the greatest slope and place the two crossover frequencies within exactly an octave of each other (say 125hz for the low, 250hz for the high)? Would not the drivers then be either positive or negative the same "amount" throught the slopes.

If so, would the object be to have both drivers, in this case the mid and the woofers, carry some of the frequency range with one driver negative and the other driver positive through the slope as they approach a crossover point exactly between the two crossover frequencies? In essence the frequency ranges between these two points are flat without any (+/-) overlap?

Or would it be more of a blend of slopes with one of the driver types "carrying more" of say the bass frequencies towards a point between the two crossovers?

I understand I am being very simplistic here. I imagine differences between speaker types, volumes, phasing and type/wattage of amps come into play.

Lee