hey now, crossover question.

[pete1729]

I'm new here. i have a pair of altec 806a/811b horns that i an going to integrate into my mcintosh xrt20's. the xrt's themselves will remain unmolested and be driven by a mcintosh mc2205 solidstate amp. The horns will be driven by a mcintosh mc240 tube amp. I have auditioned this arrangement and the horns fill in nicely, very nicely, however I wish to build a band pass filter for the horns. I'm going to use a third order high pass at 800 hz, so as to shut down response below the horn's design parameters. I am going to use a first order low pass filter at 8000 hz so that it will blend a little more gently into the xrt's very capable high end. from what I've read i should include an l-pad to match sensitivity. therein lies one of my questions. is that what an i-pad does? if the xrt's are 89db and the horns are 106db are those the values i should use in my calculations? and what about a zobel network? are either of these things necessary since there is an entirely different amp driving the horns?

[bowtie427ss]

Just my .02 here. Since you are going to drive the 806's with a dedicated amplifier, why not insert an active DSP like a behringer DCX2496 or bbe DS26 between your MC240 and preamplifier. This will give you far more flexibility in terms of shaping, EQing, phase/time alignment, and it'll extend the life of your MC240.

At the end of the day the DCX and cables/adapters won't cost much more than the passive components needed to do the same job if better/boutique components are used.

It's a more "accurate" way to go since parameters are adjusted in the digital domain, and you're not at the mercy of the spec tolerances allowed on most passive devices. It also will prevent the amplifier from "seeing" any load other than the 806 voice coils. I have a phobia about using a quality/valuable amplifier just to drive current into passive devices that produce no sound and can present a reactive load to your amp.

Just my .02..................

[Panomaniac]

You may not need an L-Pad. Since you are driving the 811s from a separate amp, you should be able to simply turn that amp down. Use the volume control on the MC240 to match levels.
But you may still run into noise issues. So you may want to use and L-Pad to drop the level a few dB. And the L-Pad will have the advantage of presenting a smoother impedance curve to the passive crossover. If you put 16R across the 806 and 8R in series, you will drop the level by ~6dB.

You didn't say if your bandpass will be active or passive. Either way, a small L-Pad on the horn may not hurt. It's easy enough to try.