Spatial Audio Raven Preamp

was just thinking sub(s) and your post said it better. I'm not sure how to attach a sub(s) to the Raven Pre? Must be an easy way? 

@wsrrsw It appears there is a single-ended output in parallel with the balanced output. You'll have to check to see how this works but it might be quite simple- the main amps on the balanced outputs and the subs connected to the RCA outputs. I would expect to see a switch that grounds pin 3 to pin 1 so the RCA connections will work properly but they may not be connected to the output transformer driving the XLRs, negating the need for a switch.

The Raven has split windings on the output transformer so both RCA and XLR’s can be used at the same time (the RCA output uses one-half of the secondary winding). So feel free to use to use the RCA output to power the active subs.

However ... the added cable capacitance on one-half of the winding, might, in principle, unbalance the XLR output a little bit. Maybe. Most likely not. Use low capacitance cable for the sub output, if possible.

Mostly, try it and see. The Blackbird power amps have pretty good common-mode rejection, so unbalance gets washed out in the input stage.

I keep hearing good things about the Rhythmik servo subwoofers, so you might check out getting a pair (using stereo bass, with the lowpass filter set to 40 Hz).

Although horn speakers have gratifyingly low IM distortion, they drop off very fast below cutoff. It's basically a brickwall cutoff, so "pushing" them below cutoff has limited utility.

The degree of overlap between the horns and the subs (at least two) will be entirely subjective. Unlike closed and vented boxes, horns do not have a smooth, predictable cutoff region (which is 12 dB/octave for all closed boxes, and 24 dB/octave for vented boxes). Instead, they drop like a stone, and the octave just above cutoff can be pretty rough as well.

Combining the horn with the subwoofer will require judicious use of the "phase" control on the subwoofer plate amplifier, and messing around with the lowpass filter. The magic spot might be anywhere from 30 to 60 Hz.

The Raven will have no trouble driving an RCA output at the same time as XLR.  This has been tested by Spatial.  You should have no problem except that the XLR output is higher level than the RCA.  That is as it should be.  If your subwoofer amps have gain controls you should be able to match levels.  Subs are always tricky.  The other option is speaker level outputs to drive stereo subs near the main speakers.  That is the way I have always done it, but thankfully, my current speakers easily play 30 Hz in room so I no longer use subs.

I should add that all folded bass horns are tricky beasts. They only exist because a true straight bass horn that is flat to, say, 35 Hz, would be the size of medium-sized car. In other words, the size of an adjacent room. Two needed for stereo, of course.

PWK compromised with the real world by folding the horn (which creates internal reflections) and using the room corners to expand the size of the horn mouth. The internal reflections create ripples in the response above 150 Hz, and the cutoff region has +/- 5 dB ripples in the response, which interact with the room modes.

This is why adding a subwoofer is kind of tricky. You have to integrate not two, but three things: the Khorn response in its cutoff region (which is definitely not flat), the built-in filter of the subwoofer amp, and the room modes. Having two (or more) subwoofers is very useful because the room modes for one subwoofer will be at different frequencies than the other subwoofer, which smoothes out both of them. It’s also why multiple small subwoofers, in widely spaced locations, is a much better choice than a single subwoofer.

I should add the Khorn horn cutoff might be a lot higher than Klipsch says it is. 60~70 Hz would not surprise me.