Know thy gradient. Classic ports fall off at 24dB/octave below their -3dB point. At 12dB, sealed boxes do it half as fast. With our sound|kaos Vox 3awf monitors unusual on a number of fronts, I asked their designer and his consultant about their gradient. With its 36Hz curved port/line, the slope then is ~16dB/octave. For augmentation mode when mains run unfiltered, a sub  enters ideally on a 2nd-order slope. In full filter mode, I'd set the spl's high pass to 4th-order like its low pass, then experiment with 50, 60, 70, 85 and 100Hz filter hinges. Our domestic solution is an analog low/high pass custom built into the preamp. With it the mains start to blend out at 100Hz, are down 6dB/40Hz, 24dB/20Hz. Our Zu Submission enters perfectly mirror-imaged with its own filter bypassed. Because our  Linkwitz-Riley 4th-order filter is fixed, I'd never experimented with different filter points. With the German Crossover, I suddenly had two convenient controls to move my inflection point up/down. I had a new lesson in sub.version on my plate. How would filter frequency impact overall dynamics, focus and the stereo panorama? To benefit from maximum room gain and run lower SPL to minimize stroke and attendant distortion, our tall down-firing 12" sub sits in the room's left front corner. With our cross filtering, there's solid 2nd-octave overlap between mains and sub. That means zero directionality issues. Whatever happens below 40Hz my ears can't locate. That's easily checked by turning the mains off. Now the low bass doesn't suddenly jump left. It's simply present. Once the mains re-enter to establish stereo cues, all the bass makers localize precisely within a 3D soundstage.

This did change with the white RiPol ModalAkustik MusikBass below. Its asymmetrical front/back radiation pattern with two severe lateral nulls from out-of-phase cancellation was directional so best placed more central. Now you have the basic setup for today's review.

"The Crossover is sold out at the moment and the entire next batch has already sold as well. It'll be 1-2 months before we can have a sample to you." Some rest for the wicked then.

… to be continued…