Snorkel Duct:
The curved-side cabinet presents some design challenges, among these being duct placement. The easy answer is a rear port; there's plenty of room for that, but I wanted to circumvent any placement issues with these, as they are appropriately used desktop, bookshelf, and wall or stand-mounted. I also liked the idea of being able to swap on different baffles with alternative driver loads and box tunings; thus a front-mount port and duct became a design objective. Offsetting the tweeter 1/2" from the centerline made room for the port on the front of the baffle.
There is an interior brace in the cabinet, shown in earlier pics. While PE says it may be removed, I prefer to leave it in place. Also, with the curved sides, the cabinet narrows toward the rear, so, even with the brace removed, a straight shot rearward is not workable (though an angled one would be.)
Another issue is location of the inside duct opening. The rear of the woofer puts out sound much like the front, and if the opening is in the immediate proximity of the driver, that sound comes out the port and interferes with the direct radiation from the front. Thus, it's important to direct the interior opening away from the back side of the woofer, and aim it at a non-reflective surface.
ABS DWV fittings are available at Home Depot and similar in a full spectrum of angles to configure a duct in just about any desired shape. Here, I've used a "Street" 45° and a regular one, plus a couple of short lengths of 1.5" ABS pipe to snake through the brace and up behind the tweeter, with an overall length somewhere between 8" and 8.5", depending upon how it's measured. There is a straight line of sight through the duct, in this case, but that is not essential:
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