Foam Core Board Speaker Enclosures?

That makes sense. Given that the driver's depth is 2.15 inches, anything less than 2.5 inches in terms of the MLTL box depth would be cutting things close.

Unless there's any glaring reason not to, I'll have a go at building the MLTL at the same height and width of 15 inches, and reduce the depth to 2.5 inches. I'll adjust the port length of the schedule 40 PVC pipe to 5.55cm (converting that value to inches resulted in a less memorable number ;) ). I'll have to stop by a craft shop soon and get some more foam core board!
Here they are in place. I used some twine and hung them like pictures...

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I'll have to wait a while before getting another pair of speakers for the Cornu speakers, but in the meantime I was thinking about using the MLTL design for the 6.5 inch polycone woofers, along with an additional tweeter. Not necessarily for the Bass boost, but because the aspect ratio of the enclosure is nice.

The Qts is also pretty high (0.95), so it seems like it might work. The mouting depth of the woofer is 2.875 inches, so I'd guess at least a 3.5 inch deep MLTL box wouold be required.

The Vas is 0.65 cubic feet, and the resonant frequency (Fs) is 52Hz. If we were scaling up the pizza box design, how big would it need to be?
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Assuming we make box about 2x Vas. You could go 25in x 25in x 4in deep. Assuming 0.5in thick plywood then you have 21in of internal width for the channels so you can make the channels 7in wide internally and it would all fit well. Total TL path is 6ft so good for 47Hz Fb on the 1/4wave fundamental frequency. Then use AMLTL method to determine port size for 47Hz. You will need to add a small fullrange or tweeter and crossover as the 6.5in won’t go high enough. One of those small Dayton snap in ND-25 dome tweeters could work.
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Unfortunately the XPS I have left over isn't that size, so I'll have to get some of this fancy plywood you've been talking about ;)

I was wondering about the box volume, and saw that a 24x24x4 inch enclosure is 2304 cubic inches.

This'll fit into a 19.2x30x4 inch format for the same volume. Would the thought end there because of how the 'pipe' would need to be created?