What is a good driver for a 17'x5.4'x3.8' form factor speaker?

17'x5.4’x3.8’

If those are feet the gross internal volumen (let’s assume 0.75” build material) is 9,263 litres. Not small.

If those are inches, is about 2.27 litres. Ideal for something like Mark Audio CHN-50 (just one of them).

Note that with a box this small i would be using 12 or 15mm material. If 12mm you could get to 3.35 litres. Ideal for a singlr Alpair 6.2m (getting hard to find).

The 3.8” dimension could be an issue. Very early reflections. The 5.4” will also be small enuff to be an issue.

And a box this shape, if vented will be an ML-TL of some sort.

dave