- Just be sure to look at the -6 and -10 dB points, which are more relevant to the REAL low frequency cutoff in a room. - 3 dB is not too meaningful, it was just a mathematical convenience. A more slowly reducing output (which can mean a higher -3 dB point, but lower -6 and -10) often works better in real rooms.
- Note that many pro woofers' parameters seem to indicate sealed boxes smaller than the cone volume, and ported designs which seem nuts. This is because they are designed to work at high SPL, meaning high continuous power input, meaning the voice coils constantly hot (i.e. like in a 24/7/365 German disco, or a rock concert). When the coils are hot, the parameters shift and work in the big boxes the woofers go in. But at home levels, yeah, ya gotta work with the low level parameters given, so many pro woofers may not work so well.
- Digital crossover can give you a lot of flexibility, and active amplification is really good for horns since their impedance can be messy making passive crossovers difficult. Try to get a constant directivity horn. Most horns "beam" to keep on-axis response flat, but going active means you can EQ the on-axis no problem. Also the woofer should have a smooth response. Not necessarily flat-gentle bumps can be EQd out. But ugly bumps or dips won't really EQ out so well, regardless of calculations on paper.