There is a scale the pertains to power requirements vs. frequency. You can use 50 watt tweeters in a 400 watt bass cab because they aren't having to handle that much power.
If it takes x amount of watt to push a freq. out at 200 hz, it takes less than that at 400, even less at 800, less at 1600, etc. By the time you get into tweeter territory, 50 watts is ok, assuming you're using your tweeter as an actual tweeter.
If it's like in most bass cabs, they're set either too low, or with not a steep enough slope, or both. Hence the single capacitor set up at 5k or 6k so it's 12db down in the 1200-1500 range or using a tweeter that's capable of lower freq's but either isn't mounted on a horn that can produce them or not taken full advantage of by cheaping out of the HPF, ie: too shallow a slope set too high instead of crossing lower/steeper. Of course that would mean having to make at least a 1st order LPF for the woofer too and that means a decent inductor and more cost.
When looking at crossover parts, you need the impedance curve of every driver being used. Your 8ohm speaker might read 15ohms at the frequency you need to cut it off at. Just buying a "8ohm" crossover isn't going to do you any good unless the drivers being used on the low side and the high side are fairly close at that particular frequency, like between 7 and 9 ohms.
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