Hi and Happy New Year everyone.
This is the problem i have a woofer rated at 100W RMS and mid-range rated at 20W RMS, where do u think i should cut the crossover to get the maximum power rating for the assembly? And what crossover topology do u think i should use?
Thx.

The power ratings have no real bearing on the XO point. The main consideration for setting the XO point between a woofer and the mid are the on and off axis frequency response of both drivers Secondary considerations are stuff like and the excursion plot of the midrange, midrange fs, height of the drivers off the floor to account for floor bounce etc.

hmm but if i cut at 600hz wont the mid-range receive more power than if i cut at 1000hz? cuz i know that the power isnt spread equally throughout the audio spectrum, so if the mid-range is only 20 W isnt it dangerous to cut too low. And if u r right than what will be the max power rating with that woofer and mid-range regardless of crossover?
Thx for post.

Your crossover point and slope will determine how much power the mid sees at a particular frequency. The real concern related to power is driving a the mid past it's excursion limits.
A midrange with a 20 watt thermal rating probably has less than 2 mm of excursion. So in theory sending it even 1 watt at a lower frequency might trash the driver.

As an example the Vifa MG10 has a power rating of 40 watts and .65 mm of xmax. Even 2 watts of power at 150 hz will drive it well past its excursion limits. So my high pass crossover would have to account for this.

But again assuming your end goal is good sound, the primary determination of where the crossover point between the drivers should be (and in fact if the drivers are even a good match for each other) is the frequency response of both drivers. Once you have that then look at the excursion plot for the mid with that XO point to see if that will work.

Finally assuming you are crossing the mid over where it will not hit it's excursion limits at any frequency below the XO frequency, your system is still thermally limited to 20 watts continuous. This will number will be higher with music than test tones but still won't double.

Thx djarchow i was worried about the thermal breakdown than the cone excursion (i'll look into that) and thought that if i raised the xover point i may lift the continuous power of the woofer+mid system. But still i have seen a 3 way systems rated at 50W rms with woofers at 50 w rms and mid at 25 w rms im not sure where they were crossed though...