Quite simple if you think of what a crossover really does. It is a voltage divider, but it is a frequency dependent voltage divider and only at crossover is the voltage actually divided among two drivers and then at a reduced level. For the SH-1810-ER to be rated at 700W would require that
any signal be split equally between the LF and MF/HF sections. However, for a 5,000Hz signal there is really nothing being sent to the low or mid drivers, the signal is going almost solely to the HF driver. I'd guess that 1,000Hz goes primarily to the mid driver and 50Hz almost all to the LF driver. Whether a cymbal crash or kick thump or vocal, the amplifier is still capable of it's full rated output at all frequencies, but the crossover is directing that particular signal primarily to just one driver, it is not spread out equally among all of the drivers in the speaker.
Looked at another way, if a component in the speaker has a particular rating and the signal to be reproduced could include the bandwidth that component covers, then that rating limits the overall rating. The LF section being rated at 400W does not affect the MF/HF section's 300W rating and if the signal will use the MF/HF section, then that 300W rating still applies.
Thus the overall speaker rating has to consider the rating of each driver within it's operating bandwidth. It comes down to which bandwidth component is the weakest link. It is common to have a crossover design that compensates for a lower rated but more efficient HF driver, with the crossover itself padding the level and dissipating some of the energy from the amplifier. It appears that this is the case with the SH-1810-ER and the overall rating in passive mode is apparently dependent upon the 300W continuous rating of the DL10X mid frequency driver.
I reread the earlier comment you referenced
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Sorry,I should've been more specific. The lows have their own amps, QSC3402 and are not in the loop as far as the tops go. I cross the them over at 200hz. The tops are 3way passive; 18-10-1.
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While 'lows' would normally be defining the 18" drivers in the SH-1810-ERs and "lows" are different than "subs", I can see how this might be defining a sub being used. However, 200Hz is a high crossover point for any sub and makes even less apparent sense when the mains have 18" woofers, a -3dB point of 46Hz and a recommended LF to MF crossover of 250Hz. You're barely using the LF section of the mains while putting a lot onto the subs. Is there any particular reason for the 200Hz crossover? Was this perhaps done to address clipping the CA12 with high levels of low frequency content?
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The problems started when the DJs arrived. I have never blown a driver in that system in t my 3+ years there doing live shows. My theory is that even though the overall level isn't enough to clip the amp, when they crank their EQs to get more highs and lows, it sending a clipped distorted signal to those drivers. Eventually they give up.
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This seems to possibly be another clue. I don't know how the DJs tie into the system or what they have access to, but it sounds like they do not have access to the DriveRack or the amps. It also sounds like the clipping is likely occurring before the amps. If that is the case, then more headroom in the amp won't prevent that.
