Originally Posted by keeper
That's interesting...if the towers have a crossover anyway how would that be?
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Regarding full band vs lfe to the BP90x0 question, if you depend on the internal crossover, it's "filtering" the active signal. By design, it should be the most "technically" ideal configuration, as the crossover is designed as an integral part of the sound of the speaker. HOWEVER, you are dropping some of the signal from the source via the amp, going into the speaker, so the main amp is amplifying 100% of the frequencies, but the amplified portion being output by the passive drivers is only some fraction (say 80%) of the source signal, with the rest being filtered down to the input stage of the speaker amp. Then the internal speaker amp for the woofers takes that last 20% of filtered sound, amplifies it back to the woofer output for reproduction of the sound. By doing this, it's feeding a modified, internally crossed-over, output to both stages of the speaker, with some design parameters around full frequency reproduction trying to match the source input.
By separating LFE to it's own stage, the pre-amp is only feeding the desired (by room calibration) range of output frequencies to the main amplifier for reproduction by the upper stage. This means the main amplifier is now amplifying a smaller portion of the total spectrum, and nothing is being filtered statically in the speaker (while maybe not strictly true, the speaker internal crossover has minimal signal remaining to handle as the pre-amp has already cut the lowpass signal out). The pre-amp is then feeding the LFE frequencies at 100% signal within the calibrated lowpass frequencies, to only the amplifier in the woofer stage of the BP. So the upper stage is playing ~100% of the source it's receiving from the external amp, and the lower stage is playing ~100% of the source it's receiving via the built-in amp.
The question then becomes, what system has a better matched crossover and desired effect for your situation. This is why the listener ultimately has to decide. The pre-amp LFE and "primary" signals need to match the speaker characteristics well to ensure a balanced output. The speaker designers have already "pre-designed" the speaker based on their knowledge of the built product, but are filtering the signal internally in a fashion that is likely different than the pre-amp LFE decision/crossover processes.
Neither are wrong, and depending on your pre-amp, and room-processing software, you may be able to get much better tuning results using the pre-amp calibration, versus the speaker's pre-determined crossover points. Calibration of the pre-amp, with the speaker crossover in place, will improve the signal to match your specific room, but the crossover is a "fixed" alteration of the signal, that may not be ideal for your specific setup. Or you may not hear any difference at all if the speaker's full-range with x-over matches your room and listening preferences well, then you'll arrive at the same result either way probably. Hope that helps some? (And this is my take on this situation, feel free to correct or contribute anything I may be in error on).