The other significant effect of the additional filter is additional phase shift. If your tops have one 24dB/octave filter and your subs have 2, they will very likely be severely misaligned, leaving you with an even bigger loss of energy in the transition range. 

When mixing brands of speakers, it’s advisable to measure the combination and correct their alignment to the extent it’s possible. Even when making changes to the settings within the same brand of cabinets, and/or when adding filters ahead of the speaker-specific processing, it’s necessary to perform these tests and make these corrections. 

This is where BASSBOSS is different. All BASSBOSS cabinets include processing that makes adjacent boxes phase coherent with each other regardless of the model and throughout all the relevant presets. We can’t provide this alignment between our products and other brands, so it’s up to the operator to verify the resulting alignments. 

In order for us to be able to ensure that all the cabinets align, we cannot allow adjustments to the internal processing that would throw off the alignments. Unfortunately, adding processing ahead of the in-cabinet processing still allows things to become misaligned, but we caution/recommend against doing anything to the signal being sent to the BASSBOSS cabinets. It should be full-range, and the only changes necessary should be changes in relative level to match the lows/highs balance to the tastes of the operator. If, if, if you find it necessary to apply EQ, the EQ should be applied equally to the subs and tops, otherwise the phase-shift introduced by the EQ to the subs will disturb the alignment between the subs and tops. 

So, to get to the point, always eliminate all low-pass and high-pass filters from the signal being sent to the sub. The processing applied to the tops isn’t relevant to the subs level but you should verify that the tops are phase-coherent with the subs, which is to say you should test them in combination and adjust the settings for the tops until they align with the sub. 

Testing them in combination means placing them next to each other, equidistant from a measurement mic. Start by measuring the sub’s output response and phase and save that measurement for reference. Then mute the sub and measure the top’s output response and phase. Ideally, use the on-board processing in the top to align the top’s phase response to the sub’s recorded phase response. If the on-board processing doesn’t allow this, use outboard processing as needed.

Of course this kind of testing requires measurement equipment, software, time, space, work and expertise. The most familiar tools for these tests start with a software like Smaart, but if you have more time than money to spend, it can be done with REW (Room EQ Wizard) or other free or low-cost options like Systune or fuzzmeasure.