+8 dB is a lot of boost in an area the driver is rolling off and distortion in increasing rapidly. I am also not sure about the power calculation as an 8 dB boost is going to take 6X the power . It doesn't make sense to me that you can get 97 dB at 32.5 Hz with 78 watts from a 7" driver. I am sure it will "work" in that is will make LF sounds but your main speakers are so good that you may make things worse, especially if you try to cross at 400 Hz with an LR 2. I love the idea of co-located subs and mains and have had success with the concept. I just don't think trying to use a 7" driver is the way to go when you really only need extra LF response. Free random internet advice and worth every penny. Good luck and have fun.
The idea for 400hz was to minimize group delay so it would work with just a passive filter. I have been playing around with Linkwitz Transform and it seems the drivers can do f3 25Hz 91dB, for the pair that is 97dB more than plenty for me. If crossing at 400hz doesn't work out I will have the get a mini dsp. Or I go second dac route with https://www.minidsp.com/products/usb-audio-interface/mchstreamer-lite so I can do dsp in foobar, in that case I will cross at 80Hz.
Makes sense, but I think group delay is probably a much less audible problem than taking the lower midrange out of the mains and into the sub, as it were. Depending on how far the sub drivers are from the mains you're going to be able to localize the drivers, and you might also get some unwanted and audible acoustic cancelation.
I would build a box say 2 stacked CB6 (bit taller) the drivers would go on top so they would sit just below the C6B woofer. But I am never going to get the passive filter right first time I think and those parts can get expensive. So I am going with plan B.
Since you are going to co-locate the speakers and subs as long as the centers are ~1/4 wavelength or less apart and lined up you can use complementary Linear Phase crossover filters because the pre-ringing will cancel and you will mostly eliminate group delay. As mentioned a high cross with shallow crossovers are going to result in many problems especially cancellation. If you try it make sure you take measurements before and after adding the sub to make sure you are not making things worse. Those Ascilabs speakers are really good above 50 Hz and you don't want to spoil that.
I hear you, I am going with the 10inchers anyway. Only time in my life I will ever build a sub so might as well do it good. Btw those 7 inchers have an incredible Xmax of 14.7mm, that is 29.4mm peak to peak lol, most of us will run out of amp power before they bottom out.
Glad you are going with the 10 " drivers, I think it will work out better for you. That Xmax is good for a 7" driver but to keep it in perspective see below
This seems a lot more reasonable to me, this is basically what I would do in your situation. Force cancelling is key for a bass stand. Should sound amazing once you get them integrated...
