Hi,
You need to use line level OUT to ______ a device that separates only the low bass frequencies, and that device then passes only the remaining upper bass/mids/highs back TO the Preamp or back TO an integrated amp.
A tape out/in loop; a processor out/in loop; a unit with preamp (line level) out, and line level input jacks
Thus the amp and the main speakers only try to make upper bass/mids/highs.
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integral crossover:
here's a Raven Blackhawk Integrated Amp with an integral high pass, 80 hz crossover: sends 80 and below out to separate amp(s), like self-powered sub(s). Crossover point is not adjustable, 80 hz is their single setting.
then the blackhawk amp and the main speakers only try to make 80hz and above
https://ravenaudio.com/product/blackhawk-mk3/
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simple self-powered subs
have built-in crossovers, you go preamp line out, to sub's line in, then sub's line out (low bass missing) to preamp line in. preset sub's adjustable crossover and preset sub's volume (, then your preamp changes the volume of main and subs together
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external crossover
use a loop out of preamp to external crossover, back into your preamp. or line out to external crossover and line in of an integrated amp
a tape loop, processor loop, line in/out loop
crossover and volume
Ideally you want an adjustable crossover to find the best setting with your main speakers and your low bass speaker(s), and
adjustable volume, remote volume ideal.
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separate amps for the sub(s) somewhere, how volume controlled?