best sub for 150 hz and below

what's the best subwoofer for 150 hz and below? Looking for a sub for Carver platinum which crosses over at 150 hz from the woofers to the ribbons. room size is 20x23x8 would like 105 dbc at 40 hz.
What is your budget?
At the risk of sounding pedantic, a point of clarification needs to be made before anyone can really accurately respond to your question.

Consider: a true subwoofer (i.e., a speaker that handles the range below the woofer) is intended to handle the lowest octave -- from 20Hz up to 40 Hz -- and will usually overlap with the woofer into the second octave (40 Hz to 80 Hz). A speaker that is handling frequencies as high as 150 Hz is at the very limit of the upper bass range, maybe even going into the lower mid-range frequencies, and is thus not really a subwoofer, but rather a woofer.

Hence, you may need to re-think the woofer vs. subwoofer issue. If you really need to cross over at 150 Hz (which may overlap at least half an octave higher, unless you use a very steep 3rd or 4th order slope crossover), you might want to consider having a custom unit built that combines both a woofer and a subwoofer. Do any Audiogon members out there have experience with such an approach?
The only subwoofers I know of that crosses-over that high are the unusual TacTs.
I don't know about the best.
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