The Neumann KH 150 requires TWO KH 750s ? Does the KH 310 require two ? Curious the reasoning it requires two.
Pretty sure you will find a lot of answers here on ASR. The 750 is a small sub, and when paired with 150s it becomes a limiting factor at low frequencies.
While it’s fun to add and tune a subwoofer, not sure if everyone realizes that it’s not that straightforward to do right.
And I’m saying as I have ancestors from those Neumann speakers, I have a foot switch to disable the sub and the high pass filter so the speakers play full range. And it is really challenging to improve one area without degrading another. Without this instant bypass from the listening position it’s much more difficult to evaluate carefully in my opinion.
So yes, with just 2 speakers bass response will hardly be perfect, but there is some value also in the simplicity of the setup. It’s cyclic also: there are times you dream of multiple subs with individual EQ, and times you’d rather have 2 KH 420.
I have only one sub though, it is possible that with 2 subs there are less compromises for alignment, and really smoother response.
My opinion is that unless you have high volume requirements (and or large room and listening distance) it makes more sense to either take full range speakers and don’t bother with the sub at least in short term, or to take smaller speaker and the sub. If you are going to add only one sub, go for the 120 but not the 150 or 310 because with classical bass management you are going to use them above 80Hz anyway.