I'm trying to find reading material on the "bass trap pit" concept.
Google search doesn't give any useful results, so I'd appreciate if anyone could please point me in the right direction; maybe it's known by a different name.

Many thanks in advance.

I never heard of "bass trap pit."

Note that while this forum is still present, I set up a new one here where I check in daily:

Ethan's Audio Expert Forum

So sign up there and describe what you're asking about in more detail.

--Ethan