Von Schweikert vr33 question

Rear-firing, side-firing (e.g., Coincident and many others), or down-firing (e.g., Vandersteen and many others)... doesn't matter a ton below about 120Hz. You just can't echo-locate down there due to the wavelengths involved... about 10ft at 120hz and a whopping 56ft at 20hz. 

Good luck getting perfect peak alignment at the listening position from the right and left woofers down at those frequencies.  What really matters is how the waves reflect as they bounce around the room, and whether you're getting reinforcement or cancellation at your listening position.  

https://www.jdbsound.com/art/frequency%20wave%20length%20chart%202013.pdf

OP said:
" I understand it allows placement closer to the rear wall."

I assume that you mean what we normally call the front wall in back of the speakers; but a rear firing woofer should actually make placement closer to that wall more difficult.  

i wasn't asking so much for frequency.  But a speaker with the bass pointing rearward sound "goofy" "funny" "naked" compared to a speaker with the bass driver firing forward?

@dpm2340 Sorry, that's really the point.  At the frequencies reproduced by that bass driver, your ears can't tell whether the waves are originating from the speaker baffle, the floor under the speaker, or the front-wall behind the speakers. 

There will be differences in sound from each launching point, but those differences will be driven primarily by how the peaks and valleys of the bass waves sum at your listening position.  

Below ~120hz, the bass quality is really driven by how those standing waves build up in your room.  For example, it is quite easy to have a room where you're getting a 10-15db reduction in some frequency slice at the listening position.  My room was killing 40hz.  No matter what driver (10", 12", 18", 21") or amplifier (5W - 5000W) were used, if the bass drivers are located in the same position and your listening seat doesn't move, 40hz is still going to be down 10-15hz.  The only things to do are to move the speakers, listening position, or add alternative bass sources (as in a distributed bass array) to change the distribution of the peaks and valleys in those standing waves.