I've had my mic out the last few days. Today I wanted to see exactly what the LF Adjust dial did on my SP1-4000-HTs.
These were close mic sweeps - a few inches from the cone of one of my HS24 MKIIs.
Here's one graph... 10hz-200hz. Trust that 0-10hz follows the same slope.
Here is a zoom in. Now, since the knob has 10 settings, going from CUT to BOOST, the closest to defeating it altogether is either detent #5
The blue and yellow lines in the middle are 5 and 6, which at 20hz are 89.5db and 93db respectively. That amount to just over twice the power at that frequency. I did most of my other measurements on detent 5, but after looking at this, I wonder if I was cutting there.
Any thoughts? It's not a huge deal, as I think I have headroom for fudging, but as I experiment with EQ and gain in an attempt to just kiss the limits of the system, a 3db boost at 20hz should be part of the equation.