It being proven is like saying there is efficiency loss at lower dc voltage.
It was blown way out of proportion.
Just like unwanted noise coming out of amplifier.
Yes, we tested it, it exists.. We also tested a well known korean branded amplifier..
It has unwanted noise output too.
One of my local friends has 2 18s in a 4th bandpass on a single hd8000 where the passband is typically demo-ed between 17-28hz ONLY.
He peaks below 30hz currently doing over 151 in meca headrest.
If users want more control over the low frequency range, they can look at the DSP line which has a -1db fluctuation all the way down to 8hz and up in the high KHz range.
So, there is nothing to worry about.