THD below 50hz at highish SPL (90 db +/anechoic or quasi anechoic) is off the charts for most speakers. Per Sarcher's post, this test is sometimes run by HT websites, especially for subwoofer testing. Subwoofers are purpose designed for clean response in this range and most of them still suck.
No one wants to see that # for a typical full range speaker.
Marty
No one wants to see that # for a typical full range speaker.
Marty