@FullRangeMan the only thing I found out about super high qts and mention of flat frequency response in the very low bass is some stuff about the Carver Amazing Woofer.. any light you can shed on it would be welcome
"The Carver "Amazing" OB speaker started with specifically designed 12 inch woofers (built by Sony to Carver specs) with a Qts of about 3.12 or so and, IIRC, a Qms of about 10. This allowed the woofers to remain flat without EQ'ing down to about 20 Hz.
Later versions used a Tonegen woofer with a lighter cone and a Qts of about 2.85 and were targeted at 28-30 Hz, again without EQ.
This was the result of original research conducted at Carver, as there really wasn't any information available and the driver build houses had never attempted anything like this before.
Best Regards,
TerryO"