That’s an easy one. We’ve played them by the hundreds over the years, and we’ve found that as our ability to reproduce the sound of these records improved (better equipment, table setup, tweaks, room treatments, electricity and the like), the gap between the better non-half-speed mastered pressings and the half-speeds got bigger and bigger, leaving the half-speeds further and further behind, in the dust you might say, again and again, with so few exceptions that they could easily be counted on the fingers of one hand.
The most serious fault of the typical Half-Speed Mastered LP is not incorrect tonality or poor bass definition, although you will have a hard time finding one that doesn’t suffer from both. It’s Dead As A Doornail sound, plain and simple. We’ve been playing half-speed mastered records since I bought my first Mobile Fidelity in 1978 or 1979. That’s forty years of experience with the sonic characteristics of this mastering approach, an approach we have found to have consistent shortcomings. These shortcomings have somehow eluded the devotees of these records, how we cannot imagine. They did not elude us, and we have taken the time to lay out their faults, chapter and verse, in the commentaries you see below.