The improvement from the L4 to the L5 was an increase in the neck length by two frets. The neck angle is greater providing more pressure to the bridge and consequently more volume. The Loar instruments enjoyed greater attention to quality of materials, construction and "tuning" similar to what is done with violins. My experience with Loars equipped with the "Virzi Tone Producer" amounts to just a few instruments. Seeing as how the back is generally a resonator with stringed instruments, I cannot see what gain one gets from this device and after 1924 it was no longer offered. A Virzi was in this Loar F5, all I can say is it didn't seem to hurt the output, this mandolin had a robust voice.

And Gillymor, I'm pleased that you liked the delivery of Hesitation Blues. Emily has made many recordings of excellent musicians playing this most excellent mandolin. I wanted to put my own spin to it.