I have the following setups: Bifrost/Lyr , Burson Conductor, Dragonfly/LD MKIV SE. To be honest, most cans sound best on the Burson Conductor ...... except the HE-500. They really shine on the Bifrost/Lyr
I tried the tone generator at that site. Very difficult to discern precisely, but it seemed to be around 12kHz. It's almost not a tone, but just a background "sparkle" from my auditory nervous system letting me know it's online. I chose 14Khz because I remember back in the day when I could hear closer to 20Khz, I could recall being able to hear the horizontal retrace of a television circuit (15.75 kHz), and I thought it was around there.
Wow, these last few pages have been very enlightening. I asked about the teeth clenching because I just recently noticed it made a difference, and had the same thoughts as James (quoted in bold). Mine sounds like an extremely low level sine wave, equal in both ears at or above the upper limit I can hear (maybe ~ 14kHz)
Depends on the tubes, of course, but the HE-500 is the only headphone I have that actually sounds better on the Lyr/Bifrost than on the Conductor. Highly recommended.... especially if you want to acquire an addictive tube-rolling habit!