Lol I tried the Quad straight out my new pixel 3a and it doesn't sound as muddy as I remember the iPhone did... Actually I think I prefer it to my fiio k5 pro which tries too hard to make the Quad sound like an electrostat with a somewhat unnatural timbre and ethereal image. It makes me wonder if we really need that much power for this headphone... I might as well sell everything and just keep the Quad with my smartphone.
I also tested treble sine sweeps for our friend
@Pinkus and I can hear a strong signal until 10khz, then a progressive roll off until 15khz. I can't hear anything after 15khz. This is very similar to what I hear on the Stax SR007. So nothing too bad.