To my ears, without the clamp, there's a subtle blurring of musical information and lack of 'focus' on instruments and voices, which with the clamp fitted is rendered as absent. Often with these things, one needs to focus on musical differences, as opposed to tonal ones (as automatically tends to be the case), which are likely to be minimal at best.

Anyway, if you can't hear any difference with or without the clamp in situ, that's probably a good thing, as it's one less thing to worry about!

Marco.