I’ve just been playing around with pre-amp settings for a new Concorde Century cartridge. Switching to IEC instead of RIAA curve seems to give it a slightly more natural sound. It’s hard to explain, but perhaps the upper mids and highs are easier on the ears and overall it’s a bit clearer and more natural sounding. So from a quick Google, apparently the IEC filter cuts very low frequencies. Assuming this is not just my imagination, could the fact that cutting the extreme lows improves the sound quality, point to some kind of setup problem, like a tonearm resonance or some other vibration issue?