Hi there, I have owned a pair of Sennheiser CX 3.00 for about 18 months. The other week I randomly decided to test them to make sure they're working OK. I did a stereo separation test and the audio is spilling over into the opposite channel.... So if I play audio to the left channel I could hear it in the right earphone too, but it's slightly attenuated (lower volume).... and vice versa; if I played audio to the right channel only, I could hear it in the left earphone too, but slightly attenuated. So I sent them off to the manufacturer under warranty, and today I received a replacement pair of CX 300S (basically same earphone but with a mic for phone use)... Unfortunately these replacements are also exhibiting the exact same problem albeit to a lesser degree (for now, I'm guessing it gets worse over time). I've done the test on two Samsung phones, a tablet, two laptops, my PC, and my TV headphone socket via HDMI from PC. My questions are; Is this is normal for low end £35 earphones? Or is it normal for 3.5mm jacks on all devices? Are consumer devices just poorly wired and should I invest in a proper headphone amp with a digital input and a 6.3mm phone out? Will I get the same problem if I get a pair of £200 IEMs and plug them into random 3.5mm jacks around the house? Has anyone else tested their headphones for stereo separation? (I assume it's more difficult to perform this test on large headphones unless you can remove the speakers from the headband and wrap each one under a blanket or something.) Should I send this replacement unit back and tell them to improve their quality control? Thank you for reading.