I didn’t use my Sennheiser MM 500 for long time but resurrected them a few days ago to compare these to my headset provided by my employer. I realized a weird cracking in the left ear which reminded me why I didn’t use these pairs for a long time. I decided to figure out what exactly causes the sound issue. After taking away the ear foam there is a mesh which also have to be dismantled. I checked the speakers and realized two plastic parts. After a little bit search I identified the small high tone speaker on top of the main speaker. The seat wall where it is pressed in is broken – on both sides. The mic still sits great there. After gently pulling out the broken plastic parts the headset is working like on day one… Give it a try if you own a pair of these, it is worth it.