This gets filed under "No Sh*t Sherlock", but the mesh filters in IEMs can make a huge difference.

[JanL]

My CCA Hydros were sounding dark and dull and I saw that the metal mesh filters in the nozzles were partially clogged up and partially corroded, so I decided to swap new ones in.

I needed 5mm ones and Amazon only had smaller sizes in the metal mesh style, but they had 5mm ones in perforated plate style, so I bought those. After swapping them in, the IEMs sounded totally different but not in a good way. There was a ton of peaky upper mids and treble, and the bass got weaker. Very unpleasant.

I started to experiment with tissue paper and open cell foam and found that I can shape the treble and upper mids by using different amounts of each in front of the metal nozzle filter. I ended up with a single ply of tissue paper followed by a small foam plug flush with the ear tip. Now the IEM sounds smooth and balanced. I think it actually sounds nicer than with the original mesh filter alone. The treble is silky smooth, which was not the case before. I wish I had a coupler so that I could run some measurements to see exactly how much difference the filters make.

Anyway, I thought I would share.

 

[NTK]

It happens that the mesh filter actually functions as an acoustic damper, and it is one of the tools used to tune/EQ the frequency response of IEMs. This screen capture was at about the 19 minutes mark in the video. Click on the picture will take you to the video.

 

[SuicideSquid]

I often use bog-cheap Skullcandy IEMs that cost about $8 for the gym, and after a little while the fabric screens over the driver will clog up and start blocking all sound. You pop them out and they actually sound better. I think the intention with the skullcandy design is to dampen the highs so that you push them harder and they sound more bassy, but they're a lot more neutral with them taken out.