Sounds like a seal/insertion problem to me. Getting these things properly inserted takes a little practice and is hard at first, but gets easy once you get used to it.

1. Roll and squeeze the yellow foam in your fingers until it is compressed.

2. With left hand insert compressed foam into ear. Look at diagram in manual to see which direction the wire should be pointing (but basically it is up and foward), at the same time with right hand, reach over your head and pull your left ear from the top away from your head (this opens up the ear canal and allows you to insert the foam part deeper into the ear canal.

3. Push the ear plug in fairly deep and then hold it in place for 15 seconds or so so the yellow foam can expand and make a good seal.

4. Repeat for other ear using the opposite hands.

5. Route the cable over the top of your ears.

They may seem uncomfortable at first inserted this way, but after a few times you get used to it and they get comfortable. Properly inserted and sealed, there is plenty of bass.

I also think they do break in with some use and start to sound better.