Cons: Overly boomy bass,
I bought my pair of cx400 to replace my cx300 and was expecting it to be a more refined version. I was, it's pretty safe to say, disappointed. The sound you get from these is far too similar to the 300's for their own good. I had the same problems with the cx400 as the 300. So I got boomy bass which drowns out the rest of the range.In this day and age I can't think of one good reason why you should buy the cx400's, there are earphones out there which are just as cheap and do everything better. They're certainly not worth the full retail price.
The shallow fit and comfort could be a good selling point but because of this and the cable design micro-phonics and isolation are not very good either. As with most sennheiser's there are many fakes of varying quality out there.