My guess is that you don't understand that the HD 518 is Senn's entry level product for their lowest level of entry line audiophile cans. While they are dark--darker than the next up the line, HD 558, they are not bass heavy cans in any respect.
I suggest that you read some reviews about them, as well as their bigger brothers the HD 558 and HD 598. You should be the gist of their sound signature and how the other two cans in this line differ.
For other cans check out the buying guides linked in the opening post of this thread.
tnx for the answer :) I do understand more or less and I'm satisfied with most reviews people are putting here and somewhere else about this pair of headhpones. its just that some poeople said how the bass can be overhelming and thats the last thing I would want from my headphones...but i guess i wont know untill i buy them and they will probably be good cuz its a bigger step from my older headphones