Laptop has built in subwoofer. Do I also need an external subwoofer?

are you referring to the asus g75?

laptop speakers are always bad. the g75 speakers are usable but underpowered (just like all laptop speakers).

the so called woofer really isnt all that great as well. a cheap $30 2.1 system is much better than the speakers which come with it.
not familiar with that one... but its going to be about the same.

the speakers might not be as bad as some basic laptops but still its worth plugging in some cheap speakers when you are at a desk. my brother plugs in a 2.1 set (as well as a keyboard and mouse) when he is at the desk. its much better to work with.