Corsa d Speaker upgrade

[David80]

Hi, have bought myself some speakers for my 1.4 t corsa d sri & I'm wondering if anybody could help?

The passenger door speaker doesn't work so bought an upgrade kit from ebay, alpine front & rear speakers, brackets & connectors. 

Swapped all of them over & apart from the passenger door still not working the other 3 don't sound good at all. The drivers door doesn't really sound any different from the stock but the rear sound really quiet, like there's no base to them. 

I bought coaxial 2-way as I thought they could be more or less be swapped straight over 

Is there a reason they sound worse? Do I need an amp or something else?

I still have the stock stereo & was hoping to replace the what I thought was broken speaker & make it sound a bit better than stock with as little effort as possible. 

Thanks for any help