I have 2 back and front NEW speakers and a 100w radio.Do i need a amp?

Question

should I by a two channel amp for the back speakers and use my 100 w radio or should i just buy a four channel amp and forget my radio?

Answer 1

You don't need an amp uless you want it louder.

Answer 2

you will need to try it out without the amp first.  it really depends on your listening habits.  

if you have a quiet car and you don't listen to the music real loud, you should get away without a amp.  instead, i would suggest you to spend money on having additional subs to broaden the frequency response that your system can reproduce.

if it's not loud enough, you can then add a 4ch amp to increase the power.