not enough volumm

After installing new, more powerfull speakers into my car,  the radio/cd player does not get loud enough,  you can hardly hear it.  Is it because of my stereo or did I install them inproperly?  Someone memtioned to me it might be because of the ohmes of the speaker, and  that the stereo wasn't powerful enough and  that I would need   to install a amp or maybe a booster,  if that is true which one would it be?   THANK YOU!Sincerely Pinkie Q.

if you could mention the brand and model number of the speakers and if the cd player is oem mention the vehicle that it is in. if its aftermarket list the brand and model numberQuad L Handyman services