Speaker Ports

I hope this is ok in this section. I recently added 2 6x9 speakers behind Gladys' seat to replace the single 8" subwoofer I had. I never liked how it was bass response only and did not really give out much of any higher frequencies. The boxes are small. Just big enough for a 6x9 speaker. I like the much higher frequency response, but now the bass response is very tight and "drummy" sounding if that makes sense. I've read properly sized speaker ports will help this, but how do I decide on size? Any help is greatly appreciated. Thanks.