Sound difference between i5s
 

I had a straight piped '00 V70XC for a while and loved the sound, then a while down the road I ended up with an '03 C70 T5, I pulled the exhaust off from the cat and it sounds dramatically different, this goes for a friend's 850R as well. Is it just the diameter of the exhaust? I thought maybe it was the exhaust manifold but they don't look to be much different. Why is the sound so different?
https://youtu.be/MeCOzmMAJ0M
https://youtu.be/oxlY-4oDU34