if u only go for the exhaust and no downpiping then bro the sound at idle is just like stock exhaust i.e no sound at all only a little bass, and below 3k rpm the exhaust's sound in cabin is minimal and a little bassy one on the oustside and when u go to high revs u can hear a bassy sound which is not so loud. so when only exhaust is installed the sound is bassy and not that loud. u can say it medium i.e not loud and not too silent either at medium to high revs. and sound is minimal at low revs.
but if u go with downpiping the sound is comparatively loud.
rest if u want to hear the sound u can come to my place my frnd has the same exhaust installed in civic exi and u can check its sound.