I drive a 1999 Honda Civic with 190k miles. All the following repairs have been done within a year:

Timing belt
Breaks
Rack and pinion
Heater core
Exhaust pipe
Brake line (several patches)
Timely oil changes
Starter

My problem is a week ago my exhaust pipe fell out from the bottom of the hood and I brought it to my mechanic for a repair. Once it was done I noticed that it is still louder when accelerating than before. I asked him if this was to be expected and he said yes because he used a larger pipe than before; he said this was better. It really makes me nervous driving the car because it's still loud, not as loud as it was when the pipe fell out but still noticeably louder than it was before all of this.

Is a larger pipe the only cause of the sudden change in loudness when accelerating? I'm very in tune with my car so I can answer any questions you have on it. Thank you.