How does exhaust pipe size affect sound?

Consequently, what does a bigger exhaust pipe do?

The optimal exhaust size is a function of exhaust volume. The greater the exhaust volume, the greater the optimal exhaust size. Exhaust volume increases with engine rpm and fuel delivery. So ideally you'd have a variable sized exhaust pipe that increases in size as rpm and fuel injection quantity increases.

One may also ask, does muffler size affect sound? Answer: A smaller muffler is going to give you a much louder sound than you would normally get with a larger muffler. The larger or longer the muffler, the less sound you will get. The smaller or shorter the muffler, the more sound you will get.

Keeping this in consideration, do bigger exhaust pipes make it louder?

The diameter of the pipe does not amplify, or dampen sound waves. If you run a straight pipe back from the engine its going to carry the same noise level under a 3" pipe as it would a 4" pipe, it won't get louder.

Does the size of the exhaust pipe matter?

Proper exhaust-pipe size is a function of both engine output and displacement. Proper exhaust-pipe size is a function of both engine output and displacement. The higher the engine's output, the larger the pipes should be. Likewise, larger engine displacements call for bigger pipes.