There are four "common" designs for mufflers. OEM, baffled exhausts are the quietest, but they are also the most restrictive. The exhaust really has to twist around some S-curves and flow through some openings before it escapes.
Turbo mufflers are basically a high-performance adaptation, offering a nice low rumble but without the harsh snarl of glasspacks, and with less restriction than OEM type. Some of the 'good ones' can flow almost as well as a straight pipe, surprisingly.
Glasspack mufflers are a perforated tube wrapped in stainless wool or fiberglass mat (hence the term glass pack), contained in a small shell. They do quiet the exhaust somewhat, but tend to drone loudly at highway speeds. They have a unique and savage exhaust note, along with a signature 'cackle' on decel. All glasspacks will get a bit louder with age, because carbon and other byproducts cake up the matting eventually. They flow very well.
Chambered exhausts are one of the most popular types now, and entered the market by force back in the 80s with Flowmaster. There's no padding, no curves, just some angled plates inside that attempt to attenuate some of the sound. They have a dull, thudding note much like firecrackers in a sewer pipe. I freely admit, I am prejudiced against chambered mufflers, but they are pretty much the mating call of the millennial as near as I can tell. What can I say? I'm a dinosaur!
There are many variations on these basic designs. For example, Magnaflow's straight through mufflers look very much like turbo mufflers (and are sometimes mistakenly called the same) but inside the wide oval case is a straight through perforated pipe at an angle. It's basically a big glasspack muffler with a lot more padding. They are actually one of my favorites, with enough sound attenuation to keep your neighbors from being mad, while still offering some attitude.
The diameter of the pipes does tend to offer a slightly lower note when they're bigger, but a lot of that will have to do with your engine's compression, headers, and your cam, too. A small block engine can sound very low and menacing, even through 2 1/2" exhaust.
Exhaust has a lot to do with tuning. For the old-school 'burble', running straight pipes with no crossover will change the tone quite a bit, but at the expense of maybe 1-2% of your total horsepower, compared to an H or X pipe. X pipe has a smoother sound; more 'indy car' or 'Ferarri' like because it shares pulses so well. An H-pipe is something in between the two. Functionally, an H or X pipe usually offer exactly the same power difference over true dual exhaust, and it's not always significant, though the sound change almost always is.
Bigger mufflers are always quieter than smaller, even when it's glasspacks. My dad had an early 70s Cadillac with the 500 that had very long (24"?) glasspack mufflers on it. It was nice and quiet, unless you were on it. The same holds true of all the other designs as well.
I suggest you get on Youtube and look up your engine along with different types of exhaust. Listen to multiples of each, and you'll get a good idea of what they really sound like.
