What kind of exhaust pipe is this?

So this is my first bike, and the pipes are just a little too loud. I'm looking to install some baffles to quiet her down and get a little better back pressure. Everything I've seen online pertains more to straight pipes and I just want to know what the technical name for these ones is and if you could possibly recommend a baffle as well, that would be incredibly helpful. They have a 3.5 inch diameter at the end. It's 1979 Honda CX500 Deluxe.

That is a stock muffler.
Perhaps a previous owner cut off the ends and removed the baffles.
http://www.partsfish.com/oemparts/a/hon/506f6afdf8700229747b798f/muffler

Google - motorcycle salvage
Call around until you find mufflers for your bike.
Salvage yards ship to anywhere.

See if you can pick up a couple of original CX500 mufflers from a wrecker - you may be lucky.
Unfortunately most aftermarket mufflers aim for more noise not less.
You could experiment with what is there already (they look like they may be originals with the back cut off - horrible!) If the central perforated tube is still there try a temporary blocking of it's end (wooden plug as a trial)
Or make you pa disk to cover the end & pack around it with fibreglass, again use wood as a trial. If you get the sound level & performance is satisfactoty get it fabricated up in steel.
(note fibreglass packing wears out & provision will be needed to allow replacement.

Looks like the stock mufler- Honda and some others used a 'short' upswept Megaphone/trumpet style muffler on their Cruiser styled cycle for some markets- and US market was a big one for that style. I have same basic muffler on my CM400 trainer a couple years newer. The pipes and muffler are a one piece unit from factory- quicker to assemble. Replacements exist from factory as a pipe/muffler unit and a few muffler only replacement kits that have a pipe bushing to go over the stub of pipe when old muffler is cutoff. The base muffler of the 'standard'/bare model can be put on- will be slightly quieter and a bit longer, will need a bit of mount adapting. Alternate to rebaffle is a Spark Arrestor Cone added to back end- amounts to a cyclonic spiral and baffle.plate, drops about 5 points on decibel meter. Some aftermarket mufflers styled like old Limey have been fitted to the Hondas- they were $50.00 instead of $75.00-$90.00 of OEM and gave clearance for saddlebags like the Wixom and Hannigan- mount kits had slight bend bushings and mount extensions to fit- these prices and availabilities are from 5 years or so back- might be higher now, might be NLA-- but if nothing else a short pipe and a Ford N tractor muffler for $19.95 could be fitted, used to do that on Limey and Honda, Yamaha choppers that had gotten a noise ticket that said 10 days to get reinspected or a pull off highway/impound order issued.

Is there an old baffle inside there? I ask because those pipes never come without a baffle, it may be less restrictive but that pipe had some kind of baffle in there. Maybe it can be removed and repacked. [fiberglass wadding I think?] If it is an aftermarket can somewhere on it is stamped a makers name and a disclaimer [for offroad use only] the disclaimer is there if it is over the legal sound limit in decibals. If there's no makers mark on it at all then it is the stock pipe and the baffle is worn out. CX 500 opposed twin I trhink that bike is? They arent very loud at all. Makers mark will be on the underside of the pipe I believe. Might have to remove the pipe to find it.

Basically called an open mouth and they are difficult to baffle.
Could try to make your own by cutting a steel disc with holes cut into it and mounted on the end of the exhaust.
Used to be what was called a Snuff R Not that had a flapper type baffle as described above but not sure if that brand is still exists.

It's from someone who eats a lot of beans.