Straight pipe exhaust dB test (baffle does not work)
 

Here is a guy who tested several baffle designs to try and quiet his straight pipe exhaust. He does a thoughtful, if not perfect job, using seemingly good quality testing equipment.

I have been considering straight pipe next time I do a muffler, but not anymore. I thought a sound-deadening battle might be a way to make a durable straight pipe of stainless steel significantly quieter than obnoxiously loud. This guy shows it's likely to stay loud. Thanks Pontiac Fiero dude with a sound meter.

https://www.youtube.com/watch?v=qmv2H9ulf3s

Baffles won't do much. Far better to have a silencer integrated into the pipe and be done with it.

Once had a set-up with a removable baffle. More trouble than it was worth. And with the silencer in, performance was worse than when I had a quieter muffler in. And the sound was awful.

Guy has a number of good videos.

(As a Fiero owner, I've got no bias in this opinion. ;) )

I have seen other, less thorough tests in which something called a "silencer" also fails to do the job a muffler does. Did you watch the video? I cannot recall readily this morning but I think he calls a few of these "silencers".... maybe not.

Also, there are "lollipops."

I imagine one could try to tune the spund with the shape and position of the baffle, but I am getting the impression that the only really effective silencer is actually called a muffler. Lol.

A well designed exhaust system reduces noise in a manner conducive to producing power in the desired RPM range.

Also hopefully reduces irritating buzzing and drones, as well.

By silencer I mean a resonator like this:

https://www.cjponyparts.com/skin/fro...r-detailed.jpg

Some smaller cars around these parts only use a resonator, as the cats already remove most of the sound and you're not getting a lot of noise out of a sub-liter breathing through a paper straw, anyway.

a thought: run a secondary CAT (the kind without sensors) that was designed for a similar engine size/output, such as a Civic hybrid in my case, instead of a resonator and muffler. There would be a muffling benefit and potentially better emissions. An aftermarket one need not be super expensive ($100-$200). Getting rid of the muffler would help compensate for added restriction from added catalyst.

This style of soundreducer, aka glasspack, are a really great way of reducing noise while maintaining exhaust flow.

The maximum velocity of gas occurs at the center of the pipe while the sound waves propagate and "ride" on the inside wall of the pipe. The perforated ID allows the sound waves to pass through into the sound absorbing material while the gas flow is relatively unaffected.

Also related to noise reduction is pressure. As the pressure increases the sound is reduced. Don't believe me? Idle your car and put something over the exhaust pipe to cover the majority, as the pressure increases the noise is reduced until it becomes a puffing sound.