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.