Well, that's not quite what I meant, so I probably should have been clearer. This can't be accomplished with a small plate near the end of the pipe. It wouldn't have enough surface area. Without a lot of surface area, the holes have to be too large, otherwise flow suffers. If the plate has a really large surface area, the holes could be made much smaller, attenuating the upper frequencies without restricting flow. I was thinking about a plate that would be nearly the length of the entire pipe. Imagine a long, skinny oval, drilled with a few thousand holes. It would be welded into the pipe at a diagonal, so all gas entering the pipe has to go through the plate. I think that might sound a little better.
