The muffler is a strip of material stretched tightly across the shell in such a way that it comes into contact with the underside of the batter head. It may be secured to the shell with staples or wedged onto the shell between the rim of the batter head and the shell.
It's difficult to assess the condition of a muffler without removing the drum head. If you muffler is mounted, as we recommend, with a loose end hanging out, you can try pulling on the end to tighten the muffler to see if that produces the result you want. If not, carefully note where and how your muffler is positioned when you remove the head so that you can replace it if necessary or tighten it if it has sagged.