If you have spent any time on stage with an acoustic-electric guitar, chances are you have had issues with feedback. These handy plugs fit down in your sound hole and help prevent that problem. They do this by shutting down some of the vibrations in the soundboard and preventing air flow through the sound hole which also means that these can be used as a mute in case you ever need to consider your neighbors when practicing at odd hours. They serve either of these functions really well and it's a recommendable accessory to keep in any well stocked acoustic guitar case.