The large, black O-Port from Planet Waves is a sound enhancement ring for acoustic or acoustic/electric guitar that fits into the soundhole and provides a richer, fuller sound with more volume, improved clarity, and better projection, as well as helping to suppress feedback. The O-Port is made from a custom blend of material that is highly flexible to prevent damage to your guitar's finish and inlays. Additionally, the O-Port is easy to install and requires no modification to your instrument. Simply loosen or remove the strings and place the O-Port into the guitar's soundhole. This model fits soundholes that are 3.88 to 4.00" / 9.84 to 10.16 cm in diameter.