This is a powerful sound booster for musical instruments using a rotary valve. As shown in the example installation, open the cap of the rotary valve, place the booster, and then close the cap. The cap will not close all the way, but that is okay. The difference from other sound boosters I am also selling is that this one resonates powerfully and with a deep tone. The way it resonates will change depending on which valve you insert it into. It might sound unbelievable, but please give it a try. *Please note that the perceived effect may vary from person to person.