A sound booster for instruments using a rotary valve. It's powerful. As shown in the example installation, open the rotary valve cap, place the booster, and then close the cap. The cap will not close all the way, but it's okay to tighten it firmly in this state. The difference from other sound boosters listed separately is that this one makes the sound powerful and deep. For bass trombone, changing the valve you insert will change the resonance. It might sound unbelievable, but I think you will feel some kind of effect, so please give it a try. *Please note that the perceived effect may vary from person to person.