Sound boosters for musical instruments using rotary valves, a set of two narrow types. As shown in the example, open the rotary valve cap, place the booster, and then close the cap. The gold one makes the sound wider and more resonant. The silver one sharpens the sound's contours. If you put both in... For bass trombone players, the resonance changes even if you change the valve where you put the booster. We offer three sizes: 【Narrow】, 【Middle】, and 【Wide】. The effect tends to increase as the size increases, but it's not necessarily better the stronger it is, and the best condition varies depending on individual condition, instrument compatibility, etc. We also offer a 【Powerful】 type, which has a different resonance. We hope you will try various types and find your best fit. ※Please note that the perceived effect may vary from person to person.