Sound boosters for instruments with rotary valves, a set of two in a medium size. As shown in the example, open the cap of the rotary valve, 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... Bass trombone players can change the valve where they insert the booster to alter the resonance. We offer three sizes: 【Narrow】, 【Middle】, and 【Wide】. The effect tends to increase with size, but stronger isn't always better, and the best condition varies depending on individual condition, instrument compatibility, etc. We also offer a 【Powerful】 version, which produces a different kind of resonance. We encourage you to try various options and find what works best for you. ※Please note that the perceived effects may vary from person to person.