This is a set of two sound boosters that can be used with instruments that utilize rotary valves. They are a thicker type. As shown in the example, open the cap of the rotary valve, place the booster, and then close the cap. The gold-colored one makes the sound resonate widely. The silver-colored 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. The best condition varies depending on individual condition and compatibility with the instrument. We also offer a 【Powerful】 type, which produces a different kind of resonance. We encourage you to try various types and find what works best for you. ※Please note that the perceived effects may vary from person to person.