A set of two medium-sized sound boosters for instruments with rotary valves. As shown in the example, open the rotary valve cap, place the booster, and then close the cap. This alone will change the way the sound resonates. For bass trombone players, changing the valve into which the booster is inserted will also change the resonance. The gold ones make the sound resonate more widely. The silver ones make the sound's outline sharper. What if you use both... We offer three sizes: [Narrow], [Middle], and [Wide]. The larger the size, the stronger the effect tends to be, but it's not always better to have a stronger effect. The optimal condition varies depending on individual condition and compatibility with the instrument. We also offer a [Powerful] type, which has a different resonance. We hope you will try various options and find your own best fit. *Please note that the perceived effect may vary from person to person.