Silver or colored resonator. It is a concave aluminum ring with three springs that is taken from the edge of the trumpet bell. The effect it produces is a very good natural return. It is ideal for playing live in loud environments where I have to make a strong effort to hear myself. This accessory allows me to play at a normal volume without tiring the embouchure and hear myself perfectly. The difference with the acrylic that is put on microphones is that this accessory will accompany me in all my movements without needing to be specifically oriented to acrylic. It can be used perfectly with a bell microphone. It is very light.