[Gimpy]

Use the material that has the highest NRC factor for your bidget. It will absorb the sound and keep it from getting out the necessary openings for air movement.

You can baffle those openings with a high NRC material, forcing the sound to hit the material and then go around a corner. However, be sure to allow enough area for air to move well. Air goes around corners fine, but sound does not, especially if the baffle is high NRC rated.

STC rating is not worth much to you, nor is vibration damping.