The classic wow-wow mute.
The Harmon B Model Aluminum Trumpet Wow-Wow is a favorite effects mute. The "wah-wah" sound is made by a sliding cup in the end of the mute. Famous musicians have used and endorsed Harmon mutes for over 25 years. Made entirely of aluminum, the Harmon B Model is free-blowing and does not alter or change the pitch in any way.