US Patent Number
A non-transposing mute having a metallic hemispherical resonator with a hollow acoustic filter attached thereto is provided for detachably fitting upon the rim of a brass musical instrument. A variety of tonal quality is available by choice of the particular filter selected by the musician.
University of Kentucky Research Foundation, Lexington, Ky.
Gossick, Benjamin R. and Schneider, Karl A., "Non-Transposing Mute" (1973). Electrical and Computer Engineering Faculty Patents. 19.