The SHS-EXT is designed to work with the SHS-6T2 strategically hidden speaker in thicker ceiling applications. The SHS-EXT can attach to the SHS sound chamber, creating a 0.5" (13mm) extension for attachment of the selected SHS diffuser. AtlasIED does not recommend using more than two SHS-EXT per SHS-6T2 in order to maintain the proper sound coverage and quality.