The Denon Professional DN-108LF ceiling subwoofer is designed to provide accurate, clear sound while meeting commercial requirements for fire resistance and multiple installations, and has a metal back panel that serves as a fire barrier behind the subwoofer to meet local commercial fire safety regulations. It also serves as a woofer cabinet to optimize bass tuning and bass frequency response. The subwoofer has 70/100 volt transformers to allow multiple units to be mounted without impedance and level matching concerns for parallelised, transformerless subwoofers.