Editing Subwoofer (section)

===Royal Device custom installation===
Another subwoofer claimed to be the world's biggest is a custom installation in Italy made by Royal Device primarily of bricks, concrete and sound-deadening material<ref name=Gordon2008 /> consisting of two subwoofers embedded in the foundation of a listening room.<ref name=RoyalDevice /> The horn-loaded subwoofers each have a floor mouth that is {{convert|2.2|m2|sp=us}}, and a horn length that is {{convert|9.5|m|sp=us}}, in a cavity {{convert|1|m|sp=us}} under the floor of the listening room. Each subwoofer is driven by eight 18-inch subwoofer drivers with {{convert|100|mm|sp=us}} voice coils. The designers assert that the floor mouths of the horns are additionally loaded acoustically by a vertical wooden horn expansion and the room's ceiling to create a 10&nbsp;Hz "full power" wave at the listening position.