Infinite baffle is one of the simplest and most acoustically pure subwoofer installation approaches. Rather than enclosing the driver in a dedicated box, the infinite baffle method mounts the subwoofer in an opening that separates two large air masses — most commonly the vehicle’s trunk cavity from the passenger cabin. The trunk itself serves as the rear chamber, and the critical requirement is that this chamber is effectively sealed from the cabin so that the driver’s front and rear wave do not interact and cancel each other.
The appeal of infinite baffle lies in what it does not do. There is no box volume to tune, no port to introduce resonances, and no enclosure walls to resonate. The driver operates in a large, compliant air mass that imposes minimal acoustic loading, allowing it to move freely and reproduce bass with natural extension and low distortion. Drivers selected for infinite baffle use should have a low Qts value and a low resonant frequency, characteristics that suit this loading condition.
Preparation of the trunk cavity is the first practical step. The space must be made airtight relative to the cabin. All gaps where the trunk communicates with the passenger compartment — around rear seatback latches, through parcel shelf openings, along body seams — must be sealed with foam tape, acoustic sealant, or custom gaskets. Even small air leaks allow the rear wave to partially cancel the front wave, reducing output and distorting the frequency response.
The driver is mounted in a baffle board that fills the opening between the trunk and the cabin — typically the rear parcel shelf, the rear seatback, or a custom-fabricated panel spanning the trunk opening. The baffle board must be rigid and well-sealed around its perimeter to the vehicle’s body structure.
Driver selection is critical because the trunk cavity’s volume, while large compared to a conventional box, is still finite and will interact with the driver’s compliance. Confirming that the driver is suitable for the estimated trunk volume using enclosure modelling software prevents the common outcome of a system that plays loudly but lacks deep bass extension.