Sundown Audio - SD-4 Sealed Box Subwoofer 8" D2/D4

Sundown Audio - SD-4 Sealed Box Subwoofer 8" D2/D4 The SD-4 series is our premier sealed box offering & is the successor to the SD-3. We started off this design knowing that the majority of sealed box applications today face a depth restriction so each SD-4 model was designed to have the lowest depth possible while still maintaining a large window of mechanical cushion (about 2 p-p maximum mechanical travel for all models). We do not consider the SD-4 an ultra-shallow but they are as shallow as possible and feature several techniques to reduce the effective depth required.As mentioned above; the SD-4 series effectively requires less depth than other woofers that are more physically shallow. First of all they lack a pole vent, thus, require no room for air venting behind the motor. This allows the motor to be completely flush against the back wall of the enclosure. To allow for efficient air-cooling we added vent channels on the OD of the pole and side-firing gap venting. Secondly t