Systems ListDIYFi Car Audio SP4 18D1 Sealed

System typeSealed
DriverFi Car Audio SP4 18D1 (HT option)
Driver Size18 "
Number of drivers1
Internal volume4.2 ft3
External volume6.16 ft3
Dimentions (Width Height Depth)22 " 22 " 22 "
Weight120 lbs


This is yet another big 18 inch out of the Fi Car Audio build house. The suspension has been softened up a bit for home theater use by changing number and type of the spiders used, but otherwise is a standard SP4 series driver. Using the standard 4.2 cubic foot sealed test enclosure used for testing nearly all 18 inch drivers, resulted in a set of performance metrics that are clearly the strongest of all of the Fi related drivers that have been tested so far. The SP4 is listed as having an Xmax of 34mm and it does indeed have a ton of mechanical stroke with the maximum deep bass output being among the top handful of 18 inch drivers that have been tested. The driver does exhibit a very pronounced response peak and large amounts of induction in the coil and motor system similar to many other drivers with massive voice coils. The driver handled extreme amounts of power quite well and was very mechanically rugged owing to the large mechanical clearances. One oddity that did pop up was a tendency to make the bridged K20 amplifier protect briefly if the driver was pushed past a certain amount of excursion. (Please read the test notes for a more in depth explanation.) You really do not want to be pushing the drivers that far on a regular basis anyway. Otherwise the driver behaved predictably and exhibited a high tolerance for punishment even greater than the other Fi drivers.