Performance Optimized Wedge Sealed 15" Enclosure Fi Car Audio Alpha 15 · Single 15" Sealed enclosure

The Alpha 15, yes, in all three coil versions: they share the frame, the 13.875 in cutout and the 7.375 in mounting depth, and the motor clears the cabinet with 2.68 in to spare. Fi publishes one parameter set for the Alpha 15 that covers the S1, S2 and S4 single coil versions, so one alignment serves all three.

Any other 15, no. The airspace is worked out from the Alpha 15's own Qts and Vas, and a different woofer that happened to drop into the hole would not see the alignment printed on this page.

2.54 cubic feet is the Butterworth volume, inside Fi's recommended 1.8 to 3.0 cubic feet. On Fi's figures (Fs 34.7 Hz, Qts 0.52, Vas 61.00 liters) that is Qtc 0.707 with half power at 47.2 Hz. At Qtc 0.71 the response is maximally flat into the rolloff, so F3 and fc coincide.

Fi's own recommended sealed range for the Alpha 15 is 1.8 to 3 cubic feet, which reads Qtc 0.77 to 0.68.

Fi rates the Alpha 15 at 1000 watts RMS, so target 700 to 1000 watts RMS at the final load.

The single coil comes as S1, S2 or S4: 1, 2 or 4 ohms, wired straight to the amplifier. Confirm your amplifier's minimum stable impedance first.

The seat-side face carries a 20 degree rake that matches the lean of a factory rear seat back, so the cabinet sits flush against it and the cargo space in front stays usable. The baffle is the vertical trunk-lid-side face, so the driver fires rearward into the trunk cavity.

The trunk acts as an acoustic extension for the sealed box, and the cabin adds real output below 50 Hz, so in-vehicle response runs deeper than the anechoic 47.2 Hz on this page.

The baffle is two bonded 3/4 inch sheets, 1.5 inches through. A single 3/4 inch panel flexes under the pressure a 15 inch woofer puts on it at 1000 watts, which smears output and works the driver loose over time; the second layer stiffens the face and gives the mounting hardware twice the material to bite.

The outer layer is machined as a flush recess to the 15.5 inch frame, so the driver bolts to the inner layer and sits flush with the gloss black acrylic insert.

Anechoic F3 is 47.2 Hz, with system resonance at 47.2 Hz. At Qtc 0.71 the response is maximally flat into the rolloff, so F3 and fc coincide.

Those figures exclude cabin gain. In a car the cabin's transfer function adds real output below 50 Hz, so in-vehicle response runs deeper than the numbers above.

No. Polyfill is already installed as a light wall lining to control internal reflections, and the quantity is chosen so it does not change the acoustic volume.

Do not add more. Packing a sealed box with fill makes it behave as though it were larger, which walks the alignment away from the 2.54 cubic feet this cabinet was built to.

No driver. This is an enclosure only. You receive the cabinet finished in plush black carpet with the gloss black acrylic baffle insert, one side-mounted pre-wired terminal cup, the polyfill lining already in place, and a threaded insert kit with stainless machine screws.

The inserts ship loose on purpose: Fi prints no bolt circle for the Alpha 15, so you set the driver in the recess, mark its holes, drill and press the inserts. The Fi Car Audio Alpha 15 is purchased separately, and the cabinet is cut direct fit to it, not a general purpose 15 inch box.