Performance Optimized Down Fire Sealed 18" Enclosure Ampere Audio AA-2.75 18 · Single 18" Sealed enclosure

The AA-2.75 18, yes, in both coil versions. The baffle is cut to 16.69 in, Ampere's published cutout, under the 18.66 in frame. The 10.12 inch motor clears the cabinet with 0.75 inch to spare.

Any other 18, no. The airspace is engineered around the AA-2.75 18'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.

1.80 cubic feet net on Ampere's published figures: the dual 2 ohm reads Qtc 0.669 with resonance at 52.4 Hz and half power at 55.5 Hz, and the dual 4 ohm reads Qtc 0.695 with resonance at 56.1 Hz and half power at 57.1 Hz. One cabinet serves both coils, built to the volume that keeps both closest to maximally flat. That is a slightly over-damped alignment: a gentle, early rolloff and tight transients rather than a flat top.

The 10.12 inch mounting depth sets the minimum cabinet height here, so the airspace is what the motor allows rather than a free choice.

Ampere rates the AA-2.75 18 at 1000 watts RMS, so target 700 to 1000 watts RMS at the final load.

Ampere sells the AA-2.75 18 as dual 2 ohm and dual 4 ohm: the dual 2 ohm is two 2 ohm coils, 4 ohms in series or 1 ohm in parallel; the dual 4 ohm is two 4 ohm coils, 8 ohms in series or 2 ohms in parallel. A parallel load at or under 1 ohm needs an amplifier rated for it. Confirm your amplifier's minimum stable impedance first.

The cabinet is 11.62 inches tall measured in the down fire position, and that figure excludes the standoffs. The standoffs hold 1.75 inches under the baffle, so plan your space around a finished stack of roughly 13.38 inches.

The footprint is the standard Performance Optimized down fire platform, 30.00 inches wide by 15.00 deep. Height is the only dimension solved to the driver, and here it is the AA-2.75 18's 10.12 inch motor that sets it.

The baffle is two bonded 3/4 inch sheets, 1.5 inches through. A single 3/4 inch panel flexes under the pressure an 18 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 Ampere's 18.66 inch frame, so the driver bolts to the inner layer.

Anechoic F3 is 55.5 Hz on the dual 2 ohm and 57.1 Hz on the dual 4 ohm. Below Qtc 0.707 the rolloff is gentle and F3 sits above fc, which is what an over-damped sealed box does.

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 1.80 cubic feet this cabinet was built to.

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

The inserts ship loose on purpose: Ampere prints no bolt circle for the AA-2.75 18, so you set the driver in the recess, mark its holes, drill and press the inserts. The Ampere Audio AA-2.75 18 is purchased separately, and the cabinet is cut direct fit to it, not a general purpose 18 inch box.