It is time to upgrade two heavily Mini-DSP Equalized cheap Monoprice subwoofers with something better. The Monoprice units are currently behind speaker cloth covered openings under a countertop that fits into the bay window-shaped area in my basement home-theater room. The main part of the room is 11.5 by 19 by 7.5 feet with openings at the back to a stairwell, kitchenette and den. This probably put the room in a medium size category from a bass perspective.

The audiovisual stage is against the shorter wall where the bottom of the projector screen drops to just below the countertop height. All primary reflection points from the three main front speakers are treated with acoustic panels and there are a couple of Rockwool bass traps in the front corners.

First measurements indicate that it will be possible to fit a couple of custom made enclosures of up to 6.1 ft^3 each (internal volume excluding ports, braces and driver) in the available spaces under the countertop (and still maintain the WAF). The positions and shape of the enclosures will allow for the drivers to be positioned on the recommended 1/4 wall length points.

Filling as much as possible of the available space with the new enclosure will (hopefully) also minimize the effect of the countertop and cabinet. A minimum gap of 1/2 inch will be maintained to prevent any potential mechanical interference with adjacent surfaces.

I really liked what the parametric equalization the Mini-DSP unit could do for the Monoprice units so the Behringer NX3000D amp is on the shopping list. (The notoriously noisy fan will be replaced).

A 60/40 music/movie ratio applies. Sound Quality is at the top of the list but if there is sound in the 20 Hz band I would like to hear it. I have absolutely no intention to break any SPL records or any interest in making the neighbour’s dentures rattle on his nightstand.

I am in two minds about ported or sealed. I like the reported “tightness” of sealed but not the roll off. Not sure if the room gain in my setup will compensate for the roll-off. The REW Room Sim does not show that and I don’t recall seeing that effect when I did the DSP calibration for the Monoprice units. So I started with ported.

In order for the box to fit around a plate on the back wall, there will be an off center 1.5 inch deep recess at the back of the enclosure. Since the back would be prime space for a conventional slotted design, this pretty much rule out the use of slotted vents.

The Parts Express recommended enclosure size (5.58 ft^3) for the Dayton Audio UM12-22 drivers appears to be the closest fit for a ported enclosure. Applying the T&S parameters for the UM12-22 to WinISD indicates that the expected 5.1 ft^3 (net) box will require two 4” ports.

The ports will be constructed from white PVC pipe and each port will require a combination of 90 degree and 45 degree elbows to shoehorn a port length of up to a 38 inch in the enclosure and still maintaining the clearances around the internal openings of the two ports. Four 3D printed flares will hopefully eliminate/minimize any chuffing.

The drawing for the enclosure layout is attached. It is not clear from the drawing but the inside openings of the two ports are swiveled inwards to move them away from the inside surfaces. Sound absorbing material against the back of the baffle across from the inside port openings will hopefully reduce any higher order frequencies potentially being reflected into, and exciting the higher order resonances of the port.

Simulating a sealed enclosure with the same net volume and UM-12-22 driver indicates that this will also keep the possibility open to plug the ports and get a transfer function very similar to that of the WinISD recommended sized sealed enclosure. Probably easy to reduce the internal volume after the fact if so required.

Should I go for sealed from the word GO I would probably select the UM15-22 mainly due to the slightly wider bandwidth (compared to a sealed UM12-22) that WinISD predicts.

Any other options that I should consider given the space available? Your opinions will be highly appreciated.