Subwoofer

To improve the low frequency sound we added a subwoofer to our home theater system. The driver was purchased from Adire Audio (out of business). It is the Shiva, an impressive dual voice coil driver specifically designed for subwoofer applications. The enclosure was built from plans in an app note from Adire audio. The outside dimensions are 18” by 18” and it is 22” high. It is internally braced side to side, rear to midbrace, and front to midbrace. It has an internal volume of 88.5 liters and a Q of 0.6.

It is constructed from a single 4’ by 8’ sheet of 3/4” MDF. Due to the size and weight of this sheet I had Home Depot do a couple of rough cuts before I left the store. MDF is a great material for speaker cabinets, it is dense, very flat, and does not warp. It drills, cuts, routes, and machines very well although it can be tough on bits/blades, carbide is recommended.

MDF also tends to absorb a lot of paint. Priming and 1 or 2 coats of paint are advised.

This view shows some of the internal bracing. All brace edges were glued before screwing.

Several 4” diameter vents were cut into the braces.

The driver opening is 11” diameter.

The finished subwoofer in the corner of our living room. I painted it with two coats of flat black paint.

The metal grill came from Adire Audio as part of an installation kit. The kit also included mounting hardware, gold plated binding post terminals, wire, and terminals.

The terminal cup has two pairs of binding posts, one for each voice coil on the Shiva. Each voice coil has a nominal 8 ohm impedance. Shorting straps are provided to parallel the coils for 4 ohm applications.

In our case I used two amplifier chips so I have each amp drive a single voice coil. Each amp chip can output about 75W into 8 ohms so we can get about 150W into the subwoofer. See the Subwoofer Amp page for details.

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