Sub-boxes, also known as subwoofers, are types of low-frequency speakers that add substantial deep-bass to sound systems. They add impact and realism to home theatre sound systems as well as to car stereos. A ported dual 12 sub-box would contain two very powerful 12-inch diameter sub-bass drivers and a tuned enclosure vent to reproduce the lowest frequencies at high levels. A vehicular sound system of this calibre with a large amplifier in the hands of an amateur can easily cause hearing damage.
- Skill level:
- Moderately Challenging
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Things you need
- Medium density particle board, 3/4-inch thick, one 4-by-8-foot sheet
- Two 12-inch subwoofer drivers, 4-ohm impedance, with driver parameter spec sheet
- Polyester fibre-fill wool
- Construction adhesive
- 2-inch long square drive wood screws
- Wood working tools
- Separate 2-channel subwoofer amplifier integrated into the car stereo
Cut the particle board according to the driver manufacturer's recommended box dimensions. Speaker drivers that are meant for ported boxes will come with a range of recommended enclosure dimensions printed on their data sheet including the enclosure size and the port diameter and length. These ranges will provide optimal box resonant tuning frequencies for that particular driver.
Drill wood screw-easement holes every 4 inches on the front and rear speaker pieces. Also drill screw-easement holes in the indicated locations on the two end caps of the speaker. These holes allow easy driving of the wood screws into the edges of the particle board without splitting the top piece or stripping or snapping the screw-heads.
Apply adhesive to the edgewise mating surface only for any particular joint. Align it squarely with the next piece and rest it on the floor and clamp against an outside corner if at all possible. Drive the wood screws into the mating piece. Build the two sets of the two tall sides of the column and join to the end caps first, which will establish the right angles needed on each end. If the two end caps are cut square and accurately, the ends and sides should come out flush with no gaps. Let dry for a day or two.
Cut holes in the front face of the enclosure to hold the woofers. Cut the inner dimension, and if possible, mill out the edges with a router to receive the woofers flush where they can set into their holes.
Cut holes in the sides or rear of the enclosure to receive the speaker's spring-loaded terminal strips. Also cut two holes for the two round tubular ported tubes in the speaker face, or in the top of the cabinet. Cut the port tubes to length and cement into the holes so their outside edges are flush with the cabinet face.
Install the speaker terminals with adhesive and screws. Attach the speaker terminals to the speaker drivers positive (red-to-red) and negative (black-to-black) by soldering them, and using 10-gauge wire. Loosely pack the inside of the enclosure with the acoustic poly-fibre filling.
Apply RTV sealant to the speaker mounting faces in the cabinet and carefully insert the drivers into their mounting recesses. Drive the speaker-retention screws into the cabinet face to complete speaker mounting. Let the adhesives and sealants set for a day.
Connect the speaker to the dual subwoofer amplifier outputs. Carefully adjust your system to balance the low frequencies. Use a audio-test CD if possible to balance your system's bass output to match the rest of the frequency spectrum of the system.
Tips and warnings
- Use speaker grills to protect your new drivers.
- Don't overdrive woofers into distortion.
- Try to purchase 12-inch woofer drivers that come with recommended box dimensions. These have been extensively tested to deliver the best results with those dimensions.
- Speakers of this size and proportion with too much amplifier power in a small space can damage hearing both short and long term.
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