A horn speaker is usually one that employs a horn for the upper frequencies in place of the more usual mid-range and high frequency speakers. Perhaps the most famous speaker ever manufactured, Altec-Lansing's "Voice of the Theater," was a horn-based design matched with a 15-inch low frequency driver. Those speakers are currently being sold by Altec for £3,900 a pair. You can build the equivalent speaker for 10 per cent of that cost, and if you use smaller components, the cost should be commensurately less. That's the big advantage of any DIY speaker.
Choose a low frequency loudspeaker to be housed in the cabinet. The loudspeaker driver is one of the most important components of the project. Choose one that is 12 to 15 inches in diameter, and pick the best quality one you can afford.
Download winISD. WinISD is among the best free speaker building software. It stands in for the otherwise significant electrical engineering knowledge you would need to accurately determine your cabinet dimensions and design the speaker cabinet.
Buy 1-inch birch plywood for the cabinet. If a major home products store doesn't have it, a lumber yard will. Cut the pieces yourself with a circular or table saw. If you have your measurements already, have the cuts done by the store where you purchase the wood; it's worth the precision and small cost.
Assemble the basic box: the sides, bottom and top. Use wood glue augmented by wood screws to further bond the joints. Countersink the wood screws using a power screwdriver or drill with a screwdriver bit; the holes will later be filled with wood putty. Clamp the enclosure with furniture clamps, and allow the assembly to dry for eight hours.
Make the cutout for the terminal cup in the back panel. Glue, screw and clamp this panel to the rest of the box assembly. Let this new box addition dry for an another eight hours.
Make the cut out for, and attach, the front panel. The cutouts are for the loudspeaker and the port (if building a ported design). Use glue and screw through the side panels, and clamp the assembly for drying. Caulk all inside seams of the box with silicone caulk prior to attaching the loudspeaker to the cabinet. Let this dry for at least 15 hours, primarily for the silicone caulk to fully dry.
Sand the box with a power or hand sander. Prepare the wood as you would for fine furniture. Fill the screw holes with wood putty. Sand again, ensuring all puttied holes are flush with the wood surface.
Install the terminal cup in the back of the box. Once the terminal cup is secure, caulk around the inside perimeter of the cup with silicone caulk. Allow sufficient time for the caulk to dry. Affix the horn driver to the top of the cabinet while the caulk dries. Use 3/4-inch wood screws and a power screwdriver to attach the horn.
Attach the crossover network inside the cabinet. Use 1/2-inch wood screws to attach the crossover. Attach 12-gauge speaker wire between the terminal cup and the crossover. Attach the additional 12-gauge wires to both the horn and the woofer speaker.
Attach the woofer speaker to the cabinet. Connect the speaker wires to the woofer's speaker terminals. Use wood screws to attach the woofer to the cabinet, followed by non-drying caulk around the woofer's perimeter to ensure an airtight seal. Finish the cabinet in your choice of paint, stain or wood veneer.
Allow at least 18 hours for the silicone caulk to dry before installing the woofer in the cabinet. Silicone caulk emits gases while drying that will erode speaker surrounds.