Big BenD Bass Horn: Mouth Section

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The final (and largest) part of the horn is the mouth section with its bracing. The mouth section was designed to consist of mainly straight panels, with only the lower panel being curved. 

Since the mouth section is quite big, I figured the best way to build it was by using the bracing and flanges as a jig. Below is the lower flange and the support for the rear of the mouth section. The two are spaced apart according to the design, and held in place temporarily by a couple of scrap pieces. 

Then the lower braces are put in place and screwed to the throat flange and the lower mouth flange.

The extra support can now be removed, and the first layer of the lower wall can be fixed to the braces by nails and glue.

Two more layers of 6mm plywood are laminated onto the first.

Note the routed slit in the lower mouth flange. This is to make a proper and good looking termination for the laminated lower panel. By doing this carefully, there is no gap between the panel and the flange. 

Side and top panels in place. Since the side panels flare outward, they have to be cut in a way that makes the top and bottom panels flush with the cut. See the Midrange Horn for one way to do it using a band saw. For this horn, I made a small jig to tilt the jig saw the right amount (equal to the angle of the side walls) when doing the cuts. 

Side braces and a top brace are added and fixed using wooden dowels. 

With the mouth section done, a support frame for the mouth bend was made. It is bolted to the outer braces of the mouth bend. 

And finally the horn can be assembled. Here is the first mock-up without using any bolts. The next stage now is to add braces to the mouth section, and the acoustic performance of the horn can be checked.

[Previous: Belts and Braces, part 3; Main; Next: Belts and Braces, part 4]