example addition of a center brace to the wavetable speaker stand.

wavetable_center_brace.scad

module speaker_stand(){
    // This module extrudes the profile() to create the
    // solid model of the stand excludin the backstop.
    linear_extrude(width, center = true)
    profile();
    // Adding a center brace
    brace();
}

module brace(){
    // Adjust these 3 variables to adjust the center brace.
    // They don't have to be based on the outer vars, but that should help it auto scale with the rest of the design.
    // Note that brace_depth doesn't directly correspond to something you could measure on the finished product.
    // The actual width of the brace 'web' that can be measured will depend on brace_angle and maybe other parameters.
    brace_depth = top_depth / 3;
    brace_angle = 3 * angle;
    brace_thickness = thickness / 4;

    translate([0, 0, -brace_thickness / 2])
    linear_extrude(brace_thickness)
    difference(){
        // hull of the profile fills in the center of the profile()
        hull() profile();

        // subtract a big chunk since brace of the full area seems overkill,
        // also rotate the subtraction so it matches the design better.
        translate([brace_depth, 0, 0])
        rotate([0, 0, -brace_angle])
        square([2 * top_depth - brace_depth, 2 * height]);
    }
}

Heh, yeah that is generally one of the harder things to do in openscad. Look into the BOSL2 library which has a fillet() function:

https://github.com/BelfrySCAD/BOSL2/wiki/shapes3d.scad#module-fillet

I've not used the library though so I'm not sure it even applies here.

For this model, about as far as I would recommend going would be placing a cylinder at the front edge of the brace. Here is a quick and dirty version, you might need to tweak the values if the cylinder sticks out or leaves a gap. Smoothing the edges into the rest of the model is more difficult, although not impossible. If you are up for the challenge I could point you in the right direction though.

module brace(){
    // Adjust these 3 variables to adjust the center brace.
    // They don't have to be based on the outer vars, but that should help it auto scale with the rest of the design.
    // Note that brace_depth doesn't directly correspond to something you could measure on the finished product.
    // The actual width of the brace 'web' that can be measured will depend on brace_angle and maybe other parameters.
    brace_depth = top_depth / 3;
    brace_angle = 3 * angle;
    brace_thickness = thickness / 4;

    // add a cylinder to round the front of the brace.
    translate([brace_depth,0,0])
    rotate([-90,0,-brace_angle])
    translate([0, 0, thickness/4])
    cylinder(d=brace_thickness, h=height-thickness/2,); //number for height could be calculated but this should work for most values

    translate([0, 0, -brace_thickness / 2])
    linear_extrude(brace_thickness)
    difference(){
        // hull of the profile fills in the center of the profile()
        hull() profile();

        // subtract a big chunk since brace of the full area seems overkill,
        // also rotate the subtraction so it matches the design better.
        translate([brace_depth, 0, 0])
        rotate([0, 0, -brace_angle])
        square([2 * top_depth - brace_depth, 2 * height]);

    }
}

Legend. I will give it a shot, if not I will finish it off in Fusion where I am a bit more comfortable :)

Just responding to say this worked great. My Diamond 10.1s sound even better. Thank you!