Updated: Jan 26, 2020
I built these full-range speakers about a year ago and just now got around to painting and finishing them. Here's the build blog.
I used Fostex FE126en 4 1/2" drivers. These are pretty efficient so they go nicely with a tube amplifier (like the AE1 Kit). The mid and high frequencies, especially vocals, jazz and acoustic, are awesome. Sounds a bit thin on lower extension below 100Hz or so, though still pretty remarkable for such a small driver. (I have some ideas about adding a powered subwoofer to match up with these speakers. A great project for another day!)
I used MDF, which I hate working with because of the dust, it's just plain evil. But it's cheap and pretty dang solid. I sealed the edges with joint compound, sanded, primed with a shellac base primer by brush, sanded all very smooth, and finished by spraying a gloss enamel colored just a teeny bit so it's not stark white and comes a touch closer to the off-white of the driver cones. The best part, of course, is the awesome hidden color on the backside--it just makes me feel good! My photo here doesn't do it justice. It's Superman Heat-Vision Vermillion, custom-color mixed flat acrylic painted by hand. You gotta have fun, right?
Interior has some recycled denim/cotton for absorbing reflections and some acoustic poly fill.
The Frugal Horn is a rear-loaded full-range speaker. It's not my own design; you can find the plans and details on the frugal horn website.
Here are a few build photos: