I never really liked horns whether commercial or DIY but after listening to a friends Altecs I thought that if ever a cheap pair of horns only came up for sale I'd buy them. A few months later refurbished Altec 511Bs came up for $500. I always felt horns a bit brittle and to tame this I added Italian FaitalPro HF108R compression drivers. The Faital compression drivers use a polymer 1" diaphragm. I built a Xover to work with the horns and added a 12" woofer in a sealed 60 ltr box to handle 1100hz and down.
The Xover crossed the horns in at 1100hz on a third order and the woofers on 2nd order. Serious padding was need on the horns to balance them against the horns and the system now at about 90db+ efficient. The horns were boxed for better appearance and shock mounted to keep vibrations from them. Also the horns are wrapped in a sound deadening foam an foil to stop ringing.
Driven by a 180W Class D amp there is plenty of deep bass (down to 30Hz) from the woofer and great clear, very dynamic mids and treble from the horns. The most natural sound I have heard rom any system. Pleased I tried them. I have since bought a second pair with top of the range FaitalPro drivers.