I really like Altec 511 and 811 horns. They work great with π two-way crossovers, like used in the three π and four π loudspeakers. The 800Hz crossover is just right for the 811 and the 600Hz crossover is just right for the 511. I've sent schematics for these to your E-Mail address, in case you don't already have them.The 2426/2370 combo is usable down to 800Hz, which is the low frequency cutoff of the horn. You might be able to reach 500Hz on a larger horn, but below that, diaphragm excursion is too great on any horn except at very low power levels.