Perhaps the best designs are 3 ways that use the woofer below 100 Hz or so and the tweeter above roughly 6,000 Hz. That would leave about 6 octaves for an extended range driver to cover and minimize crossover and driver blending issues near the precious midrange frequencies where most music exists and the ear is most sensitive to phasing issues.
Someone recently used Lowther drivers in this way and in a published report indicated that it improved driver performance significantly.
