One way to achieve this is via diffraction (like the Dutch & Dutch 8c).
Hi Chris,
I agree with most of what you wrote. The line about achieving this “via diffraction (like the Dutch & Dutch 8c)” is a bit of an oversimplification.
Below 100 Hz, which is the low-frequency crossover, the 8c is designed to work together with the front wall. The wall becomes a part of the speaker system itself in that range. The result is a phase-coherent wavefront that is radiated forward, hemispherically.
From 100 Hz to roughly 600 Hz, directivity is mainly controlled by a gradient setup. We use the out-of-phase radiation from the back of the midwoofer to cancel energy traveling toward the rear, and to a lesser extent toward the sides, top and bottom. In that region, pattern control comes primarily from controlled cancellation rather than diffraction.
Between about 600 Hz and the 1250 Hz crossover to the tweeter, directivity is increasingly determined by the natural beaming of the cone combined with constructive edge diffraction, often described as baffle step.
Above 1250 Hz the tweeter takes over. At the lower end of its range the waveguide contributes to directivity, but it is hard to separate that from controlled baffle-edge diffraction because they were designed as one system. The radius on the baffle edge is shaped to reduce unwanted diffraction above roughly 2 kHz, while deliberately using some diffraction lower down where the interference with the tweeter’s direct sound is mostly constructive on axis, which increases forward directivity.
So diffraction plays a role, but it is only one of several mechanisms at work. The real challenge is getting all of these frequency ranges and radiation principles to integrate smoothly so the speaker behaves as one coherent radiator across the bandwidth.
