Hi Peter, appreciate your approval a lot!
I'm surprised i haven't come by the K24, it's almost exactly the same! It's an interesting bandpass/phaseplug solution they have found. I'm curious as to have well it reduces the path length differences. If you consider the ray like wave propagation I'm guessing the distance from each entry point to the front lip is the same. This was a major concern when designing an aperture "smaller" than the initial source. Compared to the simple offset driver layout, where the compression itself provides the "waveguide", and therefor in theory will have a slower decay time or subjective "smearing", the horn like layout should theoretically have a very good impulse response with little smearing but higher HOMs, reflections and adiabatic distortion. I'm still not certain about this decision and found it hard to quantify. Ultimately, I went with my intuition based on my knowledge of the various kind of distortion and their audible significance.
You are absolutely right on their decision on crossover point. My design (M30) has almost exactly the same vertical dimensions but uses a much broader crossover slope (per Keele), but also centered quite high. Interaction is very wide from 550hz (the lowmid critical frequency to 50 degrees) to 1500hz (the HF horn critical frequency). This restores the coverage of the HF horn and prevents the lowmid from collapsing, manifesting in constant directivity. You could probably achieve this with low order passive crossover too if you are willing to accept some phase wrapping. The K24 and my M30 both are naturally time-aligned, and can be run passive from that perspective. The sensitivity is not at all flat however.
I believe your plots are an amazing prove to how efficiently constant directivity can be obtained in such a relatively small package. You've done an amazing job Peter.
I'm surprised how low you operate yours. What is the natural resonance frequency?
Best regards Fred
