Average human hearing is between 20Hz and 20kHz, and the tones and modulations of individual instruments, or overtones, are even much higher. Multi-cell horns have been developed for the midrange range, between 300Hz and 5kHz:  various horn types will give a lower crossover frequency, starting at 300Hz, 500Hz and 800Hz – this depending on the driver used, the respective bass cabinets and the design of the crossover.

My horns come with a choice of the number of cells, and the designation results from the frequency range and the number of cells. For example, the MK 1505 has 15 cells and gives a 500Hz crossover frequency, with the MK standing for me – Markus Klug – as the constructor.