The rich octave sound, two reeds playing together an octave apart, is one of the most appealing free-reed tonalities. It’s never been available on slider chromatics before - but now it is, in two types. My unique OctaChrom and patent-pending OctaChrom Selectable are constructed of two chromatics inline behind a single mouthpiece.
Check out the video to hear them in action:
More info here: http://www.brendan-power.com/harmonicas-twin.php#octa-chrom-bt