Riven Cambium Elk Bugle Tube - The Nature of Sound. Deep in the heart of the dark timber, there is an audible marvel that few are lucky enough to experience. It is almost impossible to describe the mystical harmonic symphony that occurs in the golden days of September. The "hair stand up on your neck" kind of sound that brings you back to the moment you heard your first real bugle. It is this rich acoustic phenomenon that led to the creation of the Cambium Bugle Tube. Crafted from premium natural tonewood for acoustic quality, realism, depth, and balanced sound resonance, we believe this to be the finest tonal elk calling instrument available. Find your voice. Live Riven. Elk Vocalizations - Powerful Deep & Low End Thump Superior Tonal Range Premium Black Walnut Crafted from premium natural tonewood