Zinc alloy single-sided chestpiece. Specially designed membrane lock within the chestpiece alters the diaphragm to achieve dual-frequency. Hold the chestpiece to achieve low frequency response (similar to dual-sided bell chestpiece). Apply firm pressure to achieve high-frequency diaphragm response. Comfortable, non-chill ring. Lightweight, steel binaurals with internal spring. Deluxe eartips. Latex-free Y-tubing. Lifetime warranty.