Outstanding acoustics with better audibility of high-frequency sounds (adult side, firm pressure). Tunable diaphragm: Hear high or low frequency sounds by slightly adjusting pressure on the chestpiece. Dual-lumen tubing: Two sound paths in one tube eliminates the rubbing noise of traditional double tubes. Next-generation tubing lasts longer and resists stains. Not made with natural rubber latex or phthalate plasticizers.