Audio-Technica ATH-CKR9 SonicPro In-Ear Headphones Delivers amazing, high-resolution reproduction of the original sound World's first dual phase push-pull drivers (13 mm x 2) provide extended frequency response by reducing intermodulation distortion Machined aluminum housings greatly reduce unwanted resonance for crisp mid- and high-range reproduction Stainless steel acoustic resister provides improved high-frequency response, while bass acoustic resister delivers accurate low-frequency response Includes silicone ear tips (XS/S/M/L) and protective carrying case