NEWER Upgraded Model Available on Amazon (2023): (See B0CC6WRFFB) For a Brass Diaphragm Piezo and All Soldered Wire Connections making it more Sensitive and More Reliable Perfect to make electronics projects such as Crystal or Transistor Radios often used in schools and STEM electronic experiments requiring high impedance ear piece High 20,000 ohm impedance with resistance over 20 million ohms and a capacitance of 15,000 pf Rated Sensitivity of 57db at 1KHz in the frequency range from 200 to 8,000Hz Highly sensitive molded earpiece with 42-in twisted wire with 3.5mm (1/8in) headphone audio male wire connector Classic Piezo Electric Crystal Earphone for DIY Electronic Projects and Kits