You can tell the impedance of the integrated sound transducers from the connection plug. The impedance is sometimes hot stamped onto the plastic shaft of the plug:
- If there is nothing there, the model has an impedance of 250 ohms.
- If it reads 32 Ω, the model has an impedance of 32 ohms.
- If it reads 600 Ω, the model has an impedance of 600 ohms.