8 ohm
https://www.youtube.com/watch?v=R8V9X4HKhms

Originally posted by _I_:

8 ohm
https://www.youtube.com/watch?v=R8V9X4HKhms

response from support and the video says that 8 ohms

The Logitech Z623 subwoofer has an impedance of 4 ohms. The satellite speakers also have a 4-ohm impedance. This information is useful if you are considering a custom subwoofer replacement or repair. Be aware that the internal amplifier is specifically designed for the 4-ohm impedance of the included driver, so using a different impedance could damage the system.

I'm confused.

a multimeter will measure speakers a bit low and change if the speaker is moving

in the vid he used a dual coil 4ohm sub, with the coils wired in series (a single jumper wire from pos on one side to neg on the other and using the other positive and negative to the amplifier)