This type of headphone was typical in the early wireless days, either for crystal sets or (one or two) valve sets without output stages to drive a loudspeaker.

I'm not sure what the orange and black design is supposed to represent behind the Ericsson logo, though it's quite nice.

These images have been heavily processed and the side picture is probably more representative of the original red colour used.

The 4000 ohm resistance was actually 2000 ohm per earpiece as they were wired in series.