Subsequent 37 headphone output impedance?

Anyone know the Subsequent 37 headphone output impedance?
I’m off to get a new set o cans.

Going by the old audiophile 1/8th rule*
Subsequent37 headphone out impedance x 8 = ??? Ohms



*rule. Used by imperialists to dictate. Overthrown by the metric rebellion.

Indeed, it’d be great to know this little technical detail.