And Sennheiser had a mic back in the 1960s with a frequency response extending to 0.1 Hz. It was an omnidirectional condenser mic using low-voltage RF bias on the capsule. Using RF bias, there is much less restriction on how low a frequency can be measured.

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Sennheiser MKH 110: Frequency response 1-20,000 Hz

Sennheiser MKH 110/1: Frequency response 0.1-20,000 Hz

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(I believe there was also a MKH 110/2; I do not know its frequency response limits)

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