At the same time as Neumann introduced the M 49, Neumann also introduced a new omni directional microphone, model M 50. This microphone distinguished itself  by not merely using a pressure transducer as its pickup, but also by mounting this capsule in a spherical body with the diaphragm flush with the surface of the sphere. As a result the microphone has a very smooth frequency response to above 1000 Hz with a gradual rise reaching +6 dB from 8000 to 16000 Hz. The unique feature of the microphone is its high frequency directivity, combined with the linear response at low frequencies, well known for pressure microphones. The M 50/250 uses the Telefunken AC 701(k) tube and the microphone pictured below has the early and desirable aluminum diaphragm. Later versions were  gold sputtered polyester foil.