Marik
Well-known member
It is not about math, but that's how the ribbon microphones work and nobody has cancelled the law of physics, yet. Take a stepper motor, short its leads together and you won't be able to turn its shaft. Put between the leads resistors of their winding value and you will barely be able to turn the shaft. This is precisely how the ribbon 'feels' the load, with its motion getting locked, or severely restricted, depending on the load. Because we are talking about mass controlled system it will mostly affect low end.
This is precisely why, for example, RCA 77dx rates its flat response when UNLOADED. The reason--because of coupling tube the air loading is too high, so any additional electronic loading would alter response. For the same reason virtually all the high end pres with 'ribbon mode' switch the phantom resistors off the circuit and run it at least with 10kΩ load. It is hard to imagine to suggest to terminate their inputs with 250 Ω, other than for some kind of special effect.
In general, with the transformer coupled microphones the ribbons are affected the most by the load. With dynamic moving coil mics the effect is less pronounced. First, usually, the impedance is quite a bit higher and transformer ratio is quite a bit lower. Also, the much heavier diaphragm and resistance controlled system put completely different damping requirements.
Regarding transformer coupled condenser microphones there was an excellent article... I think from Gotham on effect of loading of Neumann mics... hopefully, somebody remembers that one and post it here.
Best, M
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