A variable Dunbridge decade resistor box was connected across the AKG D190E mic.
The less the terminating resistance, ie more loading of the mic, the less the bandwidth as witnessed by listening tests while singing or listening to ambience sounds etc.
For example even by changing from 1KΩ to 4KΩ it sounded as if a veil was lifted from the mic.
More severe effect on HF may begin even at less than 1KHz.
600Ω worse.
200Ω even more worse.
100Ω, 50Ω etc mic soft arts sounding like a telephone.
Perhaps then it may be a better idea to leave the mic alone and do low cutting on the first output transformer if for example a Pleiades V6 mic booster is used?
(Later addition: invalid argument, the reactance of an inductor increases with frequency so there should not be a problem at HF when using an (R,L) low cut filter connected directly to voice coil. But would there be some problem in the low end due to the mic's impedance rising at its LF reasonance?)
Connecting a Pleiades (130Ω,30mH) filter to the mic did not show loss of treble but this test is inconclusive.
Or using an input transformer of small ratio?
Ie or when using a very low noise booster amp such as Pleiades V6. (The input impedance of the V6 may be as low as 100KΩ with strong Pleiades bias.)
Is this an important reason why electron tube preamps sound so special? The fact that the impeadnce at grid can be relatively high to the step up ratio needed. So that mic is presented with a high terminating input impedance.
(Later addition: the theoretic part should be that the mic's output impedance is not constant with frequency, for example at diaphragm self resonant frequency it may rise to 1000Ω. The there should also be series inductance as on MM cartridges. So This L and the terminating R forms a High Cut filter. See Pickup Loading and its Effct on Frequency Response - Fitzmaurice, Joseph - Audio Engineering. See also Microphones - Lou Burrough. There should also be a paper in AES. See also a Wes Dooley interview on ribbon microphones.
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