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[Nathanael Iversen]

I'm just fuzzy enough on the last physics course I completed that I can't be sure that anything with mass has resonant frequencies, but certainly microphone capsules do.

I understand that this causes anomalies in the frequency response, polar pattern, etc.  In some microphones this may be part of the sound.  In others, I know that equalization, either mechanical, or electrical is used to flatten or otherwise manipulate the natural response of the capsule.

What is significant about the resonant frequency of a capsule?  What limitations does it place on use or selection?  Are ribbons better than condenser microphones in a meaningful way?  Is mechanical or electrical equalization preferred, or would it somehow be best to avoid equalization at all?  Does equalization introduce other unintended artifacts?

Over the years, I've seen some strong claims on Internet boards and wonder where the truth lies.

Thanks for any insight,

Nathanael

[Oliver Archut]

Hello Nathanael,

biggest difference from a technical point of view is the resonance of ribbon/condenser. While a ribbon has a resonance in the audible low end spectrum (mostly 20 to 45Hz) condensers resonance is above the audible spectrum, only a few condensers were made that had a resonance at about 14kHz and than due to the limited material that was available in the 1920s.

Regarding the mass, the air cushion trapped behind the diaphragm is in average four times as heavy than the actual material of the skin. So the size of the capsule SD/LD is a bit more important.
Were Neumann's resonance frequencies are fairly close from capsule to capsule type, other classic capsules like the AKG CK12 had different resonance frequencies all over the scale.

There is hardly any published data on sound changes with different resonances. In my experience nearly all reskinned capsules never have the same resonance than the original manufactures spec, and always sounded different.

From a technical point of view it is nearly impossible to EQ a capsule to a flat spec, or EQ the resonances away,without introducing other problems, mostly phase angle push (a distortion of the 0 degree crossing) and phase shift is present for all frequencies in general. To some extent it is possible but careful matching of components is necessary.

Best regards,

[David Satz]

Hello, Oliver. Let's divide the condenser microphone category further:  pressure transducers vs. pressure gradient transducers. Condenser microphones operating as pressure transducers have their primary resonance at or above the top of the audio frequency band, just as you say. However, condenser pressure gradient transducers (the kind which most people use most often in studio work) have their primary resonance where the amplitude of the pressure gradient is greatest for their particular dimensions--normally at several kHz.

The following image is from page 14 of the wonderful little booklet on microphones by Bor

[Nathanael Iversen]

Thank you both for the high quality responses so far. I've got new homework to do and will be back after some reading.

Thanks!

[Oliver Archut]

Hello David,

you are quite right, I didn't want to go to close into the details, because than there are mechanical vs. electrical resonances that are EQed and shifted via resonator plates, and or mechanical EQ tunnels/ holes.

One of my preferred ways to make china mics a bit more useable (mostly for live sound were it sometimes happened the bandmembers kick and throw mics around) is just by simply enlarging the breathing hole, with a needle to reduce the cussion (do not try this at home)....

Best regards,

Oliver