Effect of resonance on mics

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ManFromMars

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Hi all
Could anyone tell me how resonance affects microphones - as in, when a sound is made at the mic diaphragm's natural frequency it will start to vibrate much more violently, so exactly how do microphones deal with this (by having a very high natural frequency?) - and would the large vibration increase simply cause a peak in the mic response at that particular frequency?
Darn physics project's we're expected to do...
Thanks very much indeed for any help.
 
The answer to both your questions is yes. Most 1/2" to 1" condenser mics are tensioned to move the natural resonant peak to somewhere around 5 to 9kHz.

There are ways to damp this resonant peak somewhat or broaden it, but there's still somewhat of a peak left over. Done right, it can add air and detail; done wrong, it can make a mic sound harsh and tinny.
 
This doesn't have to do with diaphragm resonance but, if you pull apart an AKG C12 for example, you will have a brass tube that is the main body of the mic. If you then hold it by it's edges and tap it is has a pure bell like resonance, BING! If you sing through the tube it will resonate at several different harmonic points. Hong, hing, hee...

Once you familiarize yourself with these resonant frequencies, you can hear them when recording. If you dampen the body of the mic the frequencies go away. I have damped the bodies of all my mics from my lowly V67 up to my C12. It really does make a difference.

Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com

"I should have been a plumber."
-Albert Einstein-
 
It seems to me that you would be able to tell where the diaphragm would be most likely to "resonate" from the frequency response plot. The frequncie(s) at which the mic output increases (ie the graph goes up) would be where the mic resonates most. Like Harvey said, its around 5 to 15kHz, but as with every sound produced, there are overtones and undertones which also plays into the effect. However, most of these are probably out of the spectrum of the audible range.
 
Thanks both for your replies, I was getting more at the natural frequency of the actual diaphragm rather than the effect of the actual mic body, though.
Could anyone expand on, or tell me where I could find out about Harvey's point about how microphones dampen and broaden this resonant peak? What about with dynamic mics? I'm afraid I'd like a fair amount of detail, this is for a physics project...Thanks very much again
 
Tom Cram said:
This doesn't have to do with diaphragm resonance but, if you pull apart an AKG C12 for example, you will have a brass tube that is the main body of the mic. If you then hold it by it's edges and tap it is has a pure bell like resonance, BING! If you sing through the tube it will resonate at several different harmonic points. Hong, hing, hee...

Once you familiarize yourself with these resonant frequencies, you can hear them when recording. If you dampen the body of the mic the frequencies go away. I have damped the bodies of all my mics from my lowly V67 up to my C12. It really does make a difference.

Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com

"I should have been a plumber."
-Albert Einstein-
Click to expand...

Hi Tom, how are you dampening the bodies of your mic's? Thanks
 
I use the fuzzy side of self-adhesive Velcro. I line the inside of the mic body with a few strips and that presses the fuzzy part against the internal housing. This completely stops the outer body from vibrating.

Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com

"I should have been a plumber."
-Albert Einstein-
 
phlbtphlbt...

Oh, and concerning diaphragm resonance; after recording 2 or 3 singers you won't have to worry about it. Their expectorate will have changed the frequency response and resonant frequency of the diaphragm anyway.:p :D ;)

Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com

"I should have been a plumber."
-Albert Einstein-
 
Does isolating a mic from the stand on a shock mount vs just using the solid adaptor help reduce ring / resonance from the mic stand?

I know it wil help with rumble / headphone wire taping the mic stand and low freq stuff... but thats not really a problem for me.

If it does it help, does it do 50 bucks worth of improvment ? I'm thinking about buying one.
 
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