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Gear / Technical Help => Microphones & Setup => Topic started by: BlindGuyEars on February 07, 2020, 04:06:05 PM

Title: Which Material to Dampen Plastic Microphone Housing Resonance?
Post by: BlindGuyEars on February 07, 2020, 04:06:05 PM
Although not strictly about taping, I can't think of a better place to ask this, anywhere with more expertise and DIY know-how.

I'm a ham radio operator. (think two-way FM radio).
I recently purchased this inexpensive but nicely-performing speaker mic from Amazon, for use with some portable radios.
https://www.amazon.ca/Commountain-Compact-Speaker-Reinforced-Microphone/dp/B071ZXFDLS

The microphone element is fairly far back in the case, so unlike more expensive mics of this type, it is not suseptible to plosives and other breath noises.

But, it has an annoying peak around 800 Hz. You can hear it by tapping on the plastic case.
That's what I'd like to dampen, if possible.

What thin piece of material, foam, fabric, etc. can I put in front of and behind the circuitry, between it and the plastic case, to help dampen the resonance? Is it even possible to lessen the ring from the housing, without also muffling the sound from the mic element?

Thanks for any suggestions.
Title: Re: Which Material to Dampen Plastic Microphone Housing Resonance?
Post by: morst on February 07, 2020, 04:13:41 PM
can the case be removed, and the switch wired to something else, like a foot pedal?
I'm thinking to load it with double stick foam tape if not
Title: Re: Which Material to Dampen Plastic Microphone Housing Resonance?
Post by: EmRR on February 07, 2020, 04:14:10 PM
Even gaffe tape would tell you if it's addressable, or if it's baked in.  I suspect it's somewhat baked in to things other than the material used.
Title: Re: Which Material to Dampen Plastic Microphone Housing Resonance?
Post by: DSatz on February 08, 2020, 09:53:40 AM
just to agree with EmRR and amplify somewhat: A resonance in an object often isn't due primarily to the flexing of its solid parts; it can be due to the air space within the object. Woodwind instruments are generally made of rigid materials, for example, and their body resonances are generally 40 dB or more below the level of the tone that the musician is producing at the moment. (Big exception: metal flutes.) That's why it's possible to make (for example) clarinets out of hard rubber as well as seasoned wood from endangered-species trees, and even most clarinettists find the difference negligible--there's far more difference among players and playing styles (including mouthpieces and reeds) than the difference that the material of the instrument itself makes.

So it can be instructive, but it might be frustrating, to do something to prevent the the microphone's outer casing from vibrating--say, surrounding it with cloth and placing it in a clamp or vise for purposes of testing. You may find that the sound artifacts that you object to are only slightly reduced. Or not--in which case (no pun unintended) you'll have an idea of what might be helpful and what might not.

--best regards
Title: Re: Which Material to Dampen Plastic Microphone Housing Resonance?
Post by: Oper on February 09, 2020, 01:33:59 PM
The best material to avoid resonances is bitumen mats or sheets. Electronics engineers have been using them since time immemorial.
A week ago I equipped my Lauten 320 with some strips of these self-adhesive bitumen matting on the inside of the microphone tube.
Title: Re: Which Material to Dampen Plastic Microphone Housing Resonance?
Post by: Compandered on September 13, 2020, 04:12:24 AM
Before we knew better the answer would be sheet lead. (the metal)
Because we know lead is toxic and causes brain damage, and through the wonders of modern science (!) we have high-density polymeric rubber
The Auto dudes call it "Dynamat" after the big brand name player.
It comes in many thicknesses, some offering heat insulation to car firewalls and floorboards, so choose wisely.
Better yet, stop by a higher-end auto stereo installer and ask for a scrap-end.
Polyurethane insulating foam also comes to mind, but it expands and is harder to control.

The 800hz peak is not unusual in a Comm mic, because that emphasis increases intelligibility.


About interfacing mics to your UHF radio, there are a few project boxes out there.
The challenges are RF getting into a hi-fi mic as well as type, level, and impedance matching.
Remember that Dynamic Mics are inherently more RF resistant than Electrostatic, which need power back and often Mic circuitry and pre-amp.

Ferrite beads and Faraday shielding may be adequate RF chokes, these are chosen by frequency, an easy choice when comparing 50+ MHz RF  vs. 200Hz to 8Khz communication-intelligible audio.

The home brewers way was often to use an interface testbox or ugly-board and when a solid solution revealed itself, to miniaturize perhaps to get the needed interface into the mic case.

Good Luck !
(FWIW, I am strictly CW-QRP, and mostly inactive, but the SDR has brought me back into the shack...)