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QMX Electret Microphone specs

 

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I just did a bit of digging on electret specs. It seems that most of the ones I looked at had? sensitivities down around -44 db (volts/Pa) with SNRs in the neighborhood of 60db. But the one that Hans specified is much more sensitive at -24db with SNR around 80db. This leads me to believe that grabbing a random electret is likely to give disappointing results. There are some that specify the sensitivity as a positive number (52db for example). I would take this to mean -52db. Either that or they have specifies SNR instead of sensitivity.

Anyway, I was surprised to find that the one used by Hans seems to be somewhat atypical based on my quick survey of electrets. Maybe I just looked in the wrong places?

73,

Tony
AD0VC
 

Tony,
I know from working in the audio/video production industry that there are high quality and low quality electrets. Usually, but not always, you get what you pay for. Mine is a cheap Baofeng mic, however, After doing the gain adjustments, my input audio curves looked pretty close to the ones Hans provided.?
--
73, Dan - W2DLC
 

Mic Output levels...
The -44 db Spec is due to the modern digital devices today, so that the Mic doesn't overdrive the?ADC/DAC, as used in most?modern SDRs, as well as SmartPhones/Tablet/Notebook PCs.??
In other circuits (e.g. FM Modulators) it's usually not an issue.? That said a Mic with output of -44 db will drive an older ICOM analog (traditional heterodyne type SSB transceiver), to proper ALC levels with the Mic gain set near 50%.

Then there is the difference in intended use of the?Mic and there are three types of Mics.

1) There are consumer Electret-Condenser Mics that have these output levels with the?mic at some distance to the?mouth.??
2) A Close-Talk, Noise-Canceling, "communications grade" (e.g. Aviation Mics) that level is reached with the?Mic centered in front of your mouth with it set at 1/8" from your lips.? Then the acoustic noise cancelling?works, and the?output levels are maintained.
3) Now typical Studio Electret-Condenser?Mics?are yet different again with 48V "Phantom Power" (rather than 5V through a 4.7K ohm resistor for Mic BIAS).? This likely came from the AT&T networks that provided communications from the studio to the transmitter, but I'll confirm that with Dave, WJ6W he knows this stuff.

Collins Radio set the?standards for Aviation radio interfaces, and those interfaces are still used today (.206" Mic plug to differentiate it from the .250" Headphone Plug) with a high impedance Dynamic Mic.? Today the modern general aviation radios all use Electret-Condenser Mics (600 to 2K Ohm Mics). The exception is a military helicopter headset where the Mic is typically a 5 Ohm Close-Talk, Noise-Canceling, Dynamic Mic due to the extreme noise levels they must contend with.

Dave WI6R

On Thu, Mar 27, 2025 at 8:33?AM Daniel Conklin via <danconklin2=[email protected]> wrote:
Tony,
I know from working in the audio/video production industry that there are high quality and low quality electrets. Usually, but not always, you get what you pay for. Mine is a cheap Baofeng mic, however, After doing the gain adjustments, my input audio curves looked pretty close to the ones Hans provided.?
--
73, Dan - W2DLC



--


 

Here's how microphone sensitivity is measured:
?
A lower negative dB (such as -24dB) means more Volts out of the microphone for a given sound pressure
than a higher negative dB (such as -44dB).
?
The spec might use units of dB, dBA or dBV for the gain.
My guess is that these units are all directly comparable.
?
Mouser has a selection of 179 different electret microphones:
?
Selecting for only those with a sensitivity better than 30dB gives 11 microphones:
?
Three of those are not in stock, and two of the remaining expect a supply greater than 3 volts.
?
SNR is not given in the selection summary,? it is spelled out as "signal to noise" in the datasheets so search for "noise".
Of the remaining 6 microphones that have a sensitivity better than -30dB, the SNR is generally 60 or 70 db.
The two from PUI claim 77 and 80 dB of SNR, and are the most expensive at around $3.
?
If Hans really does use -24dB microphones with an 80dB SNR, those are not typical of what's on the market.
?
Jerry, KE7ER
?
 

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Frome the QMX SSB page at QRPlabs

"All development has been done with this particular Electret microphone from Digikey, part number 668-AOM-5024L-HD-F-R-ND:

This is NOT the same microphone as the QMX supplied onboard microphone. Many thanks to?Paul?W9PEM who gifted me this microphone, beautifully enclosed with a PTT button and 3D printed enclosure."



From: [email protected] <[email protected]> on behalf of Jerry Gaffke via groups.io <jgaffke@...>
Sent: Thursday, March 27, 2025 10:45 AM
To: [email protected] <[email protected]>
Subject: Re: [QRPLabs] QMX Electret Microphone specs
?
Here's how microphone sensitivity is measured:
?
A lower negative dB (such as -24dB) means more Volts out of the microphone for a given sound pressure
than a higher negative dB (such as -44dB).
?
The spec might use units of dB, dBA or dBV for the gain.
My guess is that these units are all directly comparable.
?
Mouser has a selection of 179 different electret microphones:
?
Selecting for only those with a sensitivity better than 30dB gives 11 microphones:
?
Three of those are not in stock, and two of the remaining expect a supply greater than 3 volts.
?
SNR is not given in the selection summary,? it is spelled out as "signal to noise" in the datasheets so search for "noise".
Of the remaining 6 microphones that have a sensitivity better than -30dB, the SNR is generally 60 or 70 db.
The two from PUI claim 77 and 80 dB of SNR, and are the most expensive at around $3.
?
If Hans really does use -24dB microphones with an 80dB SNR, those are not typical of what's on the market.
?
Jerry, KE7ER
?

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