MEMS In-Ear Monitor System For Musicians

Sensors Sound & Audio
1

Hi. I’m an older musician with a very basic understanding of electronic projects. I’ve built electret and MEMS lavalier style microphones, mono and stereo, and battery boxes providing bias voltage for electrets and 3v for MEMS. That’s about the extent of my knowledge. These mics are occasionally used for recording but more often as part of a simple wired in-ear monitor system when performing acoustic guitar and vocals in noisy environments. The mic is powered as needed, attached slightly overhanging the upper bout of the guitar and routed to a headphone amp. It picks up both guitar and vocal, usually to a single earbud. Works pretty well, small and completely portable.

I’ve switched pretty much exclusively to the MEMS mics, specifically the analog ADMP401 breakout wired to a TRS jack (tip - audio, ring - 3v, sleeve - ground) This goes to to the corresponding jack on the mems battery box I built. The box output jack is audio to both tip and ring for two earbuds, sleeve to ground. The only other thing in the box is a voltage regulator, on/off switch and a 9v battery. No other components. It works.

Some questions on the MEMS breakout:

  1. Is the ADMP401 the best choice for what I’m doing?

  2. Is there a problem with my MEMS battery box wiring? I’ve had a hard time finding information on building one of these.

  3. I’ve discovered the the MEMS works without the battery box when plugged directly into a device that provides plug-in power for electret condensers. (Zoom H2n, old Minidisc recorder) The signal is hot but seems fine with minimum gain. I’m surprised this works and was wondering if there’s a problem using it this way.

Thanks for any suggestions.

2

Using the MEMS microphone without the battery box and instead powering it through plug-in power can work, but it’s not ideal. The reason for this is that plug-in power for electret condenser microphones is typically a lower voltage (around 1.5-5V) than the 3V power that the MEMS microphone is designed to receive. This means that the MEMS microphone may not be performing optimally, as it is not receiving the correct voltage. Additionally, the audio signal may be weaker or more prone to noise than when using the battery box. So while it can work in a pinch, it’s not recommended for optimal sound quality.

3

Thanks for explaining this. I’ve added a small amplifier board with potentiometer to the battery box to make everything self contained. Everything runs at 3.3 volts. Mic input, headphone output, volume knob. Pretty good at low volume. A tone control would be helpful in adding some bass and taming the highs of the mic. Other than the voltage regulator and the amp there’s really nothing to it. I’m really just winging it here and I’m wondering if there’s something I should be adding to condition the line. Thanks again.