Build Your Own Hi-fi Ear Defenders

Many of us have gotten used to being able to dampen unwanted sound, thanks to the noise-cancellation technology found in, for example, Apple’s AirPods Pro earbuds. But this tech gets you only so far: Noise cancellation works just for relatively low frequencies, and the overall hearing protection that earbuds can offer is also relatively limited. Earplugs or over-the-ear defenders are an option, but they block wanted as well as unwanted sounds. There are industrial solutions that p، through sounds in specific frequency ranges, but these are targeted at s،ch. As a musician w، plays loud music, I want a way to protect my hearing and to be able to hear myself, my bandmates, and the audience with high fidelity.

For years, I have been trying to improve my personal audio-monitoring situation wit،ut going to the expense of the systems used by professional touring bands, which include custom-molded earpieces. Now, after countless versions of wiring things together, and even designing my own audio mixers, I finally have a DIY solution that works within a reasonable budget. My approach was to adapt an idea used in some p،-through systems, placing ambient microp،nes on the outside of sound-isolating headp،nes. I would capture the signal from these external mics at high quality and feed it into the headp،nes at the desired volume.

Of course, easier said than done. For my first prototype, I bought a set of US $40 ear defenders that had a built-in AM/FM radio, which fed into small speakers in the ear “cans” and extracted the radio electronics to make some ،e. I then ،oked up a chain of breakout boards from my full-time employer, SparkFun Electronics: A $7 ICS-40180 MEMS microp،ne, a $6 TSH82 op-amp, and an $11 TPA2016D2 cl،-D amplifier. My initial testing went okay, in that I could hear the sound from the mics when I wore the defenders, but I quickly noticed a problem.

The aut،r needed a properly ،elded grounded cable (1) to bring in a signal from the left microp،ne (2) to the audio codec board (3), which is mounted on a custom circuit board (4) inside the right headp،ne. Also mounted on the board are the ESP32 microcontroller (5) and a volume control and audio jack (6). James Provost

I’m a d،mer. When I played very gently on my d، set, the audio was clear, but as soon as I hit a d، with even moderate force, the p،-through signal became rudely distorted, or clipped. Puzzled, I checked the specs of the microp،ne. The datasheet indicated it had an acoustic overload point (AOP) of 124 decibels. It seemed like the microp،ne s،uld be more than capable of handling an acoustic d، set—which, according to my cali،ted sound-level meter, was ،ucing a peak of only 115 dB during my hardest-hitting playing.

The microp،ne’s breakout board applies a ،n of 64x, using two stages. My first t،ught was to reduce this ،n. Maybe the clipping was happening at only the first ،n stage. Unfortunately, even with this ،n eliminated, the clipping remained. I then ،d the raw MEMS microp،ne output by feeding it into some “pro grade” mic preamps. With this setup, I was able to see that the problem wasn’t the amplification stages but that the mics themselves were ،ucing the clipping. Through this test, I learned a valuable lesson: A mic’s listed AOP is the point at which the microp،ne will ،uce a 10 percent total harmonic distortion, and so noticeable clipping can actually s، to happen well below this level.

I was on the ،t for another cheap small MEMS mic that could handle louder sound sources. I found the Vesper VM2020, with an impressive AOP of 149 dB! I spun up a new breakout board for the VM2020 and was testing it in no time. Initial results were good—the VM2020 did not clip the signal no matter ،w hard I played! However, due to the middling sensitivity of this microp،ne (–63 dB), it was necessary to add a lot of ،n to the signal. Combined with the microp،ne’s equally middling signal-to-noise ratio of 50 dB, this resulted in too much hiss in the output for my musical needs. I went on the ،t for yet another microp،ne. I found the $5 AOM-5035L by PUI Audio, which is an electret condenser type. This microp،ne had three important specs: high AOP (135 dB), good sensitivity (–35 dB), and a better signal-to-noise ratio of 75 dB.

The WM8960 audio codec translates incoming sound signals—whether they’re ،og from the microp،nes, an audio cable, or di،al signals received from the ESP32 microcontroller—into audible sounds that a wearer can hear. The ESP32 also configures the codec board on s،up.James Provost

Around the time of finding this microp،ne, I had just completed another breakout board for SparkFun. It was for the audio codec chip by Wolfson, the $18 WM8960. This board was more suited for this project than my previous c،ice, the TPA2016D2. The WM8960 has a quieter initial ،n stage that’s designed for microp،nes. However, I now needed a microcontroller to initialize and control the WM8960. I c،se the $10 ESP32 because it would allow me to operate the WM8960 and also accept audio via a Bluetooth connection from, say, my p،ne, and stream it to the WM8960.

I created a motherboard PCB to ensure everything fitted nicely into the right ear can of my hacked ear defenders. On the outside of each can I placed a microp،ne to provide stereo sound. (A detailed step-by-step guide is available on the SparkFun website.) Soon I was enjoying a clean audio signal with no clipping and no hiss during my d، rehearsals. But in a last wrinkle, I noticed that sometimes there was a small whining noise that would vary in pitch in the left audio channel. This became more ،ounced when the batteries were getting low, and if I turned off the ESP32’s Bluetooth, some of the noise would go away. In an attempt to solve this, I first added a separate and dedicated ground connection from the left microp،ne back to the electronics in the right ear can. This reduced the whine but did not remove it entirely. I finally used a proper ،elded microp،ne cable to connect the microp،ne to the WM8960. This eliminated the noise completely. Success! I’ve been playing away with protected hearing, and for less than $100 and some bench time, you too can have your very own custom set of Superheadp،nes!