Creating a Binaural Microphone on a “Budget”
Introduction
Binaural audio recordings have fascinated me for years. In case you haven’t heard of binaural audio before, it is a specialized recording technique designed to capture “three-dimensional audio” that allows a listener to detect where in space different sounds originate. By recording in stereo through rubber molds of human ears with two separate microphones, sound waves from any given source reach each the microphones at slightly different time intervals. The rubber ears allow sound waves to bounce around before reaching the microphones in a similar way sound waves bounce around before reaching human ears. If the resulting audio recordings are listened to through headphones, so that each microphone’s audio channel is heard only by one ear, the listener experiences incredibly realistic audio. This achieves a similar effect to surround sound, but it is even more immersive and realistic!
Still confused? Give the video to the right a listen. Be sure to wear headphones, or you will not experience any 3D binaural effect!
How I built my microphone
I built the binaural microphone in the video using relatively cheap off the shelf parts from Amazon. It consists of two lavaliere microphones, a few dongles, a Styrofoam mannequin head, and two silicone ears. Here are some rough plans for how I did this:
I purchased some lavaliere microphones in a two-pack for about $25. These came with a dongle which I assumed combined the mono audio from each microphone into a stereo signal. Unfortunately, the dongle combined the mono audio from both microphones into yet another mono signal. This would not work at all for my needs.
What are TS, TRS and TRRS?
In order to understand how I made this work, it is important to know about the different kinds of 3.5mm headphone style plugs.
There are several varieties of 3.5mm plugs. Each of these types can carry a different amount of audio signals. TS plugs have two conductors in them: one for ground, and another for mono audio. Because of this, they cannot carry a stereo signal. TRS is the most common type of plug, and it has left channel, a right channel, and ground wires. TRRS is slightly less common, but it is often used on products that plug into smartphones, such as earbuds with an integrated microphone. TRRS plugs have a left channel, a right channel, a mono microphone channel, and ground.
With that explanation out of the way, back to the project:
As the lavaliere microphones I bought were geared towards people recording audio with their smartphones, the plugs were TRRS. This style plug is great for cellphones, but it is not great for stereo microphones, as they need two conductors for a mic signal, but TRRS only carries one with its default wiring.
In order to record in stereo, I needed to use a standalone audio recorder, because my smartphone’s TRRS socket only has one microphone input channel, and so it is unsuitable. I already happened to have access to a Zoom H2n which could handle stereo perfectly, so this is what I used. Later, I utilized the microphone input socket on a Fuji XT-2 camera and this also worked fine.
The microphone input jack on my audio recorder can handle stereo, but it uses a TRS socket to do so. In this configuration, the left and right channels carry microphone signals as opposed to audio output. This TRS socket meant that I needed a way to take just the mono microphone channels from my two microphone’s TRRS plugs, and connect them to a single TRS connector. Each channel needed to stay separate in order for there to be stereo.
I utilized several dongles in order to wire the connectors together the way I wanted. First, I purchased a cable which plugged into the microphone input on my audio recorder. This cable split the two audio channels of the microphone input into two TRS sockets -one for each microphone. When I went to plug the microphones into the splitter; however, I heard nothing. This is because they had TRRS jacks which did not line up with the TRS sockets on the splitter.
In order to circumvent this issue, I purchased a pair of TRRS to TRS converters. These converters went between the connectors of the splitter and the two microphones.
I plugged everything in, and nothing happened. It was as if the audio recorder detected no signal at all! This was because the microphones I purchased required power from the recorder in order to capture audio signals. Luckily, all I needed to do was change a setting in the recorder’s preferences. Turning the power on made everything work perfectly, and I was able to capture the stereo signal I wanted.
Assembling the Binaural Microphone:
Now that I had a stereo audio capture system in place, I needed to fashion a binaural microphone system to use it with. I purchased a Styrofoam mannequin head online to use as a mounting platform -the head provides a bit of noise insulation between the two ears and improves recording realism, too. I used a 1” drill bit to make a hole that ran straight through the ears and up from the base of the neck. This formed a sort of hollow “T” shape inside the head for wires to run. As the existing ears on the mannequin head did not really resemble human ears at all, I purchased some silicone ears online to replace them with. (I’m not really sure what the intended use case for these rubber ears is, but they worked fine for my project.) I used a craft knife to make some cavities in the head for the ears to fit into, and I also cut some small holes in the center of the ears for microphones to sit. After this, I ran my microphones through the head, and out into each ear hole. The silicone provided enough friction to hold the microphones in place without further hassle. In order to secure the ears to the head, I pressed some pushpins through the rubber and into the Styrofoam head at an angle that kept everything locked into position. The wires for the microphones ran out of the bottom of the head and they plugged into the dongles, and then into the recorder. I also slipped a piece of PVC pipe up into the hole at the base of the neck; this was used to mount and carry the head without introducing noise issues.
Conclusion
While the route I took to create my recorder was somewhat convoluted, I was able to use it to achieve some great results. Admittedly, this could have been much simpler if I had just soldered the various cables together, but by using dongles, I preserved each part for future projects. This project definitely turned out more expensive than I expected, but seeing as comparable professional microphones can cost thousands of dollars, I suppose I did pretty well in terms of cost. Although I don’t quite know how I will use the microphone system yet, I am very happy with how it turned out.
Parts List (total $70):
The completed binaural microphone connected to a camera.
