First of all, let’s begin by briefly remind what binaural audio is. Binaural literally means « using two ears ». It is a method of recording invented in the late 19th Century, that uses two microphones arranged with the intent to create a 3-D stereo sound sensation, by mimicking the natural hearing cues that our heads and ears generate. In the same way as two eyes are needed for our brain to have visual depth perception, binaural audio recreates the perception of distance, making audio more immersive.
Unlike stereo audio, binaural sound can nevertheless localize sound sources on either sides, in front of them, behind them, above and below. Naturally, it requires stereo headphones for the 3D effect to be reproduced, it will not translate properly over stereo speakers. Inversely, listening to stereo programmes over headphones gives a flat impression, as if sounds coming from inside your head. It looks simple, and it what’s made binaural audio strong because we do not need surround sound system to create true realistic immersive experiences. We simply need an omni directional microphone pair and earbuds for playback.
Different solutions are available commercially, from simple Microphones/Earphones like the ROLAND CS-10 EM ( less than of one hundred euros ) to a more expensive solution, like the Neumann Ku 100 Dummy Head, which costs around 8,000 euros.
It should be pointed out that, in the case of binaural recordings, the most important things are : The polar pattern, frequency range, sound pressure level and signal to noise ratio. Generally, microphones are placed either within, or at the entrance to a dummy head which allows to recreate how sound waves interact with the contours of the entire human head.
Now, it’s time to start making the first preparations. The overall budget allocated will be around 250 euros ( dummy-head + microphones includes ). For those purposes, three things are needed :
- A matched pair of omnidirectional microphones
- A life-size replica of a head
- A pair of silicone ears
In the choice of microphones, there are a wide range of brands which delivering really good products, like DPA, SANKEN, just to mention a few. Personally, i choose Soundman with the OKM II Classic A3.
I have picked it primarily for the price/performance ( around 200 euros ) and also because i heard very positive comments. The OKM II Classic has an frequency range of 20 Hz to 20 kHz, a signal-to-noise ratio (re. 1 Pa) of approximately 61 dB and with a maximum sound pressure level (SPL) over 125 dB ( with A3 adapter ).
Once the microphone has been determined, i moved on to the next step with the construction of the dummy-head.
I made the choice to realize it from a model that does not look like conventional dummy head, because i don’t really like life-size heads, i find that it’s not discrete enough. I also choose to make it with Pine wood, because i wanted something hardy and i enjoy wood work. Then, i sought silicone ears. As you remember, the goal is to mimicking the natural hearing cues that our heads and ears generate. So what’s better than factice ears ?
Before starting the manufacturing process, a detailed manufacturing drawing should be established.
As mentioned previously, i used pine wood and more precisely a wooden plank of 18mm available from DIY stores. However, i should have bought a second wooden plank of 15mm, because i’ve had to carry out some adjustments to ensure that ears fit perfectly.
As a first step, i began by modeling the schema to provide an overview and also because i’ve used a CNC milling machine for the manufacture. It has allowed me to have a more accurate part dimensions. As you can see on the second picture, i’ve also had to level the wood to obtain 15mm.
Then, it only remains to round off the edges, clean the base, sand and finally put them together.
Note that the covers on the third picture below shall have a thickness of 3mm. They will enable to hold ears and should be introduced perfectly into the wood part once ears inserted. They can be made from any types of material like, wooden, MDF, metal or, in this case, a piece of glossy black plastic. Lastly, i used wood glue to assemble the box and eight wood screws to fix the box and ears together.
Once finished, it only remains to add the microphone into the dummy head, pull capsules through silicone ears holes and to position them as earphones.
I must say, i am satisfied with the result. As expected, the entire project cost only 250 euros and i was surprised by the quality of the OKM. The dummy head is discreet, sturdy and not too heavy or bulky. Microphones doing very well in noisy conditions. However, the signal-to-noise ratio is somewhat disappointing In quiet conditions. This is not perfect but the advantage is that i could upgrade to better microphones in the future.
Extracts of binaural recordings from 2:39 to 3:14 :