Dummy Head

I made a dummy head baffle to test out binaural recording techniques on an upcoming session. The baffle was super simple to make, looks sleek, and works quite well, so I thought I’d share how I made it.

Note: The microphones shown here are not the same brand or model. I recommend using a matched pair of omni mics for the best stereo imaging results.

Before we get into the nitty gritty details, let’s get some questions out of the way first.

What’s a dummy head?

Dummy head is either an insult you used in third grade while playing kickball at recess or the term you use for the baffle placed between two microphones while making a binaural recording.

What’s binaural recording?

Binaural recording is a technique that attempts to record audio in a way that replicates the way our human ears encode three-dimensional audio information. This is done by simulating a human head by arranging two microphones (the ears) in relationship to an acoustic baffle (the head). The result is recorded audio with a stereo image that when played back through good headphones is supposed to sound exactly like “being there.” The dummy head acts like a proxy for your own head in whatever environment it is placed in. You get to hear whatever the dummy head heard.

One of the best known binaural recordings is the inconspicuously named album Binaural by Pearl Jam. Note: If you click that link and buy the album, Amazon will give me a little kickback, which I would totally appreciate. I’m sure Amazon and Pearl Jam’s label would appreciate it too.

What’s a baffle?

In audio jargon, a baffle is an object made of sound absorbing and/or acoustic dampening materials used to block or reduce transmission, reflection, or propagation of sound waves. Baffles are like shields that can prevent or impede sounds. They can be used to isolate a particular sound source from other sound sources in the same room. Baffles are often placed around loud things like drums or guitar amps. Sometimes engineers will place small baffles on the back side of microphones to reduce early reflections and room sounds or give more directionality to an omni microphone.

Shouldn’t a dummy head look like a head?

Binaural purists say that a binaural dummy head baffle must closely resemble a human head to capture all the nuances of how sound reflects off our faces, is absorbed by the mass of our heads, tickles our nose hairs, and gets caught by those biologically amazing curvatures of our outer ears.

The purists might be right, but if we’re going to replicate a human head down to the smallest details, whose head should we use as the model specimen? When I last checked, human heads still come in all kinds of neat shapes and sizes. Sure, we could build something will all sorts of exacting specifications, but I say a board roughly 20 cm by 25 cm that’s covered in felt is Good Enoughâ„¢.

If you build one and test it out, I think you’ll agree. All we really need to get a decent binaural recording is something roughly head-sized that blocks reflections between two quality microphones.

How to Make a DIY Dummy Head Binaural Baffle

Materials Needed for This Project

1. Wood Board – Solid or plywood, roughly 20 cm x 25 cm, whatever thickness you want. I happened to have a piece of solid oak lying around. Good enough!
2. Thick Felt – Enough to cover the board on both sides. You can use multiple layers to get the thickness you want. I had enough thick black felt left over from another project to do three layers on each side. I suppose you can buy this stuff at a fabric store or directly from your local feltsmith.
3. Microphone Mounting Bar – I used this On-Stage stereo bar from Sweetwater Sound. You could probably make something instead of buying something, but you will need a way to mount the baffle and two microphones on a microphone stand.
4. Short Screws – Pan head wood screws, quantity 8, long enough to secure the felt to the wood without poking out the other side.
5. Longer Screws – Pan head wood screws, quantity 3-4, for securing the mounting bar to the bottom of the wood.

Before Getting Started

You’ll need a few other things to build this baffle. I used a circular saw to cut the wood, razor blade to cut the felt, power drill/driver with drill bits to pre-drill and drive screws, clamps to hold things together, and a bandage to put on my finger.

This is probably a good time to give the obligatory reminder to be careful when you use power tools. Really that applies to any time you do anything in life. I find it silly that from a legal stand point it’s necessary to post a disclaimer about the dangers of power tools when writing about them. Cars kill people all the time, but to my knowledge articles about using cars don’t require disclaimers. Anyway…you should probably wear gloves, eye protection, ear plugs, and a respiratory mask. Maybe put on some pants too.

Putting it Together

1. Measure and cut the board. It should measure about 20 cm x 25 cm. That’s the approximate size of a human head when looking at one from the side. Yes, I used the metric system, because it’s way better than imperial. And no, that does not make me an anti-American, unpatriotic traitor. If you want to use imperial dimensions for human head size, may I suggest starting here?
2. Cut the felt. The felt should be the exact same dimensions as the board. A razor blade works well for making nice clean cuts. A sharp knife or strong scissors could probably work too.
3. Make a sandwich. Stack up the layers of felt with the wood sandwiched in the middle. I clamped this together to keep everything in place for the next step.
4. Attach the felt. Pre-drill through the felt into the wood approximately 2-3 cm in from each of the four corners. Try not to let the wood dust get embedded into the felt, which would look bad. Do this on both sides, but offset the location slightly on each side so the screws from the back side don’t end up hitting the screws from the front side. Drive the short wood screws in deep enough to hold the felt taut, but not too tight. Puckered felt looks unprofessional.
5. Drill holes in the Microphone Bar. Figure out where you want the long screws to be. Mark those spots on metal bar and drill holes just slightly larger in diameter than the long wood screws. When drilling metal, a little oil helps to cool the drill bit, making the drilling process easier. You can use cooking oil from the kitchen; it works just as well as anything else. Also, be careful with the metal shavings this produces, which can cause trouble if they get into electronics and/or your body.
6. Attach the Microphone Bar. Once the holes are drilled in the microphone bar, align the bar to the bottom of the baffle. Mark where the holes are and pre-drill the wood deep enough for the long wood screws. Again, avoid getting the wood dust on the felt. Screw the microphone bar to the baffle.
7. Ready to Use. Mount the baffle on a microphone stand using the center mounting hole. Use the shorter adjustable arms to place the microphone shockmounts or clips so the microphones’ capsules are approximately in the center of the baffle vertically and horizontally. The microphones should be about 20 cm apart from each other, which is about an average distance between most human ear pairs.

Final Notes

So does it work? In testing the dummy head I made, I was really surprised at how accurately the stereo field mapped sounds to the real world. I was kind of expecting it not to work very well. I had two different brands and models of microphones for my test. For the record the microphones you use to make binaural recording should be a matched pair with an omni pattern. Other patterns can sort of work too, just not as well.

I’m not posting audio samples here just yet, as I didn’t have the rights microphones on hand. But I did build this for an upcoming session, so once that session is done, I’ll post some clips for you to hear just how well a DIY dummy head can work.

Update (2013-08-18)

I somewhat coincidentally stumbled across an article about a thing called a Jecklin Disk, which is a lot like this dummy head baffle only larger. Check out this Wikipedia article for more about it.

Haas Effect Panning

History

A smart guy named Helmut Haas discovered a bunch of cool things about the way our human brains decode the sounds we hear to determine the direction of where those sounds originate.

Back in 1949, Mr. Haas found that early reflections of sounds help our brains decipher where the sounds came from. We can tell a noise came from the left not simply because we hear it in our left ear, but also because the sound bounces off a wall to our right and hits our right ear a very short time after it hit our left ear. Almost instantaneously, the brain detects the short time between the two signals and tells us, “Hey, that sound you just heard came from your left. Better turn your head to see what it was!” This happens so quickly that we don’t really even think about it. We just “know” it came from the left.

Haas also recognized that early reflections are basically copies of the initial sound that are delayed slightly. He started messing with people’s heads. He pointed speakers at them and firing sounds with very short delay differences. Then he asked the test subjects which direction the sound seemed to come from.

His conclusion: Not only is it fun to play with sounds, but also 40 ms (milliseconds) is some kind of magic point for our brains. If an echo is more than 40 ms after the initial sound, then we hear the sounds as separate instances. But if the delays happen within 40 ms or less of each other, then we perceive them together as merely directionality cues of a single sound.

For example, if a sound hits our right ear and the same sound hits our left ear 0.3 ms later, we don’t hear two sounds, we only hear one sound coming from approximately our 1 o’clock position.

And so the Haas effect was named after him.

Panning

Engineers have implemented the Haas effect as an alternative to panning. Most of the time panning works just fine, but it does have limits.

Sometimes panning leaves the location of the audio feeling indeterminate, smeared, mono, or one dimensional. This is why a lot of engineers skip the pan knob altogether and mix LCR.

To effectively localize a track in a stereo field using the Haas effect, engineers have to do a couple things. They duplicate the track, pan the two tracks hard left and right, and then apply a delay to only one of the sides. The delay is applied to the side opposite of the side from which the sound is intended to perceived as originating.

Typical delay times for this technique are increments of 0.1 ms from 0.1 to 0.7 ms. This yields linear movement across the stereo field. You can think of it like this chart shows.

Example: Want the sound to come from 9 o’clock on the left? Delay the right side by about 0.4 or 0.5 ms.

Download

After researching the Haas Effect, I decided I wanted to try it out in a mix. Since the settings must be very exact, setting it up correctly can be a bit confusing. Presets to the rescue!

I made these presets for the stock Digidesign Mod Delay II plug-in. These presets only work for this specific plug-in and Pro Tools. If there’s interest, maybe I’ll make more presets for other DAWs in the future.

Installation

Download this ZIP file, unzip it, and drop the folder and included presets in the Mod Delay II folder in the Plug-in Settings folder. On a Mac it’s probably located at Library / Application Support / Digidesign / Plug-In Settings / Mod Delay II, but may be in a different location on your system.

Setting up the tracks

Insert an instance of the Mod Delay II (mono/stereo) plug-in on the mono track you want to Haas-ify. Select the preset you want. No need to duplicate tracks. Bingo.

Haas Effect Panning

Digging Deeper

Understanding how to use the Haas effect properly means you need to understand and pay attention to things like stereo-to-mono compatibility and comb filtering, as well as other stereo field mixing techniques. As with all effects, have fun but be careful not to over do it. Experiment and do your homework. Then let me know if you find learn or discover anything cool. Here’s a cool video that got me thinking about the Haas effect. This video no longer available.