On-Set Audio Monitoring: How to make $30 DIY Passive Noise Canceling Headphones

Build your own passive noise-cancelling headphones for $30...!

Build your own passive noise-cancelling headphones for $30...!

In the tutorial below you will learn how to frankenstein yourself some decent $30 Headphones that enable you to monitor sound on a noisy set with certainty – everything you hear will be the microphone feed … as if you were sitting in a quiet room.

THE BASIC PROBLEM – BLEEDING NOISE

When you are on set, and the set happens to be on an otherwise busy street with cars rushing by and people talking in the background, you are in a difficult environment. When you’re on a documentary shoot in a noisy factory or a train, it will be hard to monitor your recorded audio properly.

The basic, underlying problem is: There will always be noise unless you are in a well-controlled interior environment. And that noise will penetrate your on-set headphones and make it difficult for you to distinguish if the noise actually comes from your microphone feed, or if it just bleeds through the plastic caps of your headphones.
Is that air conditioning we can’t turn off actually being recorded by the lavalier, or do I just hear it through the headphones? Are the cars driving by part of my shotgun mic’s signal, or are my headphones just too thin? – that’s the basic problem.

The two basic ingredients: Regular but decent headphones, and construction worker earmuffs.

The two basic ingredients: Regular but decent headphones, and construction worker earmuffs.

TWO SOLUTIONS – PRO AND DIY

There’s Solution 1 for Pros: Active Noise-Canceling Headphones. These specialty headphones are equipped with small microphones on their outside shell that record the environment noise. A small processor takes this audio signal, inverts the wave information (mirrors the waveform) and injects it into the headphones. The result: The two perfectly symmetric waveforms that result from the outside noise cancel each other out, and what remains is the microphone feed.

Great idea that Mr. Bose had back in the day – but you pay. Around $300 for good ones.

Solution 2 is for the stingy DIYers out there, like myself: Building headphones that are passive Noise-Canceling. Passive in the sense that instead of working with inverted waveforms, they try to get rid of the bleeding effect that thin, loosely fitted headphones bring with them. The basic idea for this concept stems from a few DIYers online from a couple of years ago; I decided to take their concept (which was developed for listening to music) to the on-location audio world and improve on it.

STEP 1: Buy or have Headphones with a decent frequency response – $20

DIY can’t make shitty headphones into great ones – what you need as a base is decent headphones that are A) ready to be destroyed, and B) good enough that you can hear a “full” sound, i.e. cover frequencies well and project low basses as well as very high notes. I can personally recommend the Sony MDR V150 headphones, which I bought a few years back for $20. Google Shopping Link with different Vendors – cheap, and pretty good.

 

STEP 2: Hardware Store Trip – $10

Go to a hardware store and ask for construction worker’s earmuffs. They will direct you to some strange-looking plastic ear muffs that sit really tightly and isolate you from the rest of the world, pretty much. If they have multiple ones and you have a choice, try all of them and buy the ones that have the best isolation-comfort ratio. The better they insulate, the tighter they usually sit on the head – and you have to decide between quality isolation and wearing comfort. Initially, they will hurt, but you can get accustomed to the constant pressure with little practice. I personally recommend to buy thin cable ties as well, those should be part of your DIY cave already though. Cost for the Earmuffs: $10.

 

STEP 3: Headphone Surgery

Taking apart the headphones - these elements remain.

Taking apart the headphones - these elements remain.

Now the fun begins. Carefully remove the leather-type donuts (the soft parts of your headphones) – we will recycle them later. Take a screwdriver, knife, saw, dwarf prybar or jackhammer – whichever tool you have handy – and open up the ear portions of your headphones. They usually have two screws holding the shells together, and then a few snap-on plastic pieces. Be careful to not damage the interior during your surgery, as well as the felt topping on the shell. Also, be careful not to damage the cable and its wire connections to the headphone speakers. In the case of my Sony headphones, I had to use strong scissors to cut the shell where it enclosed the headphone cables – and had to be careful not to pull on the cable, since it is connected to the headphone speaker with two hair-thin wires that looked like they would love to rip. Make a note of which one was the left, and which one was the right speaker.

After your surgery, you should have the headphone cables connected to the two headphone speakers, and nothing else.

Cutting off the headphone shell, in order to remove the actual speaker element.

Cutting off the headphone shell, in order to remove the actual speaker element.

The isolated speaker element of your headphone - that's how it should look like. Leave the innermost plastic piece, it carries sensitive electronics.

The isolated speaker element of your headphone - that's how it should look like. Leave the innermost plastic piece, it carries sensitive electronics.

STEP 4: Reinforcing the Sensitive Parts

Did you ever get caught somewhere on set with your headphone cable, and janked your half head off? I have. It’s important that our DIY headphones can withstand impact and relocation attempts. While the cable itself is pretty sturdy, the tiny wires that connect it to the speaker are not.

As you can see on the picture, my headphone speakers were embedded in a small plastic platform with a few holes in it – the perfect place for cable ties. I led the cable around the speaker and gave the cable-wire transition a few millimeters of slack. Use the cable ties to tighten the cable to the plastic framing of the speakers; if you don’t have holes in your frame, I recommend making a few or coming up with another smart idea how to attach the cable tightly to the speakers. If you want to do a stress test, grab the cable by the throat and swing the speakers through the air. If they don’t rip off, you’re good to go for the next step.

Preparing the cable ties and the headphone speakers for some cable reinforcement.

Preparing the cable ties and the headphone speakers for some cable reinforcement.

The cable ties (here, already cut to length after tightened) hold the cable firmly to the frame of the headphone driver, which makes sure the sensitive wires at the driver base can't be damaged in case the cables get pulled with force.

The cable ties (here, already cut to length after tightened) hold the cable firmly to the frame of the headphone driver, which makes sure the sensitive wires at the driver base can't be damaged in case the cables get pulled with force.

STEP 5: Embedding the Speakers in the Earmuffs

Put the driver into the ear muff's hollow space, and cover it with the felt pad that the headphones came with.

Put the driver into the ear muff's hollow space, and cover it with the felt pad that the headphones came with.

The Construction Worker Earmuffs have quite a big amount of space between their inner foam insulation and the ear that will wear them – in that void space, we will place our headphone speakers. Also, note that there is a gap between the foam flooring of the earmuffs and the leathery donuts that attach to your ear, which lets outside sound bleed through – we will take care of that. You can plug in your headphones and play some music to find out which side gives off the clearest and loudest sound (usually the side that was mounted towards your ear initially). With the better side facing up, insert the speakers into the earmuffs’ floor.

Problem – they just float around. To solve that, use a knife or thin scissors to lift off the [glued-on] felt padding on the headphones’ outer shell, on each side. Place this felt disk now on top of the speakers, while making sure that the cable leading to the speakers is taking a smart path into the earmuffs. Once done, grab yourself the leather-like donuts you removed initially, and squeeze them in between the felt padding and the much thicker donuts of the earmuffs. Now everything will stay in place through the tight squeeze of the stacked pieces. The result will be two concentric donuts covering a felt disk, which is laid on top of a speaker, which is embedded in a foam flooring, which is surrounded by a thick plastic shell – as the diagram shows below:

 

Sound is all about travelling through elements. If there's a gap, there will be more sound, so this gap needs to be covered...

Sound is all about travelling through elements. If there's a gap, there will be more sound, so this gap needs to be covered...

Pushing the headphone covers into the remaining gap between felt pad and the er muff padding ... this closes the gap and secures both driver and felt pad tigthly.

Pushing the headphone covers into the remaining gap between felt pad and the er muff padding ... this closes the gap and secures both driver and felt pad tigthly.

STEP 6: Cable Running and Cosmetics

Now you have to find a way to let the headphone speaker cables stay attached to not just the speakers, but also the earmuffs – otherwise, every time you yank on the cable, the speakers will pop out of their soft embedding in the muffs. I used electrical tape, since I figured that drilling through the plastic shell would provide me with an attachment point but ruin the isolating effect of the shell itself. I also recommend making a few marks (top, bottom, side) of “L” and “R”, so you know right away where left and right is – since the earmuffs don’t have a left or right side by default.

The final outcome, labeled with "L" and "R" for each corresponding side. The red electrical tapes cover a bit of gaff tape, which holds the cables to the outside body of the headphones - another safety net in case the cables get pulled on.

The final outcome, labeled with "L" and "R" for each corresponding side. The red electrical tapes cover a bit of gaff tape, which holds the cables to the outside body of the headphones - another safety net in case the cables get pulled on.

TESTING THE HEADPHONES

By just trying it on, you will see the amazing difference these tight-fitted, passive Noise-Canceling headphones have compared to “regular” headphones – nevertheless, that’s not a very scientific statement.

Hence, I made an objective test by inserting lavalier microphones between my ears and two pairs of headphones – the frankensteined pair, and an identical, unmodified pair. I then played music from my external computer speakers, while listening to a distinctly different voice-over recording inside the headphones. By having the lavalier microphones where my ears are, I could analyze what I am actually hearing. The results are shown in a Spectrogram comparison below:

Click for a larger version! The spectrogram comparison. How to read it: left top, the voiceover by itself. Left bottom: The music by itself. Now observe the difference between Right top (the two tracks separated by unmodified headphones) and the Right Bottom (both tracks separated by the modified headphones) - it's clearly visible how much of the bleeding outside music track has been cut out of the sound operator's hearing.

Click for a larger version! The spectrogram comparison. How to read it: left top, the voiceover by itself. Left bottom: The music by itself. Now observe the difference between Right top (the two tracks separated by unmodified headphones) and the Right Bottom (both tracks separated by the modified headphones) - it's clearly visible how much of the bleeding outside music track has been cut out of the sound operator's hearing.

Bottom line: Now you will have more fun on set, when you can barely hear crew giving you instructions unless you point a microphone at them – and being able to tell exactly when the actor’s voice is clean, or washed dirty with surrounding noise. All you have to do is embracing the pressure of the earmuffs during a recording – no worries, millions of construction and factory workers around the globe have learned to like it, so you have good chances of learning it too.

The finished passive noise-cancelling headphones.

The finished passive noise-cancelling headphones.

About the Author

Tobias Deml is an Austrian Filmmaker and Visual Artist. 2012 Cinematography Reel: http://vimeo.com/53973421 Tobias Deml ist ein österreichischer Filmstudent und Möchtegernregisseur in Los Angeles. Er arbeitet derzeit als Kameramann in Los Angeles und popelt in seiner Nase.