The Open Sourcerer

Extreme passive noise cancelling on the cheap4 min read

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by

Jeff
in

It baffles me how people keep using crappy earbuds in the Montreal metro, usually cranking up the volume and competing with the incredibly loud ambient noise. With the rise of portable music players and “music as a mass product” (to be consumed in great amounts, all the time, everywhere, with little regard to quality), I am wondering if there will be a significant increase of future hearing problems. Maybe, maybe not. In any case, even when not listening to music, the noise in that subway is something to be wary of, especially when you ride it one hour per day like me.
So, lately I’ve been quite disenchanted with my active noise cancelling headphones, because the MDR-NC6 are built like a piece of crap. I reflected some more on the problem of blocking drowning the ambient noise of the Montreal subway‘s engines/fans/tires/airflow. I then came to the conclusion that I would need to try and build my own passive noise cancelling system. I did not want to buy a 130-300$ headset which could break and leave me frustrated (I did dismantle one of those in a retail store once, and they were also built like pieces of crap, even though they are more expensive than a computer).

Putting the plan into motion

I first bought a pair of ear protectors (“ear defenders”) from Canadian Tire for 35$. Yes, the kind that you wear on when you want to use a jackhammer or launch a portable ICBM.
This thing offers a noise reduction rating (NRR) of 27 decibels. That’s an average. For certain frequencies, this headset is supposed to reduce less, and for others, it goes up to 38 decibels. This is over 9000, folks. IT’S HUEG (let me remind you that decibels are a logarithmic scale; increasing by 20 decibels = multiplying the sound pressure by 10 times).

Now, the problem is listening to music in there. Nine earbuds out of ten will not fit comfortably; sure, you could use iPod-like earbuds, but you have this plastic tube thing that comes out of the ear and gets stuck right between your ear and the ear defender, causing 3 problems:

  • it hurts, especially after more than 30 minutes
  • it creates an isolation hole where noise can come in
  • it prevents the earbuds from staying in the correct position in your ear, and you lose all the bass.

I spent a while searching for canalphones (in-the-ear-canal earbuds) that did not have anything protruding out of the ear (the thing had to hold in place by itself), and something that is comfortable. One often reported advantage of canalphones is that they are also passive noise cancelling devices, since they block lots of external noise by being directly in your ear canal.
There must be an evil plot somewhere, because I once again ended up buying SONY. They were the only ones to satisfy my needs (and at a reasonable price). They look like this:

I carry them in a solid eyeglasses container (I want them to last forever), and pluck them in my ears in public transit. Then, I just have to carefully put on my “ear defenders” on top, and the ambient noise drowns. The loud roar becomes a very quiet hiss, which is more than manageable.
Combining this 27 NRR hearing protection with a pair of inexpensive canalphones (total: about 70$), I get pretty much the most “extreme” passive noise cancellation there can be (2 sound barriers in 1), without spending hundreds of dollars on something that will eventually break.
To give you an idea of how well this works:

  1. without any noise cancelling (using regular headsets such as these), I needed to set my music player’s volume to -5 dB (certain Rockbox themes seem to use a decibel scale. Not sure I can trust it, but oh well)
  2. with active noise cancelling, I needed to set the volume to -15 dB (sometimes -10 dB)
  3. with this extreme passive noise cancelling solution, I can set the music to -30 dB (or even -35 dB) and still hear the music perfectly fine. If I feel really like partying like a monkey in the subway and want to put the music at full blast, I don’t need to go higher than -25 dB.

What’s even more impressive is that I can just let the music volume set at -30, and don’t need to adjust it when the train stops, because the perceived noise was not high enough to require a music volume increase. The noise reduction is just that good. Of course I look like this now:

But I enjoy music, or silence. Looks be damned.

Jeff
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