The markings don’t do much to identify the microphone and manufacturer, but I can tell this is from Knowles, and part of their SiSonic range of MEMS mic’s.

In the string S1925 9602, the “S” indicates it is a production ready version from the SiSonic range, whereas the number is just for batch identification. To figure out what type of mic it is, let’s desolder it. Knowing the dimensions, that it is a bottom port digital mic and from the footprint below, we can narrow it down to likely being the SPH0641LM4H-1. (Interesting note, if they used the ultrasonic version, the SPH0641LU4H-1, they might have been able to do some interesting things with using higher than perceptible frequencies to learn about whether the earbud is in the ear or not, assuming the speaker create such frequencies)

Dropping the mic…

Lets go one step deeper down the rabbit hole, and remove the metal shield to see what’s inside this mic…

Removed metal shield (left), ASIC (black blob in the top right) and transducer over the microphone port (bottom right)

Here we can see the the transducer and the ASIC (circuit customized for a particular use, in this case digitizing the audio signal from the transducer). The faint gold lines are connectors “wire-bonded” to the transducer and ASIC, and essentially the only part of this whole signal chain to carry analog signals to the DSP.

Lets take a moment of silence for the buds and eulogize:

To support assistant: “I was just listening to music, when these spontaneously just fell apart”

The Pixel Buds were cleverly designed and really interesting to take apart. While they used glue, they used significantly less than the AirPods and so were slightly easier to open up — and this could potentially be done while maintaining repairability, although reducing the waterproofing unless you could recreate the seal.

One can also see now how having the connecting string between left and right sides eases the hardware design challenges, such that the battery can be in one ear and the brains in the other. Having one larger battery is more power, space and cost efficient than having one in each. Secondly, there is no need to manage wirelessly syncing between the two buds, again saving power, space and cost. Some products achieve this by having redundant Bluetooth chips, where both will connect to the phone, or only the one with the best signal (depending on which pocket your phone is in) will connect and broadcast to the other. But most use what is called NFMI (Near Field Magnetic Induction), defined as “short range wireless physical layer that communicates by coupling a tight, low-power, non-propagating magnetic field between devices”. This is well suited as the buds stay at a fixed small distance (between your two ears) and the magnetic field is not affected by the large amount of water in your head to the same extent as a Bluetooth signal would be. This however requires a large coil in each earbud, again taking up precious space, and doesn’t include other data, such as if the second earbud needed to have a microphone for improving beamforming and noise cancellation.

NFMI coil found in Here One, for sending audio between ears in completely wireless earbuds

Interaction improvements?

After tearing down the Pixel Buds, let’s take a look at some possible interaction improvements or alternatives. How might one add detection of whether they are in your ear? The Apple AirPods use infrared sensors to detect this, which would be the first idea. Some quick ideas:

Capacitance — can be used to sense the edges of an earbud being pressed against the outer ear canal, and would differentiate well between skin and other surfaces, i.e. as in a bag or on a table. The placement of these capacitive sensors would need some careful mechanical design.

— can be used to sense the edges of an earbud being pressed against the outer ear canal, and would differentiate well between skin and other surfaces, i.e. as in a bag or on a table. The placement of these capacitive sensors would need some careful mechanical design. Humidity differential — with humidity sensors becoming cheaper, and more power efficient (possibly becoming cheaper or at least lower power than IR detection), one could tell if a surface of the product was pressed against skin.

— with humidity sensors becoming cheaper, and more power efficient (possibly becoming cheaper or at least lower power than IR detection), one could tell if a surface of the product was pressed against skin. Accelerometer — the earbuds are in a pretty consistent orientation when inserted — and even if hanging upside down, you can assume they’d be in the same orientation relative to each other. Once they were determined in the ear by one or more of the other methods, the accelerometer could be used to tell if there is unexpected movement with a low-power and fast response, prompting a re-evaluation of whether they are in or not (similiar to how an altimeter in GPS helps prompt a re-evaluation of altitude).

— the earbuds are in a pretty consistent orientation when inserted — and even if hanging upside down, you can assume they’d be in the same orientation relative to each other. Once they were determined in the ear by one or more of the other methods, the accelerometer could be used to tell if there is unexpected movement with a low-power and fast response, prompting a re-evaluation of whether they are in or not (similiar to how an altimeter in GPS helps prompt a re-evaluation of altitude). Ultrasonic — more of a “creative” approach, having two microphones, you could learn a lot about the earbud’s location from measuring the response from small ultrasonic chirps. This would only work for the right ear in the current version.

Furthermore, for gestures, an accelerometer could provide a redundant means for sensing taps, or one could make use of deliberate squeezes of the bud to pause/play/activate assistant, to differentiate from accidental taps.

Lastly, having always-on listening for a wake-word (i.e. “Ok, Google”) so you won’t need to tap may seem power intensive but is becoming more feasible. I’m making a prediction that future versions will have this, based on some of the low-power DSP’s with built-in Deep Neural Net hardware acceleration being developed by chip manufacturers.

With the earbuds now violated beyond repair, let’s finally wrap-up with the case…

The case

No clean way to do this, so with a little bit of hacking and a few cuts, we can pop out the inner plastic from the fabric shell, which is attached using snaps. The fabric shell looks like it is made from a combination of vacuum-forming, injection molding, in-mold textile application, followed by application of a soft-touch finish to give that smooth velvety feel.