The Involuntary Teardown of the WF-1000XM4 Charging Case

I was cycling back home from a Saturday brunch blasting the funky audio waves of Franc Moody through my best earphones to date, the Sony WF-1000XM4 earbuds. I got home and performed the ritualistic wallet, keys, phone, earbud case pocket haka. There was no earbud case present in my pocket. I retraced my steps and sure enough they had fallen out of my pocket in the middle of an intersection whilst cycling. Sure enough the form factor was now very slimline and design somewhat minimalistic with all parts having been cold rolled several times by the local neighbourhood SUVs. Here’s a great indepth teardown: https://www.qucox.com/sony-wf-1000xm4-teardown/. The housing was completely jodido (fucked), so this will be brief. 

The Housing

The outside of the case was a premium matte black plastic with a glossed plastic on the inside. The assembly of the all the components during use was very snug, with that solid dense feeling even though much of the plastic wall used was very thin <1mm. A piece of foam was embedded in the plastic to ensure the battery was safe from any impacts or the ever dreaded Lipo swelling. There were three magnets recovered (out an assumed total of four). These were extremely strong and had gathered many of the SMD components during the cold rolling process of the charging case. Likely neodymium, n52 grade.

The Circuitry

The circuitry was also jodido, so the only things of note we can see are the custom induction charging coil, the charging USB C port and the small 520mAh single cell Li-ion. Also there was a flexible ferromagnetic material inbetween the battery and the copper coil, to redirect/sink the magnetic field coming from the wireless charging emitter. Here’s an interesting article about electromagnetic lensing of radiowaves using a ferrite core: https://en.wikipedia.org/wiki/Ferrite_core#Ferrite-rod-aerial

As for the earbuds, these are by far the best noise cancelling earbuds I have ever tried with a sound quality that’s hard to match with any other earbud.