Sony WF-1000XM4 teardown by 52Audio

We finally have a full teardown of the new Sony WF-1000XM4, time to see what secrets it reveals. The teardown was performed by 52Audio.com. Prepare for a long post and lots of photos.

First a close up of the new earbud tips.

source: 52audio.com

My Sony XBA-A3 tips also use polyurethane foam in the middle but I with regular silicone rubber on the exterior. Looking at the WF-1000XM4 tips, they appear o be a different material than rubber. Maybe someone can confirm this in the comments.

I looked at the notes in the Sony's help guide for the tips and I am kind of alarmed from what I read. For instance:

Do not subject the polyurethane foam portion of the earbud tip to pressure for over long periods of time. It may cause deformation and it may be difficult to return the earbud tip to the original shape.

Hmm, what does long periods of time mean? Hours? Days? The longest one can use the earbuds nonstop is 12 hours, so beyond this time the deformation occurs? In addition Sony states that through long-term use and storage, the tips may deteriorate. Understandable, things wear out, but does Sony (outside of Japan) offer these earbuds for purchase once you need to replace them? If not, I suspect users will be importing them from Japan or other areas where these replacement tips will be sold. The replacement tips are the Sony EP-NI1000, I only see them on Amazon Japan, but not sure if these can shipped outside of the country.

           

Finally I will point out something important from the guide, do not use any detergents, alcohol or other cleaners to clean off the tips, only use a dry cloth. I have seen a reddit post where an individual used rubbing alcohol to clean the tips and this damaged them quite severely.

Looking at the feed-forward microphone hole, 52Audio says the design is special to minimize wind noise, and if wind noise is detected, the earbuds will turn on wind noise suppression. I do hope dirt and grime do not build up in the holes because the do not look the easy to clean.

source: 52audio.com

Charging Case

Looking with the bottom removed, we can see the wireless charging coil. While I have seen some users attaching a USB type-C wireless charging pad to their WF-1000XM3 and then covering them in a case, I wonder if it would be possible adding such a coil to the inside of the original case?

I wonder if such a coil could be added to the WF-1000XM3? I know there are wireless charging coils that connect via USB type-C, so perhaps that could be somehow integrated into the WF-1000X3M3 inside the case? But that is an idea for another post.

source: 52audio.com

In this post, I speculated the coil would be soldered to the PCB and the battery in the case could be disconnected for replacement, looks like I was right.

source: 52audio.com

I would have preferred if Sony used a connector for the wireless charging coil as well, easier/quicker assembly and repairs but I understand that most people would not be replacing the this part often, unlike the battery which can just be unplugged and might need replacing in the future.

The battery is rated at 3.85V 2.0Wh (520mAh), the WF-1000XM3 battery in comparison is rated at 4.2V 2.59Wh (700mAh). The model is SP702428, meaning 7.0mm tall, 24mm wide and 28mm long. There does not appear to be much extra space around the battery, so I doubt a larger one can be installed. Looking at Aliexpress, I could no find any battery with similar dimensions.

source: 52audio.com

While you can just unplug the battery from the PCB, there is a surge protection PCB attached to the battery which must be replaced or come with the replacement battery. I would imagine most replacement batteries, especially from Sony would ship with the surge protection PCB.

source: 52audio.com

And now looking at the PCB. The upper portion of this PCB is the power management and the lower portion for the wireless charging according to 52Audio.

1. Texas Instruments BQ25618 charging IC
2. Renesas Electronics IDT P9222-R
3. Texas Instruments TPS6124x
4. 2047 323 input protection chip.
5. Voltage regulator - Mitsumi A33

The other side of the PCB has one main large chip, NXP K32 L2 MCU. This apparently controls the case functions like charging, discharging, battery power management, headset communications, etc. 52Audio claims it is a custom chip designed for Sony.

source: 52audio.com

Headset

Opening up the earbuds, we can see that the 2 PCBs are connected using a board-to-board connection. In addition, we can see the black rubber seal ring to keep moisture/dust out. This black seal is absent in the WF-1000XM3 for those curious.

source: 52audio.com

The new earbuds do no leave much room for anything extra and utilize the interior space as much as possible. The board-to-board connection will help with manufacturing and repairs.

source: 52audio.com

With the components removed, we can see the holes/openings for 2 microphones, with #1 for the feed-forward microphone and #2 for the voice pickup mic. The holes are covered by what 52Audio describes as a waterproof membrane, but I would imagine sound can still pass through the membranes. In addition, we can see the 2 contacts for the Bluetooth antenna which is printed on the black plastic underneath which also houses the touch sensor. It looks like the inner plastic piece is held in place with 2 clips which can be seen at the top and bottom of the inner earbud housing. Unfortunately 52Audio did not remove this piece in their teardown.

source: 52audio.com

In this photo we can see the new Bluetooth SoC, the Mediatek MT2822S. This chip is what Sony is calling the Integrated V1 Processor. The 2 arrows on the left show the contact points for the Bluetooth antenna and the arrow on the right shows the hole for the voice microphone.

In the original post, I was not sure what the chip on the reverse side was but now with this teardown, we have it confirmed. The chip turned out to be a memory chip, Winbond W25Q128JW. I assumed that the on chip memory would be enough for Sony, but I guess not.

source: 52audio.com

The inter-board connector board has the feed-back microphone connector (yellow arrow) and on the underside has the battery connection (red arrow). Not sure what the black material is, could be adhesive to keep the battery in place.

source: 52audio.com - click for larger size

The battery has changed, from Varta to Zenipower. This is not the first time  Sony has used a Zenipower battery, the WF-H800 also uses one, the Z55 (3.7V, 0.24Wh). The WF-1000MX4 uses a Z55H, rated at 3.85V and 0.29Wh, which if converted to mAh, yields 75 mAh. The WF-H800 converts to ~65 mAh, and the original WF-1000XM3 Varta battery was rated at 60 mAh. I am unable to find any datasheet for the Z55H, so I have contacted Zenipower for a datasheet, but I doubt I will receive a reply.

source: 52audio.com

Going further, there is more black material, probably tape/adhesive since the battery is positioned here. The yellow arrow shows the bone conduction sensor and the red arrow shows the other battery contact terminal.

source: 52audio.com

The underside of this PCB has the infrared proximity sensor (yellow arrow) and the connectors for the speaker assembly (red arrows). More of that black material here as well, probably adhesive to keep the driver assembly in place since this is where it sits.

source: 52audio.com

Next up we can see the speaker assembly and the contacts that connect to the ones on the PCB above. On the left of the photo, we can see the magnet that assists in attaching the earbuds to the case.

source: 52audio.com

I tried to outline how it all attaches using the press photo Sony provided when the headset was released. The speaker connecting wire is now printed (integrated) into the plastic piece, winds to the top and connects on the inside to the driver assembly/unit. This is similar to how the Bluetooth antenna is integrated to the touch sensor piece, using a process called Laser Direct Structuring. In the previous generation WF-1000XM3, Sony required 2 separate wires to attach the driver to the PCB. This new method helps not only with manufacturing, but also packaging of components.

Next up is the feed-back microphone. In the new model it is attached to a ribbon cable which slots into a connector on a PCB, this saves time since it does not require the person assembling the headset to solder any wires, which was the case on the WF-1000XM3. Like the previous 2 microphones, this one is also a MEMS type.

source: 52audio.com

So together with the driver assembly, Sony has been able to eliminate a total of 4 wires per each earbud that required soldering to attach the driver and feed-back microphones to the PCB. In addition, the components can now be much closer together and therefore more of them can fit inside.

And finally the driver unit/assembly. Even though the size remains 6mm, 52Audio measure the entire driver assembly (with metal casing) to be 7.3mm, so larger for sure, but I would imagine the driver is still 6mm. Unfortunately there are no straight on photos of the WF-1000XM3 driver, only the back side, so it is difficult to compare the actual drivers directly.

source: 52audio.com

While there is a membrane visible, it is not coloured but clear unlike in the WF-1000XM4 promo video. Notice that on the perimeter of the driver housing is black tape/material which helps seal the headset from water/dust. The corresponding seal can be seen on the inside of the earbuds in the photo below.

source: 52audio.com

    

Conclusion

Comparing this teardown to the WF-1000XM3 teardown, quite a lot of changes are visible. For one, all microphones are MEMS, and there is significant water/dust-proofing throughout the earbuds. We know there is no separate NC chip like the WF-1000XM3, but an integrated Bluetooth SoC but that was something I discovered in the original post. 

To help with manufacturing, Sony has opted for a lot more ribbon cables and board-to-board connectors and eliminated regular wires where they could. In fact, I do not think the earbuds have anymore individual wires, where as the WF-1000XM3 had 4 per each earbud. Likewise all the power management which was on a separate Mediatek chip is now all controlled by the Bluetooth SoC.

The battery capacity is slightly larger and it looks like there is a lot more tape/adhesive holding the battery in place versus the WF-1000XM3. Looking at the entire design, it seems like a major improvement with regards to less parts, more compact, and easier assembly. The quicker and easier Sony can make these, the more they can produce, but the parts shortage is definitely not helping with some regions having the model delayed from what I have been reading on reddit.

That is all for the teardown, if anyone notices anything else interesting, please leave a comment below.