Sony WF-1000XM4: All the facts and rumours

In case you missed it last week, Sony's WF-1000XM4 was leaked on Reddit. Rather than just keep updating the previous post, I decided to make a new one with more detail and information. If another big leak occurs in the future, I will make a separate post.

In the first post, I made a quick design analysis of the earbuds, but now I was able to examine the photos more closely to get a better understanding of the design and comparing it to Sony's other TWS headsets and other TWS competitors, I created a new detailed analysis below:

Click on photo for larger size

These are the parts which I can identify right now. I am uncertain about the feed-back microphone location (more on that later), the charging pins and the proximity (infrared) sensor. The most logical place for both the proximity sensor and charging pins is the underside of the earbud, which is not in view in the leaked photo. Looking at the WF-SP800N and WF-H800, the WF-1000XM4 could use a similar design.

My guess is we will have WF-SP800N style charging pins and a WF-H800 style proximity sensor. My reasoning is this, the WF-H800 charging pins seems to take up a lot of space on the exterior and a big part of the PCB, since the pins appear to be an entire module attached to the PCB. The pins on the WF-SP800N, are identical in design as in the WF-1000XM3 and take up much less space on the PCB. The WF-XB700 pins are similar but look to be directly attached to the PCB, you can find them in this post.

WF-SP800N (L), WF-1000XM3 (C), WF-H800 (R)

As for the proximity sensor, the design of the WF-1000XM4 is similar to the WF-H800 which also has a flat bottom and this seems like the logical place for the sensor. Hopefully more photos will leak so we can get a better view of the design.

Feed-back Microphone

The WF-1000XM3 has this microphone positioned under the main driver. If Sony were to use a similar design on the WF-1000XM4, the hole for the mic would need to be placed at the edge where the bottom side joins the foam tip, like I have pointed out in the analysis at the top. I do not think this part would be in the ear canal like with the WF-1000XM3, so this would not be the best place for the microphone.

WF-1000XM3 - Source: 52Audio.com

Looking at 2 competitors, the Bose QuietComfort Earbuds and Samsung Galaxy Buds Pro, the placement of the feed-back microphone is slightly different. Samsung has a MEMS mic placed in front of the driver, where as in he Bose, a MEMS mic is positioned inside the speaker canal (see photos below).

Feed-back mic - Bose QuietComfort Earbuds - Source: 52Audio.com

Feed-back mic - Samsung Galaxy Buds Pro - Source: 52Audio.com

This is one solution, a MEMS mic is smaller and this might help fit everything in a smaller package, but I am unaware if such a design/implementation has any advantages or disadvantages versus an electret mic. This website has a breakdown of the advantages/disadvantages of MEMS vs electret mic. Once the WF-1000XM4 is released, maybe Sony will have pictures of the mics on the product page like the WF-1000XM3, if not, a teardown will confirm what type of mic is used.

Feed-forward Microphone

Moving onto the feed-forward mic, Sony used a regular electret mic on the WF-1000XM3, the Bose and Samsung earbuds both use MEMS for their feed-forward NC mics, so hopefully Sony will switch to MEMS for their feed-forward mic on the new model. But the round shape of the NC mic probably hints at a regular electret mic. Even the WH-1000XM4 still uses regular electret mics for both NC mics.

Turning to the call/voice microphone on the WF-1000XM4. I am sticking with my initial guess that the top hole is for the voice microphone. Using the WF-H800 as an example, if the position of the voice microphone is at the end of the earbud, then this would place it in the ideal position for voice pick up on the WF-1000XM4.

The WF-1000XM3 uses the feed-forward mic for both noise cancellation and for calls, this might be the one reason why the call/voice quality is not that great. If my assumption is correct and we are looking at dedicated microphone for voice, then the call quality should improve. The WF-H800 for example has moved to MEMS mic for voice as seen in the photo below. It would be great if Sony did the same for the WF-1000XM4.

WF-H800 Voice Mic - Source - 52Audio.com

Battery life

The battery life is rated at 6h, with an additional 18h from the case. This is identical to the WF-1000XM3, which has the same battery symbol on its retail box. The 6 hours refers to  AAC playback, with noise cancellation on but with DSEE HX off. So is the WF-1000XM4 battery life with AAC or LDAC? We can try to look at some recent Sony headsets for guidance. 

The retail box for the WH-1000XM4 shows 30h for battery life (same for WH-1000XM3). Looking at the available operating time for the XM4, 30 hours corresponds to 2 settings:

• LDAC, DSEE extreme off, speak-to-chat off, NC off
• AAC, DSEE extreme off, speak-to-chat off, NC on

The Sony product page notes the 30 hours is with NC on, so this means the 30 hr battery symbol is for AAC. If we look at LDAC with NC on, then that drops down to 24 hours. The drop of 6 hours is pretty significant, and I wonder if decent playback with LDAC will be possible on the WF-1000XM4. But then the WH-1000XM4 are much larger headphones, so perhaps not directly comparable to the WF-1000XM3.

Perhaps looking at the WI-1000XM2 for a battery life comparison is a better idea since it shares a lot of components with the WF-1000XM3. The retail box shows 10h for battery life and we have the following with 10 hours of playback in the guide:

• LDAC, DSEE HX off, NC off, ambient sound off
• AAC/SBC, DSEE HX auto, NC off, ambient sound off
• AAC/SBC, DSEE HX off, NC on 

The product page for the WI-1000XM2 mentions:

Max. 9 hours (NC ON), Max. 10 hours (Ambient Sound Mode), Max. 13 hours (NC OFF)

This does not correspond to anything from the guide, so a bit confusing. Comparing playback with LDAC and AAC and NC on, there is only a difference of 0.5hr on the WI-1000XM2. So perhaps LDAC playback will be possible on the WF-1000XM4 but I do not expect 6 hours, maybe 4-5 hours? It is unknown if Sony will use the same MT2811 chip for Bluetooth and keep the QN1e. The QN1e is more power efficient than the QN1 used in the WI-1000XM2, so that should help with battery life, but I guess the LDAC codec is a bit more power hungry than AAC. which is already quite power hungry versus SBC from what I read online.

Codec Support

Both AAC and SBC will be supported, the presence of Hi-Res Wireless logo suggests we will have LDAC support. Qualcomm's aptX is unlikely, because Sony has their own Hi-Res codec. It is unknown if LDAC support will be all 3 versions (330, 660, 990) or be limited to 330 as what I was told in 2019.

So what about LE Audio support?

This is a good question. If you have not heard of LE Audio, then check out here for more information about the new codec coming to Bluetooth 5.2 headphones this year. There was no information on the sleeve that would indicate LE Audio support so who knows if it will be offered, but the sleeve/box was still in validation and not the final design. There is no specific date when Bluetooth SIG will begin certifying new products with LE Audio, it looks like it should be around the middle of this year judging from this article. It is unknown if Sony will wait for the full 5.2 spec to be released before submitting devices for certification or they will submit earlier.

What is LE Audio?

LE Audio uses the LC3 codec which is lower power and higher quality than SBC but it requires Bluetooth 5.2 support. The new codec is said to also offer lower latency and Multi-stream which will allow the transmission of multiple, independent, synchronized audio streams between an audio source device, such as a smartphone, and one or more audio sink devices. So basically independent audio streams to 2 wireless earbuds. I think this is similar to Airoha's MCSync, but I have no idea how MCSync works and what tech it uses. The Mediatek MT2811 also uses MCSync. Multi-stream, together with Broadcast Audio and Audio sharing uses LE Isochronous Channels, which is part of Bluetooth 5.2. 

So what has all of this to do with the WF-1000XM4? Well that depends if Sony will use the Mediatek MT2811 again in the new headset. The MT2811 has been certified for Bluetooth 5.2 on Bluetooth SIG, and in the support layers, "Isochronous Adaptation Layer" is mentioned, which are the LE Isochronous channels.

Likewise, Airoha chipsets, the AB1552 (found in the WF-XB700) and the Airoha AB155x (MT2811 in different clothing) also have been certified for Bluetooth 5.2. But these are just the chipsets and not actual devices/headphones. 

So does this mean the WF-1000XM4 will ship with LE Audio support? I do not know, it would be a fantastic selling point, but it all depends when the new model will be introduced. If Sony releases it earlier, May/June, I feel LE Audio support is less likely, but if an August/September release occurs, I think LE Audio is more likely. But this is only my guess and perhaps we will learn something in the FCC filing when that appears.

One question I have is can a headset be released without LE Audio support, but on Bluetooth 5.2 then have a firmware update to receive LE Audio support? I would imagine it would have to go through a second certification process?

Water resistance

I have been in contact with Key_Attention4766 from reddit, and they mentioned that the manual has something in it about an IP rating, but I am still waiting for a reply about what is written in the manual. Like the WF-1000XM3, the new Mark 4 are not sport headphones, so I would imagine we would be looking at IP4 rating like the WF-XB700, but I could be wrong.

While I was able to see more of the retail box, I was told the box/design is still in validation and should be approved in April or May, with production starting shortly after. The one thing that I saw that was of any interest was the accessories.

Supplied accessories: Earbuds (S, M, L X2), Charging case, USB Type-C Cable (USB-A to USB-C) (20cm)

Release date

If production of the retail box is slated to start in April/May, I would imagine this would also include he headset, but even if it was a month later, that could still push the retail date to late Summer, or early Fall. This could be ideal as LE Audio could be included, but not sure what Sony's priority is, features or getting it out on the market. A worse case scenario would be Holidays 2021. We have to wait for some certification filings around the web, since that would help give an estimate of when we could see the WF-1000XM4.

This concludes the post. Until receive more information from the original poster on reddit, or someone else leaks something, we will have to patiently wait for the FCC filing. While the FCC filing will not reveal much, it might reveal if LE Audio was tested for. As always leave any comments, corrections in the comments. If anyone wishes to contact me with more information about the WF-1000XM4 or other unreleased Sony products, you can check out my Contact page for details.