User Experience

Seen above is the right half of the Sennheiser CX TWS installed on an artificial ear mold that is similar enough to my own average-sized ears. I used the pre-installed size M silicone ear tips for this photo and the rest of my testing. The fit was fine given the shells are still smaller than the average ear concha. These being IEMs, the ear tips go into the ear canal for further support, as well as the necessary seal to make the most of these earphones. Passive isolation is fairly decent, but consider aftermarket ear tips, such as the SpinFit CP100+ or final Type-E tips. These weigh ~6 g each, making them not at all physically fatiguing either. The IPX4 spill resistance makes these conducive for use in the gym or outdoors.

Battery life is a key metric for TWS earphones, and these promise 9 hours of use when fully charged, which is usually a best-case scenario at lower volume and in SBC/AAC mode. There is no ANC here, so battery life in practice was pretty close, around 8 hours more often than not on aptX and my phone at ~70% volume. The case also provides more than two charge cycles, so I had a total battery life of ~30–31 hours with the case. The fast-charging feature for the earphones is quite handy, too, though it is simpler to simultaneously fully charge both the depleted case and depleted earphones for ~2 hours, which would be enough for a few days of average use.

Audio Performance

Audio Hardware and Microphones

As is the case with most TWS earphones, Sennheiser is using a single dynamic driver per channel on the CX TWS. This time around, it is a 7 mm driver, which makes sense for this form factor, and Sennheiser mentions using a "TrueResponse transducer," which has a dedicated page with lots of words but nothing useful in terms of identifying the driver composition, let alone the rest of the items inside the acoustic chamber, including the surround, magnets, and any baffles or filters. There is no mention of the driver impedance or sensitivity either, with the rated frequency response of 5 Hz to 21 kHz optimistic at best. This is clearly a set made separately from Sennheiser's more audiophile-oriented business, which is something to keep in mind as we move forward.


There is no clarification on the exact wireless chipset at this time either, but Sennheiser has a more budget-oriented feature set that is missing some options, such as increased codec support and ANC. The mobile app is also an example of the bare minimum in some cases and plenty in others, so it's a middling scenario overall on the technological side. There are several pre-programmed touch controls on the earphones, some of which are customizable in the app while others are not. The actual execution is finicky, however, with occasional double taps mistaken as single taps and the sensor going from at times being too sensitive to barely responding at others. I also wish the microphones were better at picking up my voice for calls. While the two microphones do alright in a pinch, they are certainly not as good as some of the microphones on other recently tested TWS earphones.

Frequency Measurement and Listening

I will mention that I have a general preference for a warm-neutral signature emphasizing a slightly elevated bass and smooth treble range with detailed mids and good tonal separation. I also generally prefer instrumental music over vocals, with favored genres including jazz and classical music.


Our current testing methodology begins with a calibrated IEC711 audio coupler/artificial ear the earphones can feed into to where there is decent isolation similar to real ears. The audio coupler feeds into a USB sound card, which in turn goes to a laptop that has ARTA and REW running and these TWS earphones connected to the laptop through Bluetooth. I begin with an impulse measurement to test for signal fidelity, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/12th setting, which nets a good balance of detail and noise not being identified as useful data. Also, the default tuning was used for testing, and no app-based settings were chosen unless specifically mentioned. Each sample of interest is tested thrice with separate mounts to account for any fit issues, and an average is taken of the three individual measurements for statistical accuracy. I am also using the pinna mold fitted to the audio coupler for a separate test to compare how these fare when installed in an ear and cheek geometry and not just the audio coupler by itself. The raw data is then exported from REW and plotted in OriginPro for an easier comparison.


The IEC711 is such that you can't really compare these results with most other test setups, just within our own library of measurements. The raw dB numbers are also quite contingent on the set volume, gain level, and sensitivity of the system. What is more useful information is how the left and right channels work across the rated frequency response in the Sennheiser CX TWS, or its useful part. The left earbud was separately tested from the right one, and colored differently for contrast. I did my best to ensure an identical fit for both inside the IEC711 orifice, so note how the two channels unfortunately show channel imbalance in the bass region, with a maximum 3–4 dB offset between the two. It's not a consistent offset that could potentially be fixed separately, either, and the upper mids show more of the same to where the sound often seems biased towards the right side of your ears instead of being centrally placed. On the plus side, the response with the artificial pinna in place matches the more ideal scenario of just the coupler very well, which is a good indicator of how good the fit was in the ear mold compared to the ideal case of the coupler orifice. Keep in mind that with TWS earphones, the fit and signal strength from the source are quite important.


I will refer you to my frequency response measurement database: VSG.squig.link. It allows for users to easily compare my measurements to my preferred target for a better idea of what I personally like, as well as compare to other target curves at the bottom, inspect different segments, normalize based on SPL or at a chosen frequency, and easily compare other devices to each other. Sennheiser talks about delivering "superior audio with crystal-clear sound," in addition to hilariously claiming passive noise cancellation as a selling feature, which essentially all TWS sets have anyway. But the general trend here is the bass boost, so it is what I am judging the tuning by foremost.

There is indeed a bass boost here, with the two channels averaging a ~8.5 dB bass elevation at 50–60 Hz relative to the lowest point at 800 Hz in the mids. A good amount of bass elevation, it helps appreciate the lower frequencies, including with the likes of bass guitars and kick drums; however, there are a couple of caveats. The first is that the bass seems artificially higher owing to the mids being depressed in more ways than one, especially with the upper mids that don't track with the pinna gain compensation I want to see. Secondly, the sub-bass extension could be better since there is around a 2.5 dB decrease in SPL going from 50 Hz to 20 Hz, which is also felt when listening to the likes of electronic music and harder beats. It ultimately makes for a set that has a bass boost, but I do wish it were executed better. On the other hand, using EQ to boost it further to make more of a statement adds distortion past the +2–3 dB mark, so you might want to EQ the mids and treble instead if the lowered volume is fine by you.

The mids are.. lacking, to say the least. There is bass bleed into the lower midrange, which comes off slightly bloated and has forward-facing male vocals feels unnaturally loud even compared to the bass instruments we were just talking about. It's also a lethargic response with the leading notes hanging around past their welcome, which produces a general haze for everything else here. But the biggest culprit of all is the lack of pinna gain compensation that makes female vocals and some instruments feel hollow. It can create a sense of expanded space though, thus also tricking your mind into believing the CX TWS provides a wider soundstage for vocals. When I first listened to this set, I had this effect come up with podcasts in particular. So perhaps this is a somewhat welcome side effect for general media consumption with movies and podcasts.

The treble response is where I did use the integrated EQ to turn things down ~3 dB, as it's otherwise quite bright and even shouty when coming from the upper mids, which is a jump of nearly 10 dB in the space of 2 kHz. I am struggling to understand what this tuning is supposed to be good for since it not balanced and emphasizes some string instruments far too much over vocals and other instruments. Perhaps if you have a specific artist in mind who only works in a certain frequency range. Still, there is little to like here and plenty of room for improvement. The technicalities aren't any better, with this not being a set I'd classify as well-resolving either.


Seen above are the frequency response measurements for three other non-ANC TWS sets that were chosen because they cost around as much and come from relatively large brands, with the MOONDROP Sparks a deliberate choice because it remains the only well-tuned TWS set I have tested so far. It also costs as much as the CX TWS these days, making it the obvious choice for money while also offering more accessories and having a better app. The Cambridge Audio Melomania 1+ is an acquired buy still, but I would take it over the CX True Wireless despite its slightly higher price since it has a bass boost without compromising on the rest of the frequency response. The last set is final's recently released ZE3000 TWS that will be reviewed soon, which I have some issues with too (spoiler!). It costs even more the Melomania 1+, and in a theme here, I would once again take it over the CX TWS since I can still appreciate vocals and instruments and the pure bass there. Sadly for Sennheiser, the CX TWS might be the weakest showing from a major brand to date.