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Lifewire / Jason Schneider
Truly excellent sound quality
Fairly decent battery life
Pretty affordable when on sale
aptX codec included
Less-than-premium build quality
Limited, no-frills feature set
The CX 400BTs are one of the best sound experiences you can find in the true wireless space, but the rest of their features leave something to be desired.
Sennheiser provided us with a review unit for one of our writers to test. Read on for the full review.
The Sennheiser CX 400 BT true wireless earbuds are a pair of earbuds from an audio giant that try to master the fundamentals without adding all kinds of bells and whistles. In a space where wireless earbuds are trying a lot of features to differentiate—from Qi wireless charging cases to active noise cancellation—it’s rare to see something simple. Instead, the CX 400s keep cost down while providing a rich, impressive sound response that will impress even the highest expectations.
You’ll get a lot of the features you expect, to be fair, including premium Bluetooth codecs to support the excellent sound quality and decent, though not mind-blowing, battery life. But the name of the game here is clean, high-quality audio, and I wanted to see if those promises hold true. So, read on for my hands-on review that explores how they hold up against their more full-featured competitors.
I’ve never known Sennheiser to be the top dog in visual headphone design. Many of their pro-level studio earbuds go for large, bulky builds rather than the sleek, streamlined look of other competitors. The CX 400s are made of matte plastic that doesn’t feel overly premium, and the outer edge has a glossy plastic plate on it with the silver Sennheiser logo.
The most prominent aspect of the design is the shape. When looking straight on from the outside, the CX 400s sport a square shape with rounded edges, unlike the rest of the true wireless market that opts for circular or oval designs. While this shape does give the earbuds a singular look, it appears pretty boxy and bulky when you put them in your ears. The design also has some implications for how the earbuds rest inside your ears, but I’ll cover that in the comfort section.
Even the battery charging case is pretty square, though its size and profile feel pretty good. The key point here is simplicity, and not necessarily in a good way. If you want earbuds that look expensive, these really aren’t it—which makes sense, considering these are on the cheaper end of Sennheiser’s catalog.
I’ve tried one other pair of Sennheiser true wireless earbuds (the first generation of the Momentum wireless earbuds), and the fit and feel of the CX 400s is actually very similar to those. Most of the earbuds’ construction sits inside the cube-esque enclosure, with just a small circular ear tip jutting out. You’re meant to find the right size fit for the ear tip (there are three sizes included in the box) and rely on its seal to keep the earbud in place. The larger enclosure is then slightly contoured to rest against the inside of your ear.
In the case of the CX 400s, this fit isn’t exactly perfect because the squared-off design doesn’t have a shape that will necessarily fit with everyone’s ears. I personally prefer an earbud fit that employs a secondary grip point (like a rubber wing), which isn’t present here, and as a result, these earbuds don’t feel terribly comfortable to wear for long periods. I’m frequently feeling as though I have to press the earbuds back into my ears, which isn’t ideal in general, but is especially annoying because these earbuds use touch controls right where I press to adjust the earbuds. But, for some ear shapes and sizes, these might be fine.
The larger enclosure is then slightly contoured to rest against the inside of your ear. In the case of the CX 400s, this fit isn’t exactly perfect because the squared-off design doesn’t have a shape that will necessarily fit with everyone’s ears.
Their minuscule 6-gram weight (per earbud) does make them pleasantly light, so if you aren’t picky on the shape, the CX 400s aren’t a bad option.
The feel of the plastic that Sennheiser has chosen for these earbuds is a little hard to wrap my head around. On the one hand, there’s little concern that these earbuds will scuff and scratch in any meaningful way. But, on the other hand, it is a thin, inexpensive-feeling plastic that covers the case and most of the enclosures. This does benefit the earbuds as they are lighter than something more substantial, but I’d have preferred the sportier-feeling Bose plastic you’ll find on the QuietComfort and SoundSport lines.
Sennheiser’s Momentum earbuds go for a woven, cloth-like covering for the battery case, which goes a long way toward making the whole package look and feel premium. While the CX 400 case’s lid doesn’t open easily, it does have a satisfying click when it snaps shut, and the magnets that suck the earbuds back into the case feel plenty strong. So, interacting with the earbuds feels befitting of the price, though not overly premium. There’s also no official IP rating, so you shouldn’t plan on wearing these in heavy rain, but I’d imagine they’ll work fine for a workout.
The true standout feature of the CX 400s is the sound quality you get, which isn’t exactly surprising considering Sennheiser’s prowess in this category. On paper, there’s a lot to like about these earbuds. At a range covering 5Hz to 21kHz, this is one of the widest frequency responses I’ve seen on earbuds of this category and size. The marginally larger 7mm drivers in each earbud are tuned specifically by the Sennheiser team, and they do feel extremely deep and powerful for the form factor.
Listening to these earbuds, I can confidently say that most of the money you’re spending is going toward a positive listening experience.
Sennheiser also promises less than 0.08 percent harmonic distortion within the drivers themselves, which is quite a bit better than most other earbuds in the category (though this particular spec is affected by the nature of Bluetooth transmission anyway).
Listening to these earbuds, I can confidently say that most of the money you’re spending is going toward a positive listening experience. Music of all kinds sounds completely natural but has a nice sound floor to live on, so it doesn’t quite feel as flat as is sometimes the case on earbuds. Spoken word is also nice and clear, making for a solid podcast and radio experience. Even the on-board microphone, which is only on the right ear (and isn’t even a big part of the marketing materials for these earbuds), makes for an impressive phone call experience. This last point is particularly important when so many people are working remotely and conducting video meetings.
Overall, these earbuds really are a home run for sound quality, even without the extra bells and whistles like active noise cancellation or transparency modes.
The CX 400s sit right in the middle of the range for battery; they offer neither the best nor the worst battery life. Sennheiser claims you’ll get about 7 hours on a single charge in the earbuds—a respectable total that will get you through your commutes and a full workday—and you can add an additional 12 or 13 hours with the battery stored in the case. When the best earbuds offer a full battery life of 25+ hours, but the worst hover around 12 total hours, this 20 hours of use is totally reasonable, albeit a bit lackluster.
Truth be told, my expectations were low because when I reviewed the Sennheiser Momentum earbuds recently, the borderline abysmal battery life was one of the worst features on the earbuds. It’s nice to see that even though Sennheiser has shrunk the case significantly here, they’ve increased the battery life.
In keeping with the focus on great sound quality, the Bluetooth technology packed into these earbuds fully supports the experience. Bluetooth 5.1 protocol is the driver of wireless connectivity here, meaning there’s support for multiple devices, a solid 30 feet of wireless range, and a really solid connection in practice. I was impressed with how unwavering the connection felt, though I did note one hiccup when connecting them to my laptop for the first time. A quick re-pairing (by pressing on both the earbuds simultaneously) was enough to get them connected again.
In keeping with the focus on great sound quality, the Bluetooth technology packed into these earbuds fully supports the experience.
All the standard headset and playback profiles are here, including A2DP, HSP, and HFP. When it comes to codecs, you’ll also get the standard and lossless SBC and AAC options, but if your device supports it, aptX is also an option. This clever codec developed by Qualcomm allows for your music to be compressed and transmitted with less detriment to the source file quality and a little better latency. This is really helpful when your earbuds are meant to sound great because it means that more of your source music is intact when it reaches your ears.
When it comes to codecs, you’ll also get the standard and lossless SBC and AAC options, but if your device supports it, aptX is also an option.
There’s really not a lot to talk about here. The controls available on the earbuds are touch panels on each ear, with a tap on the right earbud calling up voice assistance and a tap on the left earbud pausing your music or answering calls. You can customize some of this in the app, but overall you get the expected controls. There’s one button on the battery case, but oddly it doesn’t activate pairing mode. It is instead just an indicator button to monitor how much battery is left in the case.
You’re afforded a bit more control with the Sennheiser Smart Control app, but it is a bit more simplistic than some of the other apps out there (I’m looking at you Sony). I do like how Sennheiser handles the EQ here, giving you a traditional, curve-based graphic EQ and a slider-based option as well for versatility. While I love the sound of the earbuds right out of the box, it’s nice to have the option to up the bass if you prefer it a little heavier. You can also customize what tapping on the earbuds does and even activate a mode where the earbuds will automatically accept a call when you take them out of the case while your phone is ringing.
At a list price of $200, the quality and value of the earbuds feels about right. However, at the time of this writing, you can get deals ranging from $149 all the way down to $129. These prices make the excellent sound quality all the more compelling. To be fair, $199 is totally reasonable considering the battery life and the brand name, but if you can hold out, you’ll likely save a few bucks. It would have been nice to see slightly more premium materials at play, like a higher-quality plastic, but this is a small gripe for an otherwise solid package.
Because the price is so similar between the two, the most natural comparison to the CX 400BT is the true wireless product that started it all: Apple Airpods. You won’t get active noise-canceling with either, you’ll have to learn touch controls with both, and the connectivity is decent for each as well. You will get notably better sound quality and a more customizable fit (thanks to the changeable eartips) with the CX 400s, but the AirPods feel much more premium and will work more seamlessly with Apple devices.
A solid but simple earbud offering.
The Sennheiser CX 400 BT earbuds manage to be both a really compelling true wireless offering and a totally unexciting pair of earbuds. They do all the important things right: solid sound quality, decent battery life, and all the modern connectivity you could want. But there’s nothing to get pumped about. You won’t find ANC available here, nor will you get a premium look and feel. But that might not be important for you, and if what is important to you is great sound quality, then the CX 400s carry Sennheiser’s impressive legacy very well.
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