Sennheiser CX 400BT True Wireless [Review]

Sennheiser announced the latest edition to its in-ear personal audio offerings, the CX 400BT True Wireless, earlier this month. Following the release of its higher priced MOMENTUM True Wireless 2, this product aims to be an accessible, everyday iteration of its earbuds and True Wireless technology, seemingly targeting the commuter and city dweller as its customer..

The brand also celebrates its 75th anniversary with the release of a special edition of its HD 800 S headphones.

So how does this model shape up to its specs?

Nuts and Bolts

It's no surprise that a revered legacy brand like Sennheiser would provide tangible quality in one of its latest products. Here, the earbuds case feels weighty in the hand. The beveled magnetic charge case is a comfortably fitting piece in the hand to signal its holistic ergonomic design. This comfort extends to the feeling of these in-ear.

It's quite satisfying to feel that pull back and hear the click of the CX 400BT True Wireless in their charging case. As these charge, the light on the back of the case glows amber, and of course, stays a stationary green when charged. They charge with a USB C connection, which while annoying at its advent, provides a nice all purpose option for new electronics as you add them into your collection. For me, that started with my last pair of wireless headphones and moved onto adapters, new computers, and now this.

Overall, this setup is more than intuitive, with almost no need for reading instructions (though I did, and you should, as a precaution).

Thoughtful Features

These earbuds take into account the seriousness we assign to the media we consume. If we connect to a show, podcast, DJ set, movie or otherwise, we want to make sure we aren't missing anything along the way. These earbuds connect to your device, then waits until you have placed the product into your ears before it launches its autoplay. A small feature in theory, but keeps life smooth in practice.

Though the instructions indicate a simple 3-second hold of the headphones will allow for connection, mine did it automatically. And just the sound of the soothing voice announcing, with clarity, “pairing,” and “connected,” on the other end, was a brief but strong indication of the sound quality I was about to become immersed in.

Sound Quality

The CX 400BT are defined by Sennheiser's proprietary high-end acoustic audio technology, True Wireless. This means 7mm dynamic drivers, which in layman's terms, offers that warm sound we often associate with technology like vinyl. It also includes an internal equalizer, the latest Bluetooth 5.1 technology, along with compatibility with the latest audio compression standards AAC and aptX. In practice, this translates to crispness, defined, but not glaring, lows and highs. If you download the Smart Control app, you can also adjust the internal equalizer to your liking.

I dove straight in with a melodic electronic track from Dirty South, where the finely tuned entrance of beats and drops are felt on the receiving end as intended, I imagine. The sound quality creates room for the nuance of great production, blank spaces of silence, whether in a song or on a podcast.

The CX 400BT aren't technically noise canceling, but they do provide a dampening of outside noise that is enough to make a difference. This function, too, is controllable through your right ear bud.

Daily Use

As I attempted to adjust the headphones, I realized a tap pauses the music. It’s like a mini track pad on the outside of these headphones, with the heft signaling quality. The Smart Control app boasts its customizable touch controls, but it's a bit limited in its offering beyond fine-tuning your sound.

Competitive reviews the CX 400BT True Wireless call out that they’re not waterproof, but from experience, they do seem to be waterproof enough to work out with. I found some issues seeing them as the best for a full body workout, as the sensitivity of the track pad led me to constantly have to stop and cancel out the launch of Siri, a function that's included with one tap, every time my arm grazed my right ear.

Battery Life

The CX400BT promises 7 hours of battery life that can be extended to 20 hours with a charge, and they deliver. Man, did I try to test the battery on these earbuds: accidentally left them outside for the charging case for days on end, set out to use them for the entire day, left them connected to devices, but not in use for house. The result? Impressive compared to other earbuds. After returning to them as they were left out, I found that they had lost nearly no battery life. After using them for an entire workday, successfully switching from device to device, the promised 7-hour battery life surpassed expectations, barely hitting 50% by day’s end. After leaving them out overnight connected to my phone, they had shut off their connection properly to conserve battery. Throughout these tests, it became clear that the battery case itself holds a charge for an impressive amount of time.

Final Call

These headphones are the best you can get at this price. Access to Sennheiser's quality might normally feel out of reach, but if you're looking for everyday wear with amazing audio, this is where to start.