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Sennheiser CX 400BT True Wireless Review

Wearable audio and communication devices are near necessities in the modern world. Especially wireless earbuds that can deliver pleasing musical entertainment as well as keep you connected to the world around you.

Bluetooth earbuds occupy a huge portion of the market. Since smartphones are in practically every pocket, earbuds that can easily connect to your device are in demand. And there is a wide range of products that do just that.

Some are budget items, some are premium earbuds, and some fall somewhere in the middle. One of the mid-range options is the Sennheiser CX 400BT, a pair of high-quality earbuds built for convenience and audio excellence.

So, what are these earbuds all about? Let’s find out in our in-depth Sennheiser CX 400BT True Wireless Review…

Sennheiser CX 400BT True Wireless
Our rating:4.5 out of 5 stars (4.5 / 5)

The Build

Sennheiser has a reputation for building durable, high-quality microphones. This pair of earbuds reflects that commitment to high construction standards. They are tough and durable, even though the casings are plastic.

The appearance is minimalist and quite sleek. They come in either a black or white finish. The charging-carrying case is also compact and lightweight. The charging case also features a tough plastic housing and holds the earbuds safely and securely in place.

Additionally, the charging case has LED indicators that let you know the charging status. Yellow means the earbuds are charging, and a green light means they are fully charged.

A comfortable fit…

Likewise, the earbuds feature an ergonomic design with a slim profile. Indeed, they are quite small and lightweight. Each earbud weighs just six grams. Therefore, you can wear them for extended periods without fatigue.

Along with their ergonomic and lightweight design, there are four different sizes of silicone ear tips included. There are L, M, S, and XS soft silicone ear tips that allow you to find the most comfortable fit.

However, these earbuds do not have any IPX rating. Meaning they are not water-resistant and should not be used during workouts or exercising. Sweat could damage the internal components. These earbuds work best for commuting, traveling, or casual listening.

To top it all off, these come with a 2-year warranty.

The Controls and Connections

Every control is handled by simply tapping either the left or right earbud. This includes volume, playback, answering/ending calls, and activating voice commands. But, be aware that the touch controls can be overly sensitive.

Along with the touch controls, there is the Sennheiser Smart Control app. It is compatible with both iOS and Android devices. The app allows you to set up customized controls and voice commands. These earbuds can work with either Siri or Google Assistant.

Furthermore, the built-in audio equalization will adapt to the settings you choose. Of course, you can further adjust the EQ using the Smart Control app on your mobile device.

All the audio you need…

These earbuds feature advanced wireless operations using Bluetooth 5.1 connectivity. They support several codecs, including AAC, aptX, and SBC. Likewise, they support A2DP, HSP, and HFS profiles. This means you can listen to a variety of file formats. As well as enjoy streaming audio and video.

The Battery

Since these earbuds are made for extended listening, they have a long-lasting battery. The rechargeable Lithium-ion battery delivers up to twenty hours of continuous playback on a single charge. It takes 1.5 hours to fully charge the earbuds. But, the quick-charge function gives you one hour of playtime with just ten minutes of charging.

To charge the earbuds, you place them in the charging case. And connect using the USB-C charging cable, which is included. However, there is no mains adapter for the USB cable.

Another nice feature is the automatic on/off function. If they are not paired with any device after 15 minutes, they will switch off automatically. Also, they automatically turn off when placed in the charging case and turn on when removed from the case.

The Sound

Each of these earbuds employs a premium 7mm dynamic driver. The drivers deliver an excellent audio experience. The high-fidelity sound offers a natural mid-range, deep bass, and clear high-end.

They have a frequency range of 5Hz – 21,000Hz with an SPL of 94dB. The result is a well-defined, balanced, and full soundstage.

When it comes to taking and making calls, the microphone works well. It has a frequency response of 100Hz – 10,000Hz, which works to ensure your voice is clear and accurate.

Additionally, these earbuds feature passive noise-cancelling. It helps you focus on the music, but also helps to keep your conversations free from distractions.

Sennheiser CX 400BT True Wireless Review – Pros and Cons


  • Personal customization settings.
  • Comfortable and durable.
  • Excellent soundstage.
  • Passive noise cancelling.
  • 7mm dynamic driver.
  • Built-in EQ.
  • 20 hours of battery life.
  • Fast-charging feature.
  • Bluetooth 5.1 connectivity.
  • Support for aptX, AAC, and SBC codecs.
  • 2-year warranty.


  • Issues with Sennheiser app reliability.
  • Touch controls can be over-sensitive.
  • Not water-resistant.

Looking for Something Else?

Finding the right earbuds or headphones has never been easier. Simply check out our in-depth reviews of the Best Earbuds Under $100, the Best Headphones Under $200, the Best Wireless Bluetooth Headphones, and the Best Sound Quality Earbuds you can buy in 2021.

Also, take a look at our reviews of the Most Comfortable Earbuds, the Best Noise Isolating Earbuds, the Best iPhone Earbuds, and the Best Wireless Earbuds For Small Ears currently on the market.

Sennheiser CX 400BT True Wireless Review – Final Thoughts

When it comes to sound quality, we know Sennheiser will always deliver the goods. These earbuds are no exception. The 7mm dynamic drivers offer a superb high-fidelity audio experience. And the built-in adaptable EQ further enhances the quality.

With a range of useful codecs and compatibility with both iOS and Android devices, these are quite versatile as well.

Sennheiser CX 400BT True Wireless

While the Smart Control app may have a few flaws, the overall ease-of-use, comfort, and sound profile makes these earbuds a great option. They are not cheap, but neither are they expensive. You are getting good value at a mid-range price point, from a company that understands how audio should sound.

Until next time, happy listening.


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About Corey Hoffman

Corey is a multi-instrumentalist who has played in numerous bands over the years, some good, some not so good. He has also written countless songs and recorded five albums in professional studios across America. Today he is a hobby musician but still loves the guitar after over 15 years of playing.

He considers his writing as a way to share what he has learned over the decades with younger generations ad always can't wait to get his hands on the latest gear.

He lives just outside New York with his wife Barbara and their two German Shepherds, Ziggy and Iggy.

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