Sennheiser CX 400BT review: specs and price

The fit of the earbuds.

The first number of the IP rating refers to protection against dust, while the second number refers to protection against liquid. E.g. a first number of 6 denotes that it is completely dustproof, and a second number of 7 denotes that the device can withstand full immersion in water.

We consider a lower weight better because lighter devices are more comfortable to carry. A lower weight is also an advantage for home appliances, as it makes transportation easier, and for many other types of products.

True wireless devices have no cables connecting any part of the device together. This is an important distinction as some wireless earbuds have cables connecting the two earbuds together.

These earbuds come with wingtips that can be attached for a more secure fit. Wingtips come in handy for sports and other physical activities. When used correctly, they prevent the earbuds from falling off.

Resistance to sweat makes it ideal for use while doing sports.

The device is dustproof and water-resistant. Water-resistant devices can resist the penetration of water, such as powerful water jets, but not being submerged into water.

Devices with stereo speakers deliver sound from independent channels on both left and right sides, creating a richer sound and a better experience.

The waterproof depth rating indicates how well the device is protected against water ingress and water pressure. Devices which can withstand more water pressure are better for swimming or diving.

This type of device allows you to listen at lower volume levels, causing less ear fatigue as you don't have to crank up the volume to overcome background noise. Ideal for plane rides and morning commutes.

The device sits tightly in place, creating an acoustic seal which reduces background noise and prevents your music from leaking out.

The driver unit is the component that produces sound in the device. Bigger drivers are more powerful and can produce better bass.

The lowest frequency at which the device produces audio. The lower the low-frequency response, the stronger and juicier the bass.

The highest frequency at which device produces audio. The higher the high-frequency response, the clearer and crispier the treble.

Dolby Atmos is a surround sound technology that allows sounds to be interpreted as three-dimensional objects. By doing so, Dolby Atmos allows for immersive, 360-degree sound.

Impedance is the device’s electrical resistance to the current being pushed through it. The lower the impedance, the easier it is to get higher volume and requires less power.

Devices with a higher sound pressure level are generally louder when supplied with any given audio source.

Devices with neodymium magnets are lighter and more powerful than those which use ferrite magnets. They also have more bass and clear high notes.

The device's battery life (when in use) as given by the manufacturer. With a longer battery life you have to charge the device less often.

The battery life of the charging case as given by the manufacturer. A charging case with a longer battery life allows you to recharge your headphones on the go multiple times before having to recharge the case itself.

The time it takes to fully charge the battery.

Battery power, or battery capacity, represents the amount of electrical energy that a battery can store. More battery power can be an indication of longer battery life.

It supports a wireless charging standard such as Qi. To charge the device, you simply put it down on a compatible charging pad.

An indicator shows you when the device has low battery.

The battery can be recharged and used over again.

The USB Type-C features reversible plug orientation and cable direction.

Bluetooth is a wireless technology standard that allows data transfers between devices placed in close proximity, using short-wavelength, ultra-high frequency radio waves. Newer versions provide faster data transfers.

LDAC is a codec developed by Sony for Bluetooth audio. It is capable of a very high bitrate of 990kbps, which provides high resolution audio. It can also automatically adjust to a lower bitrate of 330kbps or 660kbps to increase stability.

aptx Adaptive is an audio codec for Bluetooth devices that is developed by Qualcomm. It has a variable bit rate (between 279kbps and 420kbps), which means it can adjust the bit rate for different scenarios, such as listening to HD audio or reducing interference from other devices.

aptX Low Latency is a codec developed by Qualcomm. It uses Bluetooth 5.0 technology to provide low latency audio (around 40ms), which is useful when you want to avoid audio lag (e.g. when playing games).

aptX HD is an audio codec for Bluetooth devices that is developed by Qualcomm. It supports high quality 24-bit audio (at a bit rate of 576kbps).

aptX is a codec used for transmitting audio wirelessly with Bluetooth. It is developed by Qualcomm, and supports 16-bit audio at a bit rate of 384kbps.

aptX Lossless is an audio codec for Bluetooth devices that is developed by Qualcomm. It supports high quality 16-bit/44.1kHz audio (at a maximum bit rate of 1200kbps). This codec provides CD-quality audio without any loss of data.

Latency refers to the time it takes for the audio signal to be transmitted to your headphones/earbuds. Lower latency reduces audio lag, and is particularly important when playing games or watching videos.

Ambient sound mode uses microphones to pass through ambient noises so that they can still be heard. It’s useful when you want to listen to music but also be aware of what’s happening around you, for example when you’re jogging but still want to be able to hear traffic.

Sensors can detect when they are removed from your ears so that the music is paused, saving battery life.

You can use the app to play a sound from your earbuds to help you locate them.

Fast charging technologies, like Qualcomm’s Quick Charge or MediaTek’s Pump Express, are used to reduce the time it takes to charge a device. For example, with Quick Charge 3.0, the battery can be charged to 50% in just 30 minutes.

Multipoint allows you to link to more Bluetooth devices and switch between them. For example you can easily switch calls from one device to another without having to manually disconnect and reconnect.

The device has an option to mute/unmute a conversation directly from the device.

A headset is one headphone or pair with a built-in microphone. Headsets can be used for apps that require communication i.e. Skype, games with voice chat, mobile phones, etc.

There is a control panel on the device body, so you can easily access the volume control or remote without having to interact with a cable or another device it's connected to.

When covered under the manufacturer’s warranty it is possible to get a replacement in the case of a malfunction. Note: This may vary by region.

More microphones result in better sound quality and enable the device to filter out background noise.

These microphones are designed to filter out background noise from the desired sound. Especially useful in noisy environments.

It's the 'loudness' of the sound that the microphone can pick up.

The highest frequency that the mic can pick up. Better for recording treble.

The lowest frequency that the mic can pick up. Better for recording bass.