JBL Synchros S400BT Review

Superior Sound On The Move

JBL Synchros S400BT Review

If you´re looking for high quality, easily transportable and comfortable headphones with which you can enjoy music on on the go, you owe it to yourself to take a closer look at JBL's Synchros S400BT.

Now, JBL is offering a wide variety of in-ear, on-ear and over-ear headphones, but it can be hard to know which one will suit you best, and figuring out what additional options you need - such as compatibility with iOS or Android devices, if they have a built-in microphone for phone calls, etc. - will make it even harder.

In this review we check out the middle model in JBL's Synchros series, the S400BT, which has support for bluetooth aptX technology and NFC for quick pairing with phones and other compatible bluetooth devices. We used phones, computers and bluetooth transmitters during the test, some with aptX as well as NFC.

JBL Synchros S400BT test


S400BT comes in a well made cardboard box adorned with a CES Innovation Award badge. The carrying case inside the box is an elegant black case made of synthetic leather with a zipper - on one side is the JBL logo, and on the other it says Synchros. This case is quite compact considering that it contains a pair of headphones. JBL S400BT have two joints that can rotate and be folded to make the headphones smaller and more portable, about the size of a hand. The headband is made of stainless steel, and can be extended about an inch on both sides in 14 steps.

When unfolding the headphones from the folded position you will hear a nice 'click', and although the S400BT at first glance does not look like they are foldable, it is a nice feature that adds to the portability. The build quality is commendable and the robustness of the headband, hinges and earcups is fantastic. The padding on the earcups is very comfortable and we never experienced any discomfort even after several hours of listening to music.

The first question you ask yourself when you open the box is - where´s the cables? Two cables and the instruction manual are located in the bottom part of the box, and it´s almost as if JBL wanted to emphasize that cables are not required. One cable is a classic 3.5 mm plug (both ends) used to connect the headphones to the source device when the battery is empty. The second cable have USB on one side and a 3.5 millimeter jack on the other, and serves only to recharge the built-in battery.

JBL claims that the headphones will work up to 15 hours with a full battery. It is a drawback that both cables utilize the same 3.5mm port at the bottom of the left earcup, which means that it is impossible to charge the battery and listen to music via a cable at the same time. In addition to the input on the headphones are two small buttons, one to turn the headphones on and off, and one for bluetooth pairing. There is also a small hole for the microphone for phone calls.

JBL Synchros S400BT touch control
JBL Synchros S400BT headband

Take Control

On the earcups are backlit white circles that reminds us of the ones you find on some of Harman Kardon's AV receivers, so we assume that these headphones utilizes the same type of technology. We advise you to have a look at the manual before you start using the headphones so you understand how they operate.

JBL Synchros S400BT control

The volume of the music is adjusted by swiping a finger from the bottom and up on the left earcup. In the same manner the volume will be reduced if you swipe your finger from the top and down. If you stop and hold the finger after swiping it, the volume will change as long as you do not remove your finger. To go to the previous or next track you simply swipe your finger from right to left or left to right, respectively. If you press the middle of the left earcup you pause the music or answer a phone call. If you keep pressing a little longer, the call will be rejected.

This may feel a bit weird and complicated at first, but it´s really not once you get used to it. Controlling these headphones is actually fun. We have noticed that some people don´t like this idea because of the possibility of accidental clicks, but we did not have such problems. The right earcup has no control functionality, but it contains the NFC tag, and if you want to pair a bluetooth device using this technology you need to hold it close to the right earcup to establish a connection.

JBL Synchros S400BT white
JBL Synchros S400BT black


As mentioned, we tested the JBL Synchros 400BT on different bluetooth devices with the bluetooth aptX codec and the pairing was very quick and painless. We also played a large selection of music from a PC using both a bluetooth transmitter and a dedicated headphone amp/DAC. We listened to music in FLAC format of the highest possible resolution, but also checked how the S400BT handled compressed files like MP3 – they sounded just fine.

We started with some high resolution (96/24) audiophile tracks with classical music. We loved it! Space, airiness and soundstage was well presented, but we immediately noticed that Synchros S400BT have the same problem as most 'modern' headphones - too much bass for our taste. The spaciousness and the beautiful stereo imagery sounded great when we listened to some classic pop, and listening to some hard and heavy metal tracks proved that these JBL's can handle almost anything and reproduce the intention and soul of the music quite adequately. All in all, we are delighted with the sound quality, except that we would recommend a bit of adjustment on an equalizer to reduce some of the bass.


JBL has made a fantastic product - sound quality is superb, and the build quality and design even better. We´re still trying to figure out why so many from the younger generation listen to Beats when you can have headphones like these. S400BT are practical, can easily be carried in a bag, are very comfortable, and a joy to use thanks to the bluetooth capabilities. It is known that bluetooth has limited bandwidth, but thanks to the aptX codec we can still enjoy CD-quality sound. Interruption and break-up in the transmission was never a problem even as we went to another room with a distance of 20 to 25 feet from the source device, so you will not have any problems if your phone is in your pocket. In other words, JBL Synchros S400BT gets a serious recommendation from us.


  • Current Price: $75.00
  • Ends: Jan 17, 2018 19:43:59 CET
JBL S400BT - On Ear Premium Bluetooth Stereo Headphones
  • Current Price: $159.99
  • Ends: Feb 9, 2018 10:15:37 CET
  • IN ThE bOX
JBL Professional Audio Sound with PureBass Performance and aptX encoding.

Sound modeled after industry leading JBL professional audio speakers delivers a balanced audio experience with amazing clarity and deep powerful bass, while advanced aptX encoding lets you experience the highest possible wireless sound quality available.

Bluetooth® 3.0 wireless freedom with innovative touch sensor controls and NFC technology simplify the user experience.

Wireless technology liberates you from the hassles of wires, while NFC technology on the right outer earcup simplifies the Bluetooth pairing process. The innovative touch sensor controls on the left earcup enable you to advance tracks, adjust volume, and play or pause your music, as well as take your calls – all with an easy swipe of your finger anywhere along the earcup’s surface.

Unique LED Lighting Feature

A unique LED lighting feature responds intuitively to every adjustment made to your headphones’ touch sensor control system, following the direction that you swipe your finger across the earcup.

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