You can easily tell apart closed back headphones from open back headphones by looking at the earcup design. Closed-back headphones have a hard shell on the back that prevents sound leaking out, which is ideal if you want privacy isolation when listening to audio.
Open-back headphones like the Hifiman Deva (pictured) have a mesh or perforated grill on the back that is designed for sound to leak in and out of the headphones. While the Deva headphones look like regular open back, they use planar magnetic drivers, which are radically different to dynamic drivers. Planar magnetic drivers integrate giant planes, incredibly powerful magnets and super thin/lightweight voice coils which are 1/10th of a human hair.
For a variety of audio tasks, the Hifiman Deva headphones go a long way, especially if you don't have the space nor the money for audio monitors. The Hifiman Deva are great for uses such as mixing, judging stereo width, gaming, referencing mixes, mastering, setting reverb trails and fine audio editing tasks like listening for clicks, pops and distortions.
The main selling point of open-back headphones are comfort and audio quality and the Hifiman Deva don't disappoint in these two departments. The Deva headphones have superb airflow, preventing heat and sweat from building up inside the earcup like it does with closed back headphones.
Despite their bulky look, the Hifiman Deva are not heavy, weighing just 365 grams. Lightweight headphones are always an advantage because they put less pressure on the headband so, you can wear them for longer. The Deva planar look very much like the new HE400SE magnet version too.
For pure enjoyment of music, nothing beats the immersive experience of sound you get with open back. The Hifiman Deva headphones produce a really wide, deep and spacious (3-dimensional) soundstage that allows you to hear all instruments clearly separated around your head.
Closed back headphones tend to have a narrower soundstage with punchier bass, while the Deva headphones produce a fuller sound with extended, deeper bass.

Thanks to being low ohm headphones and having a flat frequency response, the Hifiman Deva are perfect for studio/monitoring and general listing. The Deva speaker drivers have 18 Ohms of impedance so, they can be easily driven from any audio source, including a smartphone.
Besides impedance, speaker sensitivity also plays a big part on how loud a speaker or headphone can sound. Essentially, the higher the sensitivity, the louder the volume sound. However, high sensitivity can potentially create noise distortion, which is why headphone makers keep headphone sensitivity at a sensible level - around the 100dB mark.
The Hifiman Deva have a 93dB rating so, they are capable of very loud volume sound. That said, the volume sound is louder when playing audio via Bluetooth than via wired connection to a computer. The likely reason for this it's due to the computer sound card amplifier not getting enough power to drive the headphones so, you may need to use a headphone DAC amp.
This is because when playing audio via Bluetooth, the volume sound is determined by the amplifier in the headset; hence why the Hifiman Deva headphones sound louder in bluetooth mode because the amplifier is directly connected and exclusively powered by the battery inside the Deva headphones. When connected to a desktop computer though, the Deva headphones aren't directly connected to the sound-card amplifier and they also have to compete for power, piggybacking off other connected devices to the computer.
As mentioned earlier, the Hifiman Deva headphones are very comfortable to wear because of their lightweight. The earcup depth is 3cm deep with large earpads so, the ears won't rub against the magnetic drivers. The inner diameter of the earpads measures 57mm, while the outer diameter measures 100mm. The outer exterior of earcup has an 110mm diameter. The Hifiman Deva headband measures 3.5cm wide with 2cm thick padding underneath.
Most open back headphones have either a wireless or wired design. The Hifiman Deva have both so, they can be used with a cable or without it, thanks to the included Bluemini adapter.
Bluemini is both a Bluetooth 4.2 receiver and powerful DAC amplifier adapter with a dual function USB-C port, which is both an audio input and power output for recharging it. The Bluemini is capable of up to 20dB higher output, thanks to the integration of a buffer stage filter that amplifies the signal.
There are two buttons on the Bluemini. The button next to the USB-C port controls the dual functionality of the USB-C port, while the other button powers on and off the Bluemini. There is a small led indicator to feedback status and a good sounding microphone onboard.
On the opposite side of the Bluemini adapter, there is a 3.5mm balanced audio jack for connecting the Bluemini to the 3.5mm audio socket located below the left earcup of the Deva headphones. The material covering the Deva headband seems to be pleather, which is also found covering the outer side of the earpads. The front side of the earpads is covered with honeycomb pattern polyester fabric material.
The Deva headphone 3.5mm socket supports TRRS configuration; hence you can use a cable microphone to answer calls. You can also answer calls via the Bluemini adapter while it's connected to your phone.
The Bluemini is a fairly bulky attachment but it isn't too heavy, weighing just 44 grams. The Bluemini adapter also integrates a small battery that takes 30 minutes to fully charge. The Bluemini adapter also supports LDAC, aptX-HD, aptX and AAC so, you can enjoy high resolution audio.
You can expect lower battery life when using hi-res codecs, especially AAC, which consumes a lot of power. Anywhere between 7 hours (AAC) and up to 10 hours when using standard Bluetooth. When connected via USB DAC, the Bluemini has a battery life of 4.5 hours.
The Bluemini adapter is a very useful addition to the Hifiman Deva headphones, letting you transition quickly from bluetooth listening to wired listening very easily. You can simply remove the Bluemini adapter from the headphones without having to disconnect the bluetooth connection from the Bluemini. When you are done playing audio via the audio cable, you can simply unplug the audio cable and insert the Bluemini adapter back into the Deva headphones audio jack.
Aside from the leather-like fabric, the Deva headphones integrate aluminium metal construction for the earcups, as well as the headband inner frame and headband yoke, which is made of a single piece of metal. The Deva headband yoke attaches to the earcups via two small flat-head screws with thread locker to prevent them from undoing. The yoke allows the earcups to tilt up and down and swivel left to right slightly.
The Deva headband makes a clicking sound when adjusting the headband into the notches. The ends of the headband are also aluminium capped and feature Hifiman Deva branding on the front sides of the caps, as well as R and L lettering embossing on the under side.
Open back headphones are perfect for gaming because they reproduce soundstage and imaging better, meaning you can ascertain distance better and also tell if sound is coming from the back, front, left or right. For instance, when playing first person shooter games you will be able to tell where the gunshots are coming from and precisely tell whether the gunshots are 1 feet or 10 feet away from you.
With closed back headphones, it's not as clear when judging the distance (soundstage) of sounds and direction (imaging) because closed headphones keep the sound inside the the earcups, while open back let the sound waves escape.
When it comes to clear surroundings, nothing beats the natural sound of open headphones, not even gaming headsets with 5.1 or 7.1 virtual surround sound. Some surround sound headsets are better than others but all gaming headsets with surround sound, ultimately, use software simulation to achieve the natural effect that any open-back headphones can naturally do.
Like with all open back headphones, you can hear pretty much everything that's going on around you and that includes noise from a computer fan, keyboard or noise from extremely loud family members. If you're buying open back headphones and have a desktop computer, make sure you use a silent mouse/keyboard, as well as a quiet CPU cooler because the noise will leak into the audio you listen to.
Open back headphones are also not a good choice if you're going to use them in public because of the sound leakage. Some open headphones leak more than others. The Deva open headphones leak out sound substantially so, anyone sitting in the same room will clearly hear the audio that you are playing.
If you're sitting on a bus/train or library, you will definitely disturb and annoy anyone close-by wearing open back headphones. When it comes to sound isolation, closed back is the way to go.
Other accessories included with the Deva headphones are a 26-gram/ 1.8 meter long balanced audio cable (3.5mm to 3.5mm male), a 3.5mm to 6.35mm gold-plated adapter and a 53-gram/1.8 meter long audio/charging cable with a USB-A and USB-C connectors. You can buy the Hifiman Deva planar magnetic headphones on Amazon. Check out the HE400S planar headphones review