Open vs. Closed Headphones
While there are different types of headphones based on how they are worn—Over Ear, On-Ear, and In-Ear—there are also different types of Over-Ear headphones taht are grouped based on how open or closed they are to the outside world.
However, it's important to note that the simplicity of terms like "Open-back" and "Closed-back" actually only tell half of the story of how acoustically open a headphone is. So let's discuss how to properly classify these headphones.
How to Classify Over-Ear Headphones
Headphones are generally made of two primary "volumes," or air chambers. The first volume is the air chamber between the headphone's driver and your ear, called the "front volume". The second is the chamber behind the headphone's driver, called the "rear volume".
How we classify headphones depends on how these two volumes interact with the outside world, specifically regarding how much they leak sound to the outside or how much sound they let in.
The first way to classify a headphone is by its front volume, specifically if the front volume intentionally allows for an acoustic pathway between the external environment and the ear canal. If the headphone intentionally allows for this pathway due to having acoustically-open pads—like those found on the Sennheiser HD 600 for example—then it is classified as an "acoustically open" or open-front headphone.
If the headphone intentionally prevents an acoustic pathway between the external environment and the ear canal, then it is an "acoustically closed" or closed-front headphone.
The second parameter has to do with the rear volume, and whether the headphone emits significant sound from the rear of the driver out to the environment. Headphones that do not emit significant sound from the rear are called "closed-back" headphones, while those that do emit significant sound from the rear are called "open-back" headphones.
Open-back headphones essentially have an infinite rear volume, whereas the rear volume of a closed-back headphone is finite. The latter can be a bit more challenging to tune due to having to deal with two separate (but connected) volumes, but we'll talk about that in a later section.
Why This Matters
The reason this is important is because audiophiles don't always classify headphones properly, often only referencing the second parameter (how closed the rear is). This means it can be a bit tricky to know which headphone will suit your needs just based on that.
For example, headphones like the Audeze Maxwell and Audeze LCD-X may both have an acoustically-closed front volume, but the former also has a closed-back while the latter is open-back. This would mean the Maxwell is a typical "closed" headphone, while the LCD-X would be categorized more accurately as a "semi-open" headphone.
This is where it's important to remember that most audiophiles—and most retailers selling audiophile headphones—tend to categorize their headphones based on the acoustic scheme of the rear volume, having "open-back" and "closed-back" as the two primary options. This is likely because even headphones with acoustically-closed front volumes will have significant sound entering the front volume if the rear is open, and thus will isolate incoming or outgoing sound very little.
In Practice
Open headphones allow audio leakage from the environment into the earpieces, while—depending on the rest of the design—letting sound from the headphone out to the environment.
Fully open headphones have an open front and open rear volume, and they make no attempt to block out ambient noise or quell sound leaking from the headphone to the outside.
Semi-open headphones either have an acoustically-closed front volume and an open rear volume, or an open front volume and a closed-back.
Open headphones are useful if you need to remain aware of your external surroundings, but they're less ideal if you need to isolate yourself from your surroundings or prevent others from hearing what you are listening to.
Closed headphones are designed to isolate you from external ambient noise to varying degrees. Closed headphones also minimize the music leaking out of the earpieces - which will happen with open-back headphones.
Closed headphones are ideal if you need to shut out your surroundings in order to better hear the output of your headphones, or if you don't want any of what you're listening to leaking into the environment around you.
Which Sounds Better?
As with most things in audio, there isn't really a clear answer.
Many people seem to prefer fully open (acoustically-open + open-back) headphones, and this could be for a few reasons. The feeling of openness afforded by an open headphone is noticeable even when no music is playing, and this could have an effect on how people report their experience of things like naturalness or soundstage.
Additionally, many closed headphones have certain acoustic features due to having to manage pressure between the front and rear volumes, like a commonly occurring dip around 150-300 Hz.
The "closed-back dip" often found on closed-back headphones in a critical region of the midrange is often a culprit in people finding their tuning to be a bit less natural, whereas no such feature shows up on most open-back headphones.
Be aware that this is a common feature for closed back headphones, but it isn't present on all of them! If you're shopping for a closed-back headphone, you may want to browse the measurements in our reviews to see how the response compares to other headphones.
Regarding open headphones, our staff tends to prefer them over closed headphones. The Hifiman Susvara and Sennheiser HD 800S are among the most acoustically-open and widely-beloved headphones we sell, while the Audeze Maxwell is widely considered one of the most natural sounding closed-back headphones ever manufactured, even though it's wireless!
Further information on other headphone types that can effectively isolate listeners from ambient noise is found in our product guides for Noise Cancelling headphones and for In Ear Headphones.