I know this thread is old, but there seems to be an misunderstanding due to syntax.
The issue is that on Head-Fi, everything is an IEM (In-Ear Monitor), no matter if it is an Monitor or not.
Actually, IEM are only Monitors (hence the Monitor in the name) and with Monitors, when you're talking about Closed Monitors, you mean an All-BA set that doesn't have
OR any airvents for isolation.
Some people call them "completely closed" or "sealed" or "unvented" but its all the same thing.
With average earphone, the story is different because (for reasons that make zero sense, i'll explain soon), open back earphone to exist.
First of all, we have to understand why headphones are open.
It starts with the use of an Dynamic Driver, Dynamic Drivers are very complicated to tune, much more than people expect. And not just are Dynamic Drivers complicated to tune to begin with, the housing has an significant influence on the tuning. The same issues i explain are true for Planar and EST too
With In-Ear, thats no problem. You can have a complex housing with several tuning layers behind the drivers like here
or here
Something like that is not possible with Over Ear Headphones as the housings would be up to 50cm large. Nobody would want an headphone that sticks out of your head half an meter (or 1.5 feet for murricans)
Also In-Ear Headphones can use several drivers optimizing on the frequency range
This is not possible with Over Ear headphones.
So there are two issues. Over Ear Headphones are limited to one single driver, that is very hard to tune, to cover the whole frequency range, in addition to that, you you have much less control over the tuning with the housing as you are limited in size, in addition to that, you have more air and more variables to control (head shape, ear shape and so on).
That is why some makers just said "Screw it" and made the back open. So they have one less factor they have to care about. But this also comes with significant downsides because even though you have less variables to care about, you also loose a lot of tuning capabilities.
The reason why Open Back Headphones sound so "open" and "wide" is due to the fact that most of them have recessed bass and lots of treble due to the lack of an housing.
You can just emulate that with an EQ or you can, alternatively, just tune the Earphone the exact same way.
The Final A4000 for example sounds more open and wide than most Open Back Headphones. The E5000, even though it is warm and has a lot of bass, also sounds very wide and open (something that doesn't exist in the over head world).
So actually, you do not want the back to be open. Because when you open the back, you loose a lot of control over the tuning of something that is already hard to tune to begin with. You want the back to be closed. Open Back earphones make, imho, absolutely zero sense because they suffer from non of the issues that are the reason why Headphones are open back.
Open Back earphone are just marketing and nothing more. It solves no issue, but adds issues. Open Back Headphones are simpler/easier/cheaper to make, but generally suffer from a lack of tuning capabilities.
Look at the Stealth from Dan Clark Audio for example. They found a way to tune the driver exactly they want it to sound and the headphone is exactly what they want it to be. For purist audiophiles they made an Open Back Version but they explained in the Developer Interview, that its actually inferior. It is basically identical to the stealth, just with less control over the tuning, thats it. Again, you do not want an open back, neither with headphones, nor with earphones. With headphones, it can take away disadvantages but adds new disadvantages at the same time. With earphone, they don't have the disadvantages of headphones in the first place and so don't suffer from the same issues.
Closed earphone = All-BA sets that are sealed with no air vents --> Generally used with foam due to the lack of air pressure exchange
Normal earphone = Have an DD and so on airvent for air pressure exchange
Open earphone = Marketing scam
