If you've never checked out the head-fi.org forum, you need to join that community if you're serious about learning the ins and outs of audio.
It was on this site that I found the perfect and most sesinked answer to the question of "what is soundstage?" and "do headphones control soundstage at all?"
So instead of claiming this knowledge as mine, I'd like to give credit to the user fjrabon, who is absolutely brilliant in his knowledge of all things audio! This answer to the question of what is soundstage dives really deep into the details of headphone audio, so if you're not comfortable with audio jargon you might want to have google open as you read.
I've seen a lot of posts where people state they don't really understand the concept of soundstage "depth". Here I will relate how the concept of soundstage depth works in general, why headphones have a problem with it, and their "imperfect" solutions to the problem.
The vast majority of my knowledge about these areas comes from Gary Davis and Ralph Jones' Sound Reinforcement Handbook, Second Edition, as produced for Yamaha. It's a FANTASTIC book for learning about how audio works. It's aimed at live sound reproduction, but its so exhaustive that you can learn a TON about sound reproduction in general. I don't know of a comparable book for home audio, though I am sure there are some out there.
The fundamental stumbling block to headphones, with regards to all aspects of sound, but especially soundstage depth, really doesn't have to do with their ability or inability to reproduce sound in a quality manner, it comes from the fact that mastering is done for speakers, and headphones aren't speakers. This is sort of a background fact to keep in mind when I talk about why things are the way they are. I will constantly refer to the "producer's intent", what I mean there is what the producer/engineers/etc intended for the record to sound like, I mean proucer, just in terms of the party in charge of producing the record, which isn't necessarily the credited Producer with a capital "P". In fact a lot of people hate how producers want things to sound, and that's an entirely different topic, but for the purposes of this discussion, the goal will be to get as close to the producer's intent as possible.
So, since producers generally master for speakers, lets first talk about how speakers create soundstage depth:
Soundstage depth, in general, is created by the fact that high frequency sound waves are absorbed and dissipated more easily than low frequency waves are. This is why you can clearly and easily hear thunder from several miles away, but you couldn't hear a high pitched siren very clearly from even a quarter mile away. Or why you can hear your neighbor's bass, but not any of the words to the song. So, what your brain does is calculate the differences in amplitude of the fundamental frequency and the frequency's harmonics. Any tone is made up of a fundamental, which is the main tone, and harmonics, which are numerical multiples in frequency of the fundamental. Because the higher frequencies are absorbed by the atmosphere faster than the lower ones, if there are a lot high harmonics compared to the fundamental, your brain thinks that the sound is close by. These higher harmonics are often what is referred to as the presence frequencies. More presence frequencies = sounds closer to you.
So, speakers create soundstage depth from two areas. 1) is what is in the recording. This has to do with microphone positioning (far away mic'ing sounds farther away) and EQ'ing (pulling out or boosting the presence frequency of an instrument can make it sound closer or further away). Typically mic positioning is preferred to EQ'ing for creating soundstage depth. it's easier and doesn't have nearly as many complications. For instance an instrument with a very large range like a concert grand piano is difficult to "move" with EQ, because the presence frequencies of its lowest registers are different from its highest. But if you mic it with several different mics at different distances, you can control the soundstage depth by mixing the relative levels of closer or further away microphones. 2) is the simple distance from the listener and the speaker. This is what gives speakers the feeling of not having sound pumped into your brain, that you are watching a performance. The distance from you and the speaker will knock some of the presence frequencies off just from the air.
Now you can probably already see what the fundamental issue with headphones is going to be here. Headphones, by definition, have the driver extremely close to your ear. There isn't very much air to "knock down" those high frequencies. Meaning that a totally flat measuring headphone would sound insanely high pitched. Like an icepick being shoved into your eardrum. While with speakers the goal is a totally flat frequency response, this simply is not possible with headphones, it wouldn't sound like what we are accustomed to hearing as flat. The problem is we are trying to use a source that is mastered to be heard from a distance of several feet through headphones that are less than an inch from our ears.
Now this probably sounds grim, but headphones solve this problem by rolling off high frequencies. Even a headphone that is considered to be VERY titled towards the high frequencies, the AKG K701, has all frequencies above 8kHz MASSIVELY rolled off.
However, this is still an imperfect solution, because it's hard, if not impossible to perfectly replicate the natural, atmospheric rolloff that occurs in air with frequency response on a headphone. It's imperfect in the same way that EQ'ing an instrument in the studio is an imperfect way to create soundstage depth in the studio. Different instruments have different presence rages, and thus its impossible to accurately reproduce the correct adjustments with a single instrument that has the same sort of "EQ setting" all the time. Some do a better job than others, some are quite outstainding to the point of ALMOST sounding "speakerish" in this regard.
So now onto how some headphones create unrealistic soundstage depth. Some headphones aren't just content to try and approximate headphone depth, they want to try and beat it in some way. They do this by boosting and pulling back certain presence frequencies. A notable example is the AD700. When flat, it pulls the vocal presence back a touch, allowing vocals to less forward, which creates a sense of depth. The AKG K701 goes in the opposite direction.
It pushes the female vocal presence frequencies forward, and drum and bass presence backwards. This creates a deep sounding soundstage for female vocal performances, because the vocals sound immediate, the drums and bass sound like they are in the back and most other stuff sounds in between. However, it can become discombobulating for a bass solo, because the bass solo refuses to move upfront. Or on a male/female vocal duet, because the female vocal sounds much more forward than the male. it kind of sounds like romeo and juliet singing a duet during the balcony scene where you are standing next to juliet. This is what people mean when they say that the K701 has an artificially deep soundstage. It's not that the soundstage is "too deep", just that its artificially, and at times oddly, deep.
It's my opinion that headphones just CANT accurately reproduce soundstage depth. The best a headphone can do is strive for a flat SOUND (as opposed to a flat reading on a FR chart) and then whatever that makes the soundstage depth is the best they can do.
Now, please don't focus on the couple of headphones I mentioned here. They were only used because they were example of headphones that I personally believe exhibit a certain quality, and not because I like or dislike them. Hopefully this helps some understand what soundstage depth is and how it works.
These new IEMs are going to replace my onstage monitors!
Eh, they can, but should they?
Whether you’re a musician who’s trying to decide between wedges on a stage or IEMs. Or a weekend warrior who wants more substantial sound than the basic earbuds that come with a phone. Knowing what IEMs are, and how they’re best, or not the best for certain situations, can be a huge help.
We’re going to go over what these nifty headphones are best used for, what the advantages are, what separates them from earbuds, and why you might need to stick with onstage monitors if you’re a performer.
In Ear Monitors (IEMs) are basically earbuds used by musicians and sound engineers, and soon to be audiophiles ;).
These specialized headphones are used to hear a personal mix of vocals and stage instrumentation during a live performance or studio recording, which makes them a great tool for musicians. source
To compare IEMs to earbuds is like comparing open back to closed back headphones. The sound quality is going to be completely different between these two seemingly similar headphones.
In ear monitors are like listening to a pair of closed back headphones, because they isolate the music and block outside noise passively. Much like a pair of closed back headphones.
Earbuds are the open back version of these headphones, because there’s very little passive noise cancelation that happens with your apple earbuds. However, some of the newer models of apple earbuds have a more direct speaker shape that isolates the sound a little better. But on the whole, it’s nothing like a pair of IEMs.
The cone shape of these specialized headphones clearly prioritizes the direct delivery of sound straight to your eardrum. This shape also blocks your ear pretty well, like we said before, creating a passive noise cancelation effect. Which is a great benefit if you’re not wanting to deal with the world.
There is a pretty good final argument to choose the in ear monitors over the typical apple ear buds, and that is the overall sound quality!
The tech in these specialized headphones makes the music experience such a great experience compared to the fast and loose sound of the default ear buds…
Headphone impedance is another one of those audiophile glossary terms that goes right over people's heads who ask about headphones.
And finding out what it is and why it affects you can be almost as confusing.
So we've done our best to compile the best answers into this post that should convey what it is and why you should care. At least that's the goal, anyway.
impedance is the resistance that an electrical current faces when being driven from a power source through a circuit. Much like when you have a hose that has water coming out of it, but then you put your thumb over the hole, this would be considered impedance, which is measured in Ohms. source
Hopefully that makes some sense.
When measuring impedance in the context of sound though, the lower the Ohms means the resistance is higher. Which also means that there's a higher need for energy to force the current through the circuits.
And impedance in headphones in regards to performance means that the lower the impedance of the headphones, the louder/clearer sound you'll get. Because there's more power needed to make the sound happen.
Well if you're using high impedance headphones on a mobile device, you're going to be able to listen to them a lot longer, because there won't be as much juice required to make them work. However, if you're using low impedance headphones, you'll burn through your battery pretty fast.
And if you're using a amp with your headphones, you'll have to take into account that the impedance of your amp plays a role with your headphones as well. If you have low impedance headphones with a high impedance amp, you'll likely run out of battery quickly. (source)
So pairing high impedance amps with high impedance headphones is your best bet for power usage/conservation.
If you're anything like me when I jumped in the audio world, the first conversation you had about what a DAC is and what it's used for, went something like this.
Oh, you want to convert your binary audio signal into an analog audio file that can be pushed to an amp so you can listen to it in your headphones?
Simple, use a DAC...duh.
As I looked around I could see bits of my brain floating in space, because my mind had just been BLOWN. So we're going to break it down a bit more simply for you on this site so that you don't walk away with more questions than answers.
There are two terms you're going to need to be familiar with in order for all of the rest of what we're going to talk about to make sense. Digital & analog audio signal.
An analog signal is a representation of instantanious changes in pressure caused by a physical action, like producing a sound. This is what microphones use to collect sound and transfer it to headphones.
The fact that it detects instantaneous changes is what gives it the most realistic amplification of what is actually being produced. Because when you sing into a microphone the sound that's coming out is the result of millions of seemingly instant changes in wave frequencies. Because sound travels through air, which is just the result of a bunch of molecules bumping into each other.
Don't get too caught up on this. Just understand that an analog audio signal is the truest representation of what we hear face to face.
Digital audio information is basically binary code. Meaning that it's a sequence of 1s and 0s that can be interpreted by a computer to make a sound, picture, text, etc..(source)
If DAC stands for Digital to Audio Converter, then we can assume from the information we just went over that a DAC takes the digital audio information (binary computer talk), and converts it into an analog audio signal that can be listened to.
However, in most situations you'll need an amp if you want to use a DAC with headphones to get the absolute best sound quality.
A DAC is used to get the best sound quality out of your headphones when listening to music on your computer or mobile device. It does this, like we said before, by converting the binary information in the computer or mobile device from digital audio to a listenable analog audio signal.
If you've ever owned a computer or mobile device that plays music you're probably wondering "I've listened to music on my phone and computer before, why do I need one of these DACs??". (source)
And you would be right.
Most tech comes with a DAC built in, it's just a really mediocre one. So if you get a really high end pair of headphones and wonder why they sound the same as your apple ear buds, that's why. Your built in DAC is just not able to give you the best listening experience that a high quality DAC and amp would be able to.
So if this is something that you value, you can either buy a DAC and amp separately, or together built into one unit. That's up to you.