help me with that...
The following is an imo post:
Ear/Headphones fail to image the sound stage in stereo recordings. In order to get a sound stage, sound from the left channel needs to arrive at the right ear as well and vice versa.
So let's call what you hear 'head stage'. Some reasons why I think full-size headphones are different:
- IEMs bypass everything but the last part of your ear canal / the sound output by full-size headphones is "filtered" by the outer ear and the full length of the ear canal, to some extent even by the shape of your head
Your ears are not perfectly symmetrical, so you will naturally get a more different (ear to ear) response with a full-size headphone compared to in-ears.
- IEMs never disappeared in my ear canals like comfortable full-size headphones did, so there might be a psychological component to why IEMs sound less natural
- IEMs seal/block the ear canals, there's no crosstalk / with full-size headphones there can be some crosstalk (sound from one channel reaching the opposite ear)
- IEMs frequency response seems to be much more tightly matched / full-size headphones are much more susceptible to interchannel differences due to reasons mentioned above but also placement ...
This might cause the "illusion" of a greater head stage.
Hmm, I'd need to know what you're hearing exactly, but my guess is:
The bass boost makes differences in phase down to the mid bass more audible. The brain is interpreting these phase differences as spatial information, i.e. where is the sound coming from?
If it's put in the "foreground" by a large bass boost your attention will automatically shift to that.
(If you want me to go in detail let me know.. but it's gonna take a bit of explaining.)
So we're talking only about IEMs. Let's assume everything is identical except for the frequency response: one is flat the other one has boosted bass.
Human sound localization works by, put simply, comparing what is arriving at the left ear with what is arriving at the right ear. The differences between both ears are called interaural differences.
At low frequencies, phase differences between the ears are important. This means a bass drum slightly to your right will produce sound that first arrives in your right ear and after a very short time delay in your left ear. That's called phase shift.
At high frequencies, the wavelengths are very short so these short time delays result in huge phase shifts - too big for our hearing to unambiguously detect where the sound is coming from exactly. Luckily our head creates an "acoustic shadow" so the a high frequency sound to your right will reach the left ear at a much lower level. Yeah, your head is a physical obstacle that attenuates high frequency sounds.
With IEMs we don't have that kind of crosstalk. Left channel is fed into the left ear, right channel into the right ear, period. That's why I said there is no real soundstage with head/earphones and stereo recordings.
So we have to look at what's on the CD. First, assuming that one IEM just has boosted bass, we can ignore treble (which btw has many problems with headphones).
We can also ignore sub-bass, since on a CD that is usually very much mono (left = right). This makes sense, since our hearing is very bad at determining the source location with such low frequencies anyway.
What's left are bass to mids. An IEM with boosted bass shifts away the attention from the problematic treble to that range, especially low mids and bass where the boost is strongest.
Here what we usually have on CDs is not mono, but close: different instruments or singers are shifted slightly to the left/right by phase shifts and level differences. That's close to what our hearing expects, more natural than what we can find on modern CDs in the treble range anyway.
So the boost attracts attention to a frequency range that is more natural. The boost also counteracts the decreased sensitivity of our hearing (see equal loudness contours), bringing forward details that would otherwise go unnoticed.
That is what I think causes an increase in perceived "soundstage".
Not really, just a little. I'm a software "engineer" and am sometimes working on digital signal processing stuff.
The above is just my explanation of what I think is going on.