[Nirmalanow]

I finally got around to trying it with my new Beyerdynamic T1 headphones, and I can report pretty much the same effects as with the HD650. The sound moves a little bit forward and seems more natural and effortless to listen to. There is also a slight filling in of the tone. Seems that maybe it is boosting the mid -range since that is the only frequencies I hear when I turn down the main headphones and only listen to the Koss on-ears that are hanging from a headband and sitting outside the bigger over-ear Byerdynamics. So maybe along with a completely natural crossfeed, I am also effecting a natural EQ like boost of the mid-range. This is actually ideal with the T1 headphones as their treble is a bit bright, and so boosting some mid-range fills in the tone.
 
Again the effect is very subtle. I added a in-line volume control to the cord to the second pair of headphones so I can easily turn them on and off. Even though the effect is subtle and hard to pin down, I definitely sense a more natural soundstage that is like well placed speakers. There is a greater degree to which I can forget I am wearing headphones and just listen to the music.

 

[Nirmalanow]

Pictures are worth a thousand words, so here are some pictures of my head with two headphones at the same time. The main phones are some modded Koss Porta-Pro's that I ordered from Highflight on here. And then hanging from a grey headband are a second pair of headphones, in this case a pair of Koss KSC75 earclip headphones. The sound form the KSC75's is much softer than the main phones because they are so far away from my ear, but that seems to be enough to create the crossfeed effect that gives me a more speaker like soundstage. It is kind of a bother to hook up and arrange two headphones, so I do not use both headphones all of the time. But there is undeniably something special about the sound when I have them both playing.
 

 

[Nirmalanow]

Reviving this old thread to share that I recently got a used pair of these on Amazon: http://www.amazon.com/Aftershokz-AS301-Wraparound-Headphones-Conduction/dp/B007003J2E/ref=sr_1_4?s=electronics&ie=UTF8&qid=1399220311&sr=1-4&keywords=aftershokz
 
They work more like the Echofone in that they transmit sound through the facial bones to your inner ear. I hooked them up with the left and right channels reversed by using a pair of 1/8" to RCA adapters (one with male plugs and one with all female plugs) only with the red plugs hooked to the white plugs to switch the channels. I also included a 12db in-line attenuator to reduce the volume as it works best if the Aftershokz is lower in volume than the headphones, but an external inline volume control would work also. Here is what I used because I had them on hand: http://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0/ref=sr_1_2?s=electronics&ie=UTF8&qid=1399221290&sr=1-2&keywords=12db+attenuator
 
I am using them off of the extra headphone output on my Tera while the other headphone out feeds my iCAN Nano amp and my JVC HA-FX850 iems. The effect is very nice with a bit of crossfeed effect again. I mostly notice a more realistic sounding depth to the image and maybe a bit more instrument separation. There is also more of a 3D quality to the sound: without the Aftershokz, the sound is more 2 dimensional and a bit flat. With the Aftershokz, there is more of a sense of say a real 3 dimensional human body singing in front of me. There is also a bit more fullness to the sound even when I compare with the volume equalized to account for the added volume with the Aftershokz turned on.
 
The other quality is harder to describe, but the Aftershokz do vibrate the skin and bones instead of the ear drum. So when I combine them with my headphones, there is more the sense of involving my body in the experience. It is not the same as when your whole body is vibrated by the bass frequencies at a concert or with a powerful subwoofer, but it still shifts the experience from being totally in my head to feeling a bit more involving of my whole body.
 
The effect is subtle, but more noticeable than when I was using two regular headphones as described in the rest of this thread. And it is more noticeable on some songs than others, which may be due in large part because the volume of the Aftershokz is staying the same when I turn up the volume on the Nano amp feeding my regular headphones. So when I turn up the volume on a quieter piece of music the volume of my headphones increases, but the volume of the Aftershokz does not. I will experiment some today with just listening out of the Tera, and so then when I turn the volume up or down, it will go up and down in both the headphones and the Aftershokz.

 

[Nirmalanow]

I simplified by removing the 12db attenuators and then lowering the volume just a little on the Tera. That seems to give the right balance with the Aftershokz being a little louder than they were with the 12db attenuators in place. The crossfeed effect is even more noticeable and I hear a nice widening of the soundstage in addition to the greater depth. And this is while using the Nano amp which already has a nice soundstage enhancement feature. The combination makes for a very realistic in room sound.
 
I know it is kind of crazy, but I love fiddling with stuff like this. Probably way too much trouble for most people, but it is fun when the sound just comes alive to a greater degree.