You know how in home theater, there are more than one speakers, three in the front and two in the back and a sub-woofer somewhere, but something similar has never been achieved with wearable audio devices, like earphones, headphones, etc, this is because most earphones and headphones can only have one transducers and earphones and headphones are not far away from the ears to simulate sounds coming from front and back of the ears.
So I thought I might solve this problem by wearing bone-conduction earphones and air conduction earphones, this way I thought a personal, wearable home theater might be created, I wore bone-conduction earphones just before the ears and I wore air-conduction earphones in the ears, I connected the bone-conduction earphones to the front output on my computer’s sound card and connected air-conduction earphones to the rear output of the sound card.
Even though I configured the software to output in 4.1, I was getting a mixed up and garbled result, it seemed like bone-conduction sound was faster and louder regardless of the delay I applied to the front speakers, no matter how much I increased the distance of the front speakers in the software and decreased the volume of front speakers. Completely decreasing the volume is eliminated the front sound, reducing the sound is making rear sounds louder and dominate the front sound, even though front sounds are faintly audible but I could never get the right balance.
Is there a way to make this sound closer to a real 4.1 home theater system? Maybe by applying inversion or delayed inversion to the signal of front speakers and sending them to rear speakers?
Yes, the speed will be greater in the “bone” headphones due to the density of the medium.
As a result, the delay needed on the “air” headphones will need to be compensated for, how much? no idea.
You will have to experiment.
Another factor you have to take into consideration is, the frequency response.
I suspect that the “air” headphones will allow for a wider response versus the “bone” ones,
which will probably be restricted to low-mids and mids.
You may want to apply a band pass filter to the audio feeding the “bone” headphones to see if there
is less garbled audio.
Another factor is how the sound is picked up eventually by the inner ear.
Of course will all these different frequency responses and delays, phasing is going to be a nightmare.
I would start with 4 channels (L air + R air) and (L bone + R bone), and everything in each channel is
panned hard to it with no “overspill” onto other channels.
Once you get that sounding OK, move on to more “blended” pans.
The above is of course assuming that there is enough separation in bone conduction to allow for a stereo field.
You may find that only 3 channels (i.e 2.1) are feasible, i.e. Left “air”, Right “air”, then a center channel (mono)
made from the bone conduction, which keep in mind ,will be in the 500 - 3000 Hz range.
But, remember that if anything in the “air” channels is also in the 500 -3000 Hz range, it must be in-phase
with the “bone” channel or they will cancel out.
One more obstacle you will have to overcome is, how to actually play 3 channels.
Some sound cards do support multi-channel outputs, but they are normally 5.1 and 7.1 and
not 2.1 (assuming 3 channels).
Also, 5.1 and 7.1 outputs are sometimes automatically attenuated relative to each other according to
whatever multi-channel system it’s defaulting to.
For example, the sub-bass output, is about -20dB relative to the center channel.
This will mess with your required settings, which I doubt very much will be the same as these traditional
multi-channel formats.
this is because most earphones and headphones can only have one transducers and earphones and headphones are not far away from the ears to simulate sounds coming from front and back of the ears.
Also, with real sounds we turn our head to triangulate the location (sometimes slightly, sometimes subconsciously, and sometimes to “see” where the sound is coming from).
There are head-tracking headphones that automatically change the sound when you turn your head. I’ve never tied them but I assume they work very well.
