The human ears determine direction by time difference. A noise will reach one of the ears slightly earlier than the other (if it doesn´t come from straight ahead), and the phase difference makes it possible to decide from what direction the noise comes.
At lower frequencies, like subwoofers, the phase difference is very small compared to the wave length. This makes it much harder to decide the direction.
The distance between your ears is about 9" or 225mm. Thats about 0.00066sec delay or 0.66ms delay if you prefer. I'm pretty sensitive to lipsync errors, but loose the will to live when trying to narrow down the last 5ms which is an order of magnitude greater.
However, if it were purely down to delay, surely bass would be directional at all frequencies as delay is constant? Phase on the other hand, which varies with frequency relative to delay, is certainly more sensitive to increasing frequencies which are more directional.
Group delay is as a result of electrical phase and the resulting timing seems clear to me. So as phase is inseparable from delay, can directionality be attributed to one without considering the other?
I agree with you to some extent that the human ear is in fact rather poorly enginered, at least compared to some animals....
For example, look at the sensitivity at different frequency and levels. At low levels, bass range and treble sensitivity is lower - the Fletcher - Munson graph. The other way around would have been much more convenient, at least for us hifi-nerds.
About the delay/phase difference issue, our sense of direction seems to be mainly dependent of delay. At voice range freq. this is no problem. But the lower the freq the more it turns toward a phase difference. In fact, calculating with the above mentioned 225 mm between the ears, we get: 0.225 meters/336 m/s equals about 0.00066 seconds. This in turns corresponds to roughly 1/0.00066 = 1500 Hz. Above this freq, more than one complete cycle will pass before a sound reaches the other ear (if it comes straight from one side). I would call this a delay.
Below, there are only parts of a cycle causing our sense of direction. I would call this a phase error. But this is my humble opinion, maybe just complete rubbish.
One thing I did remember, is that the sense of directionality is not purely based on delay/phase as that would simply relay left or right information.
The Pinna of the ear (bits that stick out the side of your 'ead) has it's own set of resonant frequencies which, IIRC center on 3kHz. Some weird pseudo surround effects using two channel audio used to rely on creating sounds with a peak in the response at these frequencies to make sounds appear to be behind you, by emulating some of the extra resonances of the Pinna stimulated from behind.
It wasn't entirely successful (Try Living Color 'Stain'), but if you want to try something that will get any number of disapproving looks from your other half, turn your chair around and listen with your speakers behind you. The distances haven't changed and left/right information is still present, but you'll find it sounds very different and definitely behind you.
something like this should sort it (and described here)
now that's what I call personalisation. Incidentally I had thought in the past about the feasibility of producing a calibration file for my hearing and then feeding that into REW, it never got past the "idle chatter in my head" stage though.