"Tony" wrote in message
om...
Karl Uppiano wrote:
We don't perceive low
frequency directionality because given the spacing between our ears (as
opposed to the space between our ears) doesn't allow for much phase
difference at low frequencies.

Low frequencies can be well localised in anechoic conditions but not in a
normally reverberant room of reasonable size. I have taken part in blind
tests that indicated that you could cross over a woofer at 120 Hz without
being able to tell where it was, provided it was not very near the
listener.
In fact you could push it up to 160 Hz although I think that was the
limit.
The tests were with speech and music, using a normal stereo pair of
speakers
for the higher frequencies.

The test system did have a very steep cut-off filter, but this was over 10
years ago and I have forgotten what the slope was. The effect of
distortion in the speaker is also very important (and inevitable) so it is
a good idea to have acoustic attenuation of frequencies above the nominal
cut-off by pointing the woofer at soft materials.

I did not mean to imply that there were any absolutes in LF localization
ability by humans. It seems to drop off gradually, and of course relative
phase *and* loudness play a part in what we hear in each ear. Confounding
factors, such as harmonics and other noises coming from the LF driver can
provide clues as well (perhaps more easily discernable in an anechoic
space?).

As for whether blending LF to mono for vinyl is audible or not, might have
been less important than practical considerations related to making playable
records. Digital audio certainly does not have that constraint. I don't know
what current practice is for routing LF when mixing for CDs.