[WriteLog] Long Path

[Jim Brown]

On Mon, 01 Dec 2003 21:05:54 +0000, K4SB wrote:

>Somehow, I think from Jim's description that the signals were not
>"long delay echos"

Sorry, I need to clarify. I live in the world of acoustics and sound
systems for public spaces, where sound will come direct from a
loudspeaker to a listener, but may also bounce off of a wall and arrive
tens of milliseconds later. n the world of acoustics and human
perception, an arrival late enough to be perceived as a separate
arrival is defined as an echo. If the second arrival is late enough
(that is, if there is enough time between the direct sound and the
reflected sound) and is strong enough, the reflection will be perceived
as an echo. If the difference is small, it won't.  70-100 ms is the
arrival time difference is generally accepted as about where the ear
will begin hearing the echo. 

By the way -- Joseph Henry, the guy whose name is on the unit of
inductance, figured all of this out and published it around 1850, and
Lord Rayleigh did so a few decades earlier. Considerable subsequent
research on human perception has only confirmed their work and added
details to our understanding of it.

What I think I was hearing was a combination of several modes (or maybe
a combination of three, based on SP5UAF's comments)

1. direct short path

2. direct long path

3. aurora (I first worked aurora while in high school in the 50's) --
this is truly a reflection, albeit a very unstable one

4. equatorial -- this mode is new to me, so perhaps I need to get back
to the books and study it

Jim Brown K9YC
http://audiosystemsgroup.com