[BC] Audio Cable

[Cowboy]

 Wanting to be sure, so after doing a little fact-checking,
 by consultation with Mr. O.......

Wed Jan  2 22:43:50 2008
   
In recent years the industry has neglected that which
used to be standard. Properly terminated audio lines.
Recall we used to have 600 ohm matched loads.
Today, we employ low impedance outputs and high
impedance (bridging) inputs. While possibly convenient,
the after effects cannot be ignored.

High impedance inputs allow for greater crosstalk and
ingress of foreign signals. This would ESPECIALLY be
true of left and right channels being routed through a
common connector. Disbelieve this? Remember old
fashioned sinks with separate hot and cold water faucets?
Today with a common spigot we can have any temperature
of water from the cold to the hot. Read:Mixed signals!

Most zip cord constructed of stranded wire employ twist
of the same direction for both channels. This causes an
issue with the velocity of propagation. Ideally the left channel
should have a left handed CCW twist and the opposite for the
right channel. This creates an equality where common mode
rejection is greatly enhanced due to the inherent cancellation
of the common mode induced signals. Of course, this does
increase the manufacturing cost of the cable. We must also
consider the connector assemblies. The suggestion of using a
marker is Ludacris. This can adversely impact its shielding
properties and capacitance, thus affecting the audio.

The negligence in these matters no doubt arises from the
fact that audio engineers and designers have had no experience
with RF. Properly terminated transmission lines are essential
for efficient and clean transmission. If we used the low-Z
out (a tx) feeding a high-Z load directly (a tower) we would have
high VSWR, poor bandwidth, etc.

Whether it be audio or RF they key word here is "transmission".
Attention to line length, composition and connectors is very
important to ensure square wave performance, symmetry and 
quality reproduction.


>
> From: Tom <Radiofreetom at gmail.com>
> To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
> 
> Actually, it's not really all that hard to break out L and R to 
> different connectors - although it does tend to be a bit wasteful of one 
> of the two pairs...
> 
> Start with BOTH pairs going into one connector.  Strip the appropriate 
> amount of the outer jacket, and separate the pairs.  Cut one pair (I 
> usually trim the red/black pair, designated LEFT or CH. 1) back to a 
> normal working length, but DO NOT TRIM the drain.  Install connector in 
> normal fashion, folding the drain wire at the length you'd have trimmed 
> it to before soldering.  Before assembling to the shell, slip the 
> removed outer jacket over the second (Green/White) pair, and the free 
> end of the drain wire, and run the resulting cable back through the 
> shell connectors, bushings, strain reliefs, etc.  Install the second 
> connector to the free end in normal fashion.  You now have a cable end 
> that might LOOK a bit strange, but gives excellent performance.  I have 
> also done it with trimmed drain wire; it will give good results, as 
> well, depending on the equipment connected and the length of the 
> pigtailed second pair - even in the near-field of a 5 kw AM station.
> 
> (Oh, and use a permanent marker to designate which connector is what 
> channel.... so the next guy will have a clue, as well as in case you 
> forget between install and maintenance time.)
> 
>

-- 
Cowboy