The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
Subject: Re: audio line specifications
References: <3DEE2757.EE79B063@crf.canon.fr> <3DEFD744.3A2D8C8D@gv.net>
X-Newsreader: Forte Agent 1.92/32.572
Date: Thu, 05 Dec 2002 19:16:37 -0500
NNTP-Posting-Date: Thu, 05 Dec 2002 19:16:34 EST
Organization: Bell Sympatico
On Thu, 05 Dec 2002 14:46:28 -0800, "Michael R. Kesti"
>>Yes. The impedance of the line is NOT important.
>The impedance of the line is not usually important, because audio lines
>are usually shorter than the shortest wavelength in the audio band.
>>No body designed audio equipment to match the impedance of the line.
>Sure they did, and some still do. Early audio practice was taken from
>early telephone practice where long lines are typical. Matching to the
>line is what the whole 600 ohm thing is about. The characteristic
>impedance of open wire lines on telepone poles with glass insulators
>and about five inch spacing between conductors is about 600 ohms.
I said and clarify:
.If you are looking for the characteristic impedance of audio lines
used on home or studio installations the impedance value of the line
is of no importance.
I am talking about lines used at home or studio installations.
But if you want to talk about telephone lines... ITT Reference Data
for Radio Engineers gives the following typical impedance data for a
16 gauge at 55 degrees f
500 Hz 540-j460
1000 Hz 428-j324
When interfacing with "out of the house equipment" I always design
for 600 ohms because that is what is expected and most of the time
specified by the customer. For "in house" interface the impedance is
always less than 1 ohm, balanced or unbalanced . Impedance of the line
inside of the building is ignored.
One of the few advantages of the low impedance source is the improved
resiliency to cross-talk from adjacent lines. In most cases shielding
is not required for better than 70 db S/N
>Modern practice recognizes that for short lines, we need not bother to
>match the line. Rather than use power transfer with matching source and
>load impedances we now use voltage transfer with relatively low source
>impedances and relatively high load impedances.
>The broadcast industry has been slow to adopt voltage transfer and much
>of the analog audio that remains in many broadcast facilities still uses
>power transfer. The routing switchers and terminal equipment sold by
>Grass Valley Group, Nvision, Utah Scientific, etc., are great examples
>of this. Analog audio inputs typically have a way to select whether
>they are bridging (high impedance) or terminating (600, 300, or 150 ohms)
>either with a switch or a resistor that may be soldered between turrets.
>I don't know much about products intended to drive what little analog long
>lines the telephone companies might still be using, but you can be sure
>that all of it matches those lines' impedance.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup