03-10-2016, 08:24 PM
(03-10-2016, 06:06 PM)Gryphon Wrote: If Murphy v310 does want to terminate his line correctly, it will help him enormously to know what the Zo is. Which rather, I think, brings us back to where we started.
Well no. We started with the OP wondering about the basics of using short coax cables with audio signals. Where really, loading effect is the big "trap for young players", as David Jones would put it. Transmission line effects not an issue.
Trevor's coax came up later. But measuring Zo is a trivial piece of work; hardly worth debating...
(03-10-2016, 06:06 PM)Gryphon Wrote: I'm going to give a politician's answer to your question, which means I'm going to duck it, but unlike most contemporary politicians, I'm going to have a stab at justifying the duck...
Obviously, in engineering disciplines the answer is usually "it depends". But rules of thumb are good to get us in the ballpark before we quantify more precisely, or to sanity-check when we have. Rules of thumbs are just that; everyone (hopefully!) knows that they normally need to be qualified in reality.
So perhaps your point is that not everyone appreciates the meaning of "rule of thumb"? Perhaps you're frustrated with folk investing too much in rules of thumb rather than actually "doing the math"? If so, I can empathise with that!
(03-10-2016, 06:06 PM)Gryphon Wrote: To show how easy it is to fall over in real life, if you don't think carefully enough about what's going on, consider for a moment the situation shown in the attached drawing. S and R are two centres heavily interconnected by lines. Some of these are co-axial tubes with interstitial pairs, which are routed directly between S and R...
Fortunately, it's rare to send analogue signals any distance these days.
The idea that a stub causes problems is no surprise, and the fact it can happen in the low-km range is no surprise for an audio signal either.
In practice today you're much more likely to find that a stub causes problems for AES3 audio. It's why Guillmetti patch panels carrying AES should use special normalising plugs that blank the upper row of "listens", preventing someone from creating a stub. But a scary number of patch panels are populated with standard normalling plugs, and it's just luck that more services aren't taken off air.
