On 16/04/14 18:20, Simon Wise wrote:
On 16/04/14 17:19, david wrote:
Interesting. What is the difference between speed of sound in air and the speed
of electricity through a cable?
sound is about 3ms per metre (330 m/s) in air
... in a room, talking about sound, there is no significant delay for the signal
in the cable ... from Sydney to Hawaii via copper or fibre yes, considering
phase differences for RGB video signals in a building yes, talking about timing
on a circuit board or a bus while syncing gigahertz clocks yes, but for sound
within a building the speed over copper may as well be infinite.
I was shown a rather nice artwork that used high resolution radar (resolutions
around 1 centimetre I think) to get positions (it was made in a university
robotics department that had such things!). The way those work is very
interesting ... the frequencies are way to high to digitise, so the electronics
has to be all analogue ... the 'circuitry' is basically plumbing ... gold lined
tubes and chambers using resonances and such to measure delays and phase
differences. At those frequencies the speed of light becomes a dominant
consideration.
and there are stories around of ridiculously expensive delay units for very
short delays (paid for by US military budgets) and australians replacing them
with a much more reliable, and almost free, solution using some switches and a
circuit board with loops of 1, 2, 4, 8, ... etc centimetres each, but it's the
usual way to do that sort of delay.
Simon
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