bhaagensen;547680 Wrote: > NewBuyer: thanks for the comments and in particular pointing out one > source of the 'long-cable'-argument. Another source that I see quoted > from time to time, is this: > > http://www.positive-feedback.com/Issue14/spdif.htm > > Along with your comment I also note, in this particular context, that > Naim's own (recommended) digital coax cable is 1.25m...
You're welcome. :) A source for the opposing short-length digital coax cable argument is Dan Lavry - here's an extract of one comment from him, on this subject: Dan Lavry Wrote: > ...In fact, the shorter the cable, the better you are. I am not > suggesting to use 3 inches cables, but a 3 foot is better then 10 foot, > and at over 30 feet you are certainly asking for trouble. > > You said the reason for keeping the length at least 2 feet had to do > with reflections. Reflections have to do with MORE LENGTH, not with > less length! Reflection becomes an issue when the cable becomes LONG, > making the signal propagation delay longer (the signal travel time from > the driver end of the cable to the destination end). What does > longer time mean? Longer with respect to the digital signal rise (and > fall) time. > > A typical cable delay is around 1.5 nano second (nsec) per foot. The > velocity is slower then the speed of light, in the range of 1/3 to 2/3 > of the speed of light, and it depends almost entirely on one factor - > the cable inner material isolation (the dielectric). > > The rise time for the digital signal is between 5nsec and 30 nsec. > 30nsec is slow but still within the specifications. 5-15 nsec is nice, > and the reason that faster is not allowed has to do with setting a > limit on the electromagnetic radiation (transmission of interference). > > At say 10 feet, the cable delay is around 15 nsec, and a 5nsec rise > time is 3 times faster then the delay, so one DOES NEED to terminate > the cable and do so properly. > > But at say 8 inches length, the delay is around 1nsec and even a fast > 5nsec rise is 5 times slower then the cable delay, and the signal will > have virtually no reflections at all. The shorter the cable, the better > it is from reflections stand point as well as from many other > standpoints. > > I am not suggesting 8 inch cables. I am not suggesting not terminating. > In fact, as a rule the termination is built into the receiver side. The > issue here is cable length, and the notion that there is a minimal > cable length one should keep is just plain wrong. > > Regards > Dan Lavry > Lavry Engineering -- NewBuyer ------------------------------------------------------------------------ NewBuyer's Profile: http://forums.slimdevices.com/member.php?userid=7862 View this thread: http://forums.slimdevices.com/showthread.php?t=78736
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