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I'm considering purchasing a high quality cable to connect the SPDIF output from my Bluesound Node 2 to a SPDIF input on my Bryston BDA-2. I was told that I should favor a1.5 meter length, which supposedly minimizes digital "reflections" better than any other length, shorter or longer. I had assumed that I should just go with the shortest length possible, a .5 meter. Has anyone heard of this? I don't see how it's true. Thanks, Peter.
Follow Ups:
I am intrigued by the moderate lengths being discussed. My PC which handles what little streaming I do, is connected to my audio system via about 10 metres of coaxial SP/DIF cable. It works and I have no idea if it would sound better if this was shorter because I can't rebuild my home to move either system. As long as it is 70 ohm screened co-ax, that should surely be OK?
Dave
I believe the S/PDIF distance spec is 10 Meters over 75-ohm coax cable, and these specs are often on the conservative side.
Before I got the house wired with ethernet, I used to use a 50 ft. Monoprice USB cable to stream from my laptop to my main system.
Now I've ordered up a BNC connector for my HiFIBerry Digi+ Pro so I can go BNC from the Pi to BNC on my DAC.
1 1/2 Meters will be hard as BlueJeans Cables are measured in FEET! :-(
Maybe have to special order?
Audiophile is hard work!
Buy from amazon.ca: a 1.5m cable will work much better than a crappy 5' - as long as you avoid measuring it.
In practical terms unless you have significant impedance mismatch at each end of the cable (source and load), it's not going to matter if you go with .5m, 1m, 1.5m, 2m, etc. Reflections occur due to mismatch. Even with slight mismatch it's not going to matter a lot because the signal arriving at the load end will be amplified and reshaped. There may be a theoretical 'ideal' but whether it really matters and is plainly audible is another story.
Maybe I should just order .5 and 1.5 meter lengths of the cable I'm considering and try to hear a difference between the two. I've heard that the Wireworld Gold Starlight 7 is excellent. Perhaps my "non-digital" .5m Audioquest Coral is doing a fine job right now.
It won't hurt to go with 1.5m, but as you mentioned you could try .5m as well and see if you can hear a worthwhile improvement with 1.5m.
Years ago I ran a few meters of cheap Belden RG59 75-ohm coax cable between my 5-disc CD changer and my DAC. Works great, sounds great! But at 50-cents a foot definitely not audiophile approved. ;-)
How did you connect the RCA plugs? I hear crimping is better than soldering, which can change the impedance.
You're faced with an impedance mismatch anyway if your source & DAC have RCA jacks on them. RCA jacks and plugs were never designed to accommodate 75-ohm coaxial cabling and maintain constant impedance.I'm not suggesting that you use RG59 coax but....
RG59 (and RG6) coax are 75-ohm. F connectors are also 75-ohm. These are typically used for Cable TV hook-ups. My RG59 cable came with crimped F connectors on each end. I used type F to RCA adapters on each end for my CD changer and DAC. Technically not ideal, practically it works fine and sounds fine.
However, if you need only .5 - 1.5m or so I would just buy an audiophile brand digital cable with RCAs attached rather than dealing with adapters. If you feel better about buying 1.5m, go for it. It won't make a practical difference but since when are audiophiles practical? ;-)
My reason for using RG59 is that it is 75-ohm, it is cheap, I needed a longer length, I already had several lengths of it on-hand. I just needed a couple adapters.
Type F to RCA Adapters
Edits: 07/19/17 07/19/17
Thanks for the info! Very helpful.
" I don't see how it's true."
As you may see from the link this effect in co-axial cables has been known about since the late 1940s. There is lots of information online if you care to search.
Most calculations regarding SP/Dif connections conclude that 1.5 metres is the optimum length for attenuating the first reflection sufficiently.
I can't access the text because I'm not an IET member. I'm afraid that if I pay the $20 for the article, I may not understand much of it if it gets highly technical. Can you share the article, or do you think someone with a non EE background would get much from it if purchased?
Edits: 07/19/17
It will indeed be highly technical but you really don't need to know the details of the scientific research to buy a cable.
All you need is to read the precis contined in the link. This says that this is a paper published by the Insitute of Electrical Engineers ( note copyright notice) in 1952 and is based upon research undertaken from 1945 and 1948. It concerns reflections in a coaxial cable due to impedance irregularities. More particularly it is about differing methods for measuring it. If the effect did not exist then there could be no examination of measurement procedures.
Unless you believe that the IEE would be involved with a bogus paper and you have the technical wherewithal to effectively peer review the paper if you want to dispute it, all that you need to take on board is that the effect exists and has been recognised over a long history by major institutions. Therefore no one is fooling you by claiming that co-axial cables have signal reflections caused by impedance changes.
I would add that reflection of energy caused by a change in impedance is also well known in mechanical science.
Of course as the signal is reflected back along the cable the cable's electrical properties , particularly resistance, will mean that it is attenuated, hence the preferable length(s).
If you want to know more in layman's terms then Google is your friend. Like this kind of thing:
I.5m is usually what is recommended for Dig Coax cables. USB cables should be as short as possible
Alan
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