Shield or Unshielded


#21

Well, try both and let us know. That would be one of the cheapest experiments in this HiFi caper.


#22

Actually you don’t even need to go to China.

Blue Jeans Cable’s Cat 6A is Belden’s 10GX series cable, with a floating shield design - disconnected from the plugs at both ends.

Their Cat 6 cable is unshielded but their Cat 6a cable has the floating shield design.

You don’t need to trust me on that either - email and ask Blue Jeans Cables for confirmation.


#23

Thanks for the recommendation. I like Blue Jeans Cable. Good quality and very affordable. I sent them an email earlier.


#24

Based on posts at another audio site, I bought Cat 7 from Tera Grande, I don’t know if they make up custom sizes. I see they have 50’ & 75’, you can call them, when I did they were very friendly.
Here is the link: https://www.teragrand.com/CAT7-Network-Cables-s/132.htm


#25

Thank you.


#26

I do prefer to use shielded cable on my source. If you lift ground on one side, then you have a Faraday’d cable, (and this is done many times to remove ground loops, if present, yet not lose the advantages of the shielding) and if you disconnect both sides, the shield itself can become an antenna. (non-terminated) If you float the shield, I would suggest UTP, not STP. (for ethernet purposes)


#27

No, you don’t have a “Faraday’s cable” and you do lose advantages of shielding. Agin read here:

Your best bet is to use UTP for Ethernet in audio.


#28

speed-racer; thank you for referencing Belden’s documentation, however, I am speaking about cables for network usage, not audio. These work in the MHz range. The documentation you have referenced is about using cable intended for network, as audio cable. I use STP for my network purposes, and quad shield RG6 for interconnects.

Concerning lifting a shield at one end of a cable utilized for audio purposes, this is done on many occasions to remove ground loops between equipment. This is the intended purpose of the ‘ground lift switch’ eliminating unwanted hum and buzz by interrupting the ‘ground’ loops between equipment, preventing current flow along the cable shield between two devices.


#29

An interesting cable is the Belden6A with JSSG shield by Ghent Audio. The shield is lifted at both ends and a loop is used to connect them.


#30

No, I and the article are talking using Ethernet networking cables in an audio environment. Ethernet cables are always used in networking and always move data.

As @cxp noted, the JSSG shielding is an excellent way to shield Ethernet cables properly without creating a path for noise.


#31

“If it’s just audio, no problem. Check out Belden 1353A. It’s really a Bonded-Pair Category 5e patch cable, but it’s in the audio section of our catalog! It’s the best audio cable we’ve ever made.”

Belden 1353A is simply one pair, 24 gauge/2 conductor, each conductor a stranded wire with 7 32 gauge leads, not 4 pair utilized in ethernet cables.

“Belden Brilliance 1353A, a new Cat 5e digital audio single-pair cable, is ideal for use in professional and commercial audio applications. Since it is essentially ‘single pair-Category 5e,’ tested to 100 MHz, its low capacitance (15 pF/ft, 49 pF/m) makes it excellent for both analog and digital audio.”

I’m not speaking to interconnects in my original statement, but shielded cable for ethernet usage. If you really want to test out why I use STP for my ethernet, get a pocket AM radio, turn it all the way past 1600kHz and get close to an UTP cable that is live, and then do the very same with STP. You’ll find out really quick that egress from the noisy environment it presents isn’t something you want close to any low level signal cable. Secondly, if you use a switch with a wall wart for example, it has no reference to ground if UTP is utilized. This is why I use STP from my source to the switch. It prevents egress, and gives a ground reference to the switch. (this is not accomplished through UTP as the unused pairs are decoupled and not attached to the ground plane of the switch itself, however the shield is)

The primary focus of the article you have referenced deals with shields in the audio spectrum, and it doesn’t matter if removing one end of the shield creates a filter at 100kHz, since that is many times above the audio spectrum. It’s the way loops are dealt with in analog audio cabling utilizing shielding, and the cable is still Faraday’d if one side is lifted.

“So, instead, most installers resort to the next best thing- cut one ground. That instantly solves your ground loop problem, but which end do you cut? The answer is, leave the source (the low impedance connection) and cut the destination (the high impedance end).”


#32

Physics people. FTP CABLE inherintly has significant disadvantages for RF digital performance. Shields are ONLY useful if you have noise ingress or egress that deteriorate performance over a UTP counterpart. UTP cable is well superior at electrical stability as the ground reference, and it’s variation, is far, far lower.

A RF cables reactive variables are controlled by the proximity to the electromagnetic ground reference. Capacitance is a power law formula that says the CHANGE in the location of a shield the WORSE the capacitance will be at that location in an RF cable. The closer the shield to the core pairs, the larger the change in capacitance. Thus, the WORSE the impedance stability. And, a shield will impact internal pair to pair cross talk up to 6 dB or more and this limits the Shannon law bandwidth. The noise floor is closer to the signal.

Shields are good if the ingress noise is significant enough to upset the balanced CMRR built onto Ethernet cables. Proper balance in pairs mitigates the need for shields. If there is no noise source, more stable performance is seen in UTP Ethernet cable.

Where ingress noise reduces the Shannon law bandwidth more than the 6 dB impact shields have on internal cross talk, and the increased return loss due to worse impedance control is acceptable, then use shield, but not till then.

10g Ethernet uses FTP design to allow tighter cable to cable spacing, but still mitigates ANEXT between cable that is cable to cable magnetic field controlled. A UTP will work is fine if it is sized to increase the spacing to account for no shield. Special designs need to be used to precisely place the shield to mitigate RL reflection degradation from the use of shields in 10g cable.

10g can’t tolerate what is called alien cross talk from adjacent cables to a target reference cable as it is unpredictable. Internal NEXT, RL and other variables can be noise cancelled with electronics.

There is still a lot of misunderstanding on how cables work.


#33

Any comments on the JSSG shielding technique?

Basically they take a Belden Cat6a and connect the floated shield ends with a loop wire. One end runs all the way back to the other end via the loop but it never touches the connectors.


#34

CXP,

Shields do two things, each one independent of the other;

First shields establish a ground plane the sets capacitance, and thus determines a cables RF impedance. The variation of the shields proximity to the conductors will change the impedance variation. The electric field reaches the inner surface of the shield, and this distance is what adjusts the capacitance at AUDIO frequencies or RF. The thickness of the shield as ZERO effect on capacitance as it is the electric fields initial inner surface reference that determines the capacitance. The higher the frequency, the more physical distance variation changes the impedance, and causes REFLECTIONS in the cable. Those reflections are a form of attenuation as energy isn’t received at the load end of the cable. RF attenuation is significant as frequencies go up, so losing energy isn’t the best situation!

Second, a shield is an ingress or egress electric field shield. At audio, EMI / RFI is well above the bandwidth of most input devices, and those devices use RF shorting capacitors that look like a short to RF energy routing it to ground on the SHIELD in the case of an unbalance coaxial cable or where the signal is isolated from an earth ground. The shorting capacitor routes the NOISE to earth ground from signal ground, but leaves the lower frequency signal at signal ground. At audio the signal is too low a frequency to see the capacitor as a short. With unbalanced (Ethernet type) cables the shield is NOT a part of the signal path, so it can be tied directly to earth ground. Shield are only effective for RF frequencies as the electric field is stopped by a metallic shield and low frequency magnetic fields are not (why a magnet sticks to a metal plate through a piece of paper, for instance, it ignores that material). Materials that are low permeability to magnetic fields will re route magnetic flux lines. These include anything a magnet sticks to like a metal pipe. Put a cable inside a magnetic metal pipe will shield low frequency noise.

10G Ethernet with floating shields use a shield to establish electrical IMPEDANCE and attenuate very high frequency EMI/RFI. Since each end is FLOATING in 6A cables, it can use UTP (far cheaper) connectivity and thus the cable acts like a UTP cable and the freedom from ground loops. EMI/RFI is attenuated as it moves through a HIGH impedance shield. The foil layer is THIN so it attenuates standing waves (no where to go as each end of the shield is OPEN, so it bounces back and fourth through the shield). Care must be taken to engineer the shield to properly attenuate standing waves in this kind of shield.

The alternative is to GROUND the shield to EARTH ground. This increases the bandwidth of the shields ability to attenuate noise at the cost of a more expensive ground system. One or both ends can be grounded. If a ground loop is present, you either have to improve the ground at the higher impedance end, or ground the shield at the SIGNAL end. Why the signal end? With one end grounded, the EMI/RFI will go to ground (path of least resistance). The EMI/RFI is at the smallest potential to the signal when the signal is at a maximum potential, and that’s at the send end BEFORE it is attenuated going down the wire. So this is why it is best to ground the send end FIRST. But, if the send end ground is a higher impedance than the ground impedance at the destination end, then the opposite can work. Which ever puts the signal potential larger than the shields EMI/RFI is what you want to do. A one end only ground is often called an antenna ground. It collects the signal on the shield, and in the case of a shield verses an antenna, routes the “signal” to earth, removing it from the circuit. An antenna routes what it captures as a signal to the appropriate input resistor.

Grounding BOTH shield ends works if the grounds are essentially the same potential, as current won’t flow either way. In a good system with TIA/EIA compliant ground straps, this is what is used by default as the spec resistance of the ground bus insures ground currents don’t form ground loops.

JSSG didn’t invent anything, they converted a UTP floating shield that’s designed for HIGH RF frequencies, to a FTP shield that requires GROUNDING at one or both ends for lower frequency extended EMI/RFI (still well above audio frequencies) applications. You really don’t want a low impedance floating shield as it can’t attenuate the standing waves in the floating shield. Floating shields work well at much higher frequencies and when a shields impedance is made higher. Adding a ground wire reduces the shields ability to attenuate EMI / RFI, so it has to ROUTE the signal to a ground to work the best. One needs the opposite shield impedance of the other. Floating shield should be extremely HIGH impedance, grounded shields need to be extremely LOW impedance.

For audio, you need BALANCED pairs to remove common mode noise, that includes both EMI/RFI and low frequency magnetic interference, both. The non metallic aluminum foil tape or copper braid shields ONLY reduces E-field RF frequencies. They have no shielding for HUM and related magnetic B-field noise. This is why BALANCED XLR cables are so superior to coaxial RCA cables. RCA cables can ONLY mitigate EMI/RFI but not lower frequencies. RCA shield IMPEDANCE designed to be as low as possible helps reduce shield currents and inductively coupled electric field noise. But, the impedance is low ONLY for frequencies that see the shield as a “conductor”, and that doesn’t include magnetic verse electric waves.

USB cables use RF shields to isolate the high frequency data rates, but the lower the frequency, the more the TWIST in the wires and the BALANCE remove the noise. Foils shield are technically not needed in a perfectly balanced application, but nothing is perfect. Think of a RF frequency shield as a leaky rain coat, it REMOVES a lot of the water, leaving less to remove through the cables balance pairs. Removing 10% of a small amount of water leaking in leaves far less water than removing 10% of ALL the water that wants to leak in. MIL spec on capacitance unbalance is typically 3% max, so it isn’t prefect.

DIGITAL cables need good balance, a proper shield ground system based on the shield technology and consistent ground geometry (shield to conductor(s) distance) to work the best.

Galen Gareis


#35

I’m confused. In switched ethernet, what is the SIGNAL end?


#36

Nope…that is not what they have done.


#37

What I took from Galen’s response is that the implementation is bad. The shield needs to be grounded on one or both ends to work properly.


#38

Ray,

There isn’t a signal end on full duplex systems, and that is why the TIA/EIA puts struck requirements on the ground system resistance differentials, as both ends require a ground. For Ethernet it isn’t confusing at all.

The confusion arises when half duplex systems are used, or Ethernet is used in audio systems and people wonder, how do I treat the ground? And, if you violate TIA/EIA ground standards you may have issues with looped grounds.

Galen Gateis


#39

Question about the grounding standards.

There are tons of routers out there and switches/fmc’s that people use in their audio systems.

Do you have an idea if the ground standards are used across the board or is there a lot of variation.

I would think gigabit switches may not have grounding configured due to the fact that gigabit can be attained via cat5e and cat6 cables.


#40

Speed racer,

The JSSG description is for what has ALWAYS been done. An RCA uses the ground at each end which establishes a loop between devices. Nothing new here. The argument is a shield loop, at ground or floating above ground, but still a loop (isolate the RCA ground’s from earth ground).

XLR cables isolate the signal ground reference from true earth. Each on separate loops.

The so called special ground added on Ethernet does the same thing, grounds at each end form a low impedance loop. This requires FTP connectivity. Another external loop of wire does little to offer audio frequency shielding from magnetic interference.

Yes, the signal can FLOAT as a signal ground or be at earth in a ground “loop”. If the earth is too high impedance, you’ll have issues. The objective of a shield is to reduce the current in the loop such that the current times the resistance of the shield is a very low voltage, and the small current induces little noise into the cable core components.

A test called transfer impedance defines the shields ability to reduce shield current with the shield considered the worst case resistance in the loop.

Most won’t get near the 328 foot Ethernet standard so all kinds of mistakes can go unnoticed. Grounding a shield at one end improves a RF shield since it removes reflections back and fourth in a floating shield that requires the POTENTIAL induced in the shield from the AC signal inside to be attenuated.

Shields see ingress and egress, both. Most think shields are outside in only. Not the case. Many systems are noisy, and need shields to protect EXTERNAL circuits. Transfer impedance is bi-directional.

Loop shields, what is what is describes, are best because the shield does not need to be as highly engineered to work, and low transfer impedance numbers are best for loop shields. A shield DOES need to be highly engineered to be geometrically stable for RF signal transmission, which doesn’t impact audio.

Cat 6A is WORSE THAN best case Cat6 for signal transmission. Why? Some of the INTERNAL electrical are relaxed to meet stricter EXTERNAL ingress electrical. The advantage 6a has, is external noise that can’t be equalized out is mitigated, allowing more sensitive PAM 16 verses PAM5 encoding. Audio does not have alien near end cross talk issue as bundles of cable with high frequency RF aren’t used. DT600E has better measured internal electricals than 6A, but it can’t mitigate external noise to use PAM16 In a noise bundled cable configuration.

Stand on a golf course and hold up a metal rod in a thunderstorms standing on wet ground. There will be current flow! This is called ESD electrostatic discharge shielding, and need a super low impedance path to ground. It equalized the potential between two points through the least resistance ionization path. Static potential is always at some level of potential difference.

Non metallics shields do not block B-fields, only E-fields. Adding a copper wire loop won’t change physics. You need a low permeability shield, use field cancellation, and to work the counter rotating magnetic fields around a material conductive to electric energy, generating a current, need to be as close as possible, or use true balanced circuits With XLR type CABLE.

Show me the data to support different from what I’ve provided, which has been supported by physics for over 200 years.

Galen Gareis