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What makes a good Ethernet cable for audio applications?

What makes a good Ethernet cable for audio applications?

Put simply: It’s all about the spec!

Modern Gigabit Ethernet networks rely on very specific standards for cabling infrastructure in order to ensure that rated network performance can be reliably and consistently achieved. These standards include not only the specifications for the cable construction itself, but also specifications for the termination of cabling and physical connection to devices, creating an end to end highly engineered system. Deviations from these specifications can result in reduced performance and even data loss, so it’s important to use the right cable for the job, and to use good quality cable that meets the necessary specifications.

This rule holds just as true for audio over Ethernet applications, if not more so. Cabling that is out of spec can result in dropped packets and intermittent connections. For something like streaming a YouTube video or transferring a file, it could just mean increased buffer times or increased transfer times. For live real-time audio, it can mean audible dropouts in audio or loss of audio altogether.

 

Cable Category

Cat5e and Cat6

Most audio over Ethernet applications recommend using Gigabit Ethernet (1000BASE-T, GbE, or 1 GigE), and in high channel-count applications, it’s often even a requirement. Gigabit Ethernet’s 1 Gb/s transmission rate requires certain network infrastructure to support it, including Gigabit-capable switching hardware, and Ethernet cable of sufficient rating or category to support Gigabit speeds.

Copper-wire Ethernet networks generally use twisted-pair cable. Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources, and reducing crosstalk between neighboring pairs.

The two most common Ethernet cable categories that you’re likely to encounter are Category 5e and Category 6, both of which support Gigabit speeds at lengths up to 100 meters, as specified by the TIA/EIA-568 standard. The higher spec of Cat6 is actually designed to support speeds up to 10 Gb/s (10GBASE-T or 10 Gigabit Ethernet), but it is backwards compatible with Cat5e (as well as Cat5, Cat3 standards). The primary differences between Cat5e and Cat6 which account for their different performance ratings are the wire gauge of the conductors and the number of twists per inch in each wire pair, with Cat6 using heavier gauge wire and a higher twists per inch spec, providing for lower crosstalk and a higher signal-to-noise ratio.

Which you choose for your application will depend on a number of factors such as cost, network design, fixed install vs. mobile, and considerations for future use. Cat5e is usually a bit cheaper, can be slightly easier to work with due to differences in construction, and still fully supports Gigabit speeds (as long as it’s truly Cat5e and not the older spec Cat5), but Cat6 is generally a better choice and worth the small premium in price, especially when taking future use into consideration, given the capacity for speeds greater than Gigabit.

The most important consideration is getting cable from a reputable vendor to ensure you get a high quality product that meets the industry and engineering specifications it claims by its Category label. Avoid extremely cheap cable as much as possible, and stay far, far away from anything labeled CCA (Copper Clad Aluminum), as it does not meet the TIA/EIA specifications for Cat5e and Cat6 cabling.

 

Cable Types

Shielded vs. Unshielded

You may encounter Ethernet cable labeled as shielded or STP (Shielded Twisted Pair) cable. Shielded Ethernet cable is special Ethernet cable constructed with additional electrical shielding along the length of the cable (using braided wire, foil wrap, or a combination of both) as well as specially constructed plugs that electrically connect and properly ground the cable shielding to the device connected at each end (which also must have special shielded jacks as well).

There are some specific use cases which might call for shielded Ethernet cable to prevent electromagnetic interference (EMI) or radio-frequency interference (RFI) from affecting the performance of the cable, but this is generally only called for in severe industrial manufacturing environments around heavy machinery and large electric motors. In fact, if shielded cable is used but not implemented properly, it can actually introduce problems and actually make things worse than using unshielded cable would have been to begin with.

Because shielded cable is more expensive, heavier, more fragile, more difficult to terminate and work with, has additional technical considerations to implement correctly, and is only called for in specific cases, regular unshielded cable or UTP is actually more than sufficient and is even preferable in most situations. That said, you should always check for any specific requirements by the manufacturers of the devices you are connecting, as they may be designed and intended, or even required to use shielded connections.

Coincidentally, most XLR-style locking Ethernet connections you commonly find used for Audio Network connections on Pro Audio equipment are designed to be able to support shielded cable connections if needed, though unshielded cables and plugs will still work just fine with these locking connectors.

When in doubt, it’s safer to stick with UTP cabling, unless your specific application or equipment explicitly calls for using STP cabling.

 

Solid-core vs. Stranded

Probably the more important consideration for Pro Audio and Live Sound applications would be whether to use solid-core or stranded Ethernet cable.

Most Ethernet cable you find will be solid-core, constructed using solid insulated bare copper conductors for each of the eight wires in the four twisted pairs of the cable. These cables are meant to be used in permanent and semi-permanent installations, and are designed for longer distance horizontal and backbone cable runs. All Cat5e and Cat6 solid UTP cables are designated with minimum bend radius for performance standards. Proper cable installation is essential in order to maximize the performance of the cable.  

In the case of a mobile live sound operation, with frequent setup and teardown, solid-core Ethernet cable probably isn’t the best choice, as it’s generally stiffer and not conducive to easy layout and flat deployment runs. Solid-core cables should not be over-flexed, bent, or twisted beyond the cable’s recommended specifications, as you risk damaging the cable causing it to underperform or even fail.

Stranded Ethernet cables have multiple strands (typically 7 strands per conductor) of insulated bare copper conductors. These cables are typically used for patch cords/cables connecting devices to the network, but because these cables are more flexible than solid conductors, they are an excellent choice for portable uses and applications where repeated flexing is common, such as frequent setup and teardown of a live sound PA system.

Another variation worth considering is something usually referred to as “Tactical Ethernet Cable.” This is Ethernet cable that is intended specifically for harsh environments where repeated deployment is the norm. Tactical cable generally uses stranded-wire construction for flexibility and durability, as well as employing a heavy, often rubberized outer jacket in addition to the lightweight PVC jacket of normal cable (sometimes referred to as “up-jacketed”). Tactical Ethernet cable has very similar feel and handling characteristics to XLR microphone cable, and is much more rugged than common solid-core cable used for in-wall building installation, making it ideal for Pro Audio and Live Sound applications.

 

Plug Termination: Right and Wrong

Making your own Ethernet cables can be a great way to save money, and allows you to create cables to fit your needs and specifications exactly. If you choose to make your own Ethernet cables, it’s important to be aware of some possible pitfalls and follow some important general guidelines.

 

The right plug for the job

As mentioned, Ethernet cables can be of the solid-core or stranded variety, and just as it’s important to choose the right type of cable for the job, you should also take care to choose the right type of plug for the cable. Most RJ-45 plugs are designed to be used with either solid-core cable or stranded cable, and using a plug designed for one type of cable with a cable of the other type can produce unreliable results. There are RJ-45 plugs available that are designed to be used with both solid and stranded cable, so just pay attention to what the plugs you source are specified for and you should be fine.

The same is true of plugs for Cat5e and Cat6 cable. Most RJ-45 plugs are only meant to be used specifically with one or the other. There are sometimes even several variants of a Cat5e or Cat6 plug just for different wire gauges and overall cable jacket diameters. Again, as long as you make sure that the plugs you choose are appropriate for the cable you’re using, you should be fine.

Also worth considering is that, just like when sourcing cable, it’s important to source quality plugs from a reputable vendor. The plug itself is one of the most crucial pieces in the equation. Even the highest quality cable is only as good as the plugs terminating either end.

 

T568B or not T568B... that is sort of a question?

There are two wiring pinouts defined by TIA/EIA standards, T568A and T568B. Currently, T568B is used almost universally in the U.S. - a legacy of analog telephone compatibility - while T568A is more common worldwide. Either is perfectly acceptable as long as you are consistent. If you’re doing a new wiring install, it’s best to just choose one or the other (T568B in most cases) and stick with that everywhere. If you’re making up new cabling and not sure about an existing wiring install, don’t worry, it’s even okay to intermingle the two standards for the most part. The most important consideration and the only inviolable rule you absolutely must follow is that for a given cable or run, you must use the same wiring standard on both ends.

 

Doing the twist

One of the most fundamental characteristics of twisted-pair Ethernet cable that allows it to work are in fact the twists of the wire pairs within the cable. Because of this, it is crucial that the twists are maintained as close as possible to the contact termination within the plug as possible.

You’ll also want to make sure that for wire pairs running to adjacent pins that they’re running parallel inside the plug body all the way to the pin. You don’t want different pairs wrapped around each other or have wires bunched up inside the plug and pressed against each other.

Trimming the wire pairs to the proper length is also crucial, as you want to make sure that the back-crimp of the plug is clamping down on the cable jacket, not the wires themselves.

You might be surprised at how easy it is to create a poor termination and how narrow the window is between a working cable and a failing cable. The crosstalk performance and EMI rejection capabilities of Ethernet cable which ensure it will function up to its rated specification are entirely dependent on maintaining these tiny relationships of the wires within the cable and the plug termination. A little attention to detail goes a long way here.

 

You’re crimping my style

Another often overlooked element of Ethernet cables are the actual plug terminations themselves. RJ-45 plugs and jacks form a highly engineered connection system, with very exacting specifications and tolerances. If you’re making up your own cables, it’s very important to use quality plugs from a reputable supplier and to use a quality crimping tool that crimps the plug cleanly and to the proper contact depth.

RJ-45 plugs that are over-crimped can result in a number of issues, including intermittent connection due to physical contact lift off. It’s important that you use a quality crimping tool, as poor quality tools may be mis-calibrated and poor quality tool dies generally wear out more quickly.


PAE_crimping_style.png

The plug on the right is an example of an over-crimped plug. Notice how the contact blades are sunken a bit deeper, putting them further away from the bottom face of the plug, and how the prongs of the blade are protruding through the top of the wire into the plug body. This plug may actually have physical connection loss due to contact lift off. The crimping tool that was used on this cable may be worn out, poorly calibrated, or simply of poor quality.

Even with a good quality crimping tool, the best way to ensure you get good results is to spot check your cables with a set of calipers to ensure that your tool is crimping the plug correctly and that the contact blade depth is within spec: approximately 6.14mm to 5.9mm

PAE_crimping_style_.png

That’s a Cable Wrap!

Hopefully by now you know a little bit more about Ethernet cables than you did before. Maybe now you know more about Ethernet cables than you ever wanted to! Either way, I hope you’ve come away feeling better informed and better equipped to navigate the world of networked audio with confidence. Having a basic technical understanding of Ethernet cabling standards can go a long way towards both helping you to troubleshoot problems as they arise, as well as increasing your chances of avoiding problems to begin with.

As with just about everything, knowledge is power, so when it comes to something as important as the cable technology that your entire audio network is built on, I say more power to ya!

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