Your facility wiring... Twisted pairs - shielded or unshielded..??

[spinjector]

To some this may seem like a goofy question... I've been in radio/recording/roadie on & off for 20 years. Every facility/rig I've ever seen had all of its twisted pair audio wiring done with shielded cable such as Belden 8451. Then I started working for this place, and all the punchblocks in the rack room, studios, and a few other spots are all done with plain-old 22 gauge blue/white telephone punchblock wire - the kind the phone company has been using for decades.

And you know what? The audio is clear as a bell, and clean as my desk isn't.

So...

How many of you have broadcast facilities with some or all of your wiring unshielded...?

 

[fm-engineer]

Always shielded.

In a perfectly balanced signal, noise is naturally rejected at a differential amplifier, although most circuits change internally back to unbalanced for mixing, processing, etc. then back to balanced for outputs.

 

[grich]

You can do a lot with unshielded pairs, but you must be anal about making sure EVERYTHING is balanced well. I helped wire a new CC cluster a few years ago. The design had all audio interconnects between studios (analog and AES) made up with 25-pair CAT5 cable with an overall shield. Jumpers from punch blocks to equipment were made with 8451 (flexibility probably had something to do with it), while cross-connects between punch blocks in the rack room were made with telco cross-connect wire...white/blue stuff for analog, CAT5 for AES. Plant is nice and quiet.

 

[spinjector]

Yea this was an old CC plant years ago, and it's exactly as you describe - shielded to the blocks and then blue 22ga from block to block, and it's about as quiet as any engineer could hope for.

It isn't something I would do if the studios were near an AM site - either ours or anyone else's. And it makes sense to be careful that the twists are properly maintained, and the individual conductors are the same length when they are punched down on the blocks.

If you think about it - this is the way the phone company has been wiring things for a century. Just think of the miles of wires in a CO, and it's all 22ga UTP just like I'm talking about.

I can remember years ago when some audio gear had a nulling pot on the input. I don't remember what gear, or what for (other than the obvious telephone hybrid applications), but it was on the XLR inputs for something.

 

[TomT]

Valley People 400 mike processor--mike input shield not grounded unless you make the connection between two binding posts on the back. 4 miles from a 5 kw AM station, 1 1/2 mile from a kilowatt Class C. Tuned both in perfectly until the shield was grounded.

 

[bilco]

A highly respected radio engineer once told me he had done the cross connect telco wire bit once on a station and it was fine. I laughed at him. Later a contract station wanted new studio building built "Fast, Cheap and Good". I told the owner to pick any two, but he was insistent. I did the 22 gauge cross connect telco wire bit and was not overly disappointed. Not perfect, but adequate for what he wanted. I still used sheilded 8451 for the mic level stuff. Later engineers at that station screwed things up badly with unbalanced stuff, running AC wires next to low level audio, and/or failure to pay attention to simple things like phasing. I Never will do cross connect wire as a permanent fixture if I can help it. By the way, Belden 9451 is easier to strip and works faster but just as good as the 8451 and is about all I use now.

 

[spinjector]

Regarding 9451, yes that's what I use now. In fact - just discovered it in the past year. I've been using/saying 8451 for so long that it just pops out without thinking. =-)

 

[RF Man]

A highly respected radio engineer once told me he had done the cross connect telco wire bit once on a station and it was fine. I laughed at him. Later a contract station wanted new studio building built "Fast, Cheap and Good". I told the owner to pick any two, but he was insistent. I did the 22 gauge cross connect telco wire bit and was not overly disappointed. Not perfect, but adequate for what he wanted. I still used sheilded 8451 for the mic level stuff. Later engineers at that station screwed things up badly with unbalanced stuff, running AC wires next to low level audio, and/or failure to pay attention to simple things like phasing. I Never will do cross connect wire as a permanent fixture if I can help it. By the way, Belden 9451 is easier to strip and works faster but just as good as the 8451 and is about all I use now.

Not to mention that any mic channel being supplied phantom power must use 3 wires.

 

[bilco]

Let me be very precise about this, I would NEVER use cross conect wire for a Mic level signal, phantom power or otherwise. The cross talk at a -60 level would be murder!

 

[LA_Guy]

Except for mikes, I use cat 5 unshielded. Best thing to do is amplify the mikes with an external mike preamp (or processor) and go into a line level input on the console.

 

[spinjector]

Ok now, everyone calm down... My original question assumed 0db 600ohm line-level signals. I know about mic-level signal issues, and I'd never run mic lines unshielded. In fact, I always put the mic processor as close to the mics as possible for studio use. I used to be a roadie and built & worked concert sound systems. Try working with 40 (forty) microphones and processors all at the same time. One bad shield wire can make a show a nightmare. Especially when you mix it up with unbalanced gueetar pickups & f/x boxes, and microphones that are always hot (lost part of my left ear to a feedback accident). I was even present for the near-electrocution of a guitarist who got his lips fried on a microphone during sound check because he put a new plug on his amp and wired the plug wrong. ;D

 

[Chuck]

Ok now, everyone calm down... My original question assumed 0db 600ohm line-level signals.

From one old road dog to another, unshielded CAT-5 works just fine for line level balanced audio circuits in the studio. In fact, the lack of a shield makes ground loops a lot harder to create. I was not a believer at first, but Steve Lampin, of Belden fame, got me to try it. He was right....

 

[spinjector]

Yea that's what I've been using - CAT5 and CAT6. Right now I's sitting here listening to a Fostex 6301B of the PGM from main control, and it's run from the rack room about 150 feet away, over four hops, two patchbays, and wall wiring into my office, and it sounds clear as if I was in the studio.

Don't forget the StudioHub™ system uses CAT5/6 cable, and it seems to work just fine. I've never heard anything about it being a problem. In fact, I used some spare StudioHub XLR-to-RJ45 adapters to wire the monitor hookup I speak of above. I used the CAT6 building wiring right to the wall jack in my office, and a 20-foot Ethernet cable with one end hacked off and replaced by an XLR connector on the blue pair.

And, to widen the discussion from my original question about unshielded interconnect wire, one might ask, what is it exactly? It looks like just a single pair of what's in a CAT5/6 cable, right? Well, as I understand it, "it's all in the twist", which is a phrase I saw somewhere once. Interconnect wire and 10mbps Ethernet is CAT3, 100mbps is CAT5, and 1000mbps is CAT6, each with an increasing tightness & precision of the twist, the purpose being more perfect nulling. And they are all backwards compatible, so CAT3 is for audio, so CAT5/6 should work for audio too, but have cleaner transmission.

I have considered that using shielded CAT5/6 between patchbays and wall jacks, with the shields all centrally grounded and not passed through to the jacks would be an excellent happy-medium between shielded and not.

I have to say that if we ever remodel or move this place any time soon, and we're not all-digital by then, I will wire EVERYTHING with CAT6 - even the audio between studios & racks. Unless by then doing everything with fiber is cost effective, but that would requires us to be digital, and by then if we're not 100% digital behind the mics & cans, it'd just be kinda silly.

 

[Rich883]

You are right on point with the twists. Steve Lampen from Belden (as noted above) wrote several papers on this topic, including using cat 5 for sending digital audio and Video over with great success. Several years ago all the studios I was involved in started using cat 5. it reduces costs, smaller conduits, smaller cable trays, much less cable prep. The key is balanced line level signals.

Gepco makes a single pair in a jacket with a cat 5 twist. This is great for cross connects, and for making source cables for connecting from a console or block to a audio device. Nice and flexible, and dresses great.

All in all, beside the few mic sources noted, Haven’t used standard wire in some time, except for unbalanced devices.

All this said, my comments are on the cable, not a system like the studio hub. In that case you waste most of the pairs in the cable to use the RJ45, but everyone has their favorite.

 

[TomT]

If you run the solid wire CAT5 to jacks, then use short jumpers to the devices you can use all four pairs.
Levitron makes nice punch-down jacks that mount in cover plates and standard electrical boxes. You do need to buy a good punch-down tool.

On an RJ-45, the orange/orange white and green/green white pairs are used for communication, the other two pairs aren't used. If wiring paths are tight, you can get a cover plate that holds two RJ 45 jacks, and use the other two pairs for a second device. Had that problem getting cabling to a work station where there was both a computer and a networked printer, the shared cable works fine. Have seen cautions about shared data and telephone--presumably because of spikes from ringing voltages. But would probably work fine for audio and data in the same cable.

Of course, you need to adopt one of the two color-code standards (586A or B) and stick to it to avoid driving yourself nuts. There are diagrams/articles all over the internet.

 

[nmoore6676]

If you run the solid wire CAT5 to jacks, then use short jumpers to the devices you can use all four pairs.
Levitron makes nice punch-down jacks that mount in cover plates and standard electrical boxes. You do need to buy a good punch-down tool.

On an RJ-45, the orange/orange white and green/green white pairs are used for communication, the other two pairs aren't used. If wiring paths are tight, you can get a cover plate that holds two RJ 45 jacks, and use the other two pairs for a second device. Had that problem getting cabling to a work station where there was both a computer and a networked printer, the shared cable works fine. Have seen cautions about shared data and telephone--presumably because of spikes from ringing voltages. But would probably work fine for audio and data in the same cable.

Of course, you need to adopt one of the two color-code standards (586A or B) and stick to it to avoid driving yourself nuts. There are diagrams/articles all over the internet.

I think as a person who has wired studios, audio systems, and done extensive work on data networks I would avoid mixing data and audio in the same cable. While the twisting of the pairs offers protection against crosstalk withing the same cable, the four pairs are also twisted to provide additional protection among individual cables within a wiring tray or conduit.

You could also for audio usage use all of the four pairs but for high speed data probably not a good idea. You are correct about the spikes due to the 70-90volt 20Hz ringing voltage being a good reason not to mix telephone and other circuits in any cabling. Also ringing signals can be a bit unbalanced. At one time they used ground for ring return in some COs (multi subscriber loops) but probably not any longer since party lines are seen very much these days.

 

[TomT]

I concur, a critical audio circuit would probably not be best place to mix with a data circuit. Sometimes you need to improvise though; radio stations are not always built in places where you can easily run cables with ease.

Cat-5 being relatively cheap, if you have the room to run several cables, and if you are going to use cat-5 for audio, just buy two or three different colors to run in the trays or conduit. We had to both find a site and build a studio the end of last year. Bought a station--they were in a JSA, and other company wanted them out NOW! Ended up buying a split level house on a main drag. Nice visible location but fun to convert for radio. Used blue cat 5 for data, orange for telephone. Studios were easy--they went into bedrooms above an unfinished garage--just drilled holes in the floor, tacked to the joists & up into what was the laundry room where the switch was for the lan; telco demarc just below that in an unfinished basement room.

Offices proved to be fun--rest of the basement finished, walls all sealed. Ended up building a trough along the top of the basement walls to a point where I could bring up data/phone cables into the living room (now sales office)--then hide the wires behind new baseboard.

Which returns to the original discussion--I stuck with Belden shielded wire for audio for this project for several reasons:
1. Not that many pairs needed between rooms;
2. Could terminate in barrier blocks or even straight to the equipment at each end;
3. Much more flexible and easier to fish through/over walls/floors.
4. Used the stick-on numbers so my feeble brain could keep everything straight ;-) !

 

[radiorob2.0]

Cat-5 is a wonderful, inexpensive versatile thing. As long as it is terminated properly, it will handle everything.

 

[spinjector]

Regarding "pair sharing" of CAT5, the spec says the two unused pairs are "reserved", and for the most part they are not used.

HOWEVER...

CAT5-POE (power-over-ethernet) uses the other two pairs for the power, which is 48vdc. So if you are in a plant with a VOIP system, or other specific POE system, and/or the router/switch you are plugged into has POE enabled, there's some juice there that could fry the ins/outs of your audio gear.

CAT6 uses all four pairs for data.

So unless you are 100% legacy CAT5, be careful about pair sharing.

 

[ChiefOperator]

Interesting discussion regarding Cat5e UTP. I share the same experience: at a SBE session, Steve Lampen from Belden told us that Cat5e is, indeed, an excellent cable for studio wiring. I've used 9451 mostly...