Stupidly long audio cable run

Discussion in 'Cables & Switches' started by webspot, Jan 10, 2008.

  1. webspot

    webspot
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    I am from Twynham School and we've got our own community radio station. We'd like to make a direct link to the hall so we can get content direct from the hall. I guess we can run a cable from there to our radio studio. The distance between our studio and the hall is around 50meters (rough estimation)

    What would be the best ways to do this?
     
  2. softcookie

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    Balanced audio through a screened twisted pair cable (standard PA microphone cable). You will need two separate cables if you are using stereo. These types of cables generally have XLR connectors on them, and you will need something with a suitable balanced output to drive it. Most mixing desks have the correct inputs to match this.
     
  3. dshipp

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    I agree with softcookie, balanced audio over twisted pair cable is definitely the way to go.

    I wouldn't necessarily buy a 50 meter run of pre-made cable though. Back in my studio radio days we often used to run a few hundred meters of cable to transmit audio from other building on campus back to the radio station. We would use a few runs of CAT5 (network cable) to get all the lines we needed.

    CAT5 has 3 twisted pairs in it, so one run of CAT5 would be fine for a single stereo feed.

    If I were you I'd contact your local university based student radio station to see if they have any engineers who'd be happy to help you out.
     
  4. ben.bayliss

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    CAT5 is not suitable for balanced audio, and is almost always unscreened. I wouldn't even consider going down that unorthodox route.

    Instead, look at regular analog audio multicores, to allow for several lines back/forth. I'd suggest an 8-way as a minimum to allow for extra mics, headphones and the mix itself. Find a good way to run it through the building (I assume permanently?). Lay the cable then terminate it at either end with a wall-box for easy patching.

    Brands to look at:

    Van Damme (expensive, industry standard)
    Sommer (cheaper, also very good) here
    Unbranded equivalents (cheapest yet, may be sufficient for installation use) here

    These cables are only 13-16mm in diameter, so very easy to bury compared to lots of single runs of cable. You should be able to find a local wire-man to install this all for you. Expect to pay him around £20 per hour, and he'll probably bring a second man along to help pull the cables etc.. I'd estimate that unless the run is very tricky indeed, it's maybe 4-6 hours work to do the lot, including the wall boxes.

    PS - 50m isn't stupidly long for analog multis, 100m is not at all uncommon, and usually many more than 8 channels too!
     
  5. hornydragon

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    4 Twisted pairs in cat5 the hardware is available from lots of places with support and instructions IT department should be able to sort you out some network cable (as its a school you may need to have a contractor install the cable (cat5 between the 2 buildings)

    http://www.lektropacks.com/view_product_standard.php?product=166&department=3&sub1=23&show=23

    Hardly unorthodox and FTP Cat5e is readily available just costs a bit more, doesnt need to be balanced IMO unless your desk requires balances inputs in which case balanced will run longer anyway,
     
  6. webspot

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    I've had more discussions with people around and it seems that, after all the running the cable carefully around all the walls in order to keep it tidy, we could be looking at more than 100m.

    Now seeing as there have been two suggestions, cat 5 and standard audio cable, would both be suitable for running over lengths of 100m. Or would we have to purchase repeaters? If so, could you provide an example.

    I liked ben.bayliss's suggestion of having a wall mountable box at either end for patching, although I'd expect we'd have to get a patchbay too. Could you provide me an example of one of these wall mountable boxes and explain whether we should get a balanced or unbalanced patchbay. We have an External sources module on our board which provides 8 lots of 2 core shielded cable for us to put things on to. When you mention that we'd need "8-way" does that imply that we need to run 8 cables? Or would the links you provided give us 8-way, the picture doesn't look quite right for that?

    We already have station out going to various locations around the school, including the hall itself. This is done via a uhf transmitter (this one). I'm guessing the the latency should be fairly low, so we won't have to worry about running the mix to the hall also via a cable.

    I'm sorry if I sound slightly stupid at this, I'm only just learning.

    Thanks for all your replies!

    Andrew
     
  7. hornydragon

    hornydragon
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    check the links to the baluns they use standard RJ45 sockets so a cat5 wall box and cat5 patch cable is all thats needed
     
  8. webspot

    webspot
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    Yeah... These boxes seem a little too expensive for our budget, and I also think that we need balanced inputs to our board and we will also need more than one channel going backwards and forth. The cat5 method looks a bit expensive, seeing as we need those baluns boxes.

    Could someone explain the normal audio cable method of doing this. Whether we'd need boosters at a certain length, what sort of boxes would we require at either end of the cable to terminate. I take it we'd need a patch bay, which sounds like a good idea, to connect to our external inputs module of our board.

    Look forward to your replies
     
  9. Joe Fernand

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    Hello webspot

    You don't say what's generating the 'Content' in the Hall and what your trying to plug it into – makes it tricky to say what cables you require!

    Joe
     
  10. webspot

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    Well, actually, we haven't got anything yet apart from a small wireless microphone. We'll probably be getting content from assemblies or other events going on in our school hall. This could even be when there is a lot of noise going on, so headphones could be needed for the presenters in the hall. We'll probably start with just the basic microphone that we have at the moment, which has a stereo jack out.

    But we'd like to have something there so in the future we could have more professional mics and headphones to be plugged in. What's the best way to do this?
     
  11. Joe Fernand

    Joe Fernand
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    Hello webspot

    You still don't say what's in the Studio!!!

    It sounds like your going to want a Small 'Event' mixer in the auditorium (http://www.soundcraft.com/applications.asp) and as others have said run a pair of Balanced XLR to XLR cables back to the Studio.

    For now you can use the Cables with a Mic Pre amp – though you'd be better finding the budget for the Event mixer and get on with learning how to use it.

    Joe

    PS Another option is to Install the cables and Hire in a Mixer as and when required.
     
  12. webspot

    webspot
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    Ah yeah. In our studio we have a sonifex s2 board and one of the modules on it is a external sources module. On this external sources module there is a dsub 25 pin connector into which you can put in 6 channels of audio. The main mix of the station is broadcast to speakers around the school, including the hall, via a UHF transmitter.

    I've been looking into things a lot today, and could you comment on whether the following could work/be a good idea?

    I've decided that it could be a good idea to get a patch bay. The multi core cable that we run between the hall and the studio could connect to the patch bay at the studio end and a wall box at the hall end.

    I think we'd use the sommer multicore cable as suggested by ben.bayliss.

    The patch bay would link up the external source module inputs and the multi core cable. If we also connect the main mix up to the patch bay in half normalled mode, we could run the main mix back down one of the cores, if we require for headphones in the hall.

    The wall box at the other end could be something like this:
    http://www.radiotronics.co.uk/item.php?partcode=F267XP
    Would it be possible for a 4 way cable to be split so you can choose between a XLR or TRS connector for each way? Is this a suitable way to have the cable ended at the hall end of the multi core cable, or is there a better way?

    At the hall end we'll use the small wireless mic we have, as it will be good enough to use until we get some more professional equipment (including headphones).

    One problem that we may have is the length of the run that we'll have to do. My original thought of around 50m could be wrong. It could be 100m or more. Is there some sort of signal booster that will allow us to run the multicore cable at that length?

    I'm sorry if I sound jumbled up. I'm really no expert on this.

    Looking forward to your replies.

    Andrew Gee
     
  13. eviljohn2

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    Line level down a decent 100m balanced audio cable will be fine as long as you have half decent electronics at either end. Using a decent multicore with patch bays at either end would probably be the best option,

    There are many, many options available depending on what you actually need to achieve and the budget available for it. The 8-way cable suggested by ben.bayliss is a good compromise in terms of cost and functionality, get 4 cables wired as a "send" and 4 as a "return" so that you can send signals in either direction.

    A patch bay like this:
    http://www.thomann.de/gb/cae_stagebox_8.htm
    at either end would work well when used with the appropriate panel-mounted XLR connectors. Definitely get good Neutrik ones, it's really not worth skimping on this aspect. Be sure also to get it thoroughly labelled at either end as there's nothing worse than having myserious patch bays installed in a venue yet nobody knows where they go; this is especially true with you going between buildings. :)
     
  14. webspot

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    That's exactly what I was looking for, to put at the school hall end. However, I thought that we'd get a patch panel (like http://www.behringer.com/PX2000/index.cfm?lang=eng) for the studio end. We'd be able to have more control over the links and should be able to work them better. We will also be able to link up other things into our patch panel, which'll stop me having to open up the back of the board every time I want to change something. Would the multicore cable be able to have TRS connectors on the end to plug into the patch bay? Is this a good idea? Remember, I am not very experienced with this.

    Thanks for your help. I think I'm getting there!

    Andrew Gee
     
  15. ben.bayliss

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    Yup you are - a wallbox like either that you've posted will be just fine. Yes it's very straightforward to link together, say, an XLR and a jack on the same cable.

    The multicore (as you've probably now figured) is a single cable that contains the equivalent of 8 individual cables thus saving lots of extra work and making the thing a lot smaller. 100m of good multicore won't be a problem unless it gets very close with some nasty dimmed lighting power or similar.

    The Behringer patchbay you link to is actually unbalanced and a bit nasty, so to be honest I'd stick with another wall box at the other end - or a rack mounted XLR patchbay which is hard-wired (the Behringer has jacks on the back) and a handful of patch cables. If you do like the idea of normalising bits of kit together, look at better quality patchbays!
     
  16. eviljohn2

    eviljohn2
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    A big patch bay can work well but I'd be wary of overcomplicating things so that people other than yourself don't struggle with the system. If you want a big patch bay like that I'd be looking at a better, normalled or half-normalled one as Ben says; but if doing that you also need to be thinking about putting a bigger cable down the conduit. Think about what you're actually going to be using this for and maybe let us know.

    XLR is fairly standard and makes it obvious that the line is balanced, it also doesn't preclude using adaptors if you have other uses or the system. Have a think about your uses, I can't see why you'd need more than (say) 2 channels of stereo feed in either direction (stereo feed and maybe 2 lines back for a camera record or something) and maybe another line for comms in a show situation. If you need to do anything complicated such as a big show in the hall then you'd be better off getting the right equipment in that room rather than running everything remotely. :)
     
  17. webspot

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    Hi all,

    I've discussed this with another person working on this project, and we think it would be a good idea to get a big patch bay. Then we'll be able to integrate everything else into it as well, rather than having to crawl around changing cables, when something needs changing when we have something else to plug into the system, or troubleshoot.

    I didn't notice the behringer patch bay was unbalanced. I've had a little look around and found the Samson S-Patch (http://www.samsontech.com/products/productpage.cfm?prodID=103). Is this a good patchbay to be using?

    I didn't quite understand why ben called the behringer patch bay "nasty" apart from the fact that it was unbalanced. Is there something I'm missing, that I should be looking at. If so, could you provide some examples of what would be a good patch bay to use instead.

    The patch bay hopefully won't need to be touched by anyone but the main technical people of the station, so I hope people won't become confused with the system as eviljohn2 suggested.

    We only have 1U of space left on our rack, so I'm trying to look for something that'll fit well.

    Thanks for your help, once again.
     
  18. ben.bayliss

    ben.bayliss
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    OK answers not in any particular order.

    1) The Behringer patchbay is nasty (and altho I'm a huge fan of their stuff - it is cheap and not always well built) because it's unbalanced, cheaply constructed and (the big and) the switches which allow you to choose between isolated/normalled etc.. are on the top of the rack. When you install it or pull it out of the rack, it rubs against the rack unit above and moves all the switches!! Infuriating.

    2) The Samson looks a bit better (check it doesn't use switches tho) but read on....

    3) Jack-based patchbays are considered a BAD IDEA(TM) when dealing with microphones (as opposed to solely line-level outboard equipment. This is because as you insert the jack you briefly short out the tip to the earth, and if you're using mics which use phantom power, that means sending a blast of 48V down the earth, which many older and/or cheaper bits of kit don't get on well with.

    4) I'm not convinced that, even in a small studio, you'd be able to fit everything neatly into 24 rows, and be able to arrange it with any useful normalising. If you absolutely must go down the patchbay route, I'd suggest maybe a 4-6U rack just for patching - 2 XLR panels (remote wall sockets and desk mic inputs), then outboard, playback devices and the rest of the console on maybe another 2 jack panels.

    5) Good patch bays. XLR one like this but get their new catalog - Studiospares now stock an almost identical unit at half the price which they make themselves. Some jack patchbays would be this one, another one, or this one
     
  19. djhddnb

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    Hi all. im a freelance broadcast wireman and would like to let you know about a few things concerning your project/build.

    1. The PX200 patchbay is unbalanced as said by ben bayliss, yes but the PX3000 IS balanced!
    I have designed and built two smaller stand alone recording studios with the PX3000s. (To stop the switches on top of them being changed when you insert or extract them from the rack, push the peice of kit above them up before you screw it into the rack.)
    Yes they are cheap but it depends on A, budget and B, how much plugging in and out of the patchbay your going to be doing. If your going to plug it in and leave it there then the PX 3000s will be fine.

    2. If your going to use mics that need phantom power, try plugging in the mic into a mic pre amp with phantom power, BEFORE the signal is sent anywhere. OR use a rack mount mixer with phantom power at source i.e. in the hall.
    You can now purchase 1u Mixers for this job. Mackie make 1 as well as other companies.

    3. You said you have a wireless mic. There is nothing created that beats a cable between 2 things.
    Also you should think about the pattern pick up type of the mic to shield from unwanted sound bleed.
    Also have you heard the nasty feedback when the mic gets too close to the speakers the sound is eminating from? Nasty!

    4. Every facility that I have ever worked in uses patchbays. These facilities, either video or audio usually have a machine room, also know as an MCR/CAR that contains all the patchbays. Smaller facilities have the patchbays in the studio or in the stand alone editing suite. The patchbays are connected via cable to KRONE BLOCKS which are then jumpered to other KRONE BLOCKS which have cables attached going to/from the hall.

    5. Ben also says about purchasing from STUDIOSPARES, WARNING they are more expensive than most. For budget purposes try EBAY or if you have a little more money in the kitty try BRYANT BROADCAST in Croydon or CPC (lately sponsers of the GADGET SHOW CPC | CPC - Over 100, 000 products from one of the worlds leading distributors of electronic and related products.) but DO use NEUTRIK connectors. They are the best.

    6. If you know how many cables you need to run from the hall to the studio, double it!
    Theres nothing worse than upgrading and having to open up trunking/walls/floors etc. to run more cables.
    You don't have to connect the cables you dont need at each end but when you want to add more hardware the cables are in place ready to be added to componants at each end.

    7. CAT5 for audio? YES.
    CAT5 for Mic cables? NO!
    Yes CAT5 can be used to run audio but there is a big problem with that.
    For a wireman to wire the CAT5 patchbay PROPERLY takes at least 2 thirds of a day, and as most wireman charge at least £20 per hour, your looking at £80 just for 1 patchbay at 1 end of the cables. Multiply this by 2 and that's a £160 charge just for the patchbays.
    Soldering XLRs/Jacks is much, much quicker
    Also, I don't use CAT5 for mic cables as the earth/screen in a mic cable actually carries the phantom power for the mic and although the CAT5 has a earth/screen, it ONLY HAS 1 earth/screen. Thus you can only use 1 phantom powered mic.
    ALWAYS use proper microphone cable for microphones. NOT CAT5 OR normal audio cable.

    8. Do you need phantom powered mics?
    If your using dymanic mics (Shure SM87s etc.) you dont need phantom power, but you should still use proper microphone cable.

    9. Headphones. If you want to supply headphones to go the hall, have you thought about a headphone amp?
    In my own recording studio i have a ROLLS 4 channel headphone amp. This is connected via my Yamaha 01V mixing desks headphone output, via stereo jack to the headphone amp stereo input, and this gives me 4 seperate amplified headphone outputs, each with thier own volume control on the headphone amp.

    Now a few questions.

    Do you need separete feeds for each mic or will a summed stereo output from the hall be enough?

    Should the presenters in the hall have control of the mic volumes at the hall end?

    Will you be using phantom powered mics at any stage?

    Now a few examples.

    Lets say you want, eventually, 4 mics to run to the studio, wether phantom powered or not.

    So first, including presenter control at the hall end.

    You can buy a small mixer (with phantom power onboard) that you can plug all the mics into in the hall.
    This can be a small mixing desk, or, as stated before, a 1U rack mount mixer.
    This will give the operator in the hall control over the different mic volumes seperatly.

    It should have a stereo headphone output to plug either, a single set of headphones in, or, a multiple-output headphone amp in (with seperate volumes for each set of headphones. Not everyones ears are the same;) ).

    This mixer should have a stereo output via preferably XLR's (the pro's choice) or stereo jacks, so you can send the summed inputs back to the studio via multi-core audio cable, NOT CAT5.

    At the studio end you can now either add a patchbay for the hall mixer to attach to or plug the hall mixer directly into 2 channels of the studio mixer.

    The second way. (no phantom powered mics)

    Mics in the hall plugged directly into a wall box in the hall.
    Multi-core cable connecting the hall wall box to a patchbay in the studio or directly into 2 channels of the studio mixer.

    The third way. (again no phantom powered mics)

    Mics in the hall plugged directly into a wall box in the hall.
    Multi-core cable connecting the hall wall box to a wall box in the studio, that then plugged directly into channels of the studio mixer.

    For the second and third route you would have to send a signal back to the hall from the studio for headphones.

    Hope this has helped you decide which way you want to set up your system.
     
  20. ben.bayliss

    ben.bayliss
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    Wow what an in-depth reply with many good points!

    Unfortunate that the original posts were made quite a few months ago - in January!! :eek: :)

    I now agree that Studiospares are fairly dear for many items. Especially if you can get a trade/education account with one of the bigger suppliers. We live and learn - I made my recommendation as a low-volume buyer. Now I'm buying larger quantities, there are definitely better alternatives.

    I stand by what I said about Behringer patchbays, however! Those switches just kill it for me!
     
    Last edited: Oct 29, 2008
  21. djhddnb

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    Oops didnt see the date was just browsing the net lol.:rolleyes:

    As for the Behringer patchbays, all depends on budget, but i for one would'nt use them personally and the studios i have built with them, well, they never leave the rack so the switches are negligable.

    I personally use GPO soldered patchbays which are one of the most expensive and best (better than bantams as they have a tendency to bend the metal work inside), but as i wireman i got them free form work ;)

    I do have a couple going spare and untested with some Krone blocks still attached, if anyone wants to make an offer.:smashin:
     
  22. djhddnb

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    Also forgot to mention, although it may be academic now, is sound travels at around 344 meters per second in a temperature of approximatly 20 degrees and that equates to roughly 770 feet per second. This is through the air.

    I'm not an engineer but for more specific "delay" of the signal, work out the resistance of the cable and take that into account.

    There's a specific equation for this.

    I think it goes something like -
    Voltage = Impedance divided by resistance
    Impedance times by resistance = voltage

    It's been many years since i was at college, lol so best to check it out yourselves for the definative answer.

    djhddnb
     
  23. ben.bayliss

    ben.bayliss
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    Eek! I am a sound engineer, and have never seen anyone work out the delay of an audio signal through a cable in order to delay things... The speed of sound through cable (ie. electricity - a large percentage of the speed of light) is so fast as to make absolutely no odds whatsoever.

    [size=+2]That's why it doesn't matter if your speaker cables are the same length or not![/size][/lesson to forumites]

    Neither of those have anything to do with time, and you've written the same thing twice, except once dividing, and once multiplying.... ;):rotfl: Nice try though!

    Where did the talk of delay come from btw? I've searched the thread and you're the first to mention it! :)
     
  24. djhddnb

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    Hmm maybe i misread it in the first place.:oops: It was after 1am lol.
    Not trying to delay the signal but, will there be any delay on the signal in such a long run?

    And yes I definatly agree. It doesnt matter if cable lengths are different.
    Sound travels much too fast to worry about this.
    I had this conversation with an engineer when installing a 7.1 audio/video studio where all the cables for each speaker were different lengths.

    This problem can arise however when syncing audio to picture, which is corrected by a "BEL DELAY" unit that we install in various facilities.

    Like i said im not an engineer just a lowly wireman lol.:suicide:

    Solder, solder, crimpy crimpy. If all else fails, a wet piece of string
     

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