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Long distance audio feed - Graduation

Discussion in 'Sound, Music, and Intercom' started by CalabasasTD, May 11, 2009.

  1. CalabasasTD

    CalabasasTD Member

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    Hey gang,

    I just got told by our Asst. Principal that I'll be expected to send an audio feed from the football field to our lecture hall, which is 500 to 1000 feet away, for graduation. This is so the old people have a place out of the sun to go and watch the graduation. The video guy is taking care of his own video feed, but I'm going to be expected to send audio.

    The physical challenges of this run notwithstanding, I'm concerned that that's too far. Is there some kind of a signal amplifier that I can put inline to have it make it all the way there and not sound awful?

    Also, unless we send the audio and video together somehow, I'm guessing we may have sync. problems. Any thoughts.

    Thanks in advance for your input.

    Eric
     
  2. mnfreelancer

    mnfreelancer Active Member

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    500' and 1000' feet are two very different situations. I'd say you should be able to drive line level with decent quality for 500' on balanced cable but 1000' is pushing it. Same for doing it wirelessly...given the proper antennae a decent wireless mic with an XLR adapter should do 500' but 1000' is getting beyond design limitations. So which is it, 500 or 1000? or 750?
     
  3. CalabasasTD

    CalabasasTD Member

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    Well now I'll have to go measure!! I meet with them tomorrow. Once I know the layout, where we can set up and the distance we'll have to travel, I'll get back on. Thanks!
     
  4. rwhealey

    rwhealey Active Member

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    I've heard that you should be able to do 1000' feet with a line level signal- never done it myself.

    Are they willing to spend anything to get the sound where it needs to go?
     
  5. Derrick

    Derrick Member

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    How is the video guy doing his video? Coax, wireless, IP?

    1000' line level is no problem. However running the wire may be a chore.

    Where is the school located? Do you have a local radio station there? If so, Check and see if they have a RPU sometimes known as a Marti. If they do, see if you can borrow the tranmitter and receiver and use it to send your audio.

    If cellphone quality is acceptable, then you could use an coupler to connect the mixer to the cellphone, call the number at the remote location and use another coupler to connect the received audio to the in house PA.

    As far as sync issues, if the video is an IP protocol it will have a fair amount of delay due to the codec processing the video. you might have to apply some delay on your audio lines to match.

    What time frame are you under to make this happen?
     
  6. BillESC

    BillESC Well-Known Member Premium Member

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    Audio Technica's ATW 3110 wireless system can typically transmit 1000' line of sight. To add some confidence the addition of a high gain antenna will make your system 'good to go.'
     
  7. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    I think a line level send would work just fine. With such a long run, the chance of RFI goes up, and you may need to terminate the send with a good transformer if you are using lower-end sound gear in your auditorium (something along these lines: Radial Twin-Iso two channel Jensen transformer equipped balanced isolator).

    See my post about balanced v. unbalanced lines for some good information on transformer isolation and why you might need it.
     
  8. epimetheus

    epimetheus Well-Known Member

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    I've did an approx. 1000' line level press feed for an Air Force Thunderbirds performance at Texas A&M a couple years ago. Used a Mackie 1402 mixer on each end to condition the signal. Worked pretty well.

    Edit: Come to think of it, I believe it was a balanced line.
     
  9. museav

    museav CBMod CB Mods Departed Member

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    I'll second Derrick's comments, how is the video being transmitted? There may be some ways to effectively address both and avoid latency issues, such as using a CAT/UTP solution. However, sync may also be a concern if they are doing any digital switching or processing, you might want to find out if the video equipment being used does add any latency.

    1000' of balanced audio could probably be worked around but not if it is twenty 50' cables hooked together, you would probably just want to get a 1000' reel of good quality twisted pair audio cable and make it all one continuous run.
     
  10. epimetheus

    epimetheus Well-Known Member

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    I agree. I'd see if you can keep the audio on the same link with the video.

    When we did our 1000' run at A&M we got a 1000' reel of twisted pair audio cable, tied one end to a post near the source and put the reel on a stand in the bed of a Gator and took off.
     
  11. goodguy

    goodguy Member

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    lots of uhf diversity wireless mics will transmit "line of sight" for 1000 feet or more. to insure better coverage, consider using more than one receiver tuned to the same frequency as the transmitter. orient the receivers differently in relation to the transmitter and monitor the outputs of both. you can choose one over the other if there is a quality difference as well as having a backup in place of both seem to work equally well
     
  12. mixmaster

    mixmaster Active Member

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    Taking a slightly different view, maybe more long term. If people like doing this, your administration may be able to justify the cost of doing both the audio and video down a piece of fiber. When we do our graduation we send 4 channels of audio, 4 video, and intercom down our fiber link to the TV control room for video recording and distribution and I'm sure the distance is much greater than 1000 feet. 0 issues with the audio and video matching up. I'm sure the gear to do this is more expensive than 1000 ft of STP but if it makes for a longer term solution the additional cost may be easier to justify. Just a thought.
     
  13. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Fibre is great. Fibre itself is cheap, rugged coonectors are most deifinitely not and the gear for each end is not cheap either. It's also fragile and finicky. Literally a speck of dust can kill it totally. It provides the best bandwidth and options for the future of anything.

    As always, I would take cable over a wireless link.

    Cable option: One of the delay towers for World Youth Day last year had a 280 metre run between speaker processor and amps. It worked as well as any other tower. But at those sorts of lengths, you need 2 things. 1 - a balanced line and 2 a good string line driver feeding it. For WYD it was a Dolby Lake Processor. For the analog backup system for the Doha Asian Games, XTA DS800s were used at each node (The primary was Optocore). It's definitely possible. I know that the guys who did Athens said they could not pick the difference when they forced the system to swap to copper and the B console and all of that. They were slightly disappointed I think that fully digital system didn't sound better, but it's also evidence that the analog system was well designed.

    Check the last device in your audio chain at the field end and see how it goes for output. I'd suggest an iso transformer such as what Mike has suggested because you are very likley feeding off different power and ground loops could cause many headaches. Iso transformer goes at lecture hall end...

    Adding delay is not hard, provided you have DSP or the like available to you. I'd suggest talking to your video dude and finding out their plans. They may well have an audio in on whatever and you might just have to do some fiddling with levels and connectors.

    Now wireless: Definitely doable. We did a 500m link for WYD. That was using a beltpack. Admittedly said beltpack had been err customised... Normal beltpacks don't have BNC connectors for their antennas nor dual microprocessors to run multiband. We fed that to a paddle and then the receiver had diversity paddles. Besides a faulty preamp on one of those paddles, things were fine. Changing the transmitter battery got annoying.

    From memory, UHF-R beltpacks have removable antennas and hence could be adapted to take a real antenna. You'd have to be careful of your legal maximum power.

    You can also use an IEM system to achieve the same thing. You normally have a connector for proper antenna already. This makes point to multipoint links cheaper than doing it with mic receivers.

    You can get RF to go a LOT longer. Add an RF amp and dependent on where in the world, a licence and you can get kilometres of range. A standard PSM700 beltpack was still locked on to the transmitter in Doha at 7km, admittedly there was an RF amp in there.

    If you are looking at RF solutions that start to push the normal operational limits of systems, then you need to seek expert advice. Those results with long range RF were done with RF gurus doing frequency planning and constant monitoring.

    An out there option... If you are finding loss a bit of an issues, you could run a solution whereby you use an off the shelf paging style amp and then run your link at 100V line and then attenuate that down at the other end and feed it into a DI box.

    Plenty of ways to skin the cat, feel free to ask for clarification if I've neglected useful details...
     
  14. mnfreelancer

    mnfreelancer Active Member

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    If you had a couple of mid-grade wireless mic systems with belt packs and XLR adapters (Thinking like Shure ULX) you could make a sort of repeater chain if the link didn't make it there all the way in one hop. At the field, take a line out of your board into a belt pack using an XLR adapter (or TRS, whatever) and send it to a receiver on a given channel half way or as far as you can get while still receiving a decent RF signal. Take a line out of that receiver into another belt pack on a different channel and shoot that at the receiver in the lecture hall. This is assuming too that whatever gear you have ready access to won't cut it by itself - if you have access to one mid grade wireless mic system chances are you have access to two. Thinking about the gear my company has (all midgrade mics but tons of them) you could do a multi path redundant link with only the number of separate channels (frequencies) limiting the possibilities. With analog gear this shouldn't add very much latency either.

    Is the video guy using SDI by chance? I believe SD-SDI will handily traverse 1000' and it can carry a number of digitally encoded audio channels.
     
  15. CalabasasTD

    CalabasasTD Member

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    Wow! A host of clever solutions. As some may imagine, California public schools budgets being what they are, it's been a bit of a slog getting anyone to want to spend anything.

    We've made the decision to focus on the sound on the football field where about 2500 people will be sitting and send a balanced line from our Yamaha LS-9 down to our Mackie mixer in the Lecture hall 300-400' away where so far 6 people have reserved seats. The video guy (a pro, but also a dad who'd volunteering his time) is sending his feed separately from a switcher. Everyone's opinion has been: if there's a delay, there's a delay. We'll see how it goes.

    I love all these great solutions and will definitely be applying some of them somewhere in the future. They're too cool not to.

    Thanks again!
     
  16. Dionysus

    Dionysus Well-Known Member

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    You Certainly want to use an isolation transformer for this application, since I'm sure these areas are grounded separately and have feeds from separate transformers. not only will not isolating cause some HUGE headaches it in rare cases can be very dangerous.

    Should be feasible if you run a single good-quality line. You may wish to step-up the wire size a bit to reduce your resistance. Voltage drop over such a long distance can be substantial (even when working with the low voltages in audio signals). To compensate for the voltage drop you'd be turning up the gain, and getting into more noise.
    Good shielded cable could indeed be an asset.
    As long as the cable is good quality this should be no problem at all.

    Just think of all the buried telephone and cable lines. They are sent at a higher voltage to distribution in your neighbourhood (those green boxes you may of seen) and usually don't have far to go before going into your house.
     
  17. Derrick

    Derrick Member

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    Dionysus,

    Great suggestion on the isolation transformer. Wouldn't hurt, could save some ground loop problems.

    However, if an isolation transformer is not available, just leave the shield disconnected at ONE end of the interconnecting cable.

    That is to say, on an 3-PIN XLR just solder up pins 1, 2 & 3 on one end and ONLY pins 2 & 3 on the other. Will work fine.

    If you choose to hook up pins 1,2,3 at each end and do have problems with ground loops, just clip the shield wire to pin 1 on ONE END ONLY.

    Dinosys, what type of telephone system is in your area that uses a higher voltage to the "green distribution cabinets"? Might I suggest a lilttle more research on telephone systems?

    It's all learn as you go...
     
    Last edited: Jun 18, 2009
  18. NickJones

    NickJones Active Member

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    Would streaming it over a network be possible? Chances are you have network acess in your lecture theatre or wherever you are running it from, and you can probably get it wherever you are running to, easy software like NetMeeting that will be on your PC allows calls and does it to alright quality.
    Just an idea.
    Nick
     
  19. TimmyP1955

    TimmyP1955 Active Member

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  20. NickJones

    NickJones Active Member

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    WiFi would not be ideal, you would probably be better just to hook into your schools existing network, WiFi is typically slow.
    Nick
     

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