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Lavelier Microphone with extension

Discussion in 'Microphones' started by tomz, Nov 12, 2012.

  1. tomz

    tomz Active Member

    We want to use a wired lavelier microphone to record a lecturer in a classroom. The microphone will plug in to a camera that is installed somewhere on the ceiling or wall.

    What microphone would you recommend? And how far is it possible to extend a microphone? The distance will be about 20 meters. Is it possible to get an extension cable or does there have to be some kind of powered terminal in between to transmit the signal. I know that with USB there is a limit to how long the cables can be.

    Any suggestions are greatly appreciated.
  2. Boswell

    Boswell Moderator Distinguished Member

    You can't extend lavalier mic wiring more than a metre or so. For this sort of situation, it would be better to have the lecturer wear a radio beltpack and site the receiver on or next to the camera. There are receivers specifically made for hotshoe camera mounting, of which the A-T 1800 series is an example.
  3. tomz

    tomz Active Member

    We already bought a wireless microphone but it only last 7-8 hours and a lecture takes about 7 hours. Taking into account that a lithium-ion battery loses charge over time this is not really workable.

    Is it not possible to extend the range with some kind of device?
  4. Boswell

    Boswell Moderator Distinguished Member

    It takes less than 10 seconds to change a beltpack battery. In my theatre days, I used to do it between verses of singing numbers when soloists walked briefly into the stage wings. Mind you, we weren't putting on 7-hour shows.

    If the lecturer does not mind being tied down by a trailing wire, then you could use a local pre-amp and send the amplified signal down the 20m cabling back to your recorder. I have in the past used a portable minidisc recorder as a pre-amp for a pair of lavalier mics. The small Sharp units are best for this as they have a "record-monitor" mode that sends the mic signals out to the headphone socket without having to have the disc turning. Minidisc recorders are very cheap now on Ebay as almost everyone is dumping minidisc in favour of MP3, but make sure the mains adaptor is included.

    BTW, what do you use as a recorder for 7 hours continuously?
  5. tomz

    tomz Active Member

    Thank you for that detailed answer :)

    This will be hooked up to an IP Network Camera which records the entire lecture to a central server.

    It's true that a wireless microphone increases mobility but on the other hand we want the lecturer to stay within the view of the camera and the microphone could be a sort of leash ;p

    Having it wired is just one less possibility of things to go wrong. No battery problems, no signal problems and nothing can get lost.

    Would you mind providing me with a link to the equipment that I would need?

    Microphone + Cables + Amplifier is all that is needed correct?

    Where would I get this Amplifier? It of course does not have to be anything fancy... the cheapest and smalles possible.
  6. Boswell

    Boswell Moderator Distinguished Member

    This is a lavalier microphone with attached pre-amp that came up on a quick search. It can be ordered with output cables up to 30m.

    If I ever get a bit of spare time, I'll see if I can find some more.
  7. tomz

    tomz Active Member

    Thanks... yes that looks exactly like something we need. Not this one in particular though, looks a little cheap with the battery hanging of it.
  8. Boswell

    Boswell Moderator Distinguished Member

    You could house the pre-amp and battery separately, both in something like this. The battery is removable in its compartment, and the wires from the compartment terminals could be soldered to the battery terminals on the pre-amp in the other compartment. The mic leads (in and out) could be slotted in through cut-outs in the plastic sides. Easy.

    The result would be quite safe in a user's pocket. A refinement would be to add a 3.5mm jack plug + socket so the lavalier mic itself was detachable.

    I'll leave this up to you now.
  9. tomz

    tomz Active Member

    Is there an amplifier that is plugged in to a socket? I'm not a fan of batteries.
  10. RemyRAD

    RemyRAD Well-Known Member

    Professional lavalier microphones all have balanced XLR outputs. Within the barrel of the XLR, you place a single AA battery that will last for weeks! But as a good engineer, before important jobs or lectures, you put in a fresh battery.

    These microphones that have the XLR outputs can have cable lengths of over 300 m/1000 feet. The only hitch in your get along here is that your camera, recording this, must also have balanced XLR inputs. If it doesn't? You need a XLR to transformer to unbalanced output that will plug into your camera, crappy little 1/8 inch style earphone jacks, which are unbalanced and cannot accommodate microphone cable lengths longer than 15 feet. So that's why that little transformer XLR to 3.5 mm plug adapter, must be placed at the camera. And with that scenario, you can run 1000 feet of microphone cable from a lavalier microphone using a battery with an XLR output. Nothing to worry about that battery. These are not like wireless microphones that gobble up your battery to power a transmitter. So no worry with battery powered electret condenser microphones, otherwise, television networks wouldn't utilize them in the field.

    Former NBC television audio engineer
    Mx. Remy Ann David
  11. tomz

    tomz Active Member

    Thank you Remy, that helped me immensely :)

    I was able to order all the equipment I needed from this.
  12. Ty Ford

    Ty Ford Active Member

    Hello Tomz,

    Countryman EMW, Rode Lav or PIN mic, Sony ECM 77b or 88b. Lotta good lavs out there. They all need Phantom Power. Does your camera provide Phantom Power?


    Ty Ford
  13. RemyRAD

    RemyRAD Well-Known Member

    Personally I would look for lavalier microphone that is not solely operable with only phantom power. Getting one that has space for a AA battery, ensures that if the phantom gets interrupted any possible way from connectivity problems on the XLR, the microphone will not fail with the battery installed. Though depending upon the microphone, you may need to switch it on? These types of microphones draw such insignificant current, the battery is going to last almost as long as the smoke detector. Well maybe that's an exaggeration but, they can potentially last for weeks. And we could also help to alleviate the load of a battery-operated portable mixer if the microphone can be self powered from a AA battery. But that's just me.

    Former NBC-TV audio engineer, 20 years.
    Mx. Remy Ann David

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