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Recording Snake?

Discussion in 'Pro Audio Equipment' started by tedcrop, Dec 11, 2004.

  1. tedcrop

    tedcrop Guest

    any suggestions on a 25 foot snake to get headphones and 8 or 16 mics from main studio room to control room. XLR to XLR.
     
  2. Kurt Foster

    Kurt Foster Distinguished Member

    It's best to keep headphone level signals out of the audio snake. it’s ok to send line level out to the talent if you have the headphone amp in the performing area, but you should not be sending headphone level out of a phone amp into the same snake that carries mic level signals into the control room ... This can in some instances, induce bleeding (crosstalk) into the mic signals ...

    Check http://www.markertek, com for snakes and studio wiring....
     
  3. supahd

    supahd Guest

    I don't get that, you're already running mic level signals through the snake. If anything would cause crosstalk wouldn't they? This would seem to be a quality issue with shielding more than anything.
     
  4. Kurt Foster

    Kurt Foster Distinguished Member

    No, mic and line levels are much lower voltage than headphone feeds ... believe me, I speak from direct expierence on this one. Headphone feeds can drive a speaker ... basically, that's what headphones are, little speakers ... try pluging a mic or a line level signal into a pair of phones directly and see what you get .... Nothing? Tha's whut I mean...
     
  5. sdevino

    sdevino Active Member

    Actually headphone level can be about the same or less than line level when you consider the impedences involved.

    Headphones are driven by mW (milliwatts). For instance a pair of AKG240 Studio headphones will (according to the specs) generate 90 dB SPL when presented with 1mW of power. Their maximum power rating is 200 mW. 200mW into 55 ohms is 60mV. That's 60/1000 of 1 volt.

    MY Earthworks QTC30 mics will put out up to 10v into a 3kohm load which is 1mW.

    The head phones amps put out more power than mic level but the voltages are in the same general neighborhood or even less.

    So headphone level in mic snakes should not be a problem. Many mics drive much higher voltages than some headphone feeds since the mics are typically terminated into impedances much higher than headphones.

    At least thats what my experince and little ohm's law say.

    Just in case you don't remember your ohms law:
    Power = E x I (Voltage x Current)
    or
    Power = E^2/R (since I = E/R)

    Plug and chug.

    You can run headphones pretty well on a lot of line level outputs.

    Steve
     
  6. tedcrop

    tedcrop Guest

    I think I am just going to run some mic cables through a hole in the wall. Because I can't do math.
     
  7. Kurt Foster

    Kurt Foster Distinguished Member

    Regardless if it's volts or ohms, it cannot be argued that a phone amp puts out a much stonger signal than a microphone ...

    Seems to me that if phone level and line level were the same thing, you wouldn't need a headphone amp ... you could simply drive your phones with an aux out , which we all know you cannot do ...

    I have had problems with the phone feed bleeding into snakes when driving them with a phone amp .. and a tech that I respect very much told me to keep the phone sends out of the snake unless I was sending line level to a phone amp as I discribed ...

    So do what you want . Just remember when you have weird stuff coming up in your tracks and it's too late to do something about it, that I warned you against this ..
     
  8. sdevino

    sdevino Active Member

    A phone amp driving a 4 ohm speaker would be a whole lot more power than a phone amp driving a 55 ohm speaker. That's whats different. The 55 ohm headphone speaker is only consuming single miiliwatts in most cases. If you drive a 4 ohm speaker with 10 watts your are sending 1.6VRMS vs. 0.06VRMS for a headphone signal.

    The headphone bleed from your ears to the mic will be 1000's of times louder than crosstalk in the wires. I feed full Power amp level to a headphone soak in the control room through my snakes. There is no headphone level detectable on my mic cables above the noise floor. (according to spectra-foo measurement down to -90 dBFS)

    Being an EE helps predict performance issues sometimes.

    Steve
     

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