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Quality Loss with 45 ft. of balanced XLR cables?

Discussion in 'Accessories / Connections' started by joorocker90210, Mar 19, 2006.

  1. If I were to connect 3 balanced XLR cables together (each about 15 feet, resulting in a total distance of about 45 ft.), would this result in signal loss, or degraded audio quality?

    I would be connecting a Shure Beta 87c mic (not quite sure whether this mic is low, medium, or high impedence) to a Behringer TUBE ULTRAGAIN MIC200 (again not quite sure whether this is low, medium, or high impedence).
     
  2. Gilliland

    Gilliland Guest

    Balanced mic signals can go through many hundreds of feet of cable without any discernable loss of quality. The fact that you are chaining several cables together might be a concern, but if the cables are decent and the connectors are clean and unoxidized, then you should have no trouble at all. I've done this many, many times.
     
  3. zemlin

    zemlin Well-Known Member

    IMNSHO, no.
    I did a test a while back.
    Scroll about half way down the first page of this thread

    I compared 15' with a chain totalling 260' and did not find a signifiant difference. There was a difference in the low end, but I later realized that my test setup was very susceptible to outside noise, and a car driving by could easily have caused the low freq difference I saw.

    I have not repeated the test - I was satisfied with what I learned.
     
  4. RemyRAD

    RemyRAD Well-Known Member

    If you are running a dynamic Mike, say an SM57, up approximately 250 feet of cable, you may be down 1 to 2 DB at 15,000 Hertz. You won't lose any low end. If you are utilizing a condenser microphone, the high frequency loss may be even less because of the preamp buffered output but phantom power begins to suffer on long cable runs since it is direct current. That's the problem that Mr. Edison had in comparison to Mr. Westinghouse and why Mr. Westinghouse won the battle regarding power distribution. He created power distribution with alternating current as compared to Edison's direct current. Westinghouse used a generator. Edison used a dynamo.

    Never lick a wall outlet
    Ms. Remy Ann David
     
  5. dwoz

    dwoz Guest

    I would be remiss, here, Remy, if I did not ask you why you mention Mr. Westinghouse, the PURCHASER of the patents for AC generation, instead of Mr. Nicolo Tesla, the INVENTOR of AC generation.

    Interesting isn't it, that we use Edison plugs to work with Tesla electricity....

    Which one do you suppose hated that more?


    dwoz
     
  6. RemyRAD

    RemyRAD Well-Known Member

    I'm sorry, you are correct and I've had too many libations here. I think Westinghouse really started the trend that has become the norm lately with all of these companies buying out all of these other companies and still putting their names on things like Neve consoles, which really aren't. Neumann microphones, which are now really Sennheisers. I really wouldn't want to buy any of those imitations, with the exception of maybe Neumann??

    Well maybe Mr. Edison actually made some money utilizing his plug with Mr. Westinghouse's power systems windfall?

    Where's my cracker jacks?
    Ms. Remy Ann David
     
  7. ggunn

    ggunn Guest

    Are you sure about that? The specs on a SP B-1 say that its current draw on a 48V phantom power bus is less than 2.5 mA. Invoking Ohm and a bit of ciphering shows the load on the bus by the mic to be ~20 k ohms. The resistance of even a very long run of mic cable has got to be several orders of magnitude lower than that. Visualizing a simple voltage divider circuit, it seems to me that you'd need a whole lotta mic cable to significantly lower the voltage drop across the mic from the resistance in the wire.

    Or am I missing something?
     
  8. RemyRAD

    RemyRAD Well-Known Member

    DC never travels well over long distances, regardless of voltage drop and current draw. I have alternated back-and-forth over this question but I find a direct answer is best.

    Always coming wherever I go
    Ms. Remy Ann David
     
  9. zemlin

    zemlin Well-Known Member

    She's right. I can't say I can explain it, but I've BTDT.
     
  10. ggunn

    ggunn Guest


    Hmmmm. I'm not sure I agree with that. Have you put a meter across the power terminals of a phantom powered mic at the end of a long run and measured the voltage compared to the voltage at the source? Loss in a cable must follow Ohm's Law (or everything I know is wrong), and the DC power loss in a cable is proportional to the square of the current drawn (P = I squared R, where P is the power lost, I is the current in the wire, and R is its resistance). AC is less lossy at high current rates due to transmission line effects, but at low current there's not much difference.

    I am certainly not saying that you can't have heard a diff between phantom powered mics over long runs vs short ones, but I'm not totally convinced that DC loss in the phantom circuit is the culprit. How have the problems you have experienced been manifested?
     
  11. zemlin

    zemlin Well-Known Member

    Where I witnessed issues with DC vs AC, it was not with audio gear. It was with industrial DC motors being located remotely from their controllers.

    It was 25 years ago and I don't recall the details - I just know we had to move a lot of controllers. I don't believe it was a wire sizing issue because I think we were dealing with 120V AC vs 90V DC - not a huge difference there.

    When we ran into troubles, the electrician said we couldn't run DC for that kind of distance.

    It's possible that we were running lower voltage motors, which could explain a lot. I also understand the math involved, but figured there must be some other phenomena involved. Would the type of load come into play here? I don't know. I'm a mechanical engineer and don't pretend to be an electrical expert.

    I could be completely wrong on this
     
  12. ggunn

    ggunn Guest

    Ah, motors and high voltage - reactive loads and lots of current, especially on startup; a different ball of wax.
     
  13. ggunn

    ggunn Guest

    Ah, motors and high voltage - reactive loads and lots of current, especially on startup; a different ball of wax.
     
  14. RemyRAD

    RemyRAD Well-Known Member

    All I can say to your response, and I'm sure you're mathematically correct is that, I believe, Edison felt the same way you do. But who won the argument? Edison or Westinghouse? I think we wouldn't have to worry about induced 60 hertz hum problems as much if we were strictly a "DC society"? Of course most of our equipment runs on DC not AC, so where do we go from here? We only have the AC for distribution and then downconvert to DC. Personally I think that since I like a lot of low-end on my recordings I do love those old Crown " DC 300As" for monitoring but then again we really can't hear any DC.

    Now really, I actually had problems with phantom power with externally biased Neumann U87s, KM86s & 84s on a greater than 500 foot snake and I don't think my Neve consoles have wimpy phantom power supplies? Sure that could have had something to do with wire gauge but then Digital really doesn't sound good compared to analog but we use it anyhow.

    Digitally manipulating my DC
    Ms. Remy Ann David
    (don't ask me what DC means in my above comment because it really isn't ladylike)
     
  15. zemlin

    zemlin Well-Known Member

    In looking for information in support of what was being said here, I ran into a number of papers stating that one of the primary reasons for using AC in power distribution is the simplicity of transformers for stepping voltages up and down.

    Transformers don't work very well with DC.
     
  16. ggunn

    ggunn Guest

    Well, the Westinghouse solution doesn't really apply, as AC won out for reasons not pertinent here; AC phantom power wouldn't work so well, would it?

    What kind of prob's did you have? Do you have data which points to a deficiency in phantom power at the mic's? Did you measure the voltage at the end of the run with the mic's powered up?

    I hasten to point out that I have no axe to grind here, and I'm not trying to get over on you. My experience with this sort of thing is limited to short runs in a studio and my interests are in resolving the theory (as taught to me in school lo these many years ago) with the real world. In short, I am an engineer (BSEE) and I cannot help myself.
     

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