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What Causes Proximity Effect

Discussion in 'Recording' started by Innovations, Jun 26, 2003.

  1. Innovations

    Innovations Guest

    I know what proximity effect is, what I am wondering is what, from a physics standpoint, causes it.

    Also perhaps why some similar mics seem to have more proximity effect than others.
     
  2. realdynamix

    realdynamix Well-Known Member

    Joined:
    Feb 23, 2001
    :) This is a great question to be answered by Stephen Paul, in his forum, or Alan Hyatt on the Designing the Future forum. They are mic designers, who better, eh?

    --Rick
     
  3. Rod Gervais

    Rod Gervais Active Member

    Joined:
    Jun 8, 2003
    Location:
    Central Village, CT
    Innovations,

    this is not my specialty, (in fact - i don't know if i even HAVE a specialty), but the following is an excerpt from Tangible Technology, the entire report can be viewed there - it's really fairly easy reading - a decent primer if you will on the subject - and then Stephen Paul - Alan Hyatt or one of the other real professionals in this area can clean up the technical questions that this raises.

    I know that once i finish digesting it - i will have a slew of questions.

    Isn't an education a marvelous thing?

    You can view the entire report at:

    http://www.tangible-technology.com/microphones/proximity/proximity.htm


    To generate their published "flat" response curves, microphones are typically measured in the lab at a distance of 1-meter (39.37 inches) from the source. For directional mics, any distance closer to the source yields increasingly more "bottom," hence the proximity Effect. (Omni mics are not affected by Proximity.) Knowing that their products will be used up close and personal, directional microphone designers may incorporate a bass roll-off feature either by switch or by default, the latter can be parsed from the 1-meter response although detailed Proximity Curves are preferred. Three of the mics investigated here have published proximity response, detailing that all the action is at 1-foot or less —reinforcing an oft-suggested phrase to "move the mic first " rather than touch the EQ.


    Happy Hunting

    Rod
     
  4. Randyman...

    Randyman... Well-Known Member

    Joined:
    Jun 1, 2003
    Location:
    Houston, TX
    The "vents" on a directional mic will only operate to a certain frequency. As you become closer to the mic, the low frequencies will obviously be able to "sneak" around the vents, and thereby reinforcing the bass frequencies from front as well as behind.

    The vents will usually pick up off-axis sound that is "out of phase" with the on-axis direct sound, and this is what makes them directional. The vents acoustically combine the rear waves so that they cancel out. The "bass" is such a large waveform, it is in phase on axis and from the rear of the mic - when they combine it will re-enforce and cause this "Proximity Effect".

    I'm no Mic Engineer, but I did have one hell of an Audio Engineering teacher in college...

    Later :cool:
     
  5. Stephen Paul

    Stephen Paul Active Member

    Joined:
    Dec 11, 2000
    Proximity is caused by there being two separate gradients that drive a gradient mike.

    One is the velocity gradient which is the vector caused by the time difference between the front and rear of the capsule. Then there's the pressure gradient that's caused by the radiused side of one wave falling away from the pressure front of the previous wave.

    As the mike moves back physically from the spherical wave, the velocity wave starts to become the dominant driving force and the bottom falls off.

    That's about the best I can do with no diagrams, and I ain't makin' no diagrams.

    Nobody loves me, Everybody hates me, I'm gonna eat some worms...
     
  6. realdynamix

    realdynamix Well-Known Member

    Joined:
    Feb 23, 2001
    :) :p: On the menu tonight sir, we have delectible meal worms, sauteed in mild garlic.

    Big fat juicey ones
    small skinny slimey ones
    eooou how they squigle and squirm
    First you bite the heads off...

    Hi Stephen!

    --Rick
     
  7. hargerst

    hargerst Active Member

    Joined:
    Jan 28, 2001
    Don't eat worms, Stephen, at least not without washing them off first.

    This question is actually from another bbs. They've had 27 people respond, and nobody got it right, or even close, let alone stated it so eloquently.

    One post there actually referred people to a highly "technical-looking" article that said in essence, it's caused by the bass buildup in the mic's transformer. Complete with 8x10 pictures with lots of circles and arrows. It said that all mics have a rising response and the mic's transformer has a reciprocal compensating response. I loved that one.

    I hope your answer doesn't get posted over there - you'll just get roasted and nitpicked.

    ...and some of us DO love you, Stephen.
     
  8. chessparov

    chessparov Active Member

    Joined:
    Dec 16, 2001
    Location:
    Orange County, CA
    Brilliant explanation, thanks Stephen.

    We have a surf break (don't laugh!) in Orange County called "The Wedge" where gigantic waves form due to a somewhat analogus chain of events.
    The first wave strikes the (Northern) Newport Beach Harbor jetty, then another incoming wave joins-"wedges" with it. You have to see it to believe the massive focal power. When the wave faces exceed 20+ feet, the ground starts shaking!
    (the wave typically breaks in very shallow water)

    Also read a profound explanatory post by Fletcher,
    where he related the sound waves hitting thegrill on a microphone to waves hitting a pier. Hmm...starting to sound like that PBS show "Connections" :) .

    Chris

    P.S. Yes, in my younger/foolish days, did bodysurf
    the Wedge!
     
  9. Rod Gervais

    Rod Gervais Active Member

    Joined:
    Jun 8, 2003
    Location:
    Central Village, CT
     
  10. chessparov

    chessparov Active Member

    Joined:
    Dec 16, 2001
    Location:
    Orange County, CA
    No worms for me Stephen, just the odd sandcrab or two!

    Chris
     
  11. nuclearmoon

    nuclearmoon Guest

    :D You guys make my day everyday. :D :c:
     
  12. edaudio

    edaudio Guest

    Hey,

    I just wanted to thank Rod for mentioning my proximity article. I've been kinda on a soapbox about proximity and loudness. I know it doesn't answer the question of HOW, but awareness is rather important, I think. Basically, there are times when our instincts point us in the right direction and just a little knowledge can help us make better decisions. There is an art to audio as well as science.
     
  13. Rod Gervais

    Rod Gervais Active Member

    Joined:
    Jun 8, 2003
    Location:
    Central Village, CT
    Eddie,

    you are most welcome, i thought it was a great article - and i (for one) learned from it.

    Rod
     

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