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Thread: How does diaphragm size/polar pattern relate to mic applications?

  1. #21
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    Okay, let's start this with some interesting history as a prelude to the whole mic discussion. "Why" will become pretty clear by the third or fourth paragraph:

    In a way, the history of microphones and sound all started with Alexander Graham Bell, and Western Union. After Bell won the lawsuit with Western Union over the invention of the telephone, his fledgling AT&T company needed somebody to manufacture phones for them. Western Union had created a manufacturing division (Western Electric) to make telegraph keys and telegraph equipment. Bell bought the Western Electric division and they had the exclusive right to manufacture phones for Bell.

    By 1910, Western Electric had the ambitious task of creating a coast to coast telephone hookup to tie in with the opening of the Panama Canal, but the problem of amplifying a signal over long distances was still unsolved. In 1913, Dr. Harold Arnold (of Western Electric's research group) saw that Dr. Lee DeForest's "Audion vacuum tube" was the possible solution, and they bought the rights to it and began work on a "high vacuum" tube.

    This indeed solved their long distance problem, and led to another discovery - a "loud-speaking telephone". In 1916, they received a patent for what we now call a "loudspeaker". With the addition of the "high vacuum" amplifying tube, and another little patent for a device called a "condenser mic", they were suddenly in the P.A. business as well.

    These inventions opened the door for radio, talking movies, and sound systems in general, and with their other patent for a high quality "amplifier" in 1916, they pretty much defined the science of sound. (It would be another 12 years (1928) untill a young Georg Neumann would start his own mic company in Germany. That same year, Western Electric received a patent for a "dynamic mic" design.

    The designs Western Electric developed for movie speakers would eventually start companies like Altec and JBL making horns and loudspeakers for Western Electric, and eventually those Western Electric designs became the foundation for their own speaker lines.

    Western Electric created their own Research and Development arm called "Bell Laboratories", which went on to create the transistor and a host of audio related products. It was Western Electric and Bell Laboratories who we must thank for the development and research into microphone design that we enjoy today.

    Next, we'll look at some of the different types of microphone designs in terms of advantages and disadvantages. How a "dynamic" mic really works will definitely surprise you (hint: it's NOT just a small speaker in reverse).
    Last edited by Harvey Gerst; 05-03-2001 at 11:33.

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    Originally posted by Tekker
    That's some good stuff there Harvey, but do you know if there is a way to convert it so that it can be opened up in word? I like to be able to highlight and underline stuff as I'm reading.
    I don't know how to convert PDF's into Word documents, but there's a Text Select Tool on the tool bar in Acrobat Reader. You can copy text into Word with that. Of course, the pics would still be a problem... hmm, maybe not such a great idea after all...

    Harvey, i want to say thank you for spending all this time sharing your knowledge: Thank you! Your posts are very much appreciated on this side of the Pacific Ocean!

    micmac

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    Originally posted by micmac

    Harvey, i want to say thank you for spending all this time sharing your knowledge: Thank you! Your posts are very much appreciated on this side of the Pacific Ocean!
    I'll go ahead and speak for the Ohio Valley while seconding that sentiment. I'm with you so far...

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    Dynamic Mics

    By far, the most popular mic on the market today is the dynamic cardioid mic, so that's as good a place as any to start. "How does it work, what exactly is a cardioid, and how and where would you use it" will be our focus today. Let's look inside one and see what we find:

    Well, it has a cone (like a small speaker), a voice coil (like a small speaker), and it sits in a magnetic gap (like a small speaker), so isn't it just a small speaker in reverse? Yes, and no. The operating principle is the same, but the execution is very different. When's the last time you saw a 3/4" speaker that went down to 30 or 40 Hz? Here's how it's done:

    The system resonance is chosen for a mid band frequency. By itself, the capsule's response looks something like this:

    ......./\
    ....../..\
    ...../....\
    ..../......\
    .../........\
    ../..........\
    ./............\ - just one big resonant peak, with the response falling off rapidly on each side of the peak. Now you can tame that peak by putting in a resonant chamber that's tuned to that peak, which will give you two smaller peaks on either side, like this:

    ..../\..../\
    .../..\../..\
    ../....\/....\ And if you add two more resonant chambers, tuned for each or those peaks, you wind up looking more like this:

    ./\../\../\../\
    /..\/..\/..\/..\ And if you make the chambers a little more broad band, the response starts to really flatten out:
    ._..._.._..._
    /..\/..\/..\/..\ but remember, it's still a lot like a bunch of tuned coca cola bottles inside there.

    Now ya gotta do all of this stuff JUST to get the response usable - never mind about the mic pattern yet!

    A lot more to come!! Everybody still with me at this point? Any questions?
    Last edited by Harvey Gerst; 05-04-2001 at 13:46.

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    Ok, so where are we at, gang? Is this too easy, too hard, just right? More than you need to know? Too basic? Too difficult? Gimme some feedback so I can tailor this thing to what you really want to know.

    To quote a well-known, musical masterpiece, "Tell me what you want, what you really, really, want".

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    Sorry to keep you waiting. It's Derby Eve here in Louisville, and I've been playing gigs right and left to line the old coffers with MICROPHONE MONEY. I just got in from my last one, so I should be around for a while. And yes, I really, really want to hear this.

    So, if I understand your first post, you explain that the frequency response of your basic garden variety dynamic mic is not really a curve, but rather a series of mechanically engineered peaks, right? But we don't necessarily hear it that way, because our ears/brains fill in the sonic spaces the same way our eyes/brains do when we look at a newspaper photo that really consists of a bunch of dots rather than an actual picture. Is that pretty close?

    Is the reason for that the size of the diaphagm? It would make sense that, in order to truly reproduce a sound in the extreme low register, the diaphragm would need to be as large as the soundwave corresponding to the lowest note on the recording, which would be both incredibly impractical and terribly funny....can you see Roger Daltrey swinging one of those suckers around? So instead of that, the initial response peak is spread out so that it covers more range more evenly.

    Am I close, or did I get off track by assuming too much?

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    Thumbs up Great Questions Chris

    As soon as I read your post about our brain filling in the spaces I understood what Harvey was saying. (I think)

    Like so many of the new guys here I wouldn't know how to ask good questions like that I would just end up rambling and not making any sense. "Uhhh, could you explain the part where you were talking about the thing....ya know the t h i n g" I guess what I'm trying to say is, it's nice to have people here who know how to formulate questions for us new guys in a way that's easy to understand (and also a great teacher who can answer all our questions).

    Keep up the good work guys!!

    -tkr

    Last edited by Tekker; 05-05-2001 at 09:37.

  8. #28
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    Originally posted by Chris F
    Sorry to keep you waiting. It's Derby Eve here in Louisville, and I've been playing gigs right and left to line the old coffers with MICROPHONE MONEY. I just got in from my last one, so I should be around for a while. And yes, I really, really want to hear this.

    So, if I understand your first post, you explain that the frequency response of your basic garden variety dynamic mic is not really a curve, but rather a series of mechanically engineered peaks, right? But we don't necessarily hear it that way, because our ears/brains fill in the sonic spaces the same way our eyes/brains do when we look at a newspaper photo that really consists of a bunch of dots rather than an actual picture. Is that pretty close?
    Yes and no. The broad band resonators and filters actually do smooth out those peaks pretty well, but you hafta remember it's all done with mechanical tricks and if you hit it with enough energy in a susceptable frequency range, it will resonate.

    Is the reason for that the size of the diaphagm? It would make sense that, in order to truly reproduce a sound in the extreme low register, the diaphragm would need to be as large as the soundwave corresponding to the lowest note on the recording, which would be both incredibly impractical and terribly funny....can you see Roger Daltrey swinging one of those suckers around? So instead of that, the initial response peak is spread out so that it covers more range more evenly.
    No, that's also a function of excursion and mic design. Small omnis for example, can get down to 1 Hz fairly flat.

    Am I close, or did I get off track by assuming too much?
    A little too much assumption which I'll try to explain in the next installment.

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    Oh, well. Can't blame a guy for trying....looking forward to the next one.

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    I don't know. I'll consult my mistress.

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