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Thread: condenser mics

  1. #1

    condenser mics

    Can someone recommend a condenser mic? I'm looking for a mic that is capable of 'hearing' or picking up the smallest, most faint sound. For example, if the sound source is held right at my ear, and I can hear it, yet just five or six inches away I can't, what condenser mic would you recommend? Large or small diaphragm, or would it matter? I know I need a preamp. Perhaps someone could recommend one of those, too?

    Thanks

  2. #2
    Need more info. What, exactly, is this quiet sound source?

    The following issues come to mind:

    1. How important is fidelity? Recording something in glorious hi-fi is different from just getting a documentary record.

    2. Will the mic be close to the sound source?

    3. If the recording has background hiss, how much of a problem will that be?

    The very, very best large-diameter condenser mics have self-noise that is as much as 10dB lower than other mics, but they're thousands of bucks. Bear in mind that there's an absolute limit, too: air itself makes noise. If you're a young person with good hearing, you can hear it if you're in a quiet enough environment (like an anechoic chamber).

    In general, large diaphragm mics have less hiss than small ones, just because there's more output from the capsule. However, if you're going to be putting the mic right next to the sound source, you will run into a problem: from that close, the sound will strike the mic as a spherical, not plane, wave. This means the sound will get to different parts of the diaphragm at different times and some parts of the diaphragm will be moving in opposition to other parts. This may cause serious frequency response problems. Large diaphragm mics are not accurate at extremely close range.

    So, for close-up, this indicates a small diaphragm mic. Next problem: small mics have significant hiss. If the sound source is really quiet, you'll hear the hiss in the recording. Will this be acceptable?

    Hiss is primarily a high-frequency problem. If the sound source does not have a lot of high frequency energy, or you don't care if it's a high fidelity recording, you can remove a lot of the hiss by lowpass filtering. In crude terms, turn the treble down. If you have computer-based EQ software you can do a better job; try a 12dB/octave lowpass at 7KHz, or if you want to be radical, 4kHz. This will make a huge difference. If you're amplifying it a lot, you'll also find there's a lot of low frequency ambient noise which you can filter out by turning down the bass. In general, the narrower frequency response you can get away with, the less trouble you'll have with noise. A good portable AM radio has a response of about 150Hz to 3kHz; if that kind of sound is good enough, that suggests where you should set your filter frequencies.

    Or, if an accurate recording is more important than a quiet one, don't do any filtering and live with the hiss.

    If the sound is at a distance, you will need a shotgun or parabolic mic. Shotgun mics tend to have better sound, but they're hissy. Parabolic mics, because of the geometry of the reflector, have very artificial sound, but a good one doesn't have much background noise. (A shotgun mic works by throwing away sound you don't want; a parabolic by gathering sound you do want. This gives the parabolic an inherent advantage, in the same way that an owl's huge eyes gather enough light to make night hunting possible.)

    Frequency response of a parabolic depends on the size of the dish. A small dish will have good high frequency response but lose its reach below 1kHz. A large dish will have better low-frequency response and a longer reach, but everything above 3kHz will be garbage unless it's an extremely well-designed mic.

    So, bottom line: the answer depends on what you're trying to do and which factors are important to you.

  3. #3
    Yes, I will put the mic right up to or within an inch or so of the sound source. I just need a simple recording, nothing high fidelity. Background hiss isn't a problem as long as I can record the actual sound. The sound source is emitted from a very small speaker connected to a small receiver which receives a transmitted signal. It's a very, very low volume sound designed to be heard when it's right up to someone's ear, but any farther away it becomes useless.

  4. #4
    Are you looking to capture the noise of the speaker or might you want to try pulling the signal that drives the speaker and using that as a source?
    Eric Adler (tonsofpcs)
    http://www.videoproductionsupport.com/ Chat at: http://tinyurl.com/vpschat
    Follow me on twitter: @videosupport @eric_adler

  5. #5
    Quote
    Quote: tonsofpcs
    View Post
    Are you looking to capture the noise of the speaker or might you want to try pulling the signal that drives the speaker and using that as a source?

    I'm just trying to capture the sound and not concerned with the speaker noise. I'm not sure how to pull the signal for the source, sounds technical.

  6. #6
    How does the speaker connect to the device? What is the device?
    Eric Adler (tonsofpcs)
    http://www.videoproductionsupport.com/ Chat at: http://tinyurl.com/vpschat
    Follow me on twitter: @videosupport @eric_adler

  7. #7
    What Eric is getting at is, can you get at the electrical signal that's driving the speaker? In other words, is there a headphone jack?

    When you're trying to get an audio signal from one place to another, a direct connection is always better than turning it into sound and then back into a signal. If you can skip the whole speaker/microphone thing, you're ahead.

    If you can't, the best mic would probably be a very small condenser lapel mic, which you can get at Radio Shack. If you're willing to do some soldering, you can even get a bare condenser mic capsule for maybe $4.

    Next question: what will you be feeding the mic into? I ask because a condenser mic has to have a source of DC power.

  8. #8
    ...is there a headphone jack?
    no jack...

    the best mic would probably be a very small condenser lapel mic, which you can get at Radio Shack.

    hmm...

    If you're willing to do some soldering, you can even get a bare condenser mic capsule for maybe $4.
    I'm willing to solder...

    what will you be feeding the mic into?
    I haven't decided on a preamp yet. I'm still narrowing down the mic part. The radio shack option sounds good as does the mic capsule/solder option. I suppose these simple options are good enough technology to 'hear' very quiet sounds such as I described?

  9. #9
    Yep. Regarding the DC power necessary, if you feed it into a computer mic input the DC will already be present there. Otherwise we may have to kluge something. So it's time to choose what you'll be feeding it into.

  10. #10
    So it's time to choose what you'll be feeding it into.
    I suppose if the radio shack $4.00 bare condenser capsule is sensitive enough, I'll solder it to a line with an input jack for my computer. I wasn't aware a computer could function as a preamp.

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