Designing a Amp for MIC.

Discussion in 'The Projects Forum' started by gusmas, Jul 30, 2009.

  1. gusmas

    Thread Starter Active Member

    Sep 27, 2008
    Ok guys here goes, i received a project that requires me to design a device that will automaticly move a microphone into the direction of noise. Now my idea is to buy a whole lot of small mics and put them in a circle, and a Big MIC in the middle on sumkind of rotary device, so that the small mikes can roughly cover the whole 360 degrees of a room. I will need to build pre - amps for all the small mics so i can feed the outputs from the pre - amps into a whole lot of Comparators and then the dominating signal (from the mic that picked up the most noise) will be used to turn the Big mic in the direction of the noise.

    So now to start of i will need to build amps for all of my small mics, now i am planning to use BJT CE amps generally because they give a good Voltage and current gain. This is what i have so far plz any help/critisism of my aproach so far to this project will be highly apreciated thanks.
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    I'd have thought you only need a 'small' mike either side, then turn in the appropriate direction if that's louder than the main mike.
  3. gusmas

    Thread Starter Active Member

    Sep 27, 2008
    Well the idea is the big mic should face the person that is talking so ill need alota small mics
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    Yes, but you only have two directions to turn - Left or Right, until the two signal are equal.

    Lots of mikes just confuses things, and as soon as it starts turning the mike picking up the signal will change..

    Ah.. were you thinking of the small mikes being stationary? - very complex.. To fine-tune a position you need to compare signal from either side of centre until they are equal.

    This is easiest if you just have two 'small mikes' that turn WITH the main mike. Think of the positioning of human ears - it makes it very easy to turn in the direction of a sound.
  5. Audioguru


    Dec 20, 2007
    Most little mics pickup sounds from all around.
    A sound from the left side will be the same volume as the sound from the right side.
    If you shield the sides and rear with a tube then the tube resonates and messes up the sound.
    I you make pretty big tubes with sound absorbent padding inside then they will be huge.

    Your hearing detects the arrival time. A sound from the left side is detected by your left ear before it is detected by your right ear. Your head shields each ear pretty well so the levels are different. Your brain says the sound is from the left side.
  6. Wendy


    Mar 24, 2008
    So your thinking a simple phase shift comparitor, and 2 cheap sound sources.
  7. gusmas

    Thread Starter Active Member

    Sep 27, 2008
    ok i can go with the idea of 2 mics below my main Big mic, then after i amplified both small mics outputs i can compare them and if the right side mic amplified signal is bigger then the bigmic will move left and vice versa for the left mic, but now my problem is to stop the rotary device once the big mic is facing the direction of the sound bcz the small mics outputs will never be equal to each other ;/
  8. Søren

    Senior Member

    Sep 2, 2006

    There's no need for HiFi if their purpose is just to detect relative strength. A thin rubbber tube, or even a piece of heat shrink sleeving should be adequate for that.

    That's a gross oversimplification.
    For directional cues, your brain makes use of the head shadow effect (amplitude difference) and distance differences (for an "angled" sound i.e. phase difference - frequency dependent) and a similar effect due to the folds and crevices of the pinna (the upper part of the outer ear) which reacts with differences due to angle horizontal and vertical as well as frequency.
    Even if you loose the pinna (say on an experiment involving a chain saw and loose wrists ;)) your brain will compensate to a very large extend over time (easier if you're born without the pinna or loose it in a very young age, due to the plasticity of the young brain being larger, of course).

    No two sets of ears are identical, so it's not the folds that makes it so, but rather the brain picking up any clue it can use - your brain and my ears or v.v. wouldn't work without extensive rehabilitation.

    For two mikes to work from amplitude differences, they have to be identical in response to both soft and loud sounds (and everything in between). and the amplifiers likewise.

    To avoid the main mike spinning like crazy when somebody coughs, it could be made with a minimum stay of nn seconds.

    Personally, I find it very poor miking, if a rotating device should be needed, even the greenest sound technician should be able to make a setup that works - with nothing moving at all.
    A single boundary microphone would probably be all it takes.