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Acoustic sound emanation from electric circuit components

Discussion in 'Electronic Basics' started by Peteris Krumins, May 12, 2004.

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  1. Hello,

    I am writing a document for school on how different forms of energy
    emanated from the computer systems can be used to analyse the data
    being processed by the computer system.

    Currenly I am writing about acoustic sound emanation from the computer.
    Here is the source of information which I am describing in more detail:
    http://www.wisdom.weizmann.ac.il/~tromer/acoustic/

    The thing I cannot understand is what creates the acoustic sound which can
    be used for analysis.
    Is it the great amount of transistors in the CPU, or as I found in other
    sources, bad quality condensers? Or the quality does not matter? Do all
    condensers emanate acoustic sound? What about transistors, can
    they actually emanate sound?

    Thanks in advance.
     
  2. wavelength

    wavelength Guest

    Hiyas :),

    In regards to your question >The thing I cannot understand is what
    creates the acoustic sound which can
    be used for analysis.


    The primary source of the Sounds of computers are the Mechanical parts.
    Which, for example, are floopy drives, hard drives, fans, speakers,
    keybpards, CD and DVD units etc. Electronic parts { including condensers },
    in general, do not make any sounds unless they are being ' fried ' ;).

    Best

    :)
     
  3. Uncle Al

    Uncle Al Guest

    Current flow creates magnetic fields, then Lenz' law. Voltage
    stress. Stuff moves in response to changing fields - e.g.,
    transformer hum. Keyboard strikes may give you impulses. Almost
    everything in a computer is near- or multi-GHz square waves with their
    very high frequency harmonics. One doubts any information processing
    yeidls even ultrasonic acoustic signals carrying information -
    including sum/difference beats. Circuit elements that move will
    mechanically fail from fatique. The only part you want to hum is the
    quartz crystal that locks the board frequency (if there is one).

    Look for EM emissions. That is how the alphabet soup of jackbooted
    Federal agencies listens in on what you do. Only a fool would go
    wireless (computer or telephone).
     
  4. Did you take a look at the link I posted? It says they managed to record
    the sound (2.5kHz - 40kHz) which came from the electric parts.
     
  5. Gareth

    Gareth Guest

    Yes, I would have thought so too and I haven't noticed the capacitors in
    my computer making any noise, but some researchers think differently:

    "The sounds made by capacitors on motherboards might, in theory, give
    attackers code-breaking clues in much the same way electro-magnetic
    leakage or power fluctuations can be used in so-called "side-channel"
    attacks on secure systems"

    see:

    http://www.theregister.co.uk/2004/05/11/sounds_yield_crypto_clues/

    Gareth.

    PS condensers are more usually called capacitors.


    --
     
  6. Any component that can move a tiny bit or has parts of it that can move
    could create sound.
    Often it is transformers (because the magnetic field moves magnetic parts or
    windings even), capacitors (because of piezzo electric effect for example),
    transistors I dunno, never noticed :).
    Transistors do change (move) microscopic amounts due to heating and cooling,
    but such fast heating and cooling that vibrations in the audio range would
    come from it .. I dunno, maybe if you had an ultra sensitive microphone.
    Strongest noise in a PC comes from the fan(s).
    Next is the harddisk and floppy drive, the movement of the disk, and the
    positioning of the disk arm (very fast, milliseconds) makes a lot of noise.
    Floppies are worse (stepper motor head seek).
    Of cause 48 x speed CDROM drives and DVD drives add a lot of fun too.
    And, on top of that, PCs do have a speaker.
    beep beep
    JP
     
  7. Today there has been periodic power outages near where I live. The lights
    go out and I hear an awful racket outside, like a deep vibrating thrum. Car
    alarms go off and my cats run in terror.
    Inductive spikes can be a bitch.
     
  8. wavelength

    wavelength Guest


    Hiyas :),


    On the link .................

    One thing that you might keep in mind is that a square wave contains a
    huge number of frequencys. See Fourier Analysis. A Perfect square wave
    contains a Infinite number of frequencys. ' Square ' waves are the defacto
    signal in a computer. These frequencys will ' find ', and stimulate
    the mechanical resonances of the system. And with Sensitive equipment could
    be detected.

    They are VERY weak though unless they find resonances in which case the
    part is actually oscillating. No intensity information was given - only
    spectral.

    It would be interesting to see the spectral content of the lines in more
    detail to see how sharp they are. In the part where chill spray is sprayed
    notice how the lines more or less return to their original positions as the
    system returns to its original state. The band is from the ' noise like '
    sound of the spray itself - ie random noise.

    There are better ways to ' eavesdrop ' though if that what the goal is
    though ...........



    Best

    :)
     
  9. crynwulf

    crynwulf Guest

    All electronic parts change shape slightly when passing a current. This
    shape change is the source of the noise. Transformers are the worst.
    Capicators are next. Capicators consist of two metalic conductors separated
    by an insulator. When charged, the plates attract each other and compress
    the insulator layer. When discharged, they relax and the insulato expands.
    No, you won't be able to hear the noise from a cap, but you might be able
    to measure it. Caps also emit some em that can be turned into (amplifed)
    sound by nearby metal parts, such as the chassis of a desktop. If you can
    get close enough to measure this sound, you probably should just tap onto
    the CPU leads and log it directly.
     
  10. In sci.physics, Peteris Krumins
    <>
    wrote
    Who needs transistors? :) Dunno about modern TV sets but when I was
    younger I could hear the very high-pitched squeal of what probably
    was a transformer being abused by a 15,750 Hz sawtooth. :) Not
    sure if my hearing is good enough anymore.

    As it is, the actual sound might be an artifact of a magnetic
    covering being vibrated by electric currents. Then again, one
    could get lucky and have noisy power lines because of too few
    bypass caps; the noisy power might show up in the sound output,
    for example -- my new computer has that problem, although it's
    not noticeable unless I turn up the volume on my speakers. However,
    what you're mentioning is a microphone and/or other monitoring
    device that's not listening to the speakers.

    Of course, there is the possibility that the microphone is
    directly picking up the electromagnetic radiation as well.

    You mention low-quality condensers (caps). Since capacitors store
    energy by distorting the electric field of the surface of the
    dielectric they'd probably make low-quality piezoelectric
    transducers as well -- and they might make a bit of noise.

    I can't say for sure, but it's a bit like EEGs in that one can
    get a general idea of the activity of the system by listening
    to the noise (on my system at least, I can hear each keyclick
    as I type in, although I also hear other noises, and I can
    make a bunch of noise if I do things with my browser -- even
    moving the mouse makes interesting noises).
     
  11. Rich Grise

    Rich Grise Guest

    If you believe that they're spying on you by analyzing the various
    acoustic sounds from piezo effects and magnetorestrictive effects
    and so on, then you'd better wear your aluminum foil hat at all
    times.

    Cheers!
    Rich
     
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