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Why can bass travel through walls so easily?

  1. May 6, 2004 #1

    ShawnD

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    If I let a song play on my computer speakers (2 normal + 1 sub) then leave my room and close the door, I can't here the treble at all but the bass is as loud as if the door wasn't even there. If I turn the volume up, I can hear the bass from any part in the house (including the basement), but the treble is inaudible.
    Why does bass travel through walls but treble does not?
     
  2. jcsd
  3. May 6, 2004 #2

    chroot

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    In short, because lower frequencies have a higher transmission coefficient for most building materials. You could be quite advanced and solve for the transmission coefficients based on the actual molecular physics involved using kinetic theory. Notice that ultrasound also penetrates most materials easily; so it just happens that treble frequencies, like 5k-10k, are near the vibrational modes of many common molecules, while frequencies above and below don't.

    - Warren
     
  4. May 6, 2004 #3

    ShawnD

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    Thanks for the answer.

    Materials absorb certain frequencies of sound? This might be a little off topic...... but if certain materials absorb certain frequencies, could be that used for material analysis?
     
  5. May 6, 2004 #4

    chroot

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    It's beyond my knowledge if such analysis is actually done, but it seems like it reasonably could be done.

    - Warren
     
  6. May 6, 2004 #5

    russ_watters

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    [OT? Your thread...] Depends on what kind of analysis you mean, but yes - vibrational analysis of materials is pretty important. I did my senior design project on piezoelectric polymers - plastics that generate a voltage when deformed. These devices can be used in static conditions (they make for cool household scales) and in vibration - the company I worked for uses them for sonar transducers. www.msiusa.com

    When I was at the Naval Academy, a platoon commander marched (doubletime) his platoon across a wooden footbridge. They were marching at a frequency (180hz or so) which just so happened to be the resonant frequency of the telephone poles that made up the center span. The span bounced at higher and higher deflection until one of the poles broke.

    There was a famous case of a balcony in a club a few years back that broke for the same reason, killing a number of people.

    In my job HVAC engineering, fans, ductwork, etc all combine to create some strange accoustical effects including certain specific fan rpm's that cause enormous vibration and destroy fans. When using a variable speed fan, you have to lock out certain rpm's to avoid damaging the fan.

    Yeah, vibration analysis is pretty important in many engineering disciplines.
     
  7. May 6, 2004 #6

    ShawnD

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    Great info, thanks Russ.
     
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