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Haunted Houses Explained: Infrasound

Posted by Hemos on from the soundings-from-the-deep dept.

anagama writes "For anyone who cringes whenever accosted by topics such as psychics, haunted houses, or any sort of new age drivel; for anyone who thinks James Randi is cool or has an active subscription to the Skeptical Inquirer - you're gonna love this story about infrasound. Here's a quote: "British scientists have shown in a controlled experiment that the extreme bass sound known as infrasound produces a range of bizarre effects in people including anxiety, extreme sorrow and chills -- supporting popular suggestions of a link between infrasound and strange sensations. ... Some scientists have suggested that this level of sound may be present at some allegedly haunted sites and so cause people to have odd sensations that they attribute to a ghost -- our findings support these ideas.""

3 of 558 comments (clear)

  1. Yeah, right... by Maury+Markowitz · · Score: 5, Insightful

    "Infrasound is also produced by storms, seasonal winds and weather patterns and some types of earthquakes. Animals such as elephants also use infrasound to communicate over long distances or as weapons to repel foes."

    So now we just have to explain how the elephants got into the haunted houses. Or how it is we don't see ghosts every time there's a thundershower.

    Seriously, trying to come up with a physical explaination of ghost stories that doesn't include the mind of the person is dumb. The range of reported phenomina is so wide as to be clearly "made up".

  2. Re:BBC has a more religious spin on the story by Rostin · · Score: 5, Insightful

    Which is even more of a leap than the original story, considering that (A) "religious feelings" are not confined to churches, and (B) many (most?) churches don't have pipe organs.. and quite a few don't use instruments of any kind.

  3. Re:Can it be reproduced by nathanh · · Score: 5, Insightful
    Seriously, they don't mention what frequencies were used (can someone extrapolate from the pipe length), but getting transducers to work so low isn't easy and you would need a DC coupled amp. Bass speakers theoretically go down to 20Hz but the performance falls off.

    I don't know where you're coming from with this talk about a "DC coupled amp" but bass speakers go all the way down to DC (0Hz). There's certainly no practical or theoretical problems reproducing sub-20Hz signals from a bass speaker. Even your tiny 6" mid-range drivers can (and do) reproduce 1Hz signals. You just can't hear it because so little air is being moved.

    The actual problem is that the lower the frequency, the more air you need to move in order to hear it. The amount of air a driver can move is partially determined by the Vd figure (volume of air moved). This is simply Sd (surface area of cone) multiplied by Xmax (cone excursion). The 1Hz signal out of your 6" drivers is so quiet that you can't hear it, but it's there. Not enough air is being moved for your ears (which are heavily tuned to 2-4kHz) to detect.

    So the trick is to make the excursion large, the surface area large, thereby getting a large value for Vd. Of course, you now need a lot of power to move that much air around. That's why subwoofers have 18" cones with 1/2" excursions driven by 400W amplifiers. Grunt. Grunt. Grunt.

    Of course, super-low frequency generators don't bother with all this nonsense. They just use huge pistons behind a suitably long tube. Much easier to move the required amount of air.