I was sitting in my living room when I heard a plane overhead. It was fairly loud. I figured it was a lower-flying plane, perhaps flown by the Balloon Family. God do I hate it that the town I'm living in is nationally renowned for housing a family of aerodynamically-inclined lunatics.
Then I heard a metallic sort of tapping, coming from inside the house. It seemed to be coming from directly behind my head. My first thought, as you'd likely expect, was "Oh god, this is how they get people. They're probably reading my computer's hard drive right now. They're probably tapping my phone." (Am I the only one who gets paranoid when there's a helicopter of any kind anywhere near where I am for any reason?)
Then I realized that while the plane was causing it, it was not for the reason I'd feared. The picture (in a metal frame with a thin pane of glass covering it) that was mounted right above my head (hmm, is that a no-no? I mean, if a big chunk of glass were to fall off a wall onto a person sitting on the sofa such as myself...) was making the noise; it was the glass vibrating against the frame. Once the plane got a fair distance away (or, at least, sounded further away all Doppler-style) the vibration stopped.
So I wonder...did the noise the plane was making match the frame's resonance frequency? And how exactly would that apply in this situation? If I were to measure the wavelength of the noise the plane was emitting, would that be a) the resonance frequency of the glass, b) the resonance frequency of the metal, c) the average of the two resonance frequencies combined, or d) the distance between the glass and the frame?
And that's not even to discuss the amplitude of the noise, or the shape of the two substances involved...
I'm somewhat familiar with how sound works, having been singing in all sorts of acoustic spaces for years now, but I'm always still startled when suddenly sound will act in unanticipated (not necessarily even unexpected) ways. I have three examples: two general, one specific.
A. Most auditoriums with stages will have a spot on the stage on which the acoustics are most focused. So, of course, speaking or singing in that spot is always a bit of a trip. What's most fun is when you are walking along having a conversation and you suddenly hit the spot. However, because your conversation partner's ears aren't where yours are, they don't notice the difference in your voice. This is how I found out about...
B. The sweet spot at the Red Robin in Plymouth. I don't know if all Red Robin restaurants do this, but in the one I first worked at, I could stand just a foot or two in front of the host stand and have a lot of fun with the acoustics they'd worked into the ceiling. Above me was a perfect circular indentation with a somewhat concave surface. I don't know if it was just that shape, or some other combination of shapes and materials around the lobby, but it would instantly amplify one's voice to a very appreciable degree.
C. This one is general and specific. Bathrooms are always a great spot to find funky acoustics. Shower stalls, when made of the right material (bath curtains=fail), as well as some public bathroom stalls, will have sweet spots as well. (This leads me to believe that sharp angles must be good for very pronounced sweet spots, whereas rounded surfaces are good for more generalized, "sustained" acoustics? But then I remember what Orchestra Hall looks like, and I get thrown for a loop.) There is one specific bathroom in Grinnell that Ted Cooper showed me that has the perfect resonant sweet spot. You see, some of the aforementioned places have only a certain note, or a certain range of notes that will cause the acoustics to happen, or they must be sung from a specific spot or in a certain direction. I don't remember exactly if that shower stall had a range of resonant frequencies or just one tone that did it, but it was very dramatic.
Having the ability to play with science, to acknowledge it and include it in my perception of reality, is something I really enjoy. I want other people to be able to dig on how science affects their world. So many times have I heard "when am I ever going to use this?" in regards to a scholastic subject; normally it's to math (especially calculus) but the second largest target is science. It takes an excellent science teacher (and an even better math teacher) to teach the subject in a way that will get students to believe it's important, to use it in their lives.
Anybody who goes on a road trip and doesn't use math constantly, see me after class.
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