I just read this neat little gem in The Physics Teacher. Take a bunch of coffee stirrers (the kind that look like round straws for wee folke) and set them into a box so they’re all upright (all the little holes are looking up at you). Jiggle them and pack them tightly so that they seal flat against the side of the box with no “holes”. Then go somewhere that has a lot of loud ambient noise (I’m imagining the Exploratorium on a busy day), and put the open end of the straws against your ear.
According to The Weird Project, you’ll feel as if:
the air pressure is falling invisible pillows are drifting around your head your ears are about to pop you are going deaf your head is changing size the size of the room is shrinking you are about to faint
In other words, what happens is that part of the background sound goes away. Apparently when it works right, the effect is “very creepy.”
What happens is that certain frequency bands (eg., certain pitches of sound) are attenuated (read, “partially blocked”) by the straws. The article in the Physics Teacher describes how to use a function generator and a speaker to determine which set of frequencies are most affected. They found that for 13.3 cm round stirrers, the sound level drops off at 660 Hz (I think that’s a high “A”) and again at 2000-3200 Hz. You can get a rough idea for the pitches of those sounds here.
If you’re curious about this, definitely check out The Weird Project, it’s got a lot of good information on it.