I was busy enjoying your website and came across the column asking about
whether quacks echo. The experiment done in Lansing, MI pretty much settled
the question. But, I have a hypothesis which might explain why the topic even
comes up. If you listen closely to a quack, it has lots of high frequency
energy. It’s more like closely spaced ticks rather than a voice. And, if the
harmonics are right, we might perceive a fundamental note that isnt there.
That’s why we hear a “quaack” rather than high speed chirps right next to
each other, which is what I think a quack is anyhow. The reason I make this
distinction is that high frequencies are attenuated in air more so than low
ones, so that the sound, in some cases, never reaches the reflecting surface.
(You must be getting sick of this topic by now!) If I’m stating the obvious,
please forgive me.