A bell that rings two notes at once (2017) [video]
youtube.com
youtube.com
He is one of my favorite science educators on yt, and that may well be because he’d likely argue that his content fills a different archetype all together.
I love his casual but data, and pen and paper equations, driven approach to development.
He creates clever contraptions to collect data to challenge hypotheses.
(A recent favorite was a sleigh and a kitchen scale to measure fan thrust.[1])
All the while without the, abhorrent to me, “ScIeNcE iS FUN!” facade inexplicably so often found in science education.
Rather, the science is simply shown for what it is, and it’s just him that is fun.
~”Let me just take an angle grinder to this steel pipe!”
I definitely recommend you check out his other channel.[2]
He split it off because he felt the content was in conflict with his main channel, or yts algo did, but I feel people who enjoy this video will also enjoy what he posts there.
Oh and bell is cool too!
Some of what singer from Laybach does sound 2 voice as well. In some cultures this style is a natural.
It's the same thing we do when we shape our mouths to make different vowel sounds, only much more precise. The physical thing that underlies what we perceive as "vowel quality" is the frequency of spectral peaks ("formant" is the linguistics terminology). When we shape our mouths (more generally our vocal tracts) to say "aaa" versus "iii" we are creating resonances at certain frequencies.
Admittedly when creating vowel sounds the bandwidth of the resonator is pretty wide, and when we hear vowels we can still perceive "a" quality vs "i" quality with even a wide bandwidth.
What Anna-Maria Hefele and other overtone singers do is much more precise. They can get a very narrow bandwidth by controlling their vocal tracts more precisely.
FYI for anybody. Your A440 is not the only frequency. There’s every integer multiple (880, 1320, etc) as well. Different coefficients of those overtones are why you can sing “ahhh” and “eeee” at the same note but they sound different.
Polyphonic overtone singing is a technique where one or more overtones are heavily emphasized in the timbre.
This is also why major 3rds on pianos are noisy. A4 has a C# as it’s 5th harmonic at 2200Hz (5*440). But C#5 (A4s major 3rd) on piano has a 4th harmonic (two octaves up) slightly higher at 2217.48.
That’s why if you listen close there will be a ~17Hz oscillation around C#7 when you play A4 and C#5.
It's extremely calming and I have a weird side effect that when I stop, I can still hear it "in my head" - it's pretty cool actually.
Also, the video alludes to this briefly but worth repeating: if the bell (or the pipe) is perfectly circular, i.e. radially symmetric, there wouldn't be two separate modes as demonstrated (higher frequency harmonic modes would still exists at lower amplitudes, but not relevant to discussion here). Grinding the bell down on the sides is breaking the symmetry, and thus, separate modes.
Coincidentally, Joseph Fourier studied harmonics using a metal ring and a heat source, analogous to the circular bell shown here. With a heated metal ring, you can visually see the different modes (including higher harmonics).