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Music Science

Secret of the Banjo's Unique Sound Discovered By Nobel Prize-Winning Physicist 101

KentuckyFC (1144503) writes The banjo is a stringed instrument that produces a distinctive metallic sound often associated with country, folk and bluegrass music. It is essentially a drum with a long neck. Strings are fixed at the end of the neck, stretched across the drum and fixed on the other side. They are supported by a bridge that sits on the drum membrane. While the instrument is straightforward in design and the metallic timbre easy to reproduce, acoustics experts have long puzzled over exactly how the instrument produces its characteristic tones. Now David Politzer, who won the Nobel prize for physics in 2004, has worked out the answer. He says the noise is the result of two different kinds of vibrations. First there is the vibration of the string, producing a certain note. However, the drum also vibrates and this pushes the bridge back and forth causing the string to stretch and relax. This modulates the frequency of the note. When frequency of this modulation is below about 20 hertz, it creates a warbling effect. Guitar players can do the same thing by pushing a string back and forth after it is plucked. But when the modulating frequency is higher, the ear experiences it as a kind of metallic crash. And it is this that gives the banjo its characteristic twang. If you're in any doubt, try replacing the drum membrane with a piece of wood and the twang goes away. That's because the wood is stiffer and so does not vibrate to the same extent. Interesting what Nobel prize-winning physicists do in their spare time.
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Secret of the Banjo's Unique Sound Discovered By Nobel Prize-Winning Physicist

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  • by Anonymous Coward
  • by turkeydance ( 1266624 ) on Saturday June 28, 2014 @04:53PM (#47342007)
    You just can't sing a depressing song when you're playing the banjo. You can't go-- "Oh, murder and death and grief and sorrow!" --Steve Martin []
  • The real secret (Score:4, Informative)

    by hedgemage ( 934558 ) on Saturday June 28, 2014 @04:54PM (#47342013)
    The drum membrane is made out of 'possum skin.
  • by Lumpy ( 12016 ) on Saturday June 28, 2014 @04:54PM (#47342019) Homepage

    Just hold a thumb against it. a Lot of us players do that to adjust the sound for different "expression"

    • Re: (Score:2, Informative)

      Just hold a thumb against it. a Lot of us players do that to adjust the sound for different "expression"

      Right... this seems like more of "A scientist that doesn't know anything about music explains something everyone who plays already knew" type of thing.

      • by sribe ( 304414 ) on Saturday June 28, 2014 @05:53PM (#47342281)

        Right... this seems like more of "A scientist that doesn't know anything about music explains something everyone who plays already knew" type of thing.

        No, more like: everybody pretty much knew that the bridge being mounted on a vibrating membrane would affect the sound, but a scientist thoroughly analyzed and modeled the whole setup in order to quantitatively figure out exactly how all the parts and vibrations contributed to the sound. Then a dumbass know-nothing journalist wrote an article that misstated what had actually happened ;-)

        • by umghhh ( 965931 )
          you forgot the endless bitching on /. about dumbass half brain of a scientist while at the same time not being able to explain the exact mechanics of the banjo effect.

          I am half burnt now but I still remember times at school when this sort of explanations provided me with joy at learning stuff like physics and math instead of listening to explanation of a teacher that has no f. clue what he is talking about and what role his 'knowledge' has in my and my fellow students reality, combined with explanations in

  • by ArcadeMan ( 2766669 ) on Saturday June 28, 2014 @04:56PM (#47342025)

    I've heard some of them are still searching for that elusive Gräfenberg spot in their spare time.

  • I think he's just going for the Ig Noble prize.

  • Doesn't he have anything better to do?

    • by bswarm ( 2540294 )
      I was thinking the same, it really doesn't take a rocket scientist to figure out a banjo has dual harmonic vibrations. Duh, it has a drum and some strings. Maybe he should patent-troll it so he can try and collect for every banjo ever made.
      • As I pointed out elsewhere, it is common knowledge to traditional music makers that a vibrating bridge makes the banjo sound. That is why there are instruments like this:

        Designed just like this:

        Except, big surprise, they put a tiny drum head only under the bridge so that the bridge could vibrate and make a more banjo-ey sound.
    • by Anonymous Coward

      Yeah, that asshole better apologize wasting your precious /. time with his irrelevant, unapproved research. How dare he!!!

      • by epyT-R ( 613989 )

        I just don't see how this is really news of interest. I mean, good for him if he wanted to figure it out, but the discovery does not warrant coverage just because he's a nobel prize winner.

  • by Anonymous Coward

    So the banjo is acoustic frequency modulating. When was the first electronic FM synth invented? It would be interesting if some engineers could take this one step further and create a mechanical FM synth. How high a frequency could you get, and what kind of sounds could you build?

  • Banjo jokes (Score:5, Funny)

    by tomhath ( 637240 ) on Saturday June 28, 2014 @05:37PM (#47342209)

    Q: How can you tell if the stage at a Bluegrass concert is level?

    A: The banjo player drools out of both sides of his mouth.

    • Most of them can be recycled easily between genres; the drummer jokes (or bass player jokes) are more likely to be about the players, while the others are more likely to be about the instruments themselves, but either way.

      I did see somebody the other day with a t-shirt captioned "First violinist problems", showing a musical staff and a note about 10 lines above the staff.

  • by VAXcat ( 674775 ) on Saturday June 28, 2014 @05:37PM (#47342211)
    One day my old pal David has played a gig with some local musicians, including his roommate, Bob, who was a banjo player. After the set, Bob was going somewhere else with some other people, so he asked Dave to take his banjo home for him. On the way home, David stopped at the convenience store to get a six pack. As he was standing in line, he suddenly realized that he had left the car windows down, and that he was in a bad neighborhood. He rushed out, but, sure as hell, the worst possible thing had happened - exactly what he was afraid of - someone had spotted the open car windows, and thrown two more banjoes in the car.
    • by Anonymous Coward

    • On the plus side, you can use the disabled parking space if your banjo is clearly visible.
  • by aurizon ( 122550 ) <> on Saturday June 28, 2014 @05:57PM (#47342295)

    ! Interesting what Nobel prize-winning physicists do in their spare time. !

    This tells the tail of an inquiring mind that turns it's focus on many things. He reminds me of Fenman, among many similar Nobel Laureates, whose curiosity was not limited by a 9-5 mentality, but was active 24/7.

    It is this quality that produces the Nobels...

  • by 140Mandak262Jamuna ( 970587 ) on Saturday June 28, 2014 @08:57PM (#47342795) Journal
    He is not the first Nobel Laureate to be fascinated by the drums and vibrating membranes. Sir C V Raman, of the Raman Effect fame, was intrigued by the Indian drums, the Tabla and the mridangam. He published why and how they produce harmonics (paywall) [] back in 1920s. A synopsis [].

    In some sense it is not a surprise because his main work was on vibrating electromagnetic fields, and the natural modes of vibration of circular membranes is a very good way to practice the mathematics of vibrations.

  • by Anonymous Coward on Saturday June 28, 2014 @09:39PM (#47342883)

    Richard Feynman enjoyed playing the bongo drums, picking locks, and whatnot; and also

    Then I had another thought: Physics disgusts me a little bit now, but I used to enjoy doing physics. Why did I enjoy it? I used to play with it. I used to do whatever I felt like doing - it didn't have to do with whether it was important for the development of nuclear physics, but whether it was interesting and amusing for me to play with. When I was in high school, I'd see water running out of a faucet growing narrower, and wonder if I could figure out what determines that curve. I found it was rather easy to do. I didn't have to do it; it wasn't important for the future of science; somebody else had already done it. That didn't make any difference. I'd invent things and play with things for my own entertainment.
    So I got this new attitude. Now that I am burned out and I'll never accomplish anything, I've got this nice position at the university teaching classes which I rather enjoy, and just like I read the Arabian Nights for pleasure, I'm going to play with physics, whenever I want to, without worrying about any importance whatsoever.

    Within a week I was in the cafeteria and some guy, fooling around, throws a plate in the air. As the plate went up in the air I saw it wobble, and I noticed the red medallion of Cornell on the plate going around. It was pretty obvious to me that the medallion went around faster than the wobbling.

    I had nothing to do, so I start to figure out the motion of the rotating plate. I discover that when the angle is very slight, the medallion rotates twice as fast as the wobble rate - two to one [Note: Feynman mis-remembers here---the factor of 2 is the other way]. It came out of a complicated equation! Then I thought, ``Is there some way I can see in a more fundamental way, by looking at the forces or the dynamics, why it's two to one?''

    I don't remember how I did it, but I ultimately worked out what the motion of the mass particles is, and how all the accelerations balance to make it come out two to one.

    I still remember going to Hans Bethe and saying, ``Hey, Hans! I noticed something interesting. Here the plate goes around so, and the reason it's two to one is ...'' and I showed him the accelerations.

    He says, ``Feynman, that's pretty interesting, but what's the importance of it? Why are you doing it?''

    ``Hah!'' I say. ``There's no importance whatsoever. I'm just doing it for the fun of it.'' His reaction didn't discourage me; I had made up my mind I was going to enjoy physics and do whatever I liked.

    I went on to work out equations of wobbles. Then I thought about how electron orbits start to move in relativity. Then there's the Dirac Equation in electrodynamics. And then quantum electrodynamics. And before I knew it (it was a very short time) I was ``playing'' - working, really - with the same old problem that I loved so much, that I had stopped working on when I went to Los Alamos: my thesis-type problems; all those old-fashioned, wonderful things.

    It was effortless. It was easy to play with these things. It was like uncorking a bottle: Everything flowed out effortlessly. I almost tried to resist it! There was no importance to what I was doing, but ultimately there was. The diagrams and the whole business that I got the Nobel Prize for came from that piddling around with the wobbling plate.

    -- Surely you're joking, Mr. Feynman (c) 1985, PP 157-158

  • by Anonymous Coward on Saturday June 28, 2014 @10:22PM (#47343001)

    Florian Pfeiffle and Rolf Bader wrote a paper called "Real-Time Physical Modelling of a complete Banjo geometry using FPGA hardware technology" that explores this:,Bader_04FPGA_Format.pdf

  • by Anonymous Coward

    This effect on timbre is well known and was the basis for the range of Yamaha DX synthesizers in the 1980s. Basically when a tone is modulated (pitch changed) at high speed, instead of hearing a vibrato, you hear it as additional overtones, i.e. a change in the quality (timbre) of the sound. This technique is called Frequency Modulation (FM). It's especially useful for generating metallic and bell-like tones, like the famous FM electric piano sound of the 1980s.

    The vibration of the drumhead at audio freq

    • by Alioth ( 221270 )

      The size and construction of the head probably makes quite a lot of difference. I have an old Dallas D banjo ukulele (a George Formby branded one, no less) and the head had an inner hoop in it which makes the effective area of the head a bit smaller than the entire diameter. As such the overtones are softer and it sounds less "banjoey" (but still very different from a standard ukulele). The other consequence of the banjo uke head is that if you play a chord like F# where one string is not strummed, you need

  • "...acoustics experts with too much free time have long puzzled over exactly how the instrument produces its characteristic tones."

  • Overheard at banjo manufacturers worldwide:

    Gentlemen, we now have the technology to make a banjo that doesn't sound sucky!

    But then how would anyone know it's a banjo?

  • How long before before we field a serviceable apology?

  • It's been known for a while that if you place a banjo mute or any other metal object directly on the bridge, not only does it mute the volume but it also eliminates the characteristic, metallic ring. Placing objects anywhere else along the strings, pot, or even on the drum has little to no effect. The "valley" created by the bridge pressing into the drum is surprisingly small, so only a very small area of the drum affects the behavior of the bridge.

    The bridge is what defines the sound of the banjo, and us

All laws are simulations of reality. -- John C. Lilly