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

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.

Comments

The real secret

[hedgemage]

The drum membrane is made out of 'possum skin.

Re:dont need to replace the drumhead....

[Charliemopps]

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.

Re:Banjo = guitar + snare drum

[Kkloe]

yes but have you written it down? have you done the math behind it?
here is the original paper http://arxiv.org/pdf/1406.4907...

Sitars

[billstewart]

The sitar has several things going on with it

• -- The body has a chamber made from a big gourd, and a wooden neck with adjustable frets.
• -- There's a layer of strings that you pick, optionally pressing on the string over a fret to change the pitch.
• -- There's another layer of strings underneath that resonate when you play the note they're tuned to on the main strings, which provides some amplification and a lot of sustain; that's one of the things that gives the sitar its characteristic sound.
• -- In addition to fretting a string when you pick it, you can also bend it to the side, changing the pitch dynamically, which is another characteristic sitar sound. Guitar and bass players also use this technique, but sitar strings are long enough that it's easier to do.
• -- Generally there are two or three strings that you'll play the melody notes on, and several more strings that you pick without fretting, letting them drone like a mountain dulcimer; that's another characteristic sitar sound.
• That's most of the technology parts; the rest is about the music itself.

Indian classical music theory is complex, at least as much as European classical music theory or jazz. There's a lot of stuff about "ragas", which are a combination of a scale or scales, melodies, fixed parts and improvised parts, with a lot of rules about which ones are appropriate for which situations.