The Experimental Luthier Workshop : Hacking Chordophones

  • Examine the physics of stringed musical instruments (SMI)
  • Explore the structual components and playing techniques of SMI
  • Review the work of past SMI developers
  • Experiment with recipes for modiyfing the function and behaviour of SMI

Strings

Several waves of harmonic oscillations occur when a string vibrates. The space between two oscillations is called a node. As a rule of thumb, there is always one node at the bridge and nut and one in the middle of the string among others in between. NOTE: String oscillations are not to be confused with sound wave ocillations. The shape of a vibrating string is not an analogous to the sound wave cycles that is produces.

 

nodesimpedence

When a string is plucked, you may notice that it moves the most in the middle and less at the bridge and nut. That is becaues the impedance towards the middle is lower and higher (more taut)  at the ends of the string. This is important to think about when manipulating strings as they behave differently from the middle to the ends. I.E. If you pluck a string, you will need more distance between the plucking device and the string as you move further from the bridge (end of string) in order for the string to freely viberate.

The pitch of a string is determined by these variables – length, tension, mass, and weight.

Looser, longer, thicker and/or heavier gauge string = lower pitch

Tighter, shorter, thinner, lighter string = higher pitch

Tuning: The first modified string instruments must have been retuned to an alternative set of intervals or just tuned up or down. This is mechanically the least challenging. Below are some recipes for tuning your instrument.

  • Tune to a chord
  • Reverse or shuffle the order of strings to inspire a new fingering style (note: the nut may have to be altered to accommodate varying diameter strings)
  • Tune courses of strings in unison or in octaves. Try de-tuning one of the strings so that it is slightly sharp or flat with the rest of the course to produce a beating or chorusing effect
  • Research other musicians who have experimented with tuning and create your own recipe list of tuning specifically for your instrument

Materials: Strings can be made of any kind of material that is resilient enough to vibrate such as nylon, steel, animal gut, rope, silicone, rubber, and elastic. Here are some recipes to explore substituting different types of string material.

  • Bungee cables and rubber tubing as bass strings
  • Fishing line or weed wacker line replacing nylon strings
  • Long springs from a reverb microphone toy used as drone string: This works well on both acoustic and electric instruments
  • Partially unraveled music wire
  • Silicone strings from jewelry supply (cheaper than bass uke strings) – I.E. Stretch Magic Bead & Jewelry Cord

Actuating

Depending on their makeup, strings can be plucked, hammered, bowed, scraped, or magnetically bowed to produce various tones. Here are some recipes to explore your options.

Hammering and Hitting

  • Wooden drum sticks, rubber, felt, and wood mallets, hammered dulcimer mallets: Beat the strings near the bridge for a hammered dulcimer or piano effect
  • Percussion Mallets on hollow bodies: Make drum sounds that either resonate throughout the body of an acoustic guitar or throughout the body/strings/pickups of an electric guitar.
  • Drum Brushes: Create random crackling and scratching noises over a pickup or on a soundboard.
  • The bones of your fingers: Use the boney part of your finger to tap strings near the bridge to produce muted hammering effects.
  • Look around the kitchen for egg beater, wisps, wooden spoons, and forks: All of these are great percussion instruments.

Plucking

  • Try making your own plectrums out of various types of material such as credit cards, felt, leather, latex, cactus quills, feather quills, and wood. What types of shapes can you come up with? What other ways can you hold the plectrum or attach it to you fingers/hand?
  • A motorized plectrum (The Weed Wacker): Find a DC motor from a personal fan or toy add a tie wrap to the end of its shaft and fix it to your instrument. This will produce a strummed mandolin-like effect.
  • Finger-tips and finger nails: Classical guitar players and folk/blues players often use their finger nails to pluck strings. Try using your finger tips instead. This can produce a mellower tone. When you pinch or hold a string with your fretting hand, you can use your fingers like the felt muting tangents on an auto harp.

Bowing and Scrapping

  • ebowschematicCorrugated metal and plastic forks make great scrapers. Use them like you would bow a string.
  • Finger nail files or needle files for more scraping sounds.
  • A violin or cello bow on a guitar or banjo.
  • Purchase or make your own E-bow. E-bows use feedback to electromagnetically induce the strings to vibrate. Its basically a pickup-amp-output-coil circuit like an electric guitar circuit but much much smaller and more controllable.
  • A rotary mechanical bow. Try using a flexible shaft dremel tool with a felt buffer wheel to bow a string. You may need to add rosin.
  • Bowing with fingers and powdered resin: Covering your hands or gloves in resin, you can pinch strings to resonate them running your finger perpendicular and parallel. This may also give you some extra control to incorporate into your technique

Notes on Actuating Strings

A lot of prepared guitar/string instrument players have an arsenal of mallets, bows, and scrappers. Get yourself a bag or a box to keep them together so you can bring them to performances and practices. Try combining the use of one tool with another so you can quickly change within a piece that you are playing. I am always looking for my favorite tool for the job each time I write a piece. Don’t be afraid to develop your own either by gluing/binding parts together or designing an actuator to print on a 3d printer or laser cutter. Here are some designs that I made that you are welcome to use…

Z-Bow
Scraperbow

Bridges

The bridge transmits the tone of a vibrating string to the soundboard of an instrument. In turn the instrument’s soundboard resonates back to the string. This is how an acoustic string instrument is amplified. Bridges come in many sizes and shapes and can be designed to produce notes that rattle, sizzle, and/or ring.

Tromba Marina Bridge
Ebow Schematic

Sitar Bridge
Ebow Schematic

Kora Bridge
Ebow Schematic

Koto Movable Bridges
Ebow Schematic

EXPERIMENTS

Buzzing and Rattling strings. Adding a buzzing bridge or a rattle to a string can produce a seemingly louder effect to an instrument. Below are just a few recipes…

  • A ballpoint pen spring or thin wire wrapped over a string: Try moving the spring along the nodes of the instrument and notice the varying rattling effects. This is also a nice way to isolate the rattling effect to one string
  • Mini clothespins, hair clips, or aligator clips: This falls somewhere between rattling and actuating as the cloths pins or clips produce a hammering/rattling effect on strings below or above as the piece moves with the vibrations of the string.

Making Your Own Bridges

If your instrument has a moveable bridge you can replace it with a bridge of your own design. For example you could give a violin a tromba marina bridge or guitar a sitar bridge. Here are some designs of bridges that I have put together for you to laser cut or modify for your own purposes.

Tromba Marina Bridge
Kora Guitar Conversion Bridge
Sitar Bridge
Banjo Bridge
Single String Movable Bridge

3rd Bridge

The 3rd bridge is an extended playing technique used on the electric guitar and other string instruments that allows a musician to produce distinctive timbres and overtones that are unavailable on a conventional string instrument with two bridges (a nut and a bridge). The timbre created with this technique is close to that of gamelan instruments like the bonang and similar Indonesian types of pitched gongs. – WIKIPEDIA

EXPERIMENTS

  • Wedge a wooden spoon or any plank of wood less than 1/2″ under the 12th fret and experiment plucking on both sides of the new bridge.
  • Try placing magnets or closepins along the lengths of the strings in the same fasion
  • Twisty ties woven between strings work as well

Soundboards, Bodies, and Resonance

Body Types
Hollow Body Acoustic and/or Electric
Semi-Hollow Body
Solid Body
Skin

Resonator:
Resonator Guitar

Resonator Guitar Patent
Resonator Guitar Patent

 

Stroh Viola
Op Amp

Empty Body/Frame: This type of body accommodates the swapping of various resonance chambers IE: Baschete Balloon Guitar
Op Amp

Double resonators

Materials

Woods
Metal
Plastic
Styrofoam

 

Electronics

Amplification

Op Amp

Op Amp

Pickups

Piezo: Contacts sound transmitted through solid objects.

Volume Control Pot

Magnetic: Receives magnetic fluctuations transmitted through vibrating ferrous metal such as steel strings

Volume Control

Volume Control Wiring

 

Tone Control (Passive Low-pass Filter)

Tone Control Wiring

Pickup Box

Separating outputs or multiple pickups to multiple amps

Tearing or modify speaker

Standard Guitar Setup Diagrams

luthier-diag

Further Reading and References

Books

Nice Noise: Preparations and Modifications for Guitar by Bart Hopkin and Yuri Landman

The Luthier’s Handbook: A Guide to Building Great Tone in Acoustic Stringed Instruments by Roger H. Siminoff

Websites

Bart Hopkin’s Windworld – Bart Hopkin’s has been publishing extremely useful resources for experimental-musical-instrument-makers for over twenty years. For such a modest personality, he is a well of knowledge

Stewart Macdonald – Should be Stewart McDonalds because they are the biggest supplier of reasonably priced Luthier parts. They have great How To videos as well.

Sound Artists/Musicians who Make Instruments

Glen Branca
Pierre Bastien
Baschet Brothers
Luigi Russolo
Bradford Reed
Yuri Landman
Trimpin
Nic Collins
Godfried-Willem Raes
Shawn Decker
Nick Baginski
Harry Partch
Paolo Angeli
Eric Leonardson