Workshop Two:
Modes of Vibration
Compliments Key Stage 3 and 4 curriculum in Science. This
workshop investigates modes of vibration and resonance
through hands on activities and experiments with aeolian
harps and Chaldni plates.
Experiment with Aeolian
Devices
Explore Resonance and
Frequency
Build an Acoustic Tonoscope
aeolus-outreach.com
What is Acoustics?
Acoustics is the study of sound and vibration and our relationships
with them. Acoustics research has many applications and makes a
major contribution to our overall quality of life. Acoustics research
informs the development of the products we buy, the environments
we build, and the way we express and entertain ourselves through
art, film and music.
Careers in Acoustics
Acousticians come from a wide range of academic backgrounds
including physics, engineering, computing, medicine, psychology,
anthropology and the arts. Professionally, Acousticians often work
as acoustic consultants, broadcast engineers, acoustic designers,
software programmers, academic researchers, product noise
control/sound designers, and sound system engineers.
To find out more about a career in acoustics visit:
The University of Salford’s Acoustics Research Centre homepage
www.acoustics.salford.ac.uk
The University of Southampton’s Institute of Sound and Vibration
Research homepage
www.isvr.soton.ac.uk
Workshop Aims and Objectives
• To enthuse students about the science of sound and vibration
• To illustrate how science is creative and artistic
• To explore resonance and frequency
• To demonstrate how sound travels through different media
• To create acoustic tonoscopes
• To conduct experiments
• To have fun
Compliments:
Science Key Stage 3 & 4 curriculum
Workshop Length:
approximately 2 hours including a break.
Materials & Equipment:
PC, speakers and projector
pens and pencils
various types of string (fibrous and nylon such as fishing line)
plastic containers ( old ice cream or biscuit containers)
scissors
latex sheeting
thick card tubing (old kitchen rolls or pipes)
Workshop Outline:
Activity
Objective
KS Reference
Aeolian Harp Experiments
Introduction to resonance and
frequency.
KS4, 1B, 1C, 4A
Chladni plate activity and
demonstration
Exploring and experimenting with
resonance & frequency.
KS2, 4E, 4G, KS3, 4J, 4K, KS4,
1B, 1C, 4A
Building and testing
tonoscopes
Exploring resonance & frequency,
experimentation with design
KS4, 2a, 2b, 2cKS3, 4J, 4K,
KS3, Science 8L
Presentation of devices
Sharing and discussing research
findings, explaining results.
KS3, Science 8L
Background on Aeolian Harps
The first known description of the Aeolian Harp is found inside the book Phonurgia Nova by
Athanasius Kircher. The instrument takes its name from the Greek god of the wind, Aeolus.
Aeolian harps automatically create compositions in the changing wind, creating nature’s
music. Aeolian harps have intrigued and inspired people from around the world for generations
including famous romantic poets, painters and composers including Coleridge, Turner and
Chopin. Aeolian harps can create melodious music because of the way their strings resonate.
The different resonances of a string form a musical scale called a ‘harmonic series’. As a
changing wind blows across a string it will cause the string to play notes up and down this
musical scale.
Acoustics and Resonance
Sound is a vibration you can hear. Usually the sounds we hear come from the vibration of air that has
been caused by the vibration of other objects such as musical instruments, loudspeakers, the larynx,
etc. Objects vibrate the most when they resonate with whatever is causing them to vibrate. If an
object is forced into motion at a particular frequency (for example, when a swing is pushed a specific
time) it will resonate. These frequencies are known as resonant frequencies. Objects can have multiple resonances (or modes of vibrations) and corresponding resonant frequencies. This workshop
will show how these resonances can be heard as the strange musical notes of Aeolian harp strings
or seen with simple devices like the tonoscope.
Aeolian Harp Physics
When a string is plucked it vibrates with a range of frequencies simultaneously. We tend to
associate the pitch of the string with the lowest frequency and its corresponding first mode
of vibration. The higher frequencies contribute to the brightness and quality of its timbre.
However, you can hear each of a string’s higher modes individually, by impeding the string’s
movement at key points along it with your finger. This technique is similar to when guitarists
‘play harmonics’.
Another way to hear each higher mode individually is to gently ‘excite’ the string with
moving air. As air moves over the surface of the string, dips in pressure above and below it
push and pull the string into motion. If the frequency of motion is near the frequency of a
string’s mode of vibration it will begin to resonate. As the speed of the wind increases or
decreases it will tune into higher or lower frequency resonances and create musical sounds.
An excerpt from The Eolian Harp
by Samuel Taylor Coleridge:
And now, its strings
Boldlier swept, the long sequacious notes
Over delicious surges sink and rise,
Such a soft floating witchery of sound
As twilight Elfins make, when they at eve
Voyage on gentle gales from Faery-Land,
Where Melodies round honey-dropping flowers,
Footless and wild, like birds of Paradise,
Nor pause, nor perch, hovering on untam’d wing!
Aeolian Activities
1. Tie one end of the fishing line to a fixed
object such as a tree, a fence, or a goal post.
The line must be exposed to the wind on all
sides.
2. Feed the other end of the fishing line through
a hole in the base of a bucket or bin and tie it to
a peg inside the bucket to hold the line in place.
3. Stand so the line is perpendicular to the
wind. Pull the line taught, but be careful not to
break it.
4. Wait a few seconds for the wind to excite
the fishing line. Eventually you should hear
strange and haunting sounds emanating from
the bucket.
Luke Jerram’s instructions for making a fun aeolian device.
Make an aeolian harp with a bucket, some strong fishing
line and a peg. Use on a very windy day.
Interested in testing your aeolian devices on a day that isn’t
quite windy enough? Try using a household fan and home
made wind tunnel. With some basic tools and a cardboard
box, you’ll be testing in no time.
Needed Equipment :
Directions:
• Adjustable Electric fan
• Large cardboard box
• Smaller cardboard boxes
• Sturdy scissors
• Stanley Knife
• Gaffer tape
Cut and shape the cardboard so that it resembles a hairdryer
attachment, with a wide narrow opening (see above image).
Seal any gaps with gaffer tape. Place the wind tunnel on the
front of the fan, modifying the shape and adding extra tape if
necessary Leave the back of the fan and fan’s controls exposed.
Begin testing your aeolian devices by placing the strings just
below the airflow, waiting a few seconds for the resonances to
build up. What happens when you change the speed of the fan?
Chladni Patterns
When you strike a plate it vibrates in multiple directions and at multiple discrete frequencies.
These frequencies correspond to the plate’s modes of vibration. If you send a frequency through
the plate then it may excite one of these the modes. When a plate vibrates at a given frequency
some parts of the plate move and others don’t. The parts that stay still are called nodal points.
You can see these nodal points if you cover the plate with granular sugar or salt. The beautiful
patterns made visible are known as Chladni patterns. Higher frequencies of vibration have
higher numbers of nodal points and hence form more complex patterns. Why are we looking at
Chladni Patterns during this workshop?
Chladni patterns are created by the same phenomenon that enables the aeolian harp to
function, that is resonant frequencies. Just like locking into a natural frequency on the
plate makes beautiful patterns, locking into the natural frequency of the string creates the
mesmerising aeolian sound.
Tonoscopes
What is a tonoscope? A tonoscope is a fun acoustic device that enables you to see beautiful
patterns created by the sound of your voice. Understanding such patterns informs the use and
design of many everyday things from musical instruments to household products, cars and
buildings. How does it work? As you sing into the tonoscope, your voice creates vibrations.
As you experiment with different tones and sounds you should be able to tune into one of the
membrane’s natural frequencies. An object’s natural frequencies are the frequencies at which it is
naturally inclined to vibrate once set into motion. When using the tonoscope, you’ll know if you’ve
found one of these natural frequencies, because you will begin to see a clear, symmetrical pattern.
Some parts of the membrane begin to move and others don’t. The parts that remain still are called
nodal points. When the sand or salt moves into a nodal point, it stays there. The beautiful patterns
you see are known as Chladni patterns. You can experiment making these patterns with your own
tonoscope. For DIY instructions, please see our website’s resources for learning page
www.aeolus-outreach.com
Useful Links
To learn more about Aeolian harps
and Chladni patterns, search some
of these websites:
On Aeolian Harps
www.usca.edu
www.windmusik.com
On Athanasius Kircher
www.strangescience.net
DIY Chladni Plates
A great activity by Dangerous Decibels
www.dangerousdecibels.org
DIY electric Chladni plate
www.instructables.com
You can also find other fun activities on our website:
www.aeolus-outreach.com
Aeolus Outreach
These activities were developed as part of the Aeolus
project, a large scale public engagement programme that
was centred around a beautiful singing sculpture, Aeolus.
Aeolus was designed Luke Jerram in collaboration with
acoustics scientists from the University of Salford and
the University of Southampton. Aeolus and its associated
programme of outreach activities toured the UK in 2011,
visiting Lyme Park, the Eden Project and MediaCityUK.
The Aeolus Project sought to inspire curiosity and
wonder about sound, inspiring further interest in the
diverse discipline of acoustics through the exploration an
otherworldly work of art. To find out more about the project
and to download fun acoustics related activities, please
visit our project website, www.aeolus-outreach.com
www.aeolus-outreach.com