Instructional Unit                                                                      Grades 9-12
This is a unique, standards-based unit of instruction on Waves created by a high school teacher to be used with PhET interactive simulations on wave motion.  It includes comprehensive lesson plans and lecture presentations.  Be sure not to miss the Clicker Questions.  (Open Website)

Concept Questions                                                              Grades 9-12
This PhET Gold Star-winning resource is a set of 60+ Power Point concept questions on the topic of waves, available for free download.  They were created by a high school physics teacher to be used with three PhET simulations: Wave on a String, Fourier Analysis, and Sound.  Concept questions are designed to introduce a topic and probe student understanding BEFORE formal instruction.  This method has been correlated with improved learner outcomes in studies conducted by physics education researchers.  (Open Website)

Cooperative Learning Activities                                                  Grades 11-12
From research in physics education, there is increasing awareness that students come into a physics class with firmly held beliefs which cannot be ignored.  These tutorials on Waves and Oscillations use hands-on activities and probing questions to draw out misconceptions and facilitate learning.  They are designed for cooperative learning groups, with complete sets of student activities and problems.  Accompanying solutions are to be distributed to groups before they leave class, thus giving immediate feedback.  (Open Website)

Problem-Based Learning                                                         Calculus-Based Physics
A collection of problems developed to engage students in metacognition, or "thinking about how they think".  These are context-rich problems that attempt to link a student's qualitative understanding of concepts with real-life scenarios.  Topics include masses on springs, pendulums, sound, and waves on a string.  **Appropriate for students in AP or Section B calculus-based high school physics.  (Open Website)

Software for Video Analysis/Modeling
If you have not yet used video analysis software with your students, be prepared for a paradigm shift in your teaching!  This resource provides free software called "Tracker", developed to help students closely analyze the motion of objects in a short video clip.  It also allows them to create dynamical models that overlay the video to see how well the model matches the real world.  Detailed instructions are provided.  And it's free.  (Open Website)

Collection of Tutorials
This award-winning collection offers text explanations combined with animations to explore wave phenomena, sound, acoustics, and vibration.  It was created by Dan Russell, Kettering University.  (Open Website)

Web-based Textbook                                                          Grades 9-12
This collection is a cost-free online textbook integrating the topics of waves, sound, music, and musical instruments.  Designed for use in the high school classroom, it also provides content support for teachers 6-12.  (Open Website)

Textbook: Content Support for Teachers
This free online textbook would be a great choice for new and crossover physics teachers who want a refresher in the physics of waves and oscillations.  The combination of real-life examples and down-to-earth text set this resource apart.  Topics include vibrations, properties and behavior of waves, and simple harmonic motion.  Novice learners may skip the proofs and still understand the concepts.  (Open Website)

Pedagogy: Scholarly magazine article
A must-read article from Science magazine, this item summarizes the research efforts of the PhET project on the use of interactive simulations in the physics classroom.  Results indicate that concept mastery is measurably improved when students explore simulated physical processes in addition to traditional labs.  Use of simulations was also correlated to higher student motivation and active involvement in the learning process.  (Open Website)

Physics Education Research
This Power Point presentation condenses the results of a study on student misconceptions about wave mechanics and motion.  The results indicate that many students have incorrect mental models of waves and use these erroneous models to interpret/solve problems.  The researchers also tested teaching methods to see what may help students overcome these difficulties.  A must-read for the teacher of advanced students who will study calculus-based physics in college.  (Open Website)

Multimedia Instructional Unit
This is a unit of instruction on Waves created by a team of high school physics teachers.  It was developed to give busy teachers free access to high-quality online resources, including simulations, video clips, lecture notes, chapter tests, and content support.  (Open Website)

Introductory Tutorial
A straightforward interactive tutorial suitable for crossover teachers or K-8 physical science teachers who would like a refresher on the topic of waves.  This is part of the respected Physics Classroom tutorial collection, and covers wave categories, properties and behavior of waves, and how waves transport energy.  (Open Website)

Reference Material                                                                Grades 6-12
Don't be scared off by the title of this item.  It is a fascinating resource that features a "thematic search engine" for locating information and examples of sound, sound waves, acoustics, hearing, and other related topics.  Each topic is accompanied by audio clips from the library of the World Soundscape Project.  For example, the topic "Hearing Loss" contains an audio simulation of normal and impaired hearing as a result of noise exposure.  Students will enjoy playing around with this one.  (Open Website)

Tutorials for Students                                                            Grades 9-12
Many students benefit from a simulation-based exploration of physics phenomena that allows them to self-pace.  This is a set of 20 sequenced tutorials on the topic of Waves, developed to promote understanding of processes that can't be visualized in a textbook illustration.  Each tutorial has a discussion section, a Java simulation the students can manipulate, and self-guided questions at the end.  (Open Website)

Tutorials for Students                                                            Grades 6-9                        
A visually appealing tutorial on the fundamentals of traveling waves.  It contains video clips, short animations, and interactive Q&A sets.  Each slide is voice narrated, which could be ideal for students with disabilities.  (Part of a full module on Waves.)  (Open Website)

Formative Assessment: Warm-Up Questions
Peer Instruction, a well-researched teaching method developed by Harvard professor Eric Mazur, is intended to actively engage students while also allowing the teacher to gauge understanding of a single concept.  Students individually "vote" on a correct response to a carefully-constructed problem, then discuss their reasoning with peers.  This is a set of annotated Peer Instruction problems on the topic of waves.  (Open Website)

Hands-On Experiments                                                            Grades 8-12
Full guidelines for set-up of eight classroom activities designed to introduce students to various types of waves and the language used to describe them.  Students learn about transverse, longitudinal, electromagnetic, and water waves through simple and practical experiments.  This resource is appropriate for grades 8-12, and could also serve well as a refresher for AP physics classes.  (Open Website)

Lesson/Student Lab Guide                                                            Grades 9-12
Coiled springs are excellent materials for analyzing a variety of wave behaviors.  This is a free student activity guide for conducting a "Slinky" spring lab.  The four-page question set encourages deductive reasoning about the variables that affect wave speed, reflection and interference of waves, and how waves behave with different media boundaries.  (Open Website)

Lab/Instructor's Guide                                                                     Grades 6-12
A great way to spark student interest in wave motion is through the study of tsunamis.  This magazine article, which appeared in The Physics Teacher in 2006, provides a step-by-step blueprint for constructing your own low-cost tsunami tank for experimenting in the classroom.  Related classroom activities capture the essential physics of tsunamis.  Try teaming these activities with the interactive computer simulation below, "Michigan State Tsunami Simulator".   (Open Website)

Hands-On Activity: 30 minutes                                                            Grades 9-12
This simple, yet highly visual experiment uses dynamics trolleys, springs, and spring holders to model a transverse and a longitudinal wave.  The models are easy enough for students to set up, but allow exploration of complex concepts, such as how this dispersive system differs from a continuous wave medium like a rope or slinky (see experiment below for a companion activity).  (Open Website)

Hands-On Activity: 30 minutes                                                            Grades 6-12
A Slinky spring is one of the best ways to model both transverse and longitudinal waves.  Teaching tips in this web site explain how to get the best results. Try teaming this experiment with the one above that uses dynamics trolleys connected by springs.  Students can compare/contrast the wave motion in a continuous versus a dispersive system (trolleys).  (Open Website)

Video Clips
A set of 3 high-quality video clips that show wave pulses on a Slinky spring.  One depicts a transverse wave pulse and its reflection off an fixed end.  A second shows a longitudinal pulse, and the third shows two wave pulses passing over each other. For free software tools to do computer analysis of these videos frame-by-frame, see the "Tracker Video Analysis" item below.  (Open Website)

Cost-free Software:  Video Analysis
This resource provides free software called "Tracker", developed to help students closely analyze the motion of objects in a short video clip.  It also allows them to create dynamical models that overlay the video to see how well the model matches the real world.  Detailed instructions are provided.  And it's free.  (Open Website)

Interactive Simulation                                                                 Grades 6-12
Mechanical waves can be modeled well through computer simulations that depict the motion of particles as the wave disturbance travels through a material.  This web-based tutorial for grades 6-12, developed by the University of Utah's ASPIRE Lab, is an excellent visualization tool for students.  Don't miss the water wave simulation.  It clearly shows the repeating pattern of a periodic wave, helping students understand that the particles oscillate but are not propelled forward by the wave.  (Open Website)

Interactive Simulation                                                            Grades 6-12
This simple simulation is the best we have found to model the destructive energy of a tsunami for beginning students.  It shows very clearly how a tsunami (which may appear insignificant at the point of origination) gains amplitude as it approaches shore, thus becoming one of nature's most destructive forces.  Change the shape of the sea bottom near the coast and watch the effect on the approaching tsunami.  See the instructor's guide above under Lesson Plans for directions on building a low-cost tsunami tank for classroom experiments.  (Open Website)

Reference Articles                                                                           Grades 7-12
A great resource to augment a module on tsunamis.  These are interactive "magazine-style" articles designed to help students understand how tsunamis are generated and why they become so destructive upon reaching shore.  Don't miss the excellent animated view of a tsunami caused by subduction zone earthquake.  (Open Website)

Interactive Tutorials                                                                       Grades 9-12
One way to get students excited about wave energy is to study tsunamis.  How can a wave that is barely visible to a ship at sea become so destructive upon reaching a shoreline?  This set of tutorials, simple enough for students to understand, explains how these catastrophic wave trains originate and propagate through vast oceanic distances.  Each tutorial is accompanied by simulations that model the fundamentals of this phenomenon.  (Open Website)

Introductory Tutorial
This page, part of an award-winning web site on wave animations, depicts how particles move in four types of waves:  longitudinal, transverse, water, and Rayleigh surface waves.  Students can clearly see that the particles do not move along with the waves, they simply oscillate back and forth as the wave passes by.  (Open Website)

Tutorial for Students                                                              Grades 9-12
An interactive student tutorial that introduces students to three major types of mechanical waves:  transverse, longitudinal, and surface.  The text is easy for beginners to understand and is accompanied by animations of wave motion and a self-guided set of questions to assess understanding.  (Open Website)

Tutorial for Students                                                              Grades 9-12
This is a 15-minute interactive tutorial for introductory high school physics on the fundamentals of mechanical waves.  It is formatted in Adobe Flash, with multiple short video clips, animations, and interactive question-and-answer sets.  Narration accompanying each slide makes this resource useful for students with disabilities.  Topics covered include wave categories, amplitude, frequency, energy transport in waves, and an introduction to interference.  (Open Website)

Instructional Unit                                                                      Grades 11-12
This exemplary unit of instruction was developed by a high school physics teacher to be used with PhET simulations.  It includes six complete lesson plans that explore wave properties, the physics of sound, Fourier analysis, and wave phenomena such as reflection and superposition.  Most of the lessons require that the simulation be open on a browser while students work.  Especially helpful are the Clicker Questions, which can be readily downloaded for classroom use.  Entire unit will take 2-3 weeks, but components may be pulled out separately.  (Open Website)

Lesson Plan: Computer Lab                                                      Grades 11-12
This is a computer lab created specifically for use with the PhET simulation "Wave on a String" (see Activities below).  Students apply trigonometry and analyze how frequency, amplitude, and tension influence the motion of the wave.  It  may be downloaded as a Word file.  (Open Website)

Lab Procedural/Lesson Plan                                                            Grades 9-12
Here are two experiments on wave measurement in a ripple tank, appropriate for use in high school physical science or physics classrooms.  Students are introduced to using the stroboscope to 'freeze' waves in a ripple tank, and to confirm the relationship between wave speed, frequency and wavelength.  (Open Website)

Interactive Simulation                                                                      Grades 6-12
A wonderful way to introduce students to properties of waves.  As the students open the applet, they are invited to "wiggle" a string to create a wave.  They can set amplitude, frequency, damping, and string tension and watch the variable results.  Waves can be manually or automatically generated.  Finally, students can view the string's vibration with a fixed end, a loose end, or no end.  Part of the PhET resource collection. See related teacher-created activity (directly below), developed for use in middle school classrooms with "Wave On a String".  (Open Website)

Simulation-Based Activity                                                              Grades 9-12
Students explore relationships among frequency, amplitude, and wave speed in this inquiry-based activity developed to be used with the PhET simulation Wave on a String (see above).  It is appropriate for 9th grade physical science or algebra-based introductory physics.  (Open Website)

Cooperative Learning Exercise/Tutorial                                                   Grades 9-12    
Try using this tutorial as a cooperative learning activity.  Students explore the variables that affect wave speed by analyzing sample data and completing a question-and-answer set.  It helps build understanding that wave speed is dependent on properties of the medium in which it moves, a central idea to be applied in problems relating to wave energy.  **After students do this tutorial, we suggest the Illinois PER Interactive Homework Problem (directly below).  (Open Website)

Web-Based Interactive Problem                                                             Grades 11-12
Superb inquiry-based tutorial to help students understand how spring tension, spring constant, and wave speed are related.  The problem features a vibrating Slinky toy stretched to different lengths and given a "shake".  Students must figure out how long it takes the wave pulse to travel the full length in both cases.  They will discover for themselves that the time is the same.  **We suggest using this resource with the Physics Classroom tutorial above, "Speed of a Wave".  (Open Website)

Animation-Based Tutorial
This animated tutorial by Dan Russell illustrates the principle of wave superposition:  when two (or more) waves travel through the same medium at the same time, the waves pass through each other without being disturbed.  (Open Website)

Simulation-Based Online Tutorial                                                           Grades 9-12
This simulation-based set of homework problems lets students self-pace as they measure their own understanding of the fundamental math behind simple harmonic motion. Topics include frequency and amplitude, wave phase and period, and circular motion. Immediate feedback is provided. It was developed by the respected University of Ontario-Guelph.  **WORKS BEST IN THE INTERNET EXPLORER BROWSER.  Problems reported using this resource with Firefox.  (Open Website)

Web-Based Student Tutorial                                                          Grades 9-12
Students often confuse the frequency of a wave with its quantity period.  This short tutorial, part of the respected Physics Classroom, promotes understanding of both properties of waves.  A question-and-answer set is provided at the end.  Team it with the companion tutorial on wave amplitude and energy transport (directly below).  (Open Website)

Web-Based Student Tutorial                                                              Grades 9-12
The amount of energy carried by a wave is related to the amplitude of the wave.  This interactive tutorial, part of The Physics Classroom, explores the energy transport phenomenon of waves in a way that beginning students can understand.  Team it with the companion tutorial on frequency and wave period (directly above).  (Open Website)

Web-Based Unit Review                                                                Grades 11-12
This is an excellent unit assessment with solutions, developed by a high school teacher to be used with the PhET simulation Wave on a String (see link under "Activities" above.  It assesses understanding of fundamental wave properties, interference, standing waves, and beginning harmonics.  It is formatted so that students can make responses online at the same time they are interacting with the simulation.  **Allow two days if completed in computer lab.  (Open Website)

Lesson/Student Lab Guide                                                            Grades 9-12
Coiled springs are excellent materials for analyzing a variety of wave behaviors.  This is a free student activity guide for conducting a "Slinky" spring lab.  The four-page question set encourages deductive reasoning about the variables that affect wave speed, reflection and interference of waves, and how waves behave with different media boundaries.  (Open Website)

Educators' Guide                                                                       Grades 6-12
Students should whenever possible experiment for themselves using real equipment, rather than viewing only computer representations of ripple phenomena.  This educators' guide gives detailed information about how to acquire, set up, and implement ripple tank experiments in the physical science or physics classroom.  See related ripple tank activities developed by the same authors (below).  (Open Website)

Lab/Classroom Experiments                                                       Grades 6-12
Ripple tanks provide a powerful way to help students visualize wave behavior in general.  This set of 8 introductory labs allows students to become comfortable with ripple tanks by doing some simple experiments with pulses.  Appropriate for grades 6-12, with supervision.  (Open Website)

Lab/Classroom Experiments                                                       Grades 9-12
With the use of a ripple tank, students can observe the phenomenon of wave interference, which occurs when pulses and waves pass through each other.  Many students are amazed to discover that the two waves continue on their way as if there had been no encounter. This set of four lab experiments demonstrates interference with two sources, using fingers and vibrators to create the disturbance.  See Content Support below for links to background information on wave interference and superposition.  (Open Website)

Interactive Lecture/Concept Questions                                         Grades 11-12
For physics teachers who want give their students a thought-provoking introduction to the quantum nature of light, have a look at this PhET Gold Star winning Power Point presentation.  It was developed to supplement the PhET simulation Wave Interference (see link in Activities below).  In this simulation, students view a virtual photon aimed through two slits to mimic the double-slit experiment.  This supplementary resource helps students understand the concept of random behavior on the atomic scale.  There are no calculations.  (Open Website)

Interactive Simulation                                                            Grades 6-12
This Java applet simulates wave oscillation by using the mouse to drive the motion of a vibrating string.  Students can set amplitude, frequency, damping, and string tension and watch the results.  Waves can be manually or automatically generated.  Finally, students can view the string's vibration with a fixed end, a loose end, or no end.  (Open Website)

Interactive Simulation                                                            Grades 9-12
Students interactively explore properties of waves as they view simulations of a dripping faucet, an audio speaker, and a laser.  By observing wave sources and mediums for water, sound, and light, students can compare the behavior of different types of waves.  Choose Light as a medium and add a second source or a pair of slits to create an interference pattern.  (Open Website)

Demonstrations/Concept Questions                                               Grades 9-12
A set of three classroom demonstrations to be used with PhET simulations Wave on a String, Sound, and Wave Interference.  Students explore wave reflection, patterns from interfering waves, and the Doppler Effect.  The accompanying concept (clicker) questions may be downloaded in Power Point format and adapted for individual teacher use.  (Open Website)

Interactive Simulation                                                            Grades 9-12
When two waves interfere, their amplitudes add.  This interactive Java applet was developed by a high school teacher to help students visualize exactly what is happening to the amplitude of two waves as they pass through each other.  Students set the frequency, amplitude, and phase shift of two waves, then click "Add" to see a graph of the sum.  Students may choose either addition or subtraction, sine or cosine.  (Open Website)

Interactive Simulation                                                            Grades 7-12
This simple applet illustrates the superposition principle as it applies to two waves interacting on a string. It would be a good choice for beginning physics students, as it contains no graphs and focuses only on pairs of waves interacting in one dimension. The applet automates the addition of the waves so that students can see why the Superposition Principle works.  (Open Website)

Video Clips
Two high-quality video clips of wave motion in a ripple tank.  One shows ripples from a stationary source, which can be analyzed to find frequency and wavelength.  The second shows the source moving at constant velocity.  May be viewed in step motion to allow for video analysis/measurement.  For free software tools to do computer analysis of these videos frame-by-frame, see the "Tracker Video Analysis" item below.  (Open Website)

Cost-free Software:  Video Analysis
This resource provides free software called "Tracker", developed to help students closely analyze the motion of objects in a short video clip.  It also allows them to create dynamical models that overlay the video to see how well the model matches the real world.  Detailed instructions are provided.  And it's free.  (Open Website)

Interactive Simulation                                                              Grades 9-12
An excellent Java applet for exploring the basics of wave reflection and refraction.  It shows a single wavefront in slow motion as it reaches a medium with a different refractive index.  Students can see how each point of the advancing wavefront is the center of a fresh disturbance and source of a new train of waves.  They can adjust the refractive index and angle of incidence of either medium.  (Open Website)

Tutorial/Content Support for Teachers
A characteristic shared by all waves is that two or more of them moving simultaneously through the same space will superimpose and produce a combined effect.  This tutorial, integrated with multiple interactive simulations, promotes understanding of wave superposition in a highly engaging format.  Self-test is included.  (Open Website)

Tutorial/Content Support for Teachers
When waves meet an obstacle or pass through small openings, they may appear to bend or spread out.  This phenomena is called diffraction.  We see examples of wave diffraction every day, but what is the physics behind it?  This exemplary tutorial offers a multimedia tour of diffraction around objects, diffraction through slits, and various effects of diffraction.  (Open Website)

Web-Based Tutorial                                                                    Grades 9-12
Quite simply, one of the best student tutorials we have found on wave phenomena.  We suggest having students start with the section "Parts of a Wave", then proceed to the "Interference" section and watch the animations on constructive and destructive interference.  These sections could be viewed using a classroom projector and one internet connection.  For a related computer lab activity, see the "Wave Adder" in Activities above.  (Open Website)

Web-Based Unit Review                                                                Grades 11-12
This is an excellent unit assessment with solutions, developed by a high school teacher to be used with the PhET simulation Wave on a String (see link under "Activities" above.  It assesses understanding of fundamental wave properties, interference, standing waves, and beginning harmonics.  It is formatted so that students can make responses online at the same time they are interacting with the simulation.  **Allow two days if completed in computer lab.  (Open Website)

Interactive Simulation                                                                Grades 11-12
This applet simulates a harmonic coupled line of masses moving in one dimension. The load, damping, and stiffness of the springs are adjustable.  It includes more complex concepts, such as phases and magnitudes of normal modes.  (Open Website)

Interactive Simulation                                                              Grades 9-12
This simulation shows the standing wave patterns that are produced on a violin, a string medium that is fixed on both ends.  Students can toggle from 1st-5th harmonics to see the standing wave pattern of each. The sum of all the harmonics can also be displayed.  (Open Website)

Historic Film Clip
The phenomenon of resonance becomes very important in structural engineering, as can be observed in this historic video of the 1940 collapse of the Tacoma Narrows Bridge.  The famous suspension bridge disaster occurred when high wind gusts set up a resonant vibration in the bridge, causing large-amplitude oscillatory motion.  This video was digitally reformatted from the original film footage shot on the scene.  (Open Website)

Digital Collection                                                                   Grades 9-12
The science of music offers a great springboard to spark student interest in wave interference, standing wave patterns, and harmonics.  This unique collection takes students on an exploration of the physics behind woodwinds, brass instruments, string, and more.  Don't miss the "Sounds of World English" section: students can map their own speaking accents.  (Open Website)

Student Tutorial                                                                Grades 11-12
This tutorial is presented as a conversation between a student and a teacher about wave resonance.  It uses the context of waves bouncing around in a microwave and includes an interactive simulation.  It also features an interesting analogy of laying bathroom tile to help students understand phase phenomena in wave resonance.  (Open Website)

Student Tutorial                                                                 Grades 9-12
Standing waves are non-traveling vibrations.  They are produced when an incident wave and the reflected wave interfere in a way that they appear to be standing still.  Standing wave patterns are readily observable, notably in musical instruments.  This exemplary interactive tutorial gives students a good foundation for understanding why and when this complex phenomenon occurs.  (Open Website)

Instructional Unit                                                                Grades 6-12
A set of exemplary modules related to sound and music, developed specifically for use in middle school and high school.  It is broken into well-organized short components for teachers who may wish to teach only one element of this subject matter.  Included are lessons and activities on frequency, wavelength, amplitude, pitch, the physics of sound, rhythms and beats, standing waves, harmonic series, and tuning systems. Worksheets include answer keys.  (Open Website)

This Java applet demonstrates waves on a vibrating string which is 'plucked' with the mouse.  Options include adjusting the damping, force frequency (which can be set to resonance frequency), number of loads, simulation speed and tension.  It is appropriate for use in AP physics or with students in a Part "B" high school course.  (Open Website)

Video Collection                                                                Grades 6-12
Don't miss this collection of more than a dozen videos compiled by a physicist to help high school students understand the physics of sound.  Observe a resonating glass break, view and observe jets breaking making a sonic boom, and more.  (Open Website)

Reference Material                                                                Grades 6-12
Don't be scared off by the title of this item.  It is a fascinating resource that features a "thematic search engine" for locating information and examples of sound, sound waves, acoustics, hearing, and other related topics.  Each topic is accompanied by audio clips from the library of the World Soundscape Project.  For example, the topic "Hearing Loss" contains an audio simulation of normal and impaired hearing as a result of noise exposure.  Students will enjoy playing around with this one.  (Open Website)

Digital Collection                                                                 Grades 9-12
The science of music offers a great springboard to spark student interest in wave interference, standing wave patterns, and harmonics.  This unique collection takes students on an exploration of the physics behind woodwinds, brass instruments, string, and more.  Don't miss the "Sounds of World English" section, which allows users to map their own speaking accents.  (Open Website)

Web-based Textbook                                                          Grades 9-12
This collection is a cost-free online textbook integrating the topics of waves, sound, music, and musical instruments.  Designed for use in the high school classroom, it is quite comprehensive in scope.  Teaching suggestions and tips are included.  (Open Website)

This item, developed for middle and high school students, explores the structure of the ear and the way sound is received and understood by the brain.  It explains the physical processes by which the outer, middle, and inner ears collect sound and relay it to nerve cells.  Java simulations take the user on an interactive journey through the human ear  (Open Website)

This page ventures into the real-world applications of wave properties associated with the physics of sound, including ultrasound, diffraction horns,  noise cancellation, and harmonic synthesis.  Especially engaging is the interactive wave applet that allows students to create their own sound waves, listen to predefined waveforms, or combine both.  (Open Website)