For a visual picture of waves, you may want to browse through some of these simulations: they show animation of various concepts from waves and sound.

https://www.acs.psu.edu/drussell/demos.html 

What is a wave?

https://www.acs.psu.edu/drussell/Demos/waves-intro/waves-intro.html 

https://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html 


Wave motion in space and time

https://www.acs.psu.edu/drussell/Demos/wave-x-t/wave-x-t.html 


Reflection of waves on a string, with fixed or free boundaries.
Also includes transmission through an interface.

https://www.acs.psu.edu/drussell/Demos/reflect/reflect.html


Reflection from an Impedance Discontinuity
to form standing waves

https://www.acs.psu.edu/drussell/Demos/SWR/SWR.html 



Superposition

https://www.acs.psu.edu/drussell/Demos/superposition/superposition.html 


Superposition of waves for several cases.

https://www.acs.psu.edu/drussell/Demos/superposition/superposition.html 


Beats (show this with the two vibe tubes)

http://www.walter-fendt.de/html5/phen/beats_en.htm 


Demos from Walter Fendt:

http://www.walter-fendt.de/html5/phen/ 


Fourier synthesizer with sound.


http://www.walter-fendt.de/html5/phen/ 


Simple Pendulum

http://www.walter-fendt.de/html5/phen/pendulum_en.htm 


Coupled Pendula

http://www.walter-fendt.de/html5/phen/coupledpendula_en.htm 


Spring Pendulum

http://www.walter-fendt.de/html5/phen/springpendulum_en.htm
 


Forced oscillations (resonance)

http://www.walter-fendt.de/html5/phen/resonance_en.htm 


Coupled Pendula

http://www.walter-fendt.de/html5/phen/coupledpendula_en.htm
 

If more and more of these are coupled together, we can get waves:


Waves

Standing waves on string

http://www.walter-fendt.de/html5/phen/standingwavereflection_en.htm
 
https://www.acs.psu.edu/drussell/Demos/doppler/doppler.html 


Standing Longitudinal Waves

http://www.walter-fendt.de/html5/phen/standinglongitudinalwaves_en.htm 


Doppler Effect

http://www.walter-fendt.de/html5/phen/dopplereffect_en.htm
 
https://www.acs.psu.edu/drussell/Demos/doppler/doppler.html
 

Ripple Tank Simulation

http://www.falstad.com/ripple/
 
Fourier simulation (may need IE)

http://www.falstad.com/fourier/