Sound waves are vibrations. Vibrations have to start somewhere.  Vibrations may start from a shaking string, or from something being hit, or from moving air passing through something specifically shaped or flexible, such as air escaping from a balloon.  An artificial sound may start in a computer but will need a vibrating speaker to be heard.

A sound wave is similar to a water wave but it travels in air as well as other mediums.  Like water waves, sound waves do not physically travel but rather transfer energy.  Think of a room filled with ping pong balls.  You push one and it pushes the next, which pushes the next, etc.  By the way, thanks to Steve-O for that analogy.

Steve-o "Pops" Kureczko described it in the following way:
Imagine a room filled with ping-pong balls from wall to wall and floor to ceiling. If you touch one of the ping pong balls, it will move the next one a little bit...which will move the next one a little bit...so that the ping pong ball all the way at the other end of the room will be moved without the first ping pong ball moving away from it's location. (Thanks, Steve-o!)

Sound travels in waves.  The alternating wave movement creates air pressure.

As sound waves move (or more accurately, when they travel by transferring their energy) they interact with physical objects. Soft surfaces will absorb sound while hard surfaces will reflect it. DIFFERENT types of hard surfaces will reflect different aspect of sound more strongly than others. That is why a large wood room does not sound like a large tile room, and why closets are so quiet.

Sound waves love to bounce.

Hard surfaces reflect sound and soft surfaces absorb sound.  Parallel surfaces create waves that bounce back and forth (like looking into mirrors that are facing each other).  Non-parallel surfaces also create reflections, but they will be scattered rather than bouncing back as a discrete echo. Hard surfaces that are NOT parallel allow sound waves to bounce around in ways that break them up into smaller and softer diffuse sounds. The distinct echoes you hear from parallel surfaces can become a smooth long sound if the sound waves are allowed to spread around while bouncing.

When someone is speaking to you the sounds from their throat and mouth are going out into the room.  In the course of their travels and bouncing around the room, some of the waves are going directly to your ears and some are getting there after bouncing off of a hard wall or table.  Some of the sound waves are being absorbed into the soft surfaces within the room, such as the carpet and your clothing.

The sound waves do not reach both of your ears at the same time, and also do not sound the same when they reach each ear.  This is an important part of being able to tell the direction a sound is coming from that we learned as babies.

If you pay attention to the shape, dimension, surface materials, and contents of any room while clapping, you will be able to better understand how room differences affect sound.

Since sound is based on waves, and all waves have a positive and a negative, your stereo speakers do not simply PUSH sound out to you, but rather PUSH and PULL BACK at the air to create the sound waves.  Sound pitch (musical notes) is based on vibrations.  Slow vibrations make low sounds and fast vibrations make high sounds. The faster sound wave vibrations produce high musical pitches, and slow sound wave vibrations produce low musical pitches.

When a sound wave is seen visually, it is drawn as a line that curves up to show the wave pushing and down to show the wave pulling back, creating repeated peaks and valleys.


Here is the same wave, with clearer indications of when it is pushing (positive) and when it is pulling (negative) out from the center zero-line.


There are many different KINDS of sound waves, depending on the wave shape. When multiple waves are combined they will (depending on their frequency, phase, volume, etc) create a composite sound wave with a varied shape.  Each type of wave has different tonal characteristics.

Simple pure tones will make a Sine Wave (a complete curve).  A Square Wave is simple a square, a Triangle Wave is a triangle, and a Sawtooth Wave alternates ramps with downwards lines, like the edge of a saw blade.

Pure Sine waves have only one tone, called the FUNDAMENTAL.  Other waves contain additional tones above the Fundamental, called OVERTONES.   The Fundamental and Overtones heard together are called PARTIALS.  The strength and relative tone of Overtones will change the both a sound and its waveform.  A Sine wave is just a Foundation, but if you add Overtones you can easily create Square and Sawtooth waves.

There are different measurement devices to use with sound.  An OSCILLISCOPE will show a waveform shape (such as Sine, Square, or even complex soundwaves such as human speech).  A SPECTRUM ANALYZER will analyze the amounts of sound at different frequencies and chart them in a FREQUENCY RESPONSE CURVE.