Sound waves are compression waves in the air.

The diagram shows compressed areas and sparse areas. The compressed parts travel from the speaker to the ear as sound waves.

The particles oscillate (move back and forth) from left to right in the diagram. Since they oscillate along the same axis as the direction of the waves’ motion, they are longitudinal waves.

Speed of Sound

Speed of sound at indoor temperatures is approximately 344 m/s.

The speed of sound depends on the air, and the average amount of time it takes for one air particle to bump into a neighboring particle. This changes especially depending on the air temperature, which can change the value by a few percent or more.

Pitch, Frequency, and Hearing

We experience higher frequency sound waves as higher pitched sounds.

Humans can hear frequencies in the range of about 20 to 20,000 Hz.

That is, air pressure pulses arrive at our ear drums at least 20 times per second and up to 20,000 times per second. Depending on how often those pulses are arriving, we experience different sound pitches.

Frequency and Wavelength

Since sound waves all have (approximately) the same speed of about 344 m/s, we can say the following:

Higher frequency (higher pitch) sounds have shorter wavelengths, and lower frequency (lower pitch) sounds have longer wavelengths.

Producing Sound Waves

Anything that pushes air forward at a certain frequency can make sound waves. An electric speaker has a diaphragm that pulses forward and back, and each time it moves forward, it sends a higher pressure bunch of air particles moving away from it. When it does this many times per second, it’s producing a sound wave at a certain pressure.

Musical instruments and human voices also have various ways of quickly moving something back and forth to produce pulses of slightly compressed air at different frequencies. The thing(s) vibrating back and forth could be a string, reed, drum head, vocal chord, or lips, depending on what type of instrument is involved.