## Sound waves are due to "spring-like" wave motion of air molecules

(Sound waves are mechanical longitudinal waves)

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/tralon.html#c2

http://www.physicsclassroom.com/class/sound/Lesson-2/Pitch-and-Frequency

"If a particle of air undergoes 1000 longitudinal vibrations in 2 seconds, then the frequency of the wave would be 500 vibrations per second. "

"A guitar string vibrating at 500 Hz will set the air particles in the room vibrating at the same frequency of 500 Hz"

"The first particle of the medium begins vibrating, at say 500 Hz, and begins to set the second particle into vibrational motion at the same frequency of 500 Hz. The second particle begins vibrating at 500 Hz and thus sets the third particle of the medium into vibrational motion at 500 Hz."

## Which frequencies are more directional, higher or lower ones ?

If a marching band is approaching on a cross street, which instruments will you hear first ?

A high-pitched (high frequency) piccolo or a low pitched drum ?

Piccolo frequency range: 600 Hz – 5 Khz
Timpani frequency range : 90 Hz – 180 Hz

Reference: http://www.donbarbersound.com/media/libFrequencyRangeofInstrumentsAndVocals.pdf

Answer at his link http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/diffrac.html: "The long wavelength sounds of the bass drum will diffract around the corner more efficiently than the more directional, short wavelength sounds of the higher pitched instruments".

Conclusion: Higher frequencies are more directional than lower ones