Facts about Sound you Probably didn’t Know

The other day I kept hearing this noise from my neighbor.  I couldn’t quite figure it out, and naturally it was annoying.  I didn’t do anything about it, but it got me thinking about some random facts about sound and noise.

• Sound travels faster through concrete than air
• Sound travels faster through most materials faster than air
• Below is a list of common materials and how fast sound travels through them (Values found at http://www.engineeringtoolbox.com/sound-speed-solids-d_713.html)

• The range of human hearing is 20 Hz – 20,000 Hz, however most people can only hear between 40 Hz – 16,000 Hz
• All frequencies are not equal.  Our ears perceive certain frequencies to be louder than others (found at Wikipedia http://en.wikipedia.org/wiki/Equal-loudness_contour):

• Sound travels a smidge less than 1 foot per second at standard temperature and pressure.  Therefore if you need to place speakers in front of other speakers, you need to delay them based on distance… 40 feet = ~40ms of delay.
• If a speaker is placed in front of another without a delay, the sound from the speaker farthest from you will sound similar to an echo.  This is called the Haas effect.  However, most people don’t notice this until there is a 40ms gap between sounds, or roughly 40 feet.  After about 40ms of delay, the intelligibility of the sound also decreases.  I.e. it starts to degrade the quality, and you start having trouble understanding what you hear.

Mostly useless facts, but they are fun to know.