Tuesday, Nov. 20th 2018

Acoustical Trivia

Need something to wow that special someone at a holiday party, or the in-laws at your family gathering? Check out these interesting facts about our favorite subject: sound!

 

Properties of Sound

  • Have you heard that you can figure out how far away a lightning strike is by counting the time between when you see lightning and hear thunder? True! Light travels so fast you see the lightning flash as it happens. Sound travels much slower (about 1,130 feet per second in air). As a result, you hear the thunder later. Since 1 mile = 5,280 feet, if you count five seconds, you’re about a mile away from the lightning.
  • Sound travels faster and farther through rigid, denser materials. Have you noticed you can hear train whistles from farther away on a foggy day? This is because the air is denser from the mist.
  • If you have two identical noise sources right next to one another (for example, two loudspeakers or HVAC condensers), the overall sound pressure level only increases by 3dB, but most people recognize a 10dB increase as twice as loud (or a 10dB decrease as half as loud).

 

Quantifying Sound

  • The range of wavelengths of sound that humans can detect varies from greater than 50 feet long at low frequencies to less than an inch long at higher frequencies.
  • Decibels (dB) are not a unit of measurement. They tell us how loud a sound is compared with the quietest possible sound using relative pressures. A 60 dB sound is 1,000,000 times louder than that quietest audible sound!
  • Everyone has heard of white noise, but there are other colors of noise too: pink, brown, blue, and gray, each having a unique frequency response.
  • In free field conditions (where there are no sound-reflective surfaces around a sound source), sound level drops by 6dB every time you double your distance from the source. So a 60dB sound at 3 meters is 54dB at 6 meters and 48dB at 12 meters.  For each meter of increased distance, the effective reduction in level becomes less significant.

 

Loudspeakers

  • The first loudspeakers were made for telephones, by Johann Philip Reis, Alexander Graham Bell (the namesake of the decibel), and Ernst Siemens.
  • Loudspeaker drivers (the parts that generate the sound) have some interesting names:
    • Tweeter = high frequencies
    • Woofer = low frequencies
    • Sub-woofer = really low frequencies
  • Remember how we said light travels faster than sound? Well, sound signals in speaker-wire actually travel at the speed of light.  In a properly-designed sound system, these signals are actually delayed (or intentionally slowed down) to speakers distributed to the back of the room so that a) sounds from these speakers are in-sync with sounds from the speakers at the front of the room and b) to help it seem like the sound listeners are hearing is coming from the performers instead of the loudspeakers right above their heads.

 

Interested in learning more? We have AIA accredited classes that can bring you up to speed on the basics of acoustics, and our experts would love to help with more in-depth design and problem solving for any space.

Contact us to learn more, schedule a class, or just ask a question!

 


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One Comment on “Acoustical Trivia”

  1. Bob Coffeen Says:

    WOW – this is an entire course in Acoustics! Bob



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