Decibels & Perceived Sound
How do decibels relate to our perception of sound? On a BS practice exam, the answer given to one question about decibels explains, "Reducing sound intensity by half reduces it by 3 db." Another question later in the exam says that a change in 10 decibels is perceived as half as loud... How do we know how a change in decibels is perceived? Is there a ratio I need to know?
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Two different things: sound energy (the physics of the disturbance of air molecules) and loudness perception (subjectively how loud something sounds)
SOUND ENERGY
+3 dB: twice as much sound energy
+6 dB: four times as much sound energy (like four people singing happy birthday…which doesn’t subjectively sound four times as loud as one person singing)PERCEPTION OF SOUND
+1dB: not perceivable
+3dB: barely perceivable (and remember, twice as many people singing)
+6dB: clearly perceivable
+10dB: subjectively twice as loud
+20dB: subjectively four times as loud
-20dB: subjectively one quarter as loudPROPAGATION
+6dB: twice as far away from a point source (AC unit) in a free field (outdoors)—Michael Ermann
Amber Book Creator
Author, Architectural Acoustics Illustrated (Wiley) -
Hannah,
Research the Doppler Effect. The sound of a train horn, as the train is speeding towards you, is more intense than when it's stationary. I think the Site Planning & Design Handbook might be helpful on this topic. It covers topics about site planning to reduce noise.
Hope this helps!
Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses
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Hannah,
It's worth noting that you aren't going to hear much of anything that's below 30db unless it's right beside you.
Normal conversation is 60db, and noises don't get annoying until 70+ db. 105+ db and up causes hearing loss.
And sounds travel across water and other surfaces easily.
I have 10db hearing loss in one ear. It means I cannot tell what direction sounds are coming from. Too many concerts when I was younger. I wear ear protection now at concerts, and I don't wear headphones for longer than an hour or 2 ever, and I rarely use them. I think extreme hearing loss or tennitus from wearing earbuds all day is going to become very common, and it's super dangerous to wear them while running. People walk in front of moving cars without knowing.
I doubt you'll see this db topic on the ARE unless it relates to STC ratings or buffering a site from highway noise or something. The arch goal is to reduce speech sounds to the point where the conversation is not discernible.
Hope this helps!
Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses
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