Decibels & Perceived Sound

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    Michael Ermann

    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 loud

    PROPAGATION
    +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)

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    Rebekka O'Melia (Edited )

    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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    Rebekka O'Melia

    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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    Michael Ermann

    Nearly all of those numbers are wrong. The threshold of hearing is at 0 dB. It doesn't matter if it's "right beside you" because sound pressure level is measured at the receiver point, so 0dB or 30dB already factors in how loud it is at you.

    Noises that are just audible (slightly above zero dB) can be annoying (think: dripping faucet when you are trying to sleep). Noises that are more annoying at a given dB level: intermittent noises, pure tones (back up beeper), noises that we have little control over (neighbor's dog scratching around on the upstairs floor is more annoying than my dog would be), noises that are considered less important (motorcycle with altered muffler is more annoying than siren at the same dB level), fluctuating noises, rattles from low frequency vibrations, nighttime noise and new sources of noise. Psychoacoustics plays a surprisingly big role. . . it's not just sound level. 

    At prolonged exposure, 85 dB can cause hearing loss (actually, lower levels can too, but OSHA requires protection at a time-averaged 85 dB).

    Sound doesn't travel across water or other surfaces more easily. In the context of architectural acoustics, it travels through air. There are times when a cold lake can cause an inversion in the atmosphere that bends sound that would have otherwise headed upward so that it sounds louder across the lake than it would otherwise, but that's pretty niche and it doesn't travel across water more easily. Sound does travel under water more easily, but that's not relevant to architecture unless you're designing a submarine.

    The goal is sometimes to reduce speech to the point where speech is unintelligible--this is called speech security--but it's niche use is generally limited to securing private conversations (healthcare settings, embassies). The "arch goal" can be right-sizing reverberance, addressing an acoustic defect (echo), promoting early sound reflections for unamplified speech and music, electronic sound reinforcement, mitigating excessive loudness (elementary school cafeteria), sound isolation (between hotel rooms, for instance, but hopefully you can't hear normal conversations at all so this is different than speech security), mitigating community noise (neighboring outdoor nightclub), mitigating transportation noise, mitigating mechanical noise, and vibration control.

      

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