Vibration, Sound, and Hearing 2
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the range of differences between the smallest and largest changes in something
What dynamic rance is our hearing capable of detecting?
1 - 10,000,000
what scale is often used to compress the dynamic range into more manageable figures?
the logarithmic scale
a dimensionless unit used to compare the ratio of two quantities
the decibel is usually used in relation to what type of energy?
Acoustic energy, such as sound pressure, power, and/or intensity
- dB-SPL - (acoustic) sound pressure level
- dBm - electrical power
- dBv/dBu/dBV - electrical voltage
is the decibel a simple or accurate representation of perceived loudness?
doubling sound pressure results in an
increase of 6 dB
doubling the measurement distance results in
a decrease of 6 dB
doubling sound power results in an
increase of 3 dB
adding two similar (but uncorrelated) sounds at the same level generally produces an
increase of about 3 dB-SPL
Equal Loudness Principle
- Auditory sensitivity varies with frequency
- Our hearing mechanism is less sensitive to low and high frequencies then mid-range frequencies
- These sensitivity differences lessen as loudness increases
- One reason why people think loud music "sounds better"
Phon (pernounced fone)
unit used to express the perceived loudness level as related to the ear's subjective impressions at various frequencies
What is a more appropriate presentation of simple loudness than the decibel?
- the decibel describes intensity more than loudness
sound pressure level at 1000 Hz.
is the Phon a simple or accurate representation of perceived loudness?
- perceived loudness
- unit used to express comparative loudness of multiple sounds
- arbitrary scale created to provide a linear representation of perceived loudness
- 1 sone = 40 phons
- every 10 phons (10x intensity) = 2x sones
impedance match to inner ear
frequency and intensity analysis
combines signals from both ears
integrates all of the signals
premature hearing loss
hearing damage caused by exposure to loud sounds varies with loudness, frequency, duration, and exposure time
how does prolonged exposure to dangerous noise levels affect the auditory system?
- prolonged exposure decreases auditory sensitivity
- raises the threshold of hearing (middle ear)
TTS - Temporary Threshold Shift (aka auditory fatigue)
- creates a false perception of actual loudness
- necessitates compensation (turning the volume up even more)
- could last minutes, hours, or days
- ringing, whistling, or buzzing in the ears after prolonged exposure to loud sounds
- could last minutes, hours, or days
- indicates damage is either imminent or has already occured
PTS - Permanent Threshold Shift
Permanent hearing loss
hearing loss is more pronounced in which frequency range
high frequency sensitivity
the obscuring of one sound (or aspect) by another
pure tones close in frequency mask each other more easily than
pure tones mask ______ frequencies more easily than ______ frequencies
which tones can mask broader range of frequencies?
which bands of noise mask like pure tones?
an initial tone can mask a subsequent tone, even if it has stopped and the two do not overlap in time
a tone that begins shortly after another can mask the first
tones heard by one ear can be masked by tones in the other
binaural hearing (sound localization)
- hearing with the use of two ears
- inter-aural intensity differences
- inter-aural timing differences
- affected by wavelength (frequency)
directed sounds reached our ears first and indirect sounds interact with reflective objects before being heard
how closely must sounds reach our ears to be perceived as coming from the same direction?
20 milliseconds or less
localization becomes difficult as
the time difference increases
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