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COMD 5070: Exam 1: Week 2: Solved
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COMD 5070: Exam 1: Week 2: Solved
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COMD 5070: Exam 1: Week 2: SolvedAdding dB of Two Sounds - ANSWER-You can't simply add logarithmic numbers
(20 dB plus 20 dB isn't 40 dB)
First, add the pressures (μPa), then compute the dB:
Car passing by has pressure of 100,000 μPa (74 dB),
2 cars would be 200,000 μPa,
200,000 divided by reference level 20 = 10,000,
20 x 4 = 80 dB (log of 10,000 is 4 as it has 4 zeros),
74 dB + 74 dB = 80 dB,
double sound pressure = add 6 dB total
ANSI S3.6-1996 - ANSWER-standard to convert dB SPL to dB HL
Find thresholds in dB SPL
0 dB HL at any given frequency represents the softest sound that a person can perceive
if they have typical hearing with no hearing loss at all.
Why zero? It's a convenient reference level.
Audiogram for a Hearing Loss - ANSWER-Normal at 250, 500 and 1000 Hertz
By 2000 Hertz the threshold has gone up
Threshold is high by 4000 Hertz at 60 dB
As frequencies get higher the threshold improves but there is still a loss.
Audiogram for Normal Hearing - ANSWER-Thresholds are within +/- 5 dB of 0
Little fluctuations are normal.
The numbers descending down the Y axis will indicate a greater hearing loss as they
progress.
Comparing Intensities - ANSWER-decibels are based on comparison
, science has agreed on a reference level (20 μPa)
softest perceptible 1000 Hz tone:
0.00002 pascals or 20 μPa, vs. rifle shot = 200 Pa (the maximum sound is 10,000,000
greater than the minimum sound)
these numbers become complicated
Comparing Sizes - ANSWER-linear is intuitive:
values are directly comparable,
relative sizes are obvious,
logarithmic less familiar:
see more detail across a wide range,
need to read the axis units carefully
dB Calculation Examples, Car - ANSWER-car passing by has pressure of 100,000 μPa
(100,000 μPa/ 20 μPa = log of 3.69)
(log of 5,000 is 3.69)
20 x 3.69 = 74 dB
thus, 5,000 times stronger than 20 μPa reference
dB Calculation Examples, Whisper - ANSWER-A soft whisper has a pressure of about
200 μPa
The reference pressure is 20 μPa
(200 μPa/20 μPa = log of 10)
(20 x log 10) = (20 x 1 = 20 dB),
(20 x log 10 is 1, as it only has one zero)
thus, a whisper is 10 times stronger than 20 μPa reference
dB Sensation Level - ANSWER-dB SL:
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