3-4 Loudness Level
Review: We know that the sound intensity measures the acoustic energy transmitted by the sound wave. This is a physical quantity which can be concretely measured.
How is loudness different than intensity?
While both loudness and intensity evaluates how loud a sound is, loudness is different because it is subjective. Individual ears will detect a sound's loudness differently. What one person's determines to be "loud" may be different than another individual's loudness scale.
A great example to decipher intensity versus loudness is the volume on a television set. The number that the volume is set on can be compared to the intensity because this is a set number. This number correlates with the actual sound that is coming out of the television. However, the number someone prefers it to be on can be compared to the loudness level. An older man may need the TV set to 30 to hear his favorite show, while a young adult may only need the TV set to 20 to hear the exact same show. The old man's loudness level is 30 while the young adult's loudness level is 20.
Can we measure loudness?
Even though loudness is a subjective number we still put a numeral value to it by finding the average perceived loudness. These averages are often shown on equal loudness curves, such as the ones pictured below:
These curves show the "average" loudness of a sound measured in sones.
What is the loudness level?
On the other hand, the loudness level is the subjective measures of loudness that depends on frequency. The loudness level is determined by the comparing the loudness of the sound to that of a 1000 Hz pure tone. The curve for loudness level can be seen below:
The loudness level is measured in phons.
LL in phons = SL in db
L in phons = 2^((LL-40)/10)
Practice Problems:
1. A 200 Hz tone with a sound level (SL) of 60 db sounds the same loudness as:
(a) a 100 Hz tone with a SL of 100 db
(b) a 1000 Hz tone with a SL of 60 db
(c) a 10 kHz tone with a SL of 20 db
(d) a 100 Hz tone with a SL of 50 db
(e) none of the above
2. A 1000 Hz tone which is 20 db sounds twice as loud as one that is 10 db.
(a) True
(b) False
3. How many times louder does a 90 db pure 2000 Hz tone sound than a 70 db tone at 500 Hz?
(a) the same loudness
(b) twice as loud
(c) three times as loud
(d) it actually seems less loud
(e) none of these
4. How many times louder does a 90 db pure 2000 Hz tone sound than a 1000 db tone at 1000 Hz?
(a) the same loudness
(b) twice as loud
(c) three times as loud
(d) it actually seems less loud
(e) none of these
Continue: #REDIRECT 3-5 Perception of Two Pure Tones
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