1 Sound Intensity Level Learning Outcomes HL Define

1 Sound Intensity Level – Learning Outcomes HL: Define sound intensity and give its unit. HL: Solve problems about sound intensity. Define threshold of hearing and frequency response of the human ear. Give some examples of sound intensity level. HL: Convert changes in sound intensity to changes in sound intensity level. Discuss hearing impairment and ear protection. Describe the d. B(A) scale. Use a sound level meter.

2 HL: Sound Intensity

3 HL: Sound Intensity

Frequency Response of the Ear The ear is not like a microphone – it picks up some sounds easier than others. Certain frequencies sound louder than others at the same sound intensity. The ear is particularly sensitive to sounds in the 2000 to 4000 Hz frequency range. by Lindosland – public domain 4

5 Threshold of Hearing

6 Sound Intensity Level

7 Sound Intensity Level Noise Threshold of hearing Whisper Suburban estate Sound Intensity Level 0 d. B 20 d. B 50 d. B Conversation Car Lorry Jackhammer Rock concert Threshold of pain 60 d. B 70 d. B 80 d. B 100 d. B 110 d. B 130 d. B

8 HL: Sound Intensity Level A doubling in sound intensity corresponds to a sound intensity level increase of 3 d. B. Likewise, halving the sound intensity reduces the sound intensity level by 3 d. B. e. g. the sound intensity of a loudspeaker doubles as a person approaches it. What is the increase in sound intensity level? e. g. the sound intensity at a concert increases from 85 d. B to 94 d. B when the concert begins. By what factor has the sound intensity increased?

9 Hearing Impairment We have previously discussed Sound noise pollution, but we need to look Level (d. B) at hearing impairment in detail. 90 Exposure to sounds above a certain level can permanently damage 93 hearing over time. 96 Health and safety regulations usually require a maximum 99 exposure to sound levels without ear protection. 102 Ear protection is required for longer 105 periods. Max. Hours per Day 8 4 2 1 ½ ¼

10 d. B(A) Scale Due to the frequency response of the human ear, the d. B scale does not accurately reflect how loud sounds are. e. g. a 50 d. B sound will appear louder at 2 k. Hz than at 50 Hz, because our ears are more sensitive to 2 k. Hz sounds. The d. B(A) scale takes this into account so that 50 d. B has the same loudness to our ears regardless of the frequency.

by Lindosland – public domain 11 d. B(A) Scale

12 Sound Level Meter Sound level meters are devices used to measure sound intensity level. They use a microphone to pick up sound, then display a deci. Bel value, usually on the d. B(A) scale. Thus, they take the frequency response of the ear into account. by Harke – public domain