Although 0 dB is often referred to as the lowerthreshold of human hearing, it is important to realize that thehuman ear is not equally sensitive to all frequencies of sound. Inother words, a particular noise may sound louder or softerdepending on the frequency of the sound wave being transmitted.Because of this variation, scientists have defined a unit ofloudness, called a phon, to represent the intensityof sound waves with a frequency of 1000 Hz: A60-phon sound is one that is perceived by the human ear tohave the same loudness as a sound wave with an intensity of60 dB and a frequency of 1000 Hz.

a) At approximately what frequency do most people perceive theleast intense sounds? Answer numerically in hertz to twosignificant figures.

b) Normal conversation has a sound level of about60 dB. How many times more intense must a 100-Hz sound becompared to a 1000-Hz sound to be perceived as equal to60 phons of loudness?

Intensity (in dB) 100 80 60 40 20 0 30 50 100 500 100 phons 80 phons 60 phons 40 phons 20 phons 0 phons 1,000 Frequency (in Hz) 5,000 10,000