Intensity and Relative Intensity Level

Key Formulas

	I	intensity	W/m2
	P	power of sound source	W
	r	distance from sound source	m

	β	relative intensity level	decibels (dB)
	I	intensity	W/m2
	I0	threshold of hearing = 10-12 W/m2

Tips to Remember

• Relative intensity level is less formally referred to as the “decibel level” of a sound. It is not the same as intensity; relative intensity level uses a logarithmic scale to more accurately reflect how humans perceive loudness.
• When you enter 10^-12 into your calculator for the threshold of hearing, enter either “10^-12” or, if you use the scientific notation button, “1E-12.” Do not enter “10E-12” if you use the scientific notation button, because that would really be 10 × 10^-12, or 10^-11.
• Don’t be surprised if the problems you encounter have seemingly low sound powers. Your normal speaking voice produces only about a millionth of a watt of sound; our ears are just so sensitive that that’s enough.