Sounds travel as waves. It is the shape of the wave that determines the kind of sound that is produced. The pitch of a sound (whether it is high or low) depends on the frequency of the sound waves. The frequency is how many waves, or vibrations, the sound makes in one second. This is measured in hertz (Hz). One vibration per second is one hertz. How loud the sound is depends on the magnitude (or height) of its waves. The more energy the waves carry, the louder the sound. Loudness is measured in decibels (dB).
Sound energy travels in waves and is measured in frequency and amplitude. Amplitude measures how forceful the wave is. It is measured on a Logarithmic scale and reported in decibels or dBA of sound pressure. 0 dBA is the softest level that a person can hear. Normal speaking voices are around 65 dBA. A rock concert can reach about 120 dBA but is often at 100 dB.
Sounds that are 82 dBA or above can permanently damage your ears when exposed for a long period of time. The more sound pressure a sound has, the less time it takes to cause damage. For example, a sound at 85 dBA may take as long at 8 hours to cause permanent damage, while a sound at 97 dBA can start damaging hair cells after only 30 minutes of listening.
Frequency is measured in the number of sound vibrations in one second. A healthy ear can hear sounds of very low frequency, 20 Hertz (or 20 cycles per second), to a very high frequency of 20,000 Hertz. The lowest a key on the piano is 27 Hertz. The middle C key on a piano creates a 262 Hertz tone. The highest key on the piano is 4186 Hertz.
How loud a sound seems to depend on who’s listening. A young person playing rock up in their bedroom might not think their music is loud, but their parents in the room down below might have other ideas. In other words, how loud things seem is a subjective thing and not something we can easily measure. However, what makes one sound seem louder than another is the amount of energy that the source of the sound is pumping towards the listener in the form of pressure variations in the air. That’s the intensity of the sound.
Meters that measure sound levels work by calculating the pressure of the sound waves traveling through the air from a source of the noise. That’s why you’ll sometimes see them referred to as sound pressure level (SPL) meters. Devices like this give a measurement of sound intensity in units called decibels as we mentioned before. Telephone pioneer Alexander Graham Bell first devised this scale.