Sound Amplification & The Inverse Square Law

Amplifying sound is the act of making a sound louder to the human ear. It relies on the process of increasing the amplitude of the sound wave, which is where "amplification" comes from. As I mentioned in a much earlier post, our perception of loudness corresponds to the amplitude of sound waves. Therefore, to make a sound seem louder, you need to find a way to increase the amplitude of its waveform. This can be done in a couple of ways.

The simplest way to amplify the volume of sound is when it is produced by an acoustic instrument. Striking a guitar string harder, blowing more air or with more force into a wind instrument, and beating a drum with more force are all ways to amplify the sound produced by acoustic instruments. As you can recall, the defining characteristics that determine the pitch of the sound produced are the length and thickness of the guitar string, or length and width of the air cavity in a wind instrument. Because this does not change during these processes, the pitch is able to remain constant while the sound is amplified.

The more interesting form of sound amplification, in my opinion, is the electronic/digital amplification that exists universally in our technology today. A great example of how this works relies on a slightly older piece of technology, a record player with electronic amplification. A vinyl record reproduces sound as the needle of the record player spins through its grooves and vibrates. The record player is able to convert these small vibrations into electrical signal. In the amplifier, this current is strengthened and reproduced as sound at a much louder volume. Much of our other technology works in the same way - electrical impulses are increased in strength in order to produce a louder sound. This is how microphones work as well as musical instrument amplifiers, such as guitar amps.

The existence of sound amplification brings up a few more questions about when it is necessary and the ways in which sound travels. Obviously in a small, quiet room, a guitar amp is not needed to hear the sound produced by a guitarist. What happens if it is a long room, however, and the guitar player is very far away? Though it may seem quiet, it may not be as easy for you to hear the guitar player without amplification if you are situated at opposite ends of the room. This pertains to the inverse square law, which relates the amplitude of sound to the distance it travels from its source to a listener. The law states that as the distance doubles, the intensity of the sound is decreased by a factor of four. This corresponds to a constant drop of six decibels each time the distance is doubled. Because of this, in certain cases sound amplification may be necessary simply due to the distance that sound needs to travel. This is especially relevant in large concert halls or outdoor venues.

Works Cited:

"Amplification of Sounds." University of Leicester. Web. 13 Jan. 2016.

"Simplified Model: Sound Reinforcement." Hyper Physics. Web. 13 Jan. 2016.