More Than Meets the Ear: The Invention of the Loudspeaker
- Tuesday, November 08, 2011
Hidden in the development of the megaphone was a subtle hint of physics that would play a role in later developments. The apparent amplification was due to what, in the engineering world, is called “impedance matching.” Impedance matching can get complicated, but the simple explanation is that it provides for a way to transfer the maximum power from a sound source (like a person’s vocal chords) to the air. If you have a television connected to an antenna or a cable, somewhere in the system is a device that impedance matches the antenna or cable to your television so it will receive the maximum possible signal.
The Invention of the Loudspeaker
The loudspeaker, as we know it today, was not invented for the theater, for sports arenas, or for concert halls. It was invented specifically for converting an electrical signal to sound when Alexander Graham Bell invented the telephone. Bell found that he could convert spoken sound into an electrical signal, send it over an electrical wire, and then convert it back into the original spoken sound.
The part he spoke into is what we call a “microphone,” and the part he listened to is what we call the “loudspeaker.” Without both parts, the invention of the telephone would not have been very useful. Actually, a microphone and a loudspeaker are very similar in design. They just operate opposite of one another!
The technical name for the modern loudspeaker is “electroacoustic transducer.” That’s a mouthful, but with a little energy, it makes complete sense. “Electro” implies electricity, or in this case, an electrical signal which is a form of electrical energy. “Acoustic” means sound, or in our case, sound energy. “Transducer” means to convert one form of energy to another form of energy. Putting all of the pieces together, then, a loudspeaker is a device that converts electrical energy to sound energy!
Did you know that you can actually feel sound energy? Have you ever been in a vehicle when a car near you had a sound system blasting? You can feel the vibrations of the sound-wave energy as it strikes your car. Unfortunately, people who blast their stereos like that don’t realize that the sound energy vibrating your car is also vibrating their eardrums. Years of exposure to that level of sound energy can permanently damage a person’s hearing.
If you listen to music, you know that different instruments generate different pitches. A tuba generates low pitches, while a fife generates high pitches. Other instruments fall in between. No single loudspeaker is good at reproducing sound at all pitches. The physics behind creating the sound impose some limitations on what the speakers are capable of doing. That is why a sound system uses several different kinds of speakers to provide the best results.
A Matter of Hearing
At this point, it would be a good idea to talk a little bit about how God designed our hearing. This will be a brief overview, and readers should explore it in more detail if interested.
Hearing is the ability to perceive sounds. Sound waves are actually vibrations in the air (or some other medium like water) that travel to the ear. The outside of your ear serves to channel the sound into the auditory canal, which takes it to the tympanic membrane. The tympanic membrane, which most of us know as the “eardrum,” vibrates. Other mechanisms inside the ear convert the vibrations to electrical signals that travel to the brain and produce the sensation we call “sound.”
Our hearing has some limitations. The lowest vibrations we can hear are about 20 Hertz, which means 20 vibrations every second. These vibrations could be represented by the very low roll of thunder. The highest vibrations a person can typically hear are about 20,000 Hertz. This would be a high, squealing noise, kind of like chalk squeaking on a chalkboard, only even higher.
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