Have you ever grabbed a mallet and bashed away at a gong? If so, regardless of whether it was a tiny tabletop version or a huge one like those favored by hair-band drummers, you no doubt witnessed a continuum of changing frequencies and tones created by its varying vibration patterns. The harder you hit it, the more air it moves, the louder it gets. Those patterns of air movement you hear (and sometimes feel) are directly related to the physical properties of the hammered alloy disc. Naturally, gongs of various shapes and sizes vibrate differently—bigger ones sound deeper, smaller versions sound more shrill. And, of course, a gong player’s playing techniques affect all sorts of audible nuances, too.
These basic principles of sound also apply to a cymbal, a drum, a violin, and basically any musical instrument. But they also apply to a breaking glass, footsteps on gravel, a slamming door, a crying baby, a motorcycle engine, or any of the billions of items generating the sounds we’re exposed to daily. Physics is physics. No matter how sonically different objects may be, they all share a common factor—they create waves in the air that our ears detect as sound. And every little variance in an object’s makeup can alter its resultant sound.
Basic Anatomy and History
Like any good musical instrument, loudspeakers are designed to broadcast their signals with specific intent. They generate sounds the same way a gong—or anything else—does: by moving air. Unlike a gong, however, a speaker consists of a number of components working together. Every change in design, along with the inherent behavior of the component materials, will alter the characteristics of the sound waves it produces. The waves themselves are ultimately generated by the speaker cone— the funnel-shaped piece of heavy-duty paper you see when looking at an unenclosed speaker. But several other components combine forces to get the cone moving.
The innermost part of the cone is attached to a voice coil—the part that vibrates the cone. Appropriately named, the voice coil typically consists of a coil of copper wire. If you buy into the idea that when you play an electric guitar, you are also playing the amplifier—and, ultimately, the speaker—then the voice coil is the first speaker component you’re playing. The positive and negative wire-connection leads on the back of the speaker are directly connected to the voice-coil windings.
Despite its importance in the signal chain, the voice coil isn’t easy to actually lay eyes on. From a front view, it’s located behind a little domed protective dust cap at the center of the speaker, and from the sides the coil is surrounded by a donut-shaped magnet. The coil is fragile, but it’s well protected.
Filed with the U.S. patent office on April 20, 1925, Chester Williams Rice and Edward Washburn Kellogg’s music-optimized loudspeaker design was eventually released in 1926 by RCA as the Radiola Loudspeaker #104.
We can trace the origins of the voice coil to Hans Christian Ørsted, a Danish physicist and chemist who, in 1820, noticed that compass needles act differently around electricity. He soon figured out that when electricity flows through a wire, magnetic fields are created. Ørsted was a curious guy—in 1825 he was also the first person to produce aluminum. However, he never got the chance to hear a speaker.
Ninety years after Ørsted’s discovery, two Americans—Peter L. Jensen (also of Danish descent) and Edwin S. Pridham—created a public-address-system speaker that used a moving coil. Subsequently, one milestone in early loudspeaker history was when President Woodrow Wilson used a PA to address a crowd in 1919. In 1921, Chester Williams Rice and Edward Washburn Kellogg, respectively with General Electric and AT&T, worked to refine the idea with a focus on higher fidelity for music reproduction. They applied for a patent titled “loud speaker,” culminating in RCA’s release of the Radiola Loudspeaker #104 in 1926.
Why does RCA’s iconic early logo depict a dog up close to a mechanically amplified early phonograph? Perhaps because they were famously volume challenged prior to the invention of the loudspeaker.
History buffs are no doubt looking at the timeline here and rightfully thinking that we’ve overlooked some pretty important stuff. After all, Alexander Graham Bell invented the telephone in 1875, and Thomas Edison’s phonograph followed two years after that—and obviously both required some sort of amplification device predating Jensen and Pridham’s and Rice and Kellogg’s loudspeakers.
Bell’s early telephones managed to make intelligible sounds, but the earliest versions had little or no fidelity. And Rice and Kellogg’s design was a dramatic improvement over the horns Edison, Motorola, and the Victor Talking Machine Company (makers of the Victrola) used to mechanically amplify recordings on early phonographs. There’s a reason the original RCA “His Master’s Voice” logo shows the dog sitting right next to the horn on the hand-cranked player—volume was severely lacking. The loudspeaker changed everything.
Now closing in on its 100-year anniversary, Rice and Kellogg’s loudspeaker design is essentially unchanged from the speakers we use today. There have been countless updates in construction and materials used since the 1920s, all of which improved not just fidelity, but also power handling. But the basic configuration remains.