1. How Magnets and Coils Inside Headphones Move Air to Make Sound
If you imagine what is inside a headphone, what do you see? In the widely used dynamic type, the main parts are a magnet and a thin wire coil called a voice coil. [1] The sound signal usually arrives as changes in electric current. When this current flows through the coil, a force is created between the coil and the magnetic field of the nearby magnet. This relationship, where force acts perpendicular to the current and magnetic field, is known as Fleming’s left-hand rule. [1]
The voice coil moves back and forth, and this movement is transmitted to a diaphragm. When the diaphragm pushes and pulls the air, the vibration of the air reaches your ear as sound. [1] This method is said to easily balance low distortion with a wide frequency range, and it is used in many modern headphones. [2] Who first shaped this headphone mechanism, and where did they make it?
2. How Telephone Receivers Led to the First Headphones
The origins of headphones are said to go back to telephone technology, with the receiver that turns voice signals into sound near the ear as the starting point. [2] By the spring of 1910, Utah inventor Nathaniel Baldwin had finished the design of a sensitive receiver-style headset. His workspace was his home kitchen. [3] The prototype was sent to the US Navy and is reported to have been evaluated as significantly better than the equipment used by naval radio operators. [3] There is also an anecdote that he sent it in a tin can with a letter written in purple ink. However, this story appears in only one article, so it is best read as an anecdote that has been passed down. [4]
The Navy requested many units, and some records say they ordered 100 pairs in 1915. [4] By 1922, Baldwin’s factory reportedly ran three shifts day and night, producing about 150 headsets per day. [3] Until then, the focus was mainly on communication. When did headphones for "enjoying music" appear?
3. Why the 1958 Koss SP/3 Headphones Beat the Record Player's Speakers
In 1958, John Koss and Martin Lange created the SP/3 stereo headphones to show off the good stereo sound of a portable record player and the joy of "listening alone." [5] The record player was supposed to be the main attraction, and the headphones were just a tool to demonstrate it. However, at the exhibition, these headphones unexpectedly attracted attention. [5]
Koss Corporation explains the SP/3 as the world’s first hi-fi stereo headphones, stating that previous products were mainly for communication. [6] Since this is a company self-introduction, it is safer to read it as "the company claims this." When listening to audio sources made for speakers through headphones, the left and right sounds can feel extremely separated, seeming to play inside your head (in-head localization). This is explained by the fact that speakers send both sounds to both ears, while headphones send different sounds to the left and right ears separately. [2] As the joy of listening alone spread, a new problem emerged: surrounding noise.
4. How Noise-Cancelling Headphones Use Opposite Sound Waves
Noise-cancelling headphones have built-in microphones that pick up surrounding noise. These microphones detect the ambient sound and generate a sound with an opposite waveform (inverse phase) to cancel out the noise. [7] If you view sound waves as peaks and valleys, overlapping waves with opposite peaks and valleys weakens each other.
However, the reality is that it weakens noise rather than completely erasing it. Sony’s explanation states that it is highly effective for constant, low sounds like train, air conditioner, and airplane engine noises, but limited for sudden or fluctuating sounds. It is also less effective against high-pitched sounds. [8] This is why human conversation, horns, and station announcements are likely to be heard. On the other hand, the passive method of blocking ears with ear cups or ear tips is said to be effective for mid-to-high sounds like human voices and typing. This complements the active method that uses microphones. [9] Bose Corporation announced the "Aviation Headset X" for aircraft in 1989. Since the start of development and general release years vary by article, only 1989 is used here. [10] Convenient features are not always gentle on the ears depending on how they are used. Let’s talk about ear care.
5. A Hands-On Ear Test and Tips for Protecting Your Hearing
Try this today: gently cover both ears with your palms and listen to how the surrounding sound changes. Compare how human voices, TV sounds, and low noises like a refrigerator decrease in volume. This is just a sensory check, not a measurement.
Listening to loud sounds for a long time can gradually damage the hair cells that transmit sound to the brain, leading to hearing loss. The Ministry of Health, Labour and Welfare explains that early stages are hard to notice and lost hearing cannot be recovered. [11] Preventing this involves not raising the volume too high and giving your ears regular breaks. [11] The principles of noise cancellation and its effective sounds are written in the instruction pages of Panasonic and Sony. [7] [8]