Between music, podcasts, games, and endless online content, most people spend hours a week wearing headphones. Maybe you’re considering a new pair for the holidays, but with so many options on the market, it can be hard to know what to choose.
I am a professional musician and a professor of music technology who studies acoustics. My work explores the intersection between the scientific, artistic and subjective human elements of sound. Choosing the right headphones requires taking into account all three factors; So what makes a truly good headphone?
What is sound really?
In physics, sound consists of air vibrations consisting of a series of high and low pressure regions. These are cycles of a sound wave.
Counting the number of cycles that occur per second determines the frequency or pitch of the sound. Higher frequencies mean higher pitches. Scientists define frequencies in hertz, meaning that a 500 Hz sound goes through 500 complete cycles of low pressure and high pressure per second.
The loudness or amplitude of a sound is determined by the maximum pressure of a wave. The higher the pressure, the louder the sound.
To create sound, headphones convert the electrical sound signal into these cycles of high and low pressure that our ears interpret as sound.
human ear
Human ears are incredible sensors. The average person can hear a wide range of pitches and different sound levels. So how does the ear work?
When sound enters your ear, your eardrum converts the air vibrations into mechanical vibrations of the small middle ear bones. These mechanical vibrations turn into fluid vibrations in your inner ear. Sensitive nerves then convert these vibrations into electrical signals that your brain interprets as sound.
Although humans can hear sound ranges from roughly 20 Hz to 20,000 Hz, human hearing does not respond equally well at all frequencies.
For example, if a low-frequency hum and a higher-pitched bird have the same loudness, you will actually perceive the hum to be quieter than the bird. Generally speaking, the human ear is more sensitive to mid frequencies than low or high pitches. Researchers think this may be due to evolutionary factors.
Most people don’t know that hearing sensitivity varies, and frankly, they never need to consider this fact; it’s just how people hear it. But headphone engineers definitely need to consider how human perception differs from pure physics.
How do headphones work?
Headphones—both larger varieties that fit over your ears and small earbuds—are just small speakers. Simply put, speakers do the opposite of what your ear does: They convert electrical signals from your phone, record player, or computer into vibrations in the air.
Most speakers consist of four components: a permanent magnet, a coil of wire that moves back and forth around that magnet, a diaphragm that pushes air, and a suspension that holds the diaphragm.
Electromagnetism states that when a wire is wrapped around a magnet and the current in the wire changes, the magnetic field around the wire changes proportionally. When the electrical signal from a song or podcast passes through the wires inside a headset, it changes the current and moves the magnet. The magnet then moves the diaphragm (kind of like a piston) in and out, pushing and compressing the air, creating pulses of high pressure and low pressure. This is the music you hear.
Ideally, a speaker perfectly converts the electrical signals of the input into sound representations. But the real physical world has its limitations. Factors like the size and material of the magnet and diaphragm all prevent the speaker from perfectly matching its output to its input. This causes distortion and some frequencies to become louder or softer than the original.
While no headphone can reproduce the signal perfectly, there are infinite different ways you can choose to distort that signal. The reason two equally expensive headphones sound or feel different is because they distort things in different ways. When engineers create new headphones, they need to consider not only how human hearing distorts sound, but also the physical limitations of any speaker.
Listener preference
If all the hassle of ears and speakers weren’t enough, the listeners themselves also play a big role in deciding what a “good” headphone is. Factors such as age, experience, culture, and musical genre preference influence what type of frequency distortion someone prefers. Headphones are as much a matter of personal taste as anything else.
For example, some people prefer bass-heavy headphones for hip-hop music, while classical music listeners may want less frequency distortion. But music or recreational listening isn’t the only thing to consider. Headphones for the hearing impaired can emphasize frequencies between approximately 1,000 Hz and 5,000 Hz, helping to make speech more understandable.
Of course, you can play a hip-hop song with headphones designed for the hearing impaired, but most people would agree that the results won’t be very good. Making sure the headphones you choose are suitable for how you will use them goes a long way in determining what will sound good.
Ultimately, the science of headphone design, the art of creators, and the human experience all intersect to create the perception of “good” headphones. Despite all these moving parts, there’s a foolproof way to tell when headphones are good: pick a good song and put on a pair! Because when all the features come together, a good pair of headphones can give you the opportunity to transform with sound.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and authoritative analysis to help you understand our complex world. Written by: Timothy Hsu, IUPUI
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Timothy Hsu is a member of the Acoustical Society of America and a board member of the Indiana Chapter of the Audio Engineering Society.