Large headphones blend physique, anatomy and psychology

Helmet designers must strike a balance between scientific limits and human preferences.

What you like to listen to is also important in choosing the right pair.

Between music, podcasts, games, and the limitless supply of online content, most people spending hours a week wearing headphones. You might be 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 teacher of music technology that studies acoustics. My work studies the intersection between the scientist, artistic and subjective human elements of his. Choosing the right helmet involves considering all three aspects, so what makes a great pair?

Sound wave diagram

Sound is simply a series of areas of low and high pressure where air molecules, represented by small dots, compress or move apart. Credit: Pluke / WikimediaCommons

What is sound really?

In physics, sound is made up of air vibrations made up of a series of areas of high and low pressure. These are the cycles of a sound wave.

Count the number of cycles that occur per second determines the frequency, or pitch, of the sound. Higher frequencies mean higher pitches. Scientists describe frequencies in hertz, so 500 Hz sound goes through 500 full cycles of low and high pressure per second.

The intensity 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 transform an electrical audio signal into those cycles of high and low pressure that our ears interpret as sound.

Ear anatomy

The human ear is a complex system that transforms vibrations in the air into electrical signals that go to the brain. Credits: Iain / WikimediaCommons, CC BY-SA

Human ear

Human ears are incredible sensors. The average person can hear a wide range of pitches and different volume levels. So how does the ear work?

As sound enters your ear, your eardrum translates the vibrations of the air into mechanical vibrations of the tiny bones of the middle ear. These mechanical vibrations become fluid vibrations in your inner ear. Sensitive nerves then transform these vibrations into electrical signals that your brain interprets as sound.

Although people can hear a range of pitches from around 20Hz to 20,000Hz, human hearing does not respond equally well to all frequencies.

For example, if a low-frequency roar and a higher-pitched bird have the same volume, you will actually perceive the roar to be quieter than the bird. Generally speaking, the human ear is more sensitive to medium frequencies than to low or high frequencies. Researchers believe it may be due to changing factors.

Most people don’t know that hearing sensitivity varies and, frankly, they would never need to consider this phenomenon – it’s just the way people hear. But helmet engineers absolutely need to consider how human perception differs from pure physics.

Speaker design

The loudspeakers are basically made up of four components, a magnet (1), a coiled wire (2), a spring or suspension (3) and a diaphragm (4). Credits: Svjo / WkimediaCommons, CC BY-SA

How do the headphones work ?

Headphones – both the larger varieties that sit on your ears as well as the smaller headphones – are just small speakers. Simply put, speakers do the opposite of your ear – they convert the electrical signals from your phone, record player, or computer into vibrations in the air.

Most speakers are made up of four components: a stationary magnet, a coil of wire that moves back and forth around this magnet, a diaphragm that pushes air, and a suspension that holds the diaphragm.

Electromagnetism indicates that when a wire is wrapped around a magnet and the current in the wire changes, the the magnetic field around the wire changes proportionally. When the electrical signal from a song or podcast passes through the wires on headphones, it changes the current and moves the magnet. The magnet then moves the diaphragm in and out – much like a piston – pushing and compressing the air, creating high and low pressure pulses. It’s the music you hear.

Ideally, a loudspeaker would perfectly convert the electrical signals from the input into sound representations. However, the real physical world has limits. Things like the size and material of the magnet and diaphragm all prevent a speaker from matching its output perfectly to its input. This results in distortion and some frequencies are louder or softer than the original.

While no headphones can perfectly recreate the signal, there are endless ways you can choose to distort that signal. The reason two equally expensive headphones can sound or feel different is that they distort things in different ways. When engineers build new headphones, they not only need to consider how human hearing distorts sound, but also the physical limitations of any speaker.

Listening to headphones

What you like to listen to and how you like the sound of your headphones play a huge role in determining what makes a “good” pair of headphones.

Listener preference

If all the complications of ears and speakers weren’t enough, listeners themselves play a huge role in deciding what makes a “good” pair of headphones. Aspects such as age, experience, culture and musical genre preference all affect what kind of frequency distortion someone will prefer. Headphones are just as much a matter of personal taste like anything else.

For example, some people prefer heavy bass headphones for hip-hop music, while classical music listeners may want less frequency distortion. But music or recreational listening aren’t the only things to consider. Headphones for the hearing impaired may show frequencies of around 1000 Hz to 5000 Hz because it helps to make the speech more understandable.

You can certainly play a hip-hop song with headphones designed for the hearing impaired, but most people will agree that the results won’t be very good. Making sure the headphones you choose match how you are going to use them goes a long way in determining what will sound good.

Ultimately, the science of headphone design, the artistry of content creators, and the human experience all intersect to form the perception of “good” headphones. Despite all of these touching pieces, there’s one sure-fire way to tell when headphones are good: pick a great song and put on a pair! Because when all the attributes align, a good pair of headphones can give you the opportunity to be transformed by sound.

Written by Timothy Hsu, Assistant Professor of Music and Art Technology, IUPUI.

This article first appeared in The conversation.

Comments are closed.