How the sound signature of headphones changes your perception of music

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The sound signature can vary greatly from one helmet to another. However, this data is quite easy to establish thanks to the frequency response curve. At a glance, it allows you to roughly guess what a pair of headphones sounds like, and therefore whether you’ll like listening to those headphones or earphones. Bass, midrange, treble, fundamental frequencies and harmonics, this is what you need to know to appreciate the signature of headphones or earphones.

focal baths
Focal Bathys for illustration // Source: Tristan Jacquel for Frandroid

The sound signature of a speaker, headphones or headphones is always complex to describe, since its characteristics are numerous and the result of the personal impressions of the listener. However, there is a simple way to materialize a sound signature, through a graphical representation: it is the frequency response curve.

Beforehand, it is important to remember that the sound we hear is nothing more than the vibrations of the air around us, pressurized by a mechanical force. The higher the pitch of a sound, the more vibrations there are. To measure them, we use a unit of frequency: the Hertz. A sound with a frequency of 82 Hz, the vibration of the thickest string on a guitar, is repeated 82 times per second.

The range of audible frequencies of the human ear.

Our ear is capable of hearing a spectrum of frequencies between approximately 20 Hz and 20,000 Hz, with 20 Hz corresponding to the lowest sound and 20,000 Hz to the highest sound. Below and above, we will talk about infrasound and ultrasound, inaudible to the human ear. In order to easily refer to the different portions of this sound spectrum, it is customary to divide it into three frequency ranges: these are the famous low, medium and high registers. The low register commonly covers the range from 20Hz to 200Hzthe middle record that from 200Hz to 5000Hz and the high register from 5000Hz to 20,000Hz.

Apple AirPods 3 // Source: Frandroid

To refer more precisely to audible frequencies, the sound spectrum is divided into octave bands. These bands are designated by their center frequency: the first covers the low frequencies from 25 to 40 Hz, with 31.5 Hz in between. Throughout the audible spectrum, from 20 Hz to 20,000 Hz, we thus have the octave bands of 31.5 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz and 16kHz.

These are often the bands offered in the equalizers of headset and Bluetooth headset add-on apps, at least when the equalizers allow 10 frequency ranges to be handled; sometimes it is much less.

The frequencies used for different instruments, from 20 to 2000 Hz // Source: Frandroid

To know what each frequency range corresponds to, we can resort to different musical instruments, as we have seen previously. Each instrument produces sounds of variable frequencies, depending on the note that is played and each one corresponds to a so-called fundamental frequency, expressed in Hertz.

However, as it unfolds in the air, the played note will be enriched with additional frequencies called harmonics. To understand the principle, imagine the impact of a raindrop on the surface of the water. The impact produces a first wave (the fundamental frequency) and then a series of smaller and smaller waves (the harmonic frequencies). In air, the sound wave develops in the same way and the fundamental frequency of a plucked string is accompanied by harmonic frequencies whose value is doubled up to six times.

The frequency response of headphones and earphones.

Headphone and earphone transducers are designed to reproduce the widest possible frequency range. We talk about frequency response or bandwidth. To express it, manufacturers indicate the lowest frequency reproduced, as well as the highest, very often from 20 Hz (low frequency) to 20,000 Hz (high frequency). However, this information doesn’t tell you much, because it doesn’t let you know if all the notes are played with the same intensity or, if not, what the level differences are. But this is what matters to understand the tonal signature of headphones, speakers or headphones.

To accurately know the frequency response of a headset or headphones, it is necessary to perform a measurement. For this, we use a dummy equipped with calibrated microphones. A helmet is placed on the mannequin’s head, while headphones are inserted into its ears (where the microphones are located).

response curve
A W-shaped headphone response curve, with three peaks identified in parts of the low, mid, and high registers.

The response curve above has a W profile, this means that each of the three frequency registers is played with a volume peak. In this case, the low-bass (30 to 40 Hz) is ahead at 90 dB, as are the high-mids (2500 to 4500 Hz) at 93 dB and the extreme treble at 97 dB. An earphone with such a curve will produce a balanced and generous, often driving sound, without losing detail.

response curve
A falling response curve (treble kickback).

The response curve above is said to be downward, with a fairly significant rollback from the high frequencies. This type of curve generally results in dry, even stark playback, especially when the bass is also delayed.

V, W or descending curve, you understand, we often use the shape of the curve to qualify it.

What is a good response curve?

We can legitimately think that the ideal response curve for a loudspeaker, headphones or earphones must be linear, that is to say that the restoration of all frequencies must be done at an equivalent volume, that is to say with as flat a curve as possible. possible. However, this is neither possible nor desirable. A response curve is, by definition, uneven, because the sound before reaching the heart of the ear encounters various obstacles (shell and mold for an earphone, listening room surfaces for a loudspeaker, pinna, ear canal) and, therefore, it is disturbed. . Additionally, all loudspeakers have their own mechanical specifics that contribute colorations (peaks or valleys) to certain parts of the audio spectrum. In short, all observable accidents in the above curves are unavoidable.

mid frequencies are strongly accentuated

bathroom, a linear curve is not desirable, because our hearing is more sensitive to certain frequencies than others. Specifically, low frequencies and high frequencies are perceived below their real intensity and this phenomenon is even more marked when the music is of low intensity. On the other hand, the mid frequencies, particularly those between 2 and 4 kHz, are strongly emphasized. The explanation is simple: the ear canal naturally vibrates with these frequencies and mechanically amplifies them.

The Sony WH-1000XM4 is not very generous in the upper mids

Therefore, a response curve that gives a sense of relative balance should be generous in the low and high frequencies, but moderate in the midrange (especially in the upper midrange, 2 to 4 kHz). This is called a physiological curve. The yellow curved Sony WH-1000XM4 above is a good example.

Harman's curve
The Harman curve // ​​Source: Harman

That is why many specialists recommend not a flat curve, but a sound close to the “Harman” curve, named after the Harman Kardon group, which is known to be particularly pleasant to the ear.

The equalizer to correct the response curve of headphones

If you don’t like the sound signature of the headphones you’re using, it’s possible to change it quite easily. Most Bluetooth headsets or headphones work with an app, which probably includes an equalizer. To effectively correct the sound from Bluetooth headphones, this app should be preferred as it directly controls the processor of the headphones.

power amp equalizer
Poweramp equalizer android app allows you to correct the sound signature of headphones or earphones.

Otherwise, you have to resort to a third-party application to equalize the sound on the smartphone. There are many of them and the best ones are the ones that offer more frequencies of adjustment. We can, for example, mention the music applications you use daily, or directly the audio settings of your smartphone.

Finally, keep in mind that an equalizer makes it possible to correct minor glitches, but not to transfigure the behavior of headphones or earphones.

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