Most music lovers use it all the time, when listening to their favourite music. But how much do you actually know about this handy listening device? If you are learning to be a music producer or audio engineer, you might find yourself relying on alternative listening devices, apart from monitor speakers. Hence, the question we will ask today is – What is a Headphone?
As usual, we will go through various important topics surrounding the subject of discussion. Understand the basic principle in a headphone’s design, and find out how it impacts a user’s listening experience. We will also take a deeper look into the various factors that will affect the performance of headphones. Can’t wait to get started? Then, let us begin!
During the early times of telephony and radio, headphones are often recognised as head-phones. They are a pair of light and small listening devices that are designed with portability in mind, and are either attached on or around the head over the listener’s ears. Since they function by converting electrical signals to sound waves, they are also known as electroacoustic transducers.
Unlike a sound system’s loudspeaker (which projects sound openly, where everyone can hear), headphones are engineered to provide ample sound isolation, allowing users to listen to audio privately. Headphones are also sometimes called earspeakers or earphones. In order to hold the speakers in place, circumaural and supra-aural types have a band which goes over the top of the head.
Another type which is known as earbuds or earphones, consists of individual units that are plugged directly into a user’s ear canal. Headphones are often used to transmit audio signals coming from various sources such as an audio amplifier, FM radio, CD player, mP3 player, smartphone, video game consoles and electronic musical instruments. Wireless bluetooth technology can also be integrated into headphones.
In an effort to facilitate a more effective audio reception without causing a nuisance to others, radio pioneers together with radio telephone and telegraph operators became the first ones to use headphones within a professional capacity. The audio quality for the early headphones were not ideal, thus, the invention of high fidelity headphones was the next natural step to be taken.
Let us now have a look at the topics we will be discussing:
- Real-world applications
- Electrical characteristics
Headphones can generally be used with most CD and DVD players, home theater systems, laptops, or portable devices (such as mp3 player, smartphone). There are also cordless headphones which do not require a cable to be connected to its source. Instead, radio or infrared signals (encoded using a radio or infrared transmission link, such as Bluetooth or Wi-Fi) are received by the headphones.
In the world of professional audio, headphones are often utilised by disc jockeys with a DJ mixer (for performance), and audio engineers (to monitor signal sources). DJs who work in radio stations also use headphones in order to monitor their own voices. However, the speakers will always be turned off to prevent acoustic feedback when talking into the microphone.
For music production applications, musicians and singers typically use headphones (in recording studios) while playing an instrument or singing along to a backing track or band. Headphones are also used in the military to monitor audio signals of various types.
Wired headphones typically use 6.35 mm (¼″) and 3.5 mm phone connectors. Take note that the larger 6.35 mm connector is normally used with “fixed location” home or professional sound systems. For most portable audio devices, the 3.5 mm connector remains the ideal choice. Adapters are also available if you want to convert between 6.35 mm and 3.5 mm connectors.
When looking for a headphone in the market, there are some factors that you need to look at. Hence, in this section, we will cover the two main electrical aspects of headphones. Do take note that, since most headphones are essentially small dynamic loudspeakers, the electrical characteristics of dynamic loudspeakers may also be applied to headphones.
Depending on the model, headphones can have high or low impedance (typically measured at 1 kHz). Low-impedance is in the range of 16 to 32 ohms and high-impedance is about 100-600 ohms. The higher the impedance a headphone has, the more voltage (at a given current) is needed to drive it, resulting in a decrease in loudness of the headphones at a given voltage.
A headphone’s impedance is a huge concern due to the output limitations of amplifiers. Most modern headphones today are driven by amplifiers, and headphones with low impedance presents a larger load. On the other hand, amplifiers are also limited in the amount of power they can supply, due to having output impedance.
The output impedance of an amplifier should be less than 1/8 that of the headphones it is driving (and ideally, as low as possible). This is to ensure an even frequency response, adequate damping factor, and undistorted sound. In the event where the amp’s output impedance is larger than the impedance of the headphones, a significantly higher distortion will be produced.
Hence, headphones with lower impedance will usually be louder, with better efficiency. However, they will also need to be powered by a higher quality amplifier. On the contrary, higher impedance headphones tend to be more accommodating towards amplifier limitations, but produces less volume for a given output level.
The measure of an earpiece’s effectiveness in converting an electrical audio signal into sound waves (audible sound), is known as a headphone’s sensitivity. It indicates a headphone’s loudness (dB) at a given electrical drive level. It is measured in decibels of sound pressure level per milliwatt (dB (SPL)/mW) or decibels of sound pressure level per volt (dB (SPL) / V).
Never use high sensitivity headphones with power amplifiers, as this will lead to alarmingly high volumes and may damage the headphones. The highest sound pressure level is usually a subjective matter, with some sources recommending a maximum of 120 dB. However, the American Occupational Safety and Health Administration advises a peak level of 85 dB(A) to prevent future hearing loss.
On the contrary, the European Union standard (EN 50332-1:2013) suggests that a warning should be issued for any volume levels above 85 dB(A), and also recommends the peak maximum volume to be at 100 dB (defined using 40–4000 Hz noise), in order to minimise the chances of an accidental hearing damage.
Based on this standard, headphones with sensitivities of 90, 100 and 110 dB (SPL)/V should only be driven by amplifiers that are incapable of anything more than 3.162, 1.0 and 0.3162 RMS volts (at maximum volume setting) respectively, to minimise the risk of hearing damage. The typical sensitivity of headphones ranges between 80 and 125 dB/mW and is often measured at 1 kHz.
That should be a good basic summary of what you need to know about headphones. There are much more technical details to discuss, however I’ll leave that to future articles.
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