by Aaron Bendich
While exploring the vast world of audio equipment, particularly hi-fi headphones, you are bound to encounter both amateur and professional reviews that make reference to esoteric-sounding terminology. It is easy to get bogged down by unfamiliar terms such as timbre, soundstage, impedance or circumaural. Even relatively familiar terms such as bass, treble and frequency may be confusing in this context if unexplained. To clear the air of these troubling or confusing terms, I’m going to run through all of the terminology you may encounter on your hunt for headphones.
Overview of the Elements of Sound
Before diving into the nitty-gritty of equipment terms, it is important to start with terms relating to sound, itself. Everything we hear in our day-to-day lives reaches us through vibrations propagated through air pressure and displacement. These vibrations vary from one another in a number of ways. The variations between sounds are the sole reason we can tell one spoken word from another, or one voice from another or a guitar from a drum. The easiest of these qualities to understand is duration, simply how long a sound is sustained. In music, this is notated as the difference between types of notes, say a quarter note and a whole note. Notated music is otherwise differentiated by pitch, commonly understood as whether a note is ‘lower’ or ‘higher’ than another note. In music these differences are reflected in the literal positioning of notes, either higher or lower. In actuality, pitch reflects the frequency of the sound being played or heard. Frequency is a measure of how many individual vibrations occur in a specific amount of time to make a given sound. Modern western musical instruments are tuned to a standard pitch of A440, which establishes an A note at 440 hertz(vibrations per second). The rest of the notes’ frequencies are established relative to that first A. Loudness or intensity is another intuitive attribute of sound. These terms account for the magnitude of a given vibration. The louder something is, the more pressure is displaced by the sound’s source. Timbre is one of the most important qualities of sound, though it is also the hardest to explain. Simply put, timbre is the quality of a sound, and it informs the listener what sort of thing produced the sound. When a guitar plays an A and a saxophone plays an A it is clear that different instruments were used. Many listeners would even be able to identify the type of instrument that produced each note. While both instruments produced a sound with the same pitch, for the same duration and even with the same loudness, some quality of the two notes was different. This, in a nutshell, is timbre. Differences in timbre are complex and not immediately apparent to most listeners, and are rather difficult to explain completely. In short, timbre is affected by a given sound’s harmonics and its envelope. Harmonics refer to the number of frequencies present in a given sound and their relation to one another. Envelope refers to the way that a given sound starts and finishes, regarding intensity. Sonic texture is similar to timbre, as it involves the quality of a sound. Texture, however, refers explicitly to the number of sound sources and their relation to one another. For example, the sound of an electric guitar and a voice has a greatly different texture from a jazz quartet due to the number of musicians. Lastly, spatial localization refers to the apparent location of a given sound based on various cues. A faint but strained voice calling your name could easily be identified as originating from far away, whereas a whisper must come from nearby. Furthermore, a sound that is louder in the right ear than left, must be originating from the right side and vice versa.
Intra-aural is a fancy way of saying in-ear. In-ear headphones go directly into the ear canal. These appeal to consumers primarily because of their portability factor. Intra-aural headphones also keep out external sound by blocking the ear canal. However, many users find in-ear headphones considerably less comfortable than the alternatives. For high quality in-ear headphones, check out Etymotic ER4XR Extended Response Earphones.
Supra-aural means on the ear. These headphones are padded and sit directly on top of the ear. These are less portable than in-ear options but considerably more portable than circumaural headphones. For great quality on-ear headphones check out Sennheiser Momentum.
Circumaural means around the ear or over the ear. These headphones surround the ear cutting out sound and often providing a higher level of comfort. These are the least portable option for headphones. However, circumaural headphones are generally the top of the line regarding audio quality. For a great pair of circumaural headphones check out the Beyerdynamic T 1.
Open back headphones do not have a sealed cup, allowing ambient sound to leak in. Many consider these headphones to have a more spatially realistic sound. Grado SR225e headphones are one of the most popular open back options!
The driver is the part of the headphone that actually converts the electrical signal to sound waves. Drivers vary in size from 8 to 50 millimeters. While the size of the driver affects the power and size of the speaker, build quality ultimately determines the sound quality. Audeze SINE headphones use unusual, high quality Planar Magnetic Drivers, check them out!
Simply put, impedance is a circuit component’s opposition to electrical current. In the case of headphones, impedance affects the amount of amplification required to produce audio. Headphones with impedance under 25 ohms are considered low impedance. These require less amplification and therefore are useful with mobile devices or other low powered audio players. Higher impedance headphones, with 25-250 ohms, require more amplification to produce loud audio. However, this higher energy requirement ensures that the speakers will not fail from being overloaded. Headphones with extremely high impedances, such as the Beyerdynamic DT 1770 with 250 ohm impedance, require a serious amount of amplification, but allow for your hi-fi amplifiers to shine.
Sound Pressure Level (SPL)
Sound Pressure Level, measured in Decibels, is used to measure sound intensity. This measure is useful for minding dangerous loudness levels. Anything above 130 dB is immediately dangerous, while 95-120 dB present a risk of hearing loss in the short term.
Sensitivity is measured in SPL/Power. Power, measured in milliwatts(mW), accounts for the rate that energy passes through a wire or other circuit component. Sensitivity comes into play mostly when using an audio system with a fixed amplification power output. A highly sensitive headphone would play a fixed high power amplifier extremely loud at a high volume and sufficiently loud but unclear at low volume. Like many of these specs, sensitivity is a balancing act, and depends primarily on the applications you are using your headphones for. However, more so than the other factors, sensitivity is somewhat dangerous, as you run the risk of playing audio at harmfully intense levels.
Frequency Response is shown as a graph of frequencies in hertz versus their loudness in decibels. The graph generally covers the entire audible range of frequencies, from 20 to 20,000 Hz. Some headphones, however, extend beyond that range which may or may not result in any meaningful difference. Testing frequency response is no easy task, as each headphone user’s ears and head are different. That being said, a pair of headphones’ advertised frequency range and response carries some meaning and can give you a general sense of the headphones’ effectiveness. Audio-Technica ATH-M50x headphones advertise an extended frequency range, which may appeal to some of you audiophiles out there!
Frequencies on the low end of the spectrum are referred to as ‘lows’ or ‘bass’. Bass frequencies range from 16 to 256 Hz. While all instruments and voices contain bass frequencies in their harmonic content, certain voices and instruments are particularly ‘bassy’ and provide the bass part of a musical composition. These instruments include the bass guitar, tuba, cello, bassoon and the lower range of the piano. Different listeners like their bass handled differently. Some prioritize the lowest range over the rest of the spectrum, insisting that the rumble of bass is the most important and engaging part of their music. Others find bass overpowering, and loud bass unrealistic. These listeners prefer headphones that de-emphasize that portion of the range and/or equalize bass down. Beats by Dre are popular for their intense bass response, check out the Beats Solo2.
As the name suggests, mids constitute the middle range of the frequency spectrum, from 256 to 2000 Hz. This range is most important for the human voice. Since this is the central portion of the spectrum, the mid frequencies account for the how we perceive the loudness of a given sound. With that in mind, be careful when boosting mids, since you may over-amplify what you are listening to and hurt your ears.
Treble constitutes the upper end of the frequency spectrum, from 2,000 to 16,000 Hz. The high end of guitars and pianos are in the treble range, as well as smaller instruments like piccolos. Terms like airy-ness, brilliance and presence are used to describe qualities of sound that come from boosting specific parts of the treble range. Treble frequencies have a powerful effect on the audibility and the finer qualities of a sound. It is important not to skimp on treble range frequencies, since they tend to add necessary detail to your audio. Fostex TH-900 MK2 headphones advertise well-defined treble, so if you’re looking for the top of the line and care about treble, check them out.
Soundstage refers to a headphone’s ability to give a sense of the spacing of instruments/sound sources as well as a sense of the room where the audio was recorded. While some headphones add nothing to the original source audio and even cause a constrained sense of the original recording’s spatial layout, others actually improve the soundstage of a recording through specially designed circuits. Sennheiser HD 700 headphones utilize a high quality build factor as well as an open back design to perform excellently at soundstage reproduction.
All headphones produce unusual and unintended harmonic artifacts when the audio is amplified past a certain threshold. The harmonic interference comes at multiples of the base frequency. A 400 Hz sound will have 800 and then 1200 Hz distortion. This distortion is measured as a percentage, and in general, headphones have less than 1% harmonic distortion.