Personal phones FAQ
Types of headphones
Two terms exist in the English language: Headphone, which imply usual headphones set over the head and Earphone, which imply miniature oscillators set in the ear conches or inserted directly into the ear canal.
Besides special headphones are singled out intended for high quality monitoring phonograms: full-size Monitors and In-Ear Monitors (IEM)
Types of oscillators
Most of о headphones are designed on the basis of the dynamic oscillator (or dynamic). It is the most popular kind of oscillator with a copper wire coil placed in a round magnetic space (between two poles of a magnet). It vibrates at a sound frequency thus activating a thin lavsan membrane, which reproduces the sound. The advantages of such oscillator are: high sound pressure, wide frequency range, simplicity and low price. The disadvantages are: rather high non-linear distortions caused by deformations of the membrane.
In isodynamic (or orthodynamic) oscillator a coil is applied as a thin spiral-formed layer of foil on a thin plastic film. This film is placed between two rows of magnets so that electromagnetic induction forces move the film. As the flat coil is applied uniformly over the total surface of the membrane, the motive force acts uniformly on the whole membrane thus excluding any deformation. Therefore such oscillators feature very low distortions, high accuracy of playback however narrower frequency range and lower sound pressure as compared with dynamical oscillators.
Electrostatic oscillator — a very rare representative in the world of headphones. Its design is based on a metal-plated membrane, placed between two metal nets. A very high polarization voltage is supplied to the membrane and the nets, so that the membrane is drawn to one or the other net thus generating a sound wave. Acoustic characteristics of such oscillators are similar to those of isodynamic oscillators but with lower distortions. However one of the main disadvantages of these devices is the need in special amplifiers to generate polarization voltage within the range of hundreds and even thousands Volts.
"Balanced Armature” oscillators. This type of oscillators exists since twenties of the recent century, but it was used mainly as hearing aids. The main component of this oscillator is a U-shaped metal plate, one end of which is placed in the magnetic field of the coil and the other end is fixed rigidly. The non-fixed end of the plate actuates the membrane through a thin needle. The membrane is made of a rigid material and is not subject to deformation. The advantages of such design are low level of distortions, high response, high sound pressure, miniature size. The disadvantages are: high irregularity of the frequency characteristic, narrow frequency range and a very high price. Two disadvantages out of the three are avoided by manufacturers by making in-ear headphones with several oscillators, allotting them various sections of the frequency range. As a result miniature “monsters” with built-in filters appear in the market with 2 – 10 oscillators at incredibly high prices. There is a special market of “customs” – in-ear headphones, custom made by the cast of the ear canal and the ear conch of the customer.
Acoustic design of headphones
Two items are important in the design of full-size headphones: the type of the ear cup (the embouchure) and the level of isolation from external noises.
As to the type of embouchures, headphones are divided into supra-aural and circum-aural models. The term supra-aural means "directly on the ear” (a pad), а circum-aural - "round the ear" (a roller).
As to the level of isolation from external noises headphones are divided into open-back and closed-back models. The open-back headphones are practically free from spurious overtones of the shell, but certain bass cuts and substantial penetration of external noises are present. Open-back headphones often provide more spatial sound than closed-back ones. At high volume open-back headphones emit sound outside, which may disturb people surrounding you. Closed-back headphones suppress penetration of sounds from outside and propagation of sound into the surrounding space.
In-ear headphonesи are mainly of closed-back design and they provide perfect isolation from external noises due to application of soft silicone or foam embouchures that seal the ear canal.
Types of cables
As to the type of connection cables are divided into removable and fixed. Removable cables are connected directly to headphones by means of adapters.
As to the form of cables they are divided into straight and twisted. Straight cables are usually used among amateurs, twisted cables – among professionals. The advantage of twisted cables is that they occupy less space but if necessary they can be extended to a distance up to 3 m.
Cables may be fitted with 3.5 mm (mini-jack) adapters, which are suitable for portable players or with 6.3 mm adapters for fixed professional equipment. In some cases cables with 3.5 mm adapters are fitted with a 6.3 mm connector.
Frequency Response (or amplitude-frequency response –AFR).
This parameter characterizes the level of bass tones and high frequencies that can be replayed and reflects non-uniformity of the frequency response within the total frequency range.
The range of frequencies is usually reflected until a certain drop at highest and lowest frequencies is reached. However manufacturers never specify non-uniformity of the frequency response nor the drop of level at the margins of the range, which in some cases may vary drastically. Absence of strict requirements to description of technical characteristics of headphones resulted in the fact that the frequency characteristic declared of cheap in-ear headphones can be the same and even better than that of expensive full-sized studio headphones.
Resistance and Impedance
Sound coils of the dynamic are defined by two main characteristics: Resistance (Re) and Impedance (Z).
Resistance (Re) – is DC resistance of the coil, which is determined at a frequency close to 0Hz or is measured directly by the ohmmeter. This parameter has practically nothing to do with the sound of headphones.
Impedance (Z) – total resistance of the sound coil at a certain sound frequency (according to standards it is measured at a frequency of 1000 Hz). Total resistance is the sum of the resistive and reactive components, so the level of resistance depends on frequency, at which it is measured and characterizes impedance—frequency response (IFR). This parameter can influence substantially on AFR of the output signal of the amplifier distorting the tonal balance.
Manufacturers of headphones specify any of these parameters often embarrassing their customers. You must read attentively, which of the said parameters is specified in technical characteristics to decide if the headphones suit you or not. For portable equipment headphones with low resistance (16-32 Ohms) suit better. Such headphones can provide sufficient volume though with greater distortions, which are not very important in the street. For high class fixed equipment high-ohmic headphones (up to 600 Ohm) are preferable.
Sensitivity
This parameter shows what sound pressure can be developed by the oscillator when activated by a standard signal. The higher is the parameter the higher will be the volume of your headphones and the more fine musical nuances can be replayed. As a rule armature oscillators feature highest sensitivity and isodynamic oscillators –lowest sensitivity.
Output
Three kinds of output are identified: nominal, rated and peak output.
Nominal output — the output, at which all other parameters correspond to the values specified in the technical description.
Rated (sinusoidal) output —the output, at which the oscillator can work during a long period of time with a real musical signal without any physical damage. Usually this value is 2-3 times higher than the value of nominal output.
Peak (instantaneous) output — a short-term output, at which the oscillator can remain efficient. Exceeding the peak output or maintaining this output during a long period of time usually results in mechanical or technical destruction of the oscillator.