| Connection cable |
| When one speaks about headphones, the emphasis is on such things as sound quality and frequency response. There is rarely any mention of the connection cable. Most Sennheiser headphones are fitted with an OFC (oxygen-free copper) cable. This ensures linear and low-loss transmission in the broad frequency spectrum of the headphones. Many Sennheiser headphones also have detachable cables, which make it very easy to replace them. |
| Contact pressure |
| The wearing comfort of a set of headphones is determined not only by its weight but also by the force with which the earpieces are pressed onto the ears. This force is given in newtons (N), whereby 1 N corresponds to the compressive force which a mass of about 100 g exerts on a solid surface. The DIN Standard 45500 Part 10 limits the maximum permissible contact force to 5 N. Values of between 1.3 and 4 N are common, although lower values apply for open headphones. Higher values can be found in the case of closed headphones. Here, a higher contact pressure is required in order to achieve sufficient sealing, which is important for the reproduction of low frequencies. |
| Ear coupling |
| A distinction is made between headphones which are worn on the external ear (supra-aural) and those which surround the ear (circumaural). Open headphones have foam ear pads that rest on the ears or ring pads that surround the ears. Closed headphones, on the other hand, nearly always have circumaural ear pads. |
| Frequency response (headphones) |
| The frequency response of a pair of headphones is given within limits defined by the manufacturer. |
| Frequency response (microphone) |
| The frequency response of a microphone is given within the limits defined by the manufacturer. In studio condenser microphones it is generally within the range of between 20 Hz and 20 kHz. |
| Impedance |
| Impedance expresses the AC resistance of a microphone or a set of headphones. It is dependent on frequency and is given at 1 kHz as the so-called nominal impedance. Impedance is measured in ohms. In recent years, an industrial standard has developed, setting the impedance of headphones at 50 or 600 ohms. Sennheiser headphones are manufactured according to this standard, thus practically ruling out connection problems. With microphones, the input impedance of the following microphone amplifier should have at least three times the value of the nominal impedance, in order to prevent it from unnecessarily attenuating the microphone signal. |
| Operating temperature |
| Gives the range of temperatures at which a unit can be operated without damage. |
| Pick-up pattern |
| Also known as polar pattern, directivity. According to their acoustic design, microphones differ in their sensitivity towards sound from different directions. Pressure microphones have a sensitivity that is largely independent of direction (omni-directional pick-up pattern). Pressure gradient microphones have the pick-up patterns wide cardioid, cardioid, super-cardioid or figure-of-eight. Interference microphones can be used to achieve a further concentration of the pick-up pattern (lobar pick-up pattern). As a special case, dummy head microphones achieve the pick-up pattern of the human ear/head (dummy head stereo). |
| Sensitivity in free field, no load (1kHz) |
| Voltage measured at the unloaded output of a microphone which is exposed to a sound pressure of 1 Pa and a frequency of 1 kHz in an anechoic chamber. |
| Storage temperature |
| Gives the range of temperatures at which a unit can be stored without damage. |
| Total harmonic distortion (THD) |
| Total harmonic distortion is a measure of non-linear harmonic distortion and is given in %. Non-linear harmonic distortions are signals which were not present in the original before the signal was converted by the headphones. These unwanted signals are caused by the diaphragm, whose movements do not precisely move in time with the electric signals that cause it to move. Unfortunately, this is a feature of all electroacoustic transducers. Although it cannot be completely eliminated, suitable steps can be taken to minimise it. However, the user is not interested in why this distortion takes place but in how great the level of distortion must be for it to become perceptible. According to the findings of several research projects, a total harmonic distortion of 1% in the frequency range of 100 to 2000 Hz is imperceptible. Below 100 Hz, the perceptibility threshold lies at 10%. |
| Transducer principle |
| Two transducer principles have become established for the conversion of electric energy into mechanical energy: electrodynamic and electrostatic transducers, whereby the latter is only to be found in audiophile systems, due to their relatively high manufacturing costs. Electrodynamic transducers basically consist of a ring-shaped permanent magnet and an oscillation coil, which is fixed to the receiver diaphragm. When an audio-frequency alternating current is passed through the oscillation coil, it is caused to vibrate in accordance with the audio-frequency alternating current, thus causing the diaphragm to vibrate in the same way. |
