A loudspeaker driver that produces the frequency range from approximately 300–5000 hertz is known as a mid-range.
Midrange drivers are usually cone types or, less commonly, dome types, or compression horn drivers. The radiating diaphragm of a cone midrange unit is a truncated cone, with a voice coil attached at the neck, along with the spider portion of the suspension, and with the cone surround at the wide end. Cone midranges typically resemble small woofers. The most common material used for midrange cones is paper, occasionally impregnated and/or surface-treated with polymers or resins in order to improve vibrational damping. Other midrange cone materials include plastics such as polypropylene Cobex, or Bextrene, woven Kevlar, fiberglass, carbon fiber, or light metal alloys based on aluminium, magnesium, titanium, or other alloys. The radiating surface of a dome midrange is typically a 90-degree section of a sphere, made from cloth, metal or plastic film, with its suspension and voice coil co-located at the outer edge of the dome. Most professional concert midrange drivers are compression drivers coupled to horns. A very few midranges are electrostatic drivers, planar magnetic drivers, or ribbon drivers.
A midrange driver is called upon to handle the most significant part of the audible sound spectrum, the region where the most fundamentals emitted by musical instruments and, most importantly, human voice, lie. This region contains most sounds which are the most familiar to the human ear, and where discrepancies from faithful reproduction are most easily observed. It is therefore paramount that a midrange driver of good quality be capable of low-distortion reproduction.
Most television sets and small radios have only a single midrange driver or two for stereo sound. Since, in the case of television the most important aspect is the talking, it works out well. Since the ear is most sensitive to the middle frequencies produced by a midrange the driver and amplifier can both be low power while still delivering what is perceived to be good sound both in terms of volume and quality.
Midrange drivers are usually used in three way multi driver speaker systems. There are therefore special considerations involved in the acoustic join between the midrange and both the low frequency (woofers) and the high frequency drivers (tweeters). The nature of the drivers on both sides of the midrange, and the midrange itself affect the selection of crossover frequency and slope. Nearly all crossovers are passive circuits, designed to match the characteristics of the drivers and their mounting, and are built of capacitors, inductors, and resistors. Active or 'electronic' crossovers are used in some high performance hi-fi speakers, and in professional sound reinforcement systems.
Placement of the midrange (and tweeter) drivers on the enclosure baffle significantly affects the output of the driver, and the material surrounding the midrange and tweeter drivers on the baffle can produce (or inhibit) reflections of energy from the baffle face, or other items, further influencing the output. Grilles, especially those with structural frames, can further modify the output of the entire speaker system. One of the terms used in design circles to describe some of these diffraction and reflection artifacts is the baffle step effect.
Some manufacturers mount midrange drivers in their own small enclosures, isolating them from the air pressure changes generated by the woofer. These enclosures, especially if they are very small, can increase the Qtc† of the midrange driver/enclosure combination, degrading transient response, in exchange for increased output at the lower end of the midrange driver's range.
† – Qtc is the total Q (or resonance magnification) of a particular speaker driver in a box, and it is a function of the driver's Qts (resonance magnification at its free-air resonance frequency), the driver's Vas and the enclosure's volume Vb. For example, for a sealed enclosure, Qtc = Qts√(1 + (Vas / Vb)). Given Qts and Vas, it is possible to either design a box (i.e., Vb) for a particular target Qtc, or compute the Qtc of a box of known volume Vb, for the purpose of equalisation.