Mid-range speaker
From Wikipedia, the free encyclopedia
A loudspeaker driver that produces the frequency range from approximately 300–5000 hertz is known as a mid-range driver. They are also called, less commonly, squawkers.
Midrange drivers are usually electro-dynamic cone types or, less commonly, electro-dynamic dome types, or compression horn drivers.
The diaphragm of a cone speaker is a truncated cone, with the voice coil attached at the narrow end, along with the rear suspension spider (damper), and with the cone surround at the wider end. Cone type midranges resemble small woofers. Midrange domes are typically a spherical section with a single suspension and the voice coil located at the periphery. These dome midranges resemble large dome tweeters. A very few midranges are horn drivers, electrostatic loudspeakers, Heil drivers, planar magnetic drivers, or ribbon drivers.
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[edit] Materials
The most common material used for midrange cones is paper, occasionallty 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.
[edit] Installation issues
The capabilities and limitations of the drivers employed above and below the midrange driver, as well as the midrange itself, influence the choice of crossover frequencies and the slope of the filters. The dramatic majority of speaker systems use passive crossover networks, constructed of capacitors, inductors, and resistors to split the signal after it has been amplified. A select few hi-fi and some professional speaker systems require electronic crossovers, with active circuitry to split the signal before it is amplified, a technique called bi-amping or tri-amping.
Placement of the midrange (and tweeter) drivers on the enclosure baffle significantly effects the output of the driver, and the material surrounding the midrange and tweeter drivers on the baffle may promote or inhibit re-radiated energy from the baffle face, further influencing the output. Grilles, especially those with structural frames, can further modify the output of the entire speaker system.
A term often used in design circles is the baffle step effect. Baffle step is the result of different dispersion patterns at different frequencies. Lower frequencies radiate essentially omnidirectionally (or in a 4-pi spherical pattern), whereas higher frequencies radiate in a more restricted pattern, termed 2-pi, pi or 1/2-pi. At the baffle step frequency, the same quantity of energy is radiated into approximately half the acoustic space, raising the perceived level for listeners within that defined area. As the frequency increases further, the dispersion pattern continues to narrow, and may become quite directional. At the upper-end of the audible range (above 10kHz) radiation may be less than 0.1-pi.
Some manufacturers mount midrange drivers into their own small enclosures, isolating them from the air pressure generated by the woofer. These enclosures, especially if they are very small, can increase the Qtc of the midrange system, degrading transient response, in exchange for increased output at the lower end of the midrange drivers range.
[edit] Role
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.
