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. 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 with the spider portion of the cone suspension, and with the cone surround at the wide end. These midranges resemble small woofers. A dome is a usually spherical section with both suspension and voice coil located at the outer edge of the dome. These midranges resemble large dome tweeters. A very few midranges are electrostatic loudspeakers, Heil drivers, planar magnetic drivers, or ribbon drivers.
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[edit] Materials
The most common material used in midrange cone construction is paper, often treated with various impregnating and/or surface-applied polymers or resins in order to improve reliability, longevity and vibrational damping. Other materials often used are other paper-like materials made from plant fibers, plastics such as polypropylene or bextrene, special fabrics, woven Kevlar, carbon fiber, light metal alloys based on aluminium, magnesium or titanium, ceramic etc.
[edit] Installation issues
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 crossover circuitry which is required for best performance of the speaker system. Crossovers can be either passive (ie, only capacitors, inductors, and resistors) and after the power amplifier or active (dividing the signal between the drivers before sending it to a power amplifier for each driver), with active crossovers being more expensive, but capable of better performance. Most crossovers are passive and come after a single full range power amplifier.
As well, placement of the midrange (and tweeter) drivers on the enclosure baffle is significant, depending on the size of the cabinet, the crossover frequency (low-mid or mid-high), the material surrounding the midrange and tweeter drivers on the baffle, and the front-to-back location of each driver's acoustic center with respect to the others. Together with grills or covers (if any), each of these aspects affect the performance of both midrange and tweeter drivers and so the loudspeaker system as a whole.
A term often used in design circles is the baffle step effect. Baffle step is the result of different dispersion effects for different frequencies. Low frequencies tend to have a 4 pi spherical radiation but high frequencies usually perform a 2 pi hemispherical radiation. Different acoustical loads are presented to the loudspeaker, and the result is a loss of about 6dB's in the bass region.
Some manufacturers mount midrange drivers on their own small enclosures, so as to isolate them from the backwave of a larger woofer and to increase the QTC of the midrange system for better transient response in the lower section of the related frequencies.
[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 any discrepancies from faithful reproduction will be most easily be observed. It is therefore paramount that a midrange driver of good quality be capable of low-distortion reproduction.
