Midrange
Speakers
The
midrange of the sound spectrum is of critical importance, as this is where
the heart of the music lies. Vocals and instruments should sound natural
and detailed, not too prominent or recessed, nor too bright or too dull.
A midrange speaker is usually much smaller than a woofer, but with a radiating
surface area greater than the typical tweeter. It reproduces the mid frequency
range from approximately 300 to 5000
Hertz.
This operating range can vary considerably from one driver to the next,
thus giving the system designer more flexibility in choosing crossover
points for the other drivers. Since the midrange, like the tweeter, is
designed to produce optimum response with much less power than is required
for the woofers, the magnet structure is usually quite a bit smaller,
and the rated power handling is also much less. But since it must be isolated
from the direct current of the amplifier by the crossover circuitry, this
should not effect the speakers over-all power handling performance.
Dispersion
- the extent to which a sound emitter yields acoustic radiation over a
given area - is a particular concern in midrange speakers, whose portion
of the audio spectrum has a much more directional character than woofers.
Midrange drivers mounted in enclosures with woofers will usually have
a closed back design, to prevent interference from the woofer's internal
backwave. Such interference is usually a source of intermodulation (IM)
distortion.
In
a typical car system you might see a woofer in a box in the rear, tweeters
mounted on the dash panel, and midrange speakers in the side or door panels.
In surround applications, midrange and tweeter drivers carry all the directional
source information.
Three-way
or triaxial speakers take the separate woofer and tweeter from a two-way
design and add a dedicated midrange
driver
.
This arrangement can produce a more uniform response, depending on how
well it is designed. With the inclusion of a midrange driver in any system,
the design of the crossover must be more precise.