
Highs
are reproduced by the tweeter, a small driver separate in many systems, but
mounted in front of woofer cones in multidriver 2 and 3 way car speakers.
Tweeters provide the sizzle and sibilance that give a more lifelike sense
of presence to the experience of music. They come in three common types:
Cones, Domes, and horns. Tweeters usually do not require very much power
to create relatively loud sound. High frequency wavelengths are quite small
and only a few watts can generate piercing levels of sound. Compare the tweeter
whose radiating surface seems almost rigid, to a typical woofer where the
cone may move up to 2 inches.
Cone
tweeters are efficient and the most economical. They have a limited
dispersion pattern.
Dome
tweeters - the type found in
most home speakers - have a more linear response and are more accurate. They
also have a much wider dispersion pattern than any other type. Some domes
are made of metals like neodymium or titanium that yield extended high frequency
response. Others are made of Mylar, or a fine cloth like silk for a less
extended but somewhat more linear, smoother sound. Some are made from a combination
of materials.
Horn
Tweeters are powered either by a dynamic (magnet & coil) diaphragm,
or by a Piezo driver. They are the most powerful high frequency emitter but
more directional, and may lack the extended range of the domes.
A typical
car system might consist of a woofer in a box in the rear, midranges at the
side and tweeters mounted on or in the dash panel. Here are some more detailed
descriptions of the various types and aspects of tweeters.
Diaphragm
This term describes the sound-producing element in a tweeter or horn
and is the surface that produces the sound you actually hear. The motor that
drives it can be any of several technologies including Piezo, conventional
dynamic, or ribbon types. See below for a description of each type. Diaphragms
do not produce bass and low midrange frequencies well, so they are not usually
found in those applications.
Dispersion
The extent to which a sound emitter yields acoustic radiation over a given
area, dispersion is a particular concern in tweeters whose portion of the
audio spectrum has a much more directional character than woofers. Many
horn tweeters, while very energetic, have a more limited area of dispersion
within which their effect can be fully perceived. Generally, dome tweeters
can be heard over a much wider area, all other factors being equal.

Dome
Tweeters
Tweeters are of several different types; cones, horns and domes being the
most popular. Dome types are heavily favored in many standard applications.
They are efficient, and have low Distortion
and wide dispersion. There is a choice between hard and soft dome materials,
but all have relatively low mass and high power handling capabilities.
Hard
Dome Tweeter
A characteristic of some Dome tweeters in which the dome is made of some
light, hard metal such as neodymium, and titanium as well as some of the
more rigid plastic compounds. The differences in reproduction between hard
ad soft dome tweeters are present, but very subtle. The essential difference
is in the higher frequencies that are often reproduced by hard domes, up
to 25kHz or more. Since many people tend to have acoustic sensitivity that
is sharply reduced or rolls off at 12 to 15 kHz, this may not be an advantage.
Silk
Dome Tweeter
Dome tweeters in which the dome is composed of a treated soft silk like material.
This is a design that is much less susceptible to mechanical deformation,
and yet yields a fairly smooth response over the extent of its range.
Piezo
Tweeter
A tweeter whose motor is simply a crystal of Piezo material through which
the signal current flows. The crystal lattice responds to this by bending
in proportion to the Amplitude and frequency of the incoming signal. Piezo
tweeters are very efficient drivers and are relatively inexpensive. They
come in a large variety of designs and radiators. As
a high impedance device, no crossover is needed in most cases.
Horn
Tweeter
A driver consisting of a relatively small emitter at the apex of a curvilinear
or exponential horn. This is an effective system for radiating high frequencies
in a variety of situations. The size and shape of the horn will usually dictate
the pattern and use of the driver. Long horns with narrow apertures, tend
to have the narrowest radiation pattern, and are very useful in large listening
rooms, especially where highly directional effects, such as surround sound
requires, are desired. Shallower versions, with wider radiation patterns,
have more general applications, especially in car stereo applications where
a wider field of coverage is desired, along with a robust driver that can
withstand severe environments. In such situations, a Piezo driven emitter
(driver) is highly desirable for its ability to handle high-energy inputs
on a variable basis.
Bullet
Horn Tweeter
A type of Dome tweeter in which the radiator has a large passive, bullet-shaped
device above its center that extends the nominal dispersion angle of the
sound so that it covers a greater area with a relatively small driver. The
illustration in the center of this page is an example.
Super
Tweeter
A driver constructed to reproduce the highest possible frequencies from
roughly 10 kHz to well beyond the usual threshold of audibility, 25 kHz
and up. While most standard Tweeters can do an excellent job right up to
16 or 20 kHz, these units deliver the most extreme parts of the upper range
for those fortunate (or not) few, who can actually hear them.
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