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Woofer
(Subwoofer)
The bass and lower midrange sounds are reproduced by the woofer. To operate efficiently,
a woofer's cone should be made of material that is stiff, yet lightweight. Cones
made of polymers, polypropylene, light metals, or poly mixed with other materials
including carbon strands and metals, provide excellent sound, and stand up to
the heat, cold and moisture that car speakers face daily. Paper cones treated
for moisture resistance also do a good job, and are usually very efficient. For
car usage, untreated cones should be avoided.
The
term "Subwoofer" came into common parlance as a result of the need for
marketing departments to boost the "heavy hitting" image of their woofer
products. Most such subwoofers are more dependent on the accompanying electronics
than on the woofer itself. It was a campaign so successful, it is now as difficult
to find a woofer as it is to find a "regular strength" antacid tablet.
But as far as describing a particular type of Driver, the term is virtually worthless.
The ludicrous extent to which the trend has gone is illustrated in the recent
appearance of 4 inch "subwoofers."
Study the ratings, specifications,
and construction of any woofer you are considering, to see if will be appropriate
for your system. In constructing your system, remember to start with the goal
first, then the woofer and enclosure, and finally, the amplifier. Everything must
work together, and fit together as one coherent system, if you are to be successful.
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GLOSSARY
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SPEAKERS
Choosing
Speakers
How Speakers
Work
What's A Woofer?
What's A Midrange?
What's A Tweeter?
What
Are
Two-Way,
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Dual-Cone, Dual-Voice-Coil & Full-Range Speakers?
Understanding Theile/Small Parameters
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Right Tools For The Job
Woofers are loudspeakers designed to reproduce the lowest frequencies, or bass end of the audible sound spectrum. They may be anywhere from 4" in diameter all the way up to huge 36" giants meant for highly specialized scientific purposes. For most consumer purposes however, sizes are pretty much standardized at 4, 5, 6, 6.5, 8, 10, 12, 15, and 18 inches, with the 6.5 to 12 inch sizes being the most popular. For a general discussion of speaker operating principles see How Speakers Work.
Because
woofers are specialized reproducers, their design maximizes their
potential for reproducing the lowest frequency. Thus they will have
cones that are suspended in such a way as to promote the maximum back
and forth motion, called XMAX. Middle frequencies by contrast, have
smaller cones and less excursion, or cone travel. Tweeters have cones,
domes, or diaphragms that may seem practically motionless. Even so,
they can produce sound in their frequency range that is just as powerful
(and piercing) as their larger siblings.
Woofer cones must move in and out with the longest possible extension
because sound waves get longer as they get lower in frequency. Current
technology provides us with stiff and rigid cone materials such as
Polypropylene, Carbon and Polymer Laminates that maintain their shape
under stress, resist moisture, and are very light. The cone works
as a piston to compress and alternatively evacuate large masses of
air. To do this most effectively, the woofer must be connected to
an amplifier that produces the high amplitude waveforms that can produce
this motion. Because such signals require considerable electrical
power behind them to control the cone movement, the highest power
available is needed strictly for bass reproduction. Similar levels
in the midrange and high frequency areas require comparatively little
power for the same apparent loudness, all other things being equal.
Because of the powerful dynamic motions of the woofer cone, the frame or basket is often cast in a heavy metal to reduce the tendency for the speaker to "ring" at certain resonant frequencies. This arrangement also allows for the most precise alignment of the voice coil within the magnetic field and is particularly useful in speakers at or greater than 15" in diameter. In the larger drivers, after years spent resisting the tug of gravity, there is a tendency for the heavy magnet to be pulled out of alignment on the stamped frames of the larger sizes. This is of little practical concern with 12" and smaller woofers.
High
power woofers often have dual voice coils in vertical arrangement
on the cylindrical former. These allow different impedance configurations
to be used. With two 4 ohm coils in two woofers, a parallel circuit
can be used that creates a total mono impedance of 1 ohm. This is
a very efficient arrangement to transfer energy from a compatible
amplifier.
Magnetic structure design is fairly standardized with pole pieces
constructed to put a concentrated magnetic field around the voice
coil or coils. Over the past 30 years, the magnetic materials used
have changed considerably to permit ever-larger concentrations of
magnetic energy rated in "Gauss" to be created from smaller quantities
of lighter compounds. Coupled with the use of Kapton multiwound coils
and more powerful amplifiers, speakers - when designed with even a
modicum of commitment to high fidelity - can much more easily achieve
that end.
For
speakers to truly work well and achieve their maximum audio potential,
they must be housed in an appropriate enclosure. Indeed without some
elementary means of preventing the front radiated wave from interacting
with the back wave, no bass would be heard at all. This is simply
because the two waves are precisely 180 degrees out of phase with
each other and cancel out when they meet. For more on this important
subject, see SPEAKER BOXES AND ENCLOSURES.
Check
our Easy selection System
See
our high power Woofer Selector
Here.
Once you have selected a woofer or two, go to the amp selector to
Find a Compatible Amplifier
Here
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