Subwoofer Design
A Decade of technological improvement
By: Paul Sonoda
The basic operation of the woofer hasn’t changed since the invention of the moving coil transducer (that’s tech for speaker). Yes there have been changes in construction techniques. Of course, there has definitely been a change in materials that have allowed for stronger, more robust woofers. So the real question is has there been real technological innovations? Believe it. The last ten years have been great to car audio and woofer design. Let’s take a look.
Precision Power’s Powerclass 10” Woofer
Ten years ago, some said that 160dB barrier may never be broken. Two things happened: a retired school teacher and Precision Power. The year is 1996 and the location is Greenville, SC. Instead of making an enclosure inside of a cab, Team Gates made the passenger compartment the enclosure. The PPI Power Class woofer had two innovative aspects to its design. It was the first flat-piston type woofer offered by a major manufacturer and instead of a traditional paper of poly cone, the flat piston diaphragm was made of a sandwich construction using carbon fiber facing with a honeycomb Nomex core. The combination of extreme strength (you could punch it without denting or breaking it), light cone weight and innovative enclosure design gave Team Gates the SPL world record of a 164.8 dB. Team Gates Bronco went for three more years breaking its on world record several times including the first subwoofer to exceed 170dB.
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topGround Zero – The First High-Excursion Woofer
In 1997, a German company was working of a woofer design that would forever dominate the look of high-performance subwoofers. Inspired by the innovative Sunfire home subwoofer (brain child of Bob Carver), the Ground Zero subwoofer was the first car audio subwoofer with a high-excursion large surround design. The linear excursion of this woofer was nearly double that of any other commercially available car subwoofer. These woofers had aluminum cones and woven-in tinsel leads (wires that connect to the voice coil). This design is the starting point for all other big surround high excursion woofers.
Pioneer - The Surroundless Woofer (Patent #5,848,173)
A slightly different approach to getting more bass was Pioneers display in 1996. It was a six inch woofer with about two inches of excursion. How did they do that? They removed the one limiting component: the surround. The design utilized a cylindrical frame that incorporated a cone that moved inside the same way a piston moves inside an engine block. A seal between the diaphragm and the side of the cylindrical frame resembled a felt ring very similar to a piston ring of an engine. To date, here have been no commercial applications of this design in car audio.
Kicker – Square Woofer (Patent #6,611,604)
In 2000, Stillwater Desgins (a.k.a. Kicker) filed a patent for a rectangular or square concave diaphragm. The idea behind this design is to maximize the cone area for a given space. In SPL competitions, using round woofers leaves gaps on the mounting baffle. (Even if the woofers are nested) By using a square woofer shape, Kicker square woofers are able to increase their effective cone area by 27%. For such a simple concept, it is surprising that this had not been done before. Of course, ideas do not become obvious until someone else does it.
Different shapes
There have been other interesting shapes. Bazooka introduced triangle shaped woofers. This gives you a similar, although more complicated, ability to get more cone area out of a given mounting baffle. Two companies have introduced woofers with traditional mounting holes but different cone shapes. Xtant woofers are hexagonal and can be nested to maximize cone area on a mounting baffle. Sony introduced pentagon woofers whose shape is designed to increase cone stability. Still, the dominant woofer shape is still round.
Kicker - Replaceable Cone Assemblies (Patent #6,731,773)
Kicker’s answer for the ultimate SPL woofer resides in the Kicker Solo x18. Its design is so innovate that is was awarded a patent in May of 2004. Dual baskets are used with the larger basket and motor assembly is mounted permanently in the enclosure. A second smaller basket is designed to be replaceable with a self-aligning cone assembly. Especially beneficial in SPL Competitions, this type of configuration allows for a quick easy rebuild of a speaker between competition rounds.
JL Audio W7 Series – Patent Mania
In the world of "me too" engineering, JL
Audio's W7 has eight application patents and one design
patent.
In most "large roll surround" woofers, the
actual cone area is reduced to accommodate the huge
surround. In the W7, the surround actually goes over
the mounting flange right to the edge of the basket. (U.S. Patent #5,687,247
and #5,949,898). The OverRoll surround result is more cone area for a given
size basket. The rest of the patents can be grouped into two different areas:
structural reinforcement and thermal stability. Patents #6,496,590, #6,501,844,
and #6,118,884 refer to the cone and spider assemblies and account for the
excellent control the W7 has over its massive linear excursion (1.5 inches
peak-to-peak linear excursion to be exact). Patents #6,243,479, #D472, 891,
#6,219,431, and #6,229,902 refer to the pole piece and basket which maximizes
the thermal power handling by directing cool air more effectively and efficiently
over the voice coil.
Up front bass – Small and Thin woofer solutions
In the sound quality competitions, the illusion of upfront bass is paramount for winning competitions. There are several different companies that have developed innovative solutions to create this effect. Focal solved this solution with a small compact 5 inch subwoofer with tuned response down 38Hz. Several other companies have worked to develop thin woofer solutions so unique that each one was awarded patents. Pioneer TS-SW124D design shrinks the depth of a 12 inch woofer to a mere 4 inches. Earthquakes SWS woofers (Patent #6,863,152) are available in sizes up to 15 inches and depths ranging 1-3/4 inches to 3-1/4 inches. Even thinner, Blaupunkt has introduced the Overdrive Series (Patent #6,862,361) subwoofers that do not exceed 2 inches in depth.
MTX – The SPL Woofer of Today
What does it take to be competitive in the world of SPL today? MTX thinks they have the answer with the MTX RFL152. The RFL (RFL stand for Real something Loud) is designed to be one of the biggest and baddest woofers on the planet. This 56 pound woofer has 4.35 inches of total peak-to-peak excursion. Instead of glue, the woofer suspension is bolted to the cast basket. The cone, spider and voil coil assembly is field replaceable. All told, this woofer delivers power handling in excess of a claimed 4000 watts. A claim supported by the video on the MTX website.
Pioneer TS-W5000SPL Current SPL King
In 2005, Edge Audio’s Scott Owens, armed with 13 12 inch woofers with 54,000 watts, delivered an SPL of 177dB. WOW! To accomplish this feat, the TS-W5000SPL has an extremely robust design with three patent pending design aspects. The Interlaced Carbon Fiber Reinforced IMPP Cone (Patent pending) combines long carbon fibers into a strong, lightweight cone capable of withstanding the enormous pressure levels. The Aramid Fiber Reinforced Rubber Radial Surround (Patent pending) uses Aramid Fiber (the same material used in bullet-proof vests) woven into the rubber surround that eliminates puckering and improves high power performance. The overhung design allows for a 22% larger cone surface. Finally, the Ceramic-Coated Voice Coil Wire (Patent pending) design doubles the input power handling and improves reliability by allowing the voice coil to withstand extreme heat. The results are a woofer that handles 5,000 watts and has the current World SPL Record.
Ten years ago, dB Drag Racing was in its infancy, top SPL performer Mark Fukuda won dB Drag Racing with an SPL of 158.4 dB. Today, SPL competitions have seen 177.9dB. That’s a difference of nearly 20dB. To put this in perspective, a 3dB increase in SPL required either doubling amplifier power or doubling the number of woofers. An increase of 20dB is equal to 100 times the amplifier power. Woofers today are better built, fit in more places, handle more power and generate more SPL than every before. If the next ten years are as innovative as the last, car audio will see some amazing woofers.
