subwoofer driver material

[dieselpower1966]

Hey guys,
I was wondering. what are your opinions on different driver material for subwoofers
such as: aluminum polypropalene kevlar paper etc.

do you think there is much of a difference. I understand that the material should be light and firm , but how much difference do you think there is



John

[Sonnie]

From Stones Sound Studio

Paper cones still perform amazingly well, proving they're not as low-tech as many assume. Light and stiff, using an almost infinite variety of fibers, paper can be engineered to meet almost any requirement. Treated/ coated paper cones largely address the issue of degradation due to atmospheric conditions. The effectiveness of these treatments varies, depending on the specific technology. If properly done (a big IF), paper remains one of the best possible materials for cones. Some of the better paper technologies include:

Paper - is used by Scan-Speak Vifa Peerless Vifa and most speaker manufactures
Carbon fiber paper -as used by Scan-Speak

CSX - Composite sandwich cone - as used by Peerless

HDS series - Composite 5 layer pressed paper - as used by Peerless

Polyglass - Glass microsphere beads coated paper as used by Focal

Slitted paper - used exclusively by Scan-Speak and their clones

Kevlar paper - currently used primarily by ATI/Dulcet/HiVi, and used in the Shiva subwoofer Kevlar paper appears poised to become a significant technology.
Polypropylene
(PP) has become almost as ubiquitous as paper. It's reasonably rigid, has inherently high internal damping, and is totally non-hygroscopic. Without a particularly high stiffness to weight ratio, many PP cones are reinforced with fillers such as mica, talc, carbon black, acrylic, Miraflex (fiberglass), and Kevlar. Unadulterated PP is obvious by its milky white translucent appearance. Generally a very good material combined with very mature technology. PP cones are manufactured either by thermoforming or injection modeling.

Although not currently available in any drivers available to the DIY community, a new form of PP developed by the University of Leeds (UK) called variously Vantex or Comtex is potentially the most significant new technology to come along for quite a while. Researchers developed a process to form a material which consists of aligned PP fibers in a matrix of thermoformed PP. The resulting material therefore consists of approximately 80% molecularly aligned PP fibers in a matrix of 20% PP resulting from melting and cooling the "skins" of the fibers. Currently, only Wilson Benesch is using Vantex/Comtex drivers in its proprietary loudspeakers. Vantex/Comtex is currently being evaluated for automobile body parts due to its strength, low cost, and recyclability. It's also being tested for use in aircraft radomes. Vantex/Comtex appears poised to become a significant PP technology.

Carbon fiber
has become a popular material for cone designers. Depending on the vendor, you'll find it as part of a high-tech composite, woven and formed, or used as a coating over paper. This suggests a material which is somewhat hard to work with and which still needs some research to figure out the best way to utilize. Still, many of the carbon fiber coned drivers do offer excellent characteristics.

KevlarTM
is the fiber used to make body armor for military and police use. Many speaker vendors have incorporated Kevlar into their cones, usually woven and formed, either alone and coated, or as part of a sandwich construction. Many of the same comments for carbon fiber also apply to Kevlar, although I've received many more caveats for Kevlar drivers than for carbon fiber ones.

The problem with Kevlar is similar to that of metal - lightweight and rigid, it tends to ring like a bell! The internal damping of Kevlar is enough to damp some of these high frequency resonances, but the effect can still clearly be heard, as well as seen in the data (especially waterfall plots), requiring the careful use of notch filtering. It's also worth noting that several of the three vendors with the most positive recommendations using Kevlar (Scan-speakFocal, Eton, and Audax) use it as part of a sandwich structure.

Aluminum
cones are produced by a number of manufacturers. Metal cones exhibit the least distortion and coloration in the passband of any cone material, combined with excellent group delay characteristics. The penalty, as noted above, is undamped resonances and severe breakup modes in the upper stopband. Typically used as a woofer material (i.e. well below its resonances), you may still find it necessary to use a HF notch filter to fully tame an aluminum cone.. Whether the advantages of metal cones outweigh the problems is a matter of taste. The DIY'er should definitely think twice about using aluminum in anything other than a woofer or subwoofer application.

Magnesium
cones are a staple of Seas (see Section 3 below) top of the line Excel series. All comments made for aluminum apply to magnesium, only more so. Magnesium is lighter than aluminum, with comparable strength and stiffness. It also has even less internal damping. What is true is that getting good results out of these drivers is beyond the capabilities of many DIY'ers. These should be considered for use by experts only

Sandwich - Composite Cones
Sandwich/composite and/or proprietary materials in common used by Peerless . Many of these are proprietary and apply to only or more manufacturers.

Carbon paper. This technology, used only by Scan-Speak, uses a carbon fiber surface treatment applied to a paper cone. The results are generally excellent making this one of three premier paper technologies currently available.

Carbon fiber reinforced PP. This technology, apparently used only by Versa-Tronics, tries to combine the best characteristics of both materials. The results are mixed. Again, whether this is due to the material technology or the vendor (Versa-Tronics is not usually considered a high-end vendor), is debatable.

Ceramic. Accuton produces a line of proprietary drivers using thin aluminum oxide ceramic diaphragms. Similar technology is also used in several highly regarded high-end systems.

Damped Polymer Composite (DPC). A proprietary Morel technology, DPC is used in their top of the line woofers ad mid/bass drivers. Results have been generally reported as good.

Fiberglass. Some manufacturers have fabricated cones both from woven fiberglass in a matrix of unspecified polymer, as well as fiberglass filled papers. This is only used by a few companies, One company which uses it with excellent results is Seas. On the other hand, another company using fiberglass extensively is Versa-Tronics (which normally isn't considered a high-end vendor) with mixed results. The principle disadvantage of fiberglass is weight.

Expanded foam. Used only by Cabasse, this is an adaptation of the same material used to produce cases for many consumer products. If you've ever seen an older Apple computer, you've probably seen an expanded foam case. The unexpanded foam is injected into a highly polished mold. As it expands, it forms a hard surface wherever it touched the mold, combined with in internal structure of very lightweight foam. This would appear to be an ideal cone technology, but, to date, only Cabasse has managed to use it effectively.

HD-Aerogel (HDA).An Audax proprietary material, HDA combines carbon fiber and Kevlar in a matrix of acrylic. In the past, some of the Audax HDA drivers have been well reported while others have caused problems. As the technology has matured, Audax has been able to achieve a level of performance and consistency that was lacking in their first-generation HDA drivers. The key to this is in Audax's part numbering system where the digit(s) following the material designation ('Z' in the case of HDA) represents the design number. In the past, Audax changed specs without changing the part number. The most recent drivers clearly designate their generation - up to 18 in the case of the 6.5" HDA drivers.


Hexacone. This Eton-proprietary technology combines two layers of woven Kevlar over an inner layer of honeycomb Nomex. Nomex is the same material used to make fire-retardant suits for race car drivers. Eton's Hexacone drivers exhibit properties similar to Kevlar, having vary high stiffness to weight ratio, but with underdamped breakup modes in the stopband.

Neoglass.A Focal proprietary technology, Neoglass consists of a polymer cone (probably PP) with a surface treatment including microscopic glass microspheres. Neoglass drivers can be found in several highly-regarded high-end systems.


Nomex-carbon fiber honeycomb. A proprietary technology, this material is used for a unique line of flat cone woofers

Polykevlar. Another Focal proprietary technology, Polykevlar consists of two outer layers of woven Kevlar over an inner layer of their glass microsphere technology. As with Neoglass, Polykevlar drivers can be found in several highly-regarded high-end systems.

Polyglass.Yet another Focal proprietary technology, Neoglass consists of a paper cone with a surface treatment that includes microscopic glass microspheres. As with the other Focal glass microsphere technologies, Polyglass drivers can be found in several highly-regarded high-end systems. Polyglass is the second of the three premier paper technologies in use today due to its stiffness, light weight, and excellent damping.

Slitted paper. An unusual paper technology which appears on Scan-Speak drivers and used extensively the new revelator series of Scan-Speak bass mids available from WES Components , The cone starts out as a more or less conventional paper cone, then diagonal slits are cut into it. The cone is then glued back together and coated. The result is a cone as light and stiff as paper, but with controlled discontinuities along the glue lines to eliminate internal resonances. This is the third of the three premier paper cone technologies.

TPX. TPX is an unspecified polymer material (a plastic, reportedly polymethylpentene) used by both Audax and Seas. Seas' version specifically mentions PP as well. The presumption is that Seas uses an alloy of PP and TPX.
T

W sandwich.The "W cone" A honeycomb material is used in most of Focal's top of the line drivers. It's pedigree was as an exclusive material used in Focal/JMlab's high-end Utopia series loudspeakers for several years before being offered to the public. Srtucturally, W cones use a thin layer of foam material sandwiched between outer layers of "woven glass tissue".

XPP. XPP is a Seas proprietary clear plastic used in their latest "T" series drivers. Although quite new, initial reports of this material are highly favorable.

[dieselpower1966]

Sonnie

HOLY COW man!! you covered everything all in one breath.
the one interesting this that stands out is the Kevlar. you said that like metal it "rings"
I do believe that B&W uses Kevlar in their drivers, maybe it's woven in, I don't remember.
But I don't recall any reviews mentioning about metal, e.g. aluminum drivers ringing.

But great job reviewing all the different materials.

John