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Ceramic Metal Matrix Drivers (Cerametallic)


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For whatever reasons, I can't seem to get anyone to read the white paper at the Infinity site written by Floyd E. Toole and Allan Devantier regarding ceramic metal matrix drivers.

So here is the whole freaking thing for the most part, with the exception of the really cool pictures, charts, diagrams, and tables.

I am really growing tired of "Cerametallic" being referred to as mere "marketing hype".


...Of all the problems that surfaced in these investigations, resonances stood out as being one of the principal causes of listener dissatisfaction. Why are resonances so important? It is probably because almost all of the sounds we want to hear are made up of resonances. In voices and musical instruments, high-Q (narrow-band) resonances define the pitches (the notes), while combinations of medium- and low-Q resonances add the timbral character that make a violin sound like a violin, and Pavarotti sound like himself. Loudspeakers with strong resonances change

the timbre and, therefore, the sound of instruments and voices...

...It is obvious that audible resonances should not exist within the frequency ranges over which the drivers are used. One might erroneously conclude, therefore, that a resonance at a frequency above a crossover frequency is not a problem. Our sensitivity to resonances is such that they remain audible even after being reduced many dB by the attenuation of the crossover network. The greater the reduction in amplitude, by whatever means, the more neutral the loudspeaker system will sound.

All mechanical structures have natural vibrational modes or resonances. For loudspeaker diaphragms (cones or domes), resonances are the primary source of audible coloration. There are two commonly used methods to handle diaphragm resonances. One is to allow the vibrational modes to exist, but to apply damping to the modes to reduce their Q, or bandwidth. The damping can be a coating applied to the diaphragm material, or it can be an integral part of the material structure. For woofers, popular cone materials are paper, polymers and various matrix hybrids because they are inexpensive and supply large amounts of damping.

This sounds as though it should work, and it does, like tapping a wine glass to make it ring, and then lightly touching it with the fleshy part of a finger. The ringing is damped, and further taps produce only dullish thunks. Two factors prevent this from being the only solution to the problem. One is that damping is a lossy process, and damping materials can add mass to critical moving parts. Increased mass reduces the sensitivity, or efficiency, of the driver because of the extra effort needed to move the more massive diaphragm. The other factor is much less obvious: the resonances, even with their reduced Q, can still be audible. The dull thunk of the wine glass is still there; it is still recognizable as glass, not cardboard or rubber.

As long as the resonances are present in the frequency range over which the transducer is to be used, damping can minimize their audible effects and, with skill, reduce them to inaudibility, but they cannot be absolutely eliminated...They (engineers) keep looking for ways to push the frequencies of these pesky

resonances outside of the frequency band the driver operates in.

For tweeters, metal domes have become common because they are very stiff, moving most of the severe natural modes above 20kHz; thus the modes themselves become inaudible.

...Ceramic Metal Matrix Diaphragms (C.M.M.D) are much stiffer than standard metal diaphragms, moving the natural modes significantly upwards in frequency.

At the same time, C.M.M.D. cones have more damping than metal cones, making this an excellent cone material for all transducers.


For a given diaphragm geometry, the frequencies of the natural modes are determined by the speed of the sound in the material which, in turn, is determined by the formula at the right. Thus, for every doubling of the speed of sound, we move the cone modes up a full octave.

Sound propagates at a higher velocity in metals than in materials such as polymers and papers. A third class of materials, ceramics, has an even higher speed of sound. Table 1 shows the parameters of several common loudspeaker diaphragm materials. Once a diaphragm is attached to a surround and a voice coil, the frequencies of the natural modes of the entire moving system become difficult to predict. To calculate the natural modes of the entire moving assembly, engineers use a computational tool known as Finite Element Analysis (FEA). FEA breaks a mechanical system into thousands of small elements and then calculates the behavior of the total system based on the properties of the elements.

...with a typical 3kHz crossover to a tweeter, a mid-bass driver constructed of paper, Kevlar, or polypropylene would be operating in resonant breakup over a large portion of its range. The metal cone drivers would operate as perfect pistons over the operating band but they would have flexural modes near the crossover due to the mechanical resonances. As a result, a complex crossover would be needed to filter out the frequency-response and time-domain aberrations, so that they will not be heard. Such complicated networks are costly, and can introduce other problems.

However, it is also evident that the first modes of alumina (ceramic) cone are so high that they can be filtered out with traditional, simpler and less costly crossover techniques. Clearly, alumina would offer performance superior to any of the other materials. Unfortunately, pure ceramics are also very brittle, and a diaphragm made of pure alumina would shatter under normal operation, a good reason why such materials are not popular for loudspeaker diaphragms.

Show below is the frequency of the first natural cone-bending mode for the entire moving assembly of a 5-1/4" driver for each of six different cone materials attached to a typical voice coil and surround.

Cone Material Frequency of First Cone-Bending Mode (Hz)

Polypropylene 1500

Kevlar 1920

Paper 2160

Titanium 7440

Aluminum 6700

Ceramic 10800

Ceramic Metal Matrix 10190


Stiffness is most important at the surface of a material. Two common large scale examples illustrate this concept. The first is the ubiquitous I-beam used to construct skeletons of buildings and bridges. The top and bottom parts of the I offer increased stiffness due to their physical separation. The farther apart they are, the stiffer the beam.

Another more esoteric example is the new class of honeycomb panels used in aerospace applications and to construct the walls of these same skyscrapers. Here two stiff membranes are attached to a light honeycomb structure. The distance between the membranes provides much more resistance to bending than a solid sheet of the same weight.

C.M.M.D material scales this simple principle down to the microscopic level. The diaphragm is made of two layers of ceramic separated by a light metal substrate. Of the common metals, aluminum has the lowest density, making it the ideal substrate. A C.M.M.D. cone is made by first forming the cone to shape in aluminum. A unique patented process is then used to grow a skin of alumina on each side of the aluminum core. The alumina supplies strength and the aluminum substrate supplies the resistance to shattering. The resulting laminated material is less dense and less brittle than traditional ceramics, yet is significantly stiffer than titanium or aluminum,

and much stiffer than nonmetallic materials.


For a given geometry, we know that the frequency of the natural modes is determined by the speed of sound through the material. The amplitude of these modes, and thus their impact on the loudspeakers frequency response, is dependent on the damping of the material. Polymers have very high amounts of damping, and metals have almost none at all. Ceramic diaphragms have significantly more damping than metals.

C.M.M.D.s have damping characteristics similar to ceramics, but have a distinct advantage over them. Because of the sandwich constrained layer construction of the diaphragm, and because the speed of sound in the C.M.M.D. substrate is different than the speed of sound on the surfaces, there is additional damping. Indeed, when properly engineered, a C.M.M.D. cone can be designed to have no frequency-response peaks in the entire audible range.


As mentioned earlier, there are two options in cone design: reduce the amplitude of the in-band resonances by using material with high internal losses, or move the resonances out of the frequency band over which the driver is used.

Figure 14 shows the bending activity in a 6-1/2 inch Kevlar® cone at 3.5kHz, near the upper end of its useful range. As can be seen, the diaphragm is anything but pistonic, showing an interesting rectangular flexure, obviously following the stiffness lines of the rectangular fabric weave.

In contrast, at the same frequency, the C.M.M.D. cone, shown in Figure 15, is perfectly pistonic, showing no sign of flexure there is no resonance. Whatever one may claim about the damping of in-band resonant modes, it is clearly better to simply not have any to deal with. This is the philosophy on which...C.M.M.D. is based.

Ceramic materials can withstand extreme temperatures, moisture, humidity and sunlight, and C.M.M.D. diaphragms share these properties. Finally, because the

metal substrate is protected by a skin of ceramic, C.M.M.D. cones do not deteriorate even under extreme humidity, salt and moisture.


This message has been edited by deang on 06-08-2002 at 09:21 PM

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Ceramic Metal Matrix Drivers aren't what Klipsch is selling now STOP confusing yourself, you falling into the LLC's trap. They are taking aluminum and anodizing it, the coating is too thin to contribute to the stiffening that would be observed in a real composite system.

Do you think that a coat of stain

on a sheet of plywood is going to improve its strength???

Anyway, this is what they are all after. These cones run about $2000 each (cone only still need a motor structure). I heard a system in the Netherlands with these cones, the bass was scary.

THIS is the ULTIMATE CONE, a glass-ceramic-


This message has been edited by John Warren on 06-09-2002 at 05:41 AM

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I don't think I'm confused. However, I do admit to not being fully educated regarding the process of anodization.

Casual reading about the process however, certainly leads me to believe the process is a little more involved than just coating the driver in the same way stain is applied to a piece of plywood.

Anodization utilizes electrolysis , whereby the base metal and coating material are bound on the molecular level. The coating could also be applied using an auto-catalytic method, where electricity is not utilized at all.

However we decide to understand the process, it's certainly more involved and sophisticated than pressing out a plastic or paper cone.

It might be easier if I just said I believe 'coated' metal drivers sound very clean, very fast, and very good.




Cary AE-25/ S F Line 1/ S9000ES/ HSU x-over/ SVS CS+/ RF-7 Klipschcones®f>s>

Exigency is the matriarch of ingenious contrivancef>c>s>

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It's NOT anodization, it's anodizing. It's done in a tank. Ever see a blue aluminum bottle opener? thats blue anodizing, ever see that fancy red/blue aluminum fittings on race car fuel lines, that's red and blue

anodizing, it is done in garage operations for fractions of a penny per part. It is primarily for corrosion and cosmetics.

BTW, aluminum oxide is almost 2X the density of aluminum (twice the weight for equal volume).

Do you *really* think that that helps???

Christ, the coating is so thin that you can actually *see* the reflection off the base material.

Dean, that picture looks like JBL consumer audio which is pure garbage.

This message has been edited by John Warren on 06-09-2002 at 08:49 PM

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You're right "anodization" isn't a word. Of course, I didn't know that until I just tried to look it up. Hey, I told you I wasn't an expert.cwm35.gif

If the process doesn't make any difference, than why do these anodized drivers sound so different compared to more conventional drivers?

I listened to some NEAR's once (with metal drivers) and you could clearly hear the ringing at higher SPL's. I don't hear this with the Reference speakers.

How much damping should one expect find on the surface of metal to make a difference? Doesn't seem like it would take much.

The speaker in my last post is not JBL Northridge, it is made by Infinity.

Man, you're brutal.



Cary AE-25 * S F Line 1 * S9000ES * HSU x-over * SVS CS+ * RF-7 Klipschcones® f>s>

Exigency is the matriarch of ingenious contrivancef>c>s>

This message has been edited by deang on 06-09-2002 at 09:07 PM

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I don't know what CMMD *really* is but if its coming out of Infinity and JBL Consumer then its anybodys guess. JBL comes out with CMMD so Klipsch has to comes out with Cerametallica, etc, etc..

At least Klipsch states that they are anodizing.

Aluminum cone drivers sound different and Rudy Bozak in 1965 new the same thing, he developed aluminum drivers (mids and tweeters) and sold them with a thick black anodized finish which spalls off.

This message has been edited by John Warren on 06-10-2002 at 05:12 AM

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Whoa! Hardcore cone flame post! It's so pathetic, NOT!!!

JBL's BEST stuff (woofers) is all paper, cheap paper, and that is on $20,000 spekaers!


Receiver: Sony STR-DE675

CD player: Sony CDP-CX300

Turntable: Technics SL-J3 with Audio-Technica TR485U

Speakers: JBL HLS-610

Subwoofer: JBL 4648A-8

Sub amp: Parts Express 180 watt

Center/surrounds: Teac 3-way bookshelfs

Yes, it sucks, but better to come. KLIPSCH soon! My computer is better than my stereo!

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Sorry Dean...couldn't tell the quotes of the article from your own thoughts because...well, there was no delineation, I'm sure you had your own contribution...but I seemed to miss it. And why is it that you feel that this article is so useful?

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Everything past my signature 'Dean' is from the white paper.

Many feel Klipsch not adding a midrange horn to the Reference speakers -- objectionable.

I counter that 2-ways sound better anyway.

The 'Heritage Brigade' counters that since most 'music' actually occurs in the midrange -- dropping the midrange horn means that the Reference speakers are not really horn driven, and that the horn loaded tweeter amounts to nothing more than a 'token' horn.

I counter that two-ways sound better.cwm35.gif Actually, I would say that the horn in Reference is handling all of the higher harmonics associated with the fundamental tones -- and so is largely responsible for much of the low level detail.

I also point out that the new drivers are far superior to other drivers using conventional driver materials (straight aluminium, paper, polyproylene, and Kevlar)-- and that the Reference cones, though not horns -- are very dynamic due to their thinness (light) and stiffness.

They counter that this is B.S., and that the aluminium cones are nothing more than that -- aluminium. This means that in addition to not providing the hair trigger dynamics of a horn midrange, they are subject to main problem associated with metal drivers, ie - 'ringing'.

The ringing on the highs is no problem, since most of it takes place around 22Khz. Only your dog or cat will hear it.

The ringing in the bigger cones is a problem. In spite of the great transients and speed found in the metal cones -- the ringing is clearly audible at the higher SPL's.

I don't hear this property with the Reference speakers. If anyone would notice it, it would be me -- because I drove my previous RB5's, and my present RF7's to blistering levels. They don't ring. Why?

I say the anodizing process creating the thin layers of ceramic on either side of the cone creates the damping necessary to squelch the ringing.

John, obviously thinks I'm deluded -- and that the anodizing doesn't amount to a hill of beans.

The white paper explains the benefits of the process.




Cary AE-25 * S F Line 1 * S9000ES * HSU x-over * SVS CS+ * RF-7 Klipschcones® f>s>

Exigency is the matriarch of ingenious contrivancef>c>s>

This message has been edited by deang on 06-12-2002 at 04:16 PM

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I don't think you are *deluded*. I read the white paper, it needs to go further in proving the claims.

When I was in grad long time ago, my thesis advisor said once that he was smart enought to *theorize* 1000 different reasons why something would (or wouldn't) work only to be proven wrong.

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That's true, you can theorize all kinds of nifty stuff -- that is why I originally kept trying to put the emphasis on how the new cones sound. I keep resorting to throwing up this damn white paper to back up my experience.

The truth is -- I just think they do a hell of a job.

Something 'engineering' related has to account for the cleanliness of the midrange, and dynamic punch found in the upper bass -- all together without falling apart.

If we don't credit these new drivers with 'something', then what do we credit for the grand sound of these boxes?



Cary AE-25 * S F Line 1 * S9000ES * HSU x-over * SVS CS+ * RF-7 Klipschcones® f>s>

Exigency is the matriarch of ingenious contrivancef>c>s>

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There is a difference between hard anodizing(hard coat) and color anodizing. Any surface hardening such as hard anodizing or oxidizing should stiffen an inherently soft material, such as aluminum, in thin sheet form. As a matter of fact, mild rust formed on the exterior of cast iron parts relieves the surface in such a way as to reduced the incidence of stress fractures. Chemistry is our friend.cwm1.gif

This message has been edited by SOUNDJUNKIE on 06-12-2002 at 11:04 PM

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