[Herbie]

Carbon and graphite isolation products have in recent years taken on sort of a unique mystique in the audio world. That mystique seems to be fading somewhat because this material is not all it has been cranked up to be.
 
Herbie’s Audio Lab has experimented extensively with carbon because of its resonant and vibrational qualities. When used in vibration-control applications, it has an uncanny way of seeming to bring out an immaculate detail in music and reducing some of the blurring and distortion caused by micro-vibrations. Problem is, its effect is not linear across the frequency spectrum nor is it particularly faithful to the "musicality" of the recorded event. Frequencies themselves tend to be rendered fairly well across the spectrum, but the transient peaks are not. Some of the higher-frequency transient peaks tend to over-emphasize, not in amplitude but in "sharpness" or staccato. This is likely because some of the underlying transient fabric is missing. Like lead, carbon has a unique and identifiable, though subtle, sonic character. Besides tending to be borderline "analytical" and sometimes crossing that line, carbon has a particular "twang" to it that once recognized can be a constant irritant to the discerning listener.
 
We believe the reason for Carbon’s unique character is partly because of the way that vibrations travel through the material. Vibrations travel through carbon primarily in two planes, with vibrations traveling faster in one plane than they do in the other. A vibrational array traveling through carbon from point A to point B will therefore be altered. Similar frequencies traveling simultaneously through the opposing planes will be out-of-phase to each other at point B to some degree or another, thus weakening. Diminishing the impact of vibrations is of course generally beneficial. Unfortunately, certain frequencies also encounter resonant partners that did not exist at point A in the same phase relations, thus creating emphases and sonic signature unique to the material.
 
Carbon fiber seems to overcome this sonic anomaly because the material is broken up into tiny pieces. Carbon fiber has superior isolation qualities, but has no more structural integrity than a heap of goose feathers. It must be woven, laminated, and/or impregnated with resins.
 
Herbie’s Audio Lab uses non-laminated, woven, epoxy-impregnated carbon fiber for our Super Black Hole CD mat. Carbon fiber is not used because of its sonic nature, however, but because of its physical qualities. The material is thin, lightweight and rigid. These physical qualities, especially the rigidity, are what’s important.
 
For the Super Black Hole, a thin sheet of carbon fiber is embedded on a thin sheet of medical implant-grade silicone while the silicone is still in its curing stages, making a strong bond. Then, the Super Black Hole is punched out from this carbon fiber/silicone sheet and sanded smooth around the edges. The rigidity of the carbon fiber has overcome the major problem inherent with earlier versions of Herbie’s CD mats--staying flat in order to stay put on the CD without adhesive. The major functional qualities of the mat and superb sonic results are primarily due to the qualities of the silicone--not the carbon fiber.
 
Carbon microfibers (unwoven) are also used with Herbie’s Tenderfeet and turntable mats (in percentages ranging from 2% to 4%). Again, it’s not the sonic qualities of carbon that are important, but its atomic qualities. Because carbon readily forms covalent bonds with silicone molecule chains, carbon microfibers are used as a filler to strengthen the silicone-based formulas. Our silicone blends are very loosely crosslinked--resulting in very poor tear strength. A higher cross-linkage would make the material stronger, but lessen its vibration-absorbing ability and sonic neutrality. Carbon mirofibers allow strength without having a more-vulcanized rubber-like product (and subsequent resonance issues).
 
Many carbon-based isolation devices are commercially available. We have found that carbon has better sonic qualities than most materials. It’s just not quite there by itself, though. Combined with other materials, sandwiched between other materials, or with a strategic coating of epoxy or lacquer, it has significant potential. Of its own character, however, carbon is not magic.
 
Here is a vibration graph of a pair of 1/8"-thick steel plates (6"x6") on an MDF shelf of a stereo rack with a Sonic Frontiers SFS80 amplifier on a separate shelf playing pink noise at -24dB through AR Classic 30 loudspeakers. The red line represents the vibrations of one steel plate sitting on three 1" diameter x 1" tall solid carbon cylinders. The blue line is the vibrations of a steel plate sitting on four Tenderfeet (unavoidably, the following graphs also include some degree of electronic "noise" and EMI):
　

　
In this next graph, the steel plate is left alone (red line). On the steel plate sitting on Tenderfeet (blue line), a pair of Herbie's SuperSonic Stabilizers is placed on top of the steel plate:
　

 
Magic?
 
Steve Herbelin
Herbie’s Audio Lab

[gooberdude]

Sorry to bring up an old topic.

Steve, have you been able to measure why MDF sounds so bad...as in comparison to Birch plywood of the same thickness?

[Herbie]

I have measured vibrational contributions of MDF and Baltic birch plywood. MDF tends to have stronger resonant peaks with many harmonics alongside the major resonant frequencies. Baltic birch has weaker resonant peaks with fewer (or weaker) harmonics alongside.

Steve
Herbie's Audio Lab