Herbie's compliant feet are molded from proprietary blends of platinum-cured silicones and inorganic fillers. The blended materials have a strategic balance of compatibility and incompatibility, resulting in strong viscoelastic compounds that never fully cure and achieve incredible vibration-absorbing and vibration-blocking ability. Having gone through incremental improvements over the years, Herbie's isolation feet are presently faster, more sonically neutral, and more articulate than ever.
What's wrong with factory-supplied rubber feet?
Rubber doesn't conduct energy well; worse, it conducts energy at some frequencies, absorbs at others, and stores and releases energy at other frequencies. In other words, a rubber or Sorbothane foot acts as a kind of passive equalizer/phase shifter. Also, because rubber has non-linear storage and release characteristics, it can interfere with and distort important time information by introducing spurious group-delay characteristics back into your system. ‑from Symposium USA.
How do Herbie's audio/video feet compare to other "soft" footers like Iso-Nodes, SD Feet, and Vibrapods?
Although they damp vibrations, most rubbery audio products respond too slowly to microphonic compression and decompression for superior audio resolution. Most are made of industrial rubbers like Vitron or Nitrile, or cheap plastics like PVC, all of which have resonance issues that muddy-up the audio spectrum. Soft polyurethanes like Sorbothane and Norsorex lack the reflexive counter-punch needed to fight microphonics and have a tendency to produce ill-defined bass and some high-frequency loss or false emphasis. Footers that are simply stamped out of engineering foams, like Sonic Design Damping Feet, tend to be weight-specific to a narrow range. Though they do very well in some situations their use is virtually always at the cost of some sonic trade-off or in deference to personal taste. After all, the raw materials from which these products are made have been formulated primarily for purposes other than audio, e.g., footwear insoles, cushions, industrial seals, motor supports, microwave gaskets, or just general purposes.
The main advantage of Herbie's compliant footers is the cellular structure of the material. Most industrial compliant materials are tightly cross-linked, molecularly and structurally, so that the entire piece resonates as a single unit. This makes the material strong and durable, but inefficient at neutralizing micro-vibrations even-handedly. Herbie's formulations, however, are loosely crosslinked and weakly vulcanized, so that the molecular and cellular structures of the material can "breathe" independently. It's like the difference between a rubber cushion and a goose down cushion: both might have similar degree of softness (durometer), yet the rubber being more structurally cross-linked, will bounce and reverberate, whereas the goose-down, being loosely crosslinked, will absorb vibrations without reverberation. Herbie's compliant footers act somewhat in-between the two extremes of this example.
Herbie's isolation materials are formulated exclusively for and only for audio/video component applications. The compliant materials neutralize acute vibrations and resonance with firm counter-pressure, responding with lightning speed to micro-vibrational impulse. They will neither dull nor enhance frequency response. By simply reducing vibration, resonance, and microphonic influence in the audio electronics realm, they help bring out more of the full sonic potential of your components.
Are Herbie's isolation feet as effective as cones or roller bearings?
When cones or bearings are performing well, they inhibit vibrations from reinforcing and amplifying themselves. Instead of acting as vibration barriers or absorbers, cones act as conduits to "drain" vibrations away. Components working well with rigid devices are basically in a state of vibrational equilibrium rather than being truly isolated and are dependent on the integrity of the shelf or platform they are used with. Particular "sonic signatures" and glare are quite common, though. (The idea of draining vibration from a component into a rack which in turn supports other components is in itself a perplexity. A loudspeaker spiked to the floor will generate floor-borne vibrations that will subsequently reverberate vibrations right back up the spikes the way they came, imposing glare and distortion into the music. Likewise with a component spiked to a shelf or platform. In audio applications, the idea of "draining" vibrations works better in theory than in actual practice.)
Herbie's isolation feet, by contrast, decouple and isolate components and work well with just about any kind of shelf or platform. In most systems, components perform closer to their best potential with Herbie's isolation feet. We've had hundreds of customers over the years replace spikes, cones, roller bearings with our products under their components and speakers for substantially improved sonic results; scarcely ever the other way around.
What causes microphonic vibrations?
Microphonic vibrations are caused by internal component electronics like transformers and relays, motors, and external vibrations like sound waves. These vibrations create mechanical impulses inside vacuum tubes, inducing small parts to move, altering their capacitance and voltage, resulting in amplified distortions. Inside tubes, alternating opposing charges between plate and filament cause those parts to vibrate. Symptoms of tube microphonics can be fuzziness throughout the frequency spectrum, high-pitch "glare," blending of similar frequencies, acoustical feedback, and mushiness in the soundstage. You may hear emphasis of sibilant sounds (s, z, ch, etc.) in vocals. Herbie's vacuum tube damping instruments significantly reduce all forms of microphonic distortion.