Tenderfoot isolation footer



Q: What are Herbie's isolation feet made of?

A. 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.

Q: What's wrong with factory-supplied rubber feet?

A. 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.

Q: How do Herbie's audio/video feet compare to other "soft" footers like Iso-Nodes, SD Feet, and Vibrapods?

A. 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. 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 the full sonic potential of your components.

Q: Are Herbie's isolation feet as effective as cones or roller bearings?

A. 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" are quite common. (The idea of draining vibration from a component into a rack which in turn supports other components is in itself a perplexity.)

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.

Q: How do Herbie's footers compare to high-end feet that cost $300 or more a set?

A. Because there are so many interdependent variables involved with any audio system, no single isolation device works best under every circumstance. Herbie's compliant feet, however, perform optimally over a broader range of parameters than most, synergizing well with just about any audio system. Herbie's isolation feet are not priced on how well they do compared to others, but are priced simply on what it costs to produce them. Don't let the low prices fool you; our products are simple, yet very effective high-end devices. In many blind and ongoing A/B comparisons with many different audio and video systems, Herbie's Tenderfeet (and Iso-Cups) have consistently equaled or outperformed highly engineered "marvels" costing many times more. With very small components, there is sometimes nothing at all that works better than a simple, inexpensive set of Baby Booties. Likewise with tube amps, economical Iso-Cups are rarely outperformed by any other kind of footer.

Deciding which isolation device is "best" is often just a matter of personal preference. For those of us who enjoy being absorbed in a real, up-front, musical presence—neither artificially "smooth" nor dryly "analytical"—Herbie's isolation feet are an ideal choice.

Q: Doesn't too much detail give you a dry, analytical sound?

A. An "analytical" sound is the result of some but not enough detail resolution. In such cases, subtle micro-detail and transients are lacking; major notes and dynamics are present but subharmonics and ambient indicators are weak. With sensitive and accurate detail resolution, you don't have to sacrifice "smoothness" to get detail, and vice versa.

Q: Does the audio component have to be a certain weight for maximum benefit?

A. Unlike soft feet that work best only within a narrow weight range, Herbie's footers give superior performance over a considerably wide weight range. Herbie's isolation feet will handle weight loads greater than the recommended limits; beyond a recommended range, however, a beefier footer with more vibration-absorbing capacity is sometimes preferable.

Q: How do I attach the feet to my component?

A. We recommend feet be used free-standing. Although they do not "attach" to components, Herbie's compliant feet make a firm, slip-free contact. When your component is placed on them, everything will stay put, almost as if the component were on suction cups.

If you wish to attach the isolation feet to the bottom of your component, however, some are available with pressure-sensitive adhesive, or you can adhere them with a dab of Permatex Blue RTV Silicone Gasket Maker (available at most auto parts stores for about $5).

(Iso-Cup footers do not "attach." The component sits on balls, which rest securely in concave, hemispherical "cups.")

Q: Would it be sufficient to use three footers instead of four under a component?

A. With compliant footers like Tenderfeet and Baby Booties, we usually recommend four for maximum benefit and stability. Usually, the more vibration-absorbing material in intimate contact with the component chassis, the more effectively the component's internal vibrations will be absorbed. (Depending on the component itself, however, three is often sufficient.)

With Herbie's Iso-Cups and frosted acrylic domes, we generally recommend three footers per component, although using four (or more) is not detrimental. (Some audio people recommend to always use three footers because "three points defines a plane." With cones and other rigid footers, this is appropriate advice—with compliant footers, however, that have some "squish" to them (including Iso-Cups) to compensate for a slightly uneven or unlevel surface, the "three points defines a plane" doctrine is basically moot.)

Q. Will my component have a tendency to "roll around" on Herbie's Iso-Cup footers?

A. No. Iso-Cup balls are held firmly in place and roll only minutely, imperceptibly.

Q: Do Tenderfeet "ooze" or leave a residue?

A: No. Silicone-based products may on rare occasions react mildly with some surface oils and waxes, though. Any smudge left behind will buff out readily.

Q: Is it okay to put Tenderfeet under the factory feet?

A: Herbie's footers always work best when in direct contact with the component chassis. This allows them to most effectively isolate the component and absorb chassis vibration.

Q: Does placing weight on top of a component help?

A: Placing a moderate amount of weight on a component usually helps isolation feet to perform most efficiently (choice of material is critical, though; inappropriate materials can introduce unwanted resonance). As opposed to rigid coupling devices that often require heavy weights for mass-loading, components sitting on compliant feet usually work best with just a small amount of weight (grungebuster Dots make an excellent decoupling interface between a weight and component chassis). Moderate damping inside the chassis is usually beneficial also, (regular hardware-store rope caulk is ideal for this).

Hard Feet (carbon) versus Tenderfeet

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 the other steel plate sitting on four Tenderfeet:


Vibration Control Comparison of carbon vs Tenderfeet

With SuperSonic Stabilizer

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:

Vibration comparison with Tenderfeet and SuperSonic Stabilizers