FAQs

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.

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.

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.

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.

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. We've found that the materials used for isolation are virtually always more important than the particular design or other engineering involved.

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, Fat Dots and Gliders 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, Extra-Firm Tenderfoot isolation feet are scarcely ever 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 the ideal choice.

An "analytical" sound is the result of some but not enough detail resolution. In such cases, you might have lots of lickety-split staccato detail but 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.

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.

In most cases, we recommend component 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, like having the brakes on.

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 $6).

Three is often sufficient. With most components and speakers, however, we usually recommend four. With four, you have more vibration-absorbing material in intimate contact with the component chassis to more effectively arrest the component's internal vibrations, areas of the component are more evenly divided for vibration control, you have superior lateral stability, more latitude with placement of the footers and most importantly, you'll usually achieve a sonically superior result.

No. Our silicone-based products do not ooze or leave a residue. They they do not stiffen and crack over the years like rubber or squish out of shape like some footers. They'll be just as good as new for a lifetime and longer.

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. Placing compliant material under stock rubber feet somewhat unconstrains the rubber, allowing it more freedom to resonate and reverberate to sonic detriment.

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).

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.

No. Although each tube has a primary resonant frequency, you have octaves, harmonics, and subharmonics directly associated with that frequency, and internal parts with different and unique resonant qualities. Most of the vibrations that cause microphonics have nothing to do with a tubes' resonant frequency. The material used for a weight, i.e., brass or lead, will influence the tubes' results with its own character and the more mass, the more its character will dominate. Simply loading weight to a tube does not deliver a whole solution and is usually counterproductive in some ways.

Herbie's damping instruments do not work by mass loading. A titanium C-ring weighs only a few grams, yet its spring tension provides resistance to vibration equal to many times its weight without the drawbacks of weighing down the tube. With vibration-absorbing pads interfacing the C-ring and tube, each damping instrument works similarly to stabilizing a tube with your fingertips.

In ambient air, tubes are "cooled" naturally by air rising up their sides (tubes heat the air, causing the air to rise, with fresh air swooping in to take its place). Herbie's open-air designs allow for natural cooling. Tests have shown that tubes will run at about the same overall temperature with or without our damping instruments. (Audio tubes generally perform best in ambient temperature without being artificially cooled or heated.)

We have found that, in general, output tubes are just as sensitive to microphonic distortions as small-signal tubes. Because of their close proximity to transformer hum and other factors, power tubes often suffer considerably from microphonics. The same is true with rectifier tubes; with reduced microphonics, a truer rectified current improves everything.

With a limited budget, it's not always feasible to install damping instruments on all tubes in a system. Beginning with the source/preamp and rectifier tubes is generally the most frugal approach.

For an amplifier or pair of mono amps that has lots of output tubes, damping every other stereo pair usually achieves fully satisfactory results; damping half the power tubes seems to achieve substantially more than 50% of the benefit.

We believe that optimal tube life is extended by damping bulb vibration. This has been thoroughly proven with ordinary light bulbs, which are vacuum tubes. Although there seems to be little empirical data, plenty of anecdotal evidence supports this to be true also with audio tubes. Regardless of whether usable tube life is extended though, music will sound better with reduced microphonics.

Vacuum tubes tend to become more sensitive to microphonic distortions as they get older. Herbie's damping instruments will keep your tubes sounding like new for years and years to come.

Herbie's damping instruments are best at bringing out the highest potential in your tube gear, resulting in better sound that's more enjoyable to listen to. For a more comprehensive answer, please open new page.

Herbie's damping instruments all deliver the goods. Though all versions deliver linear frequency response with little or no tonal coloration, each provides subtle differences in microdynamic impact, just as different brands and labels of the best NOS tubes have subtle differences in dynamics.

The website description of each damping instrument is brief and straightforward, so you don't have to read "between the lines" to understand the general qualities. For example, if your system is somewhat "dry" or analytical, UltraSonic Rx would be the best choice to give you a more fluid, musical result with no loss of detail. With many systems, a hybrid combination is ideal for cost/effectiveness: for example, use UltraSonic SS for the small-signal/preamp tubes, HAL-O III for rectifier and output tubes.

Oftentimes, the main difference between premium-quality and ordinary tubes is their ability to deal with microphonics. By reducing the microphonics factor, Herbie's damping instruments allow a greater variety of tubes to compete on a more level playing field. Then again, inherently better tubes will usually sound even better with damping instruments. In general, the more a tube suffers from microphonic distortion, the more it will be improved with damping instruments. We have seen significant improvements in the performance of most every kind of tube, including some of the world's best NOS tubes like Amperex, Siemens, Mullard, Telefunken, and others. For specific examples, Siemens CCa tubes present an extremely linear, uncolored musical result, but tend to have a slight bit of microphonic "fuzz" on the dynamic edges; Herbie's damping instruments eliminate that artificial fuzz while maintaining the same uncolored integrity. Amperex white label 6922 PQ'a are amongst the finest tubes ever. With PQ's, Herbie's damping instruments reveal just a little more of the inner, intricate nuance present in the music by lifting a thin microphonic veil.

Tubes that are most revealing of subtle, sonic nuance are often equally sensitive to microphonic distortion. Damping instruments really bring out the best in these tubes. Different tubes each have their own unique character, so determining whether one sounds better than another is usually just a matter of personal preference. Almost all, however, do a better job with Herbie's damping instruments.

In the past, most tube dampers added an abundance of "coloration" to the music or altered some areas of frequency response; if your tubes didn't suffer terribly, it was best to leave them alone. However, we have never heard a tube component that did not suffer from the effects, to some detrimental degree, of microphonic distortion.

If you have a great-sounding tube component and don't perceive any microphonic "issues," you would probably be surprised after placing damping instruments on the tubes. With a sudden increase in musical clarity, you would realize you had been listening to some amount of "grunge" and distortion all along. You'll find there is much more "music" in the music.

In almost all cases, one damping instrument is all you need, reducing audible microphonics so efficiently that a second usually adds little or no additional effect. With extremely microphonic tubes and with some huge tubes like 8.5" tall 805 tubes, however, a second damping instrument is sometimes beneficial.

Unwanted microphonics add fuzziness to musical detail, blur the focus, add glare, and cause other distortions. Herbie's damping instruments diminish or eliminate these problems. We believe tube gear generally sounds better than solid state for reasons other than "microphonics."

We don't think it's microphonic distortions that most audiophiles really want to hear, but rather the soundwave phase-shifts, natural reverberations, and other nuances that occur in a live music environment. Herbie's damping instruments reveal more of this acoustic dimension and subtlety. Ironically, some tubes that are the most sensitive to microphonic distortions are also the most revealing with musical nuance.

Excellent-quality damping instruments often enhance the uniqueness of tubes. For example, a "warm" sounding tube sounds better because the tonal qualities are more pure and true-to-life. The "warmth" is still there, but with a more focused soundstage. Open-layered and transparent qualities are enhanced because the background is quieter, imaging is better focused, decay has more of a purity of tone and texture. Tubes that work well on the high end have less fuzz and glare, better presence, stronger dynamics, while keeping the high-end response and ethereal sustain.

Although exact placement usually isn't critical, Herbie's damping instruments are usually most effective in the area approximately 1/3 of the way down from the top. Some experimentation might reveal a "sweet spot" where they sound best (many customers have reported best results with damping instruments placed even with the tube's top getter plate, some around the middle, and a few have preferred placement near the top or bottom).

With shouldered tubes, a damping instrument can be placed either around the widest part of the "shoulder" or at the base of the "neck," where the neck meets the shoulder.

Bulb-shaped tubes use a single damping instrument around the widest part of the tube.

UltraSonic Rx, UltraSonic SS, and Guitar Amp UltraSonics are ready to go, but improve gradually with age as the isolation pads further cure from tube heat and achieve a somewhat "tighter" resolution. HAL-O III needs no break-in period other than warming up along with the tubes.

Herbie's damping instruments simply reduce vibrations and their associated distortions, resulting in an a more open and lively, seemingly "undamped" presentation. Eliminating microphonics at the tubes, however, might cause unwanted resonances or other anomalies elsewhere in the system to become more apparent. Audiophiles sometimes "tweak" their systems with Sorbothane or other damping materials to attenuate overly bright or sibilant tube microphonics; this artificial attenuation can cause the system to then seem overdamped when microphonics are subsequently corrected at their source.

Conversely, introducing damping instruments to a system can sometimes "overclarify" by revealing the true musical signal the tubes are receiving. Overly "bright" cables might be exposed for their true nature, or a bright coloration from metal cones might come through more distinctly.

If a damping instrument seems to "overdamp" or "overclarify," its effects can usually be lessened by simply placing it closer to the base of the tube or near the top. Like introducing any new "tweak" or accessory, sometimes it takes adjustments elsewhere in the system to bring everything together at the next level, i.e., adjust the speaker positioning a little. Sonic benefits are usually achieved right "out of the box" though, without additional adjustments needed.

Damping instruments with titanium C-rings extend less than 1/4" from the tubes. Although the pads extend almost 1/2", they can be positioned on tubes as close as 1/4" from each other, or even closer if only a pair of tubes (by placing the open ends of the C-rings facing each other).

Metal sleeves (some are spring-loaded) are sometimes placed around tubes to prevent radio frequency interference and/or to hold them in place in a hostile environment (and for international shipping). In home audio applications, the sleeves have negligible utility and sometimes add a bit of weird-sounding influence. You can safely remove them and install damping instruments in their place.

Likewise, some components have little cages around each tube, to protect the tubes from errant thrown balls, children, pets, or to alter proximate electromagnetic waves. These cages can be removed and damping instruments placed on the tubes for significant sonic improvement.

Herbie's damping instruments work perfectly on tubes in the horizontal position (or even upside-down!).