Vibration:
Origins, Effects, Solutions

Little has been written concerning the effects of vibration on high-end audio components. I am surprised. I feel that the effects of this very important, little discussed and almost unknown topic is detracting from our listening pleasure. Unwanted vibrations have a serious, adverse impact on the performance of most, if not all, modem audio and video equipment. The reduction or removal of these vibrations can significantly improve the resolution of every system. I offer my observations on the topic in the hopes that you may enjoy some of the same improvements I have gained in my own system from the implementation of the methods to follow.

All of us have seen attempts at vibration control. Soft, resilient feet, spiked feet, cones, isolation bases, turntable suspensions, tube damper rings, etc., are just a few of the many ways manufacturers deal with the vexing problem of vibration control. Here, we will examine each in the context of their specific contribution to the control of unwanted vibrations. But first, let us explore the interesting and complex phenomenon of vibration itself.

The vibrations that cause us such great concern, are those that comprise the very nature of our hobby - sound. Our loudspeakers produce sound by the motion of their drivers, creating compressions and rarefactions of air molecules within the room. The eardrum vibrates in sympathy with these modulations of the air. Electrical impulses are sent to the brain, and there interpreted into meaningful, recognizable sound.

In the same way that the modulation of the air causes our eardrums to move in sympathy, so to they produce motion in all objects they encounter. If the amplitude of these motions is sufficient, and vibration within the component occurs, audible degradation results. Therein lies the rub.

Two major types of vibration will occupy our discussions. These vibrations reach our equipment via two distinctly different paths, hence their names: structure borne and air borne vibration. Structure borne vibrations enter through the shelf or platform upon which the component rests. Airborne vibrations are the results of fluctuating air currents produced by the loudspeakers, which vibrate the enclosure of the component.

The two types of vibration differ considerably in terms of the methods necessary to control them. First, let us examine air borne vibration, it is created, and how we can deal with it.

Airborne Vibration:

As we have seen, a speaker produces sound by moving air. Sound within the room causes vibrations-and/or resonances in the chassis, circuit board (s) and individual component parts of all electronic equipment. These vibrations induce various distortions in the signal, causing a masking or veiling of the music to occur. Audiophiles have long been aware of the sensitive nature of tubes and tubed electronics to vibration. This condition has been termed microphonics when applied to the tube itself. Indeed, simply tapping on the glass envelope of a vacuum tube, or on the chassis of a very sensitive unit, produces audible emanations from the loudspeakers. In much the same way, but on a smaller scale, air borne (and structure borne) vibrations will subtlety affect the sound produced by these units.

In the same way vacuum tubes are sensitive to external vibration, so to I believe, solid state and passive components are too. Capacitors (in particular), resistors, transistors and the like are sensitive, at least to some degree, to the influence of vibration. More and more we are seeing designers take these concepts into consideration when designing a new product. Chassis damping, improved structural rigidity/integrity and individual component damping are now almost commonplace.

Physical orientation (i.e. placement within the room) may well be the most crucial aspect in reducing unwanted colorations induced by air borne vibration.

The areas of greatest air pressure (hence the loudest sounds), will be the worst areas for placement of sensitive equipment - especially CD players and turntables. Ultimately, placement of all sensitive components in a room separate from the speakers would be ideal. If this approach is practical in your situation, I would recommend it. Short of that, keep your equipment out of comers and as far away from the loudspeakers as circumstances permit. Additionally, be sure that you select a stable non-resonant mounting surface for all your components. We will examine this aspect in more detail later.

Structure Borne Vibration:

Structure boom vibrations affect equipment in much the same way as do their air born counterparts, and generally to a greater degree. These vibrations create various colorations and distortions that blur or veil the music, confuse the image and generally wreak sonic havoc. Luckily, the control methods necessary to deal with structure born vibrations are more straightforward, and easily employed, than those measures needed to manage air born vibration. In general, all we need to is effectively isolate the equipment from its resting place. While it may prove difficult to totally eliminate all structural vibrations, we can significantly reduce them with some simple to use, and readily available, techniques and materials.

Most audiophiles are familiar with soft de-coupling feet. These pliable, resilient, rubber-like pucks absorb vibrations, converting their motion to heat, dissipating their effect. Vibrapods are the most common today, their predecessors included Sorbothane (Audioquest) and NAVCOM (Sims Vibration Dynamics).

Spikes and cones, by decreasing the contact area with the support, act as a mechanical diode - allowing vibration to travel away from the component, while limiting the return path. New materials now available (composite, ceramic, carbon fiber) seem to have improved cone performance over metal cones of the past.

Damping of equipment chassis and internal components can offer truly amazing sonic results. Manufacturers are just beginning to scratch the surface of this very important aspect of equipment design/construction. In most designs, vibrations in the cabinet and/or chassis are readily transmitted to the sensitive circuitry within. These vibrations are the cause of quite serious sonic aberrations that significantly limit the sonic potential of the component. One might consider experimenting with surface mounted materials to damp chassis/cabinet resonances. The application of surface damping to the larger metal parts of equipment enclosures can greatly reduce vibrations and improve sound quality.

Sheets made from EAR Iso-Damp or Q-Pads can be applied to a variety of surfaces to provide damping. Some are available with adhesive backing, others can be attached with contact cement or simply applied without adhesive for temporary applications.

Another more elaborate method of surface damping employs an exotic material (borosilicate) that is applied like paint, hardening to form a stiff non-resonant barrier to mechanical vibrations. This approach is most often applied to the inside of loudspeaker enclosures as a means of increasing the rigidity of cabinet walls and thus reducing resonant modes. The effects of this treatment will vary with the material used, the enclosure quality and the uniformity of application. Totem uses this type of material in the construction of their loudspeakers.

As mentioned previously, I believe capacitors, resistors, transistors and other component parts are sensitive to vibration. Therefore, anything we can do to reduce vibration in these components could be sonically beneficial. To this end, we shall explore a few of the options available for the more ambitious tweaks among you.

Capacitors, in particular, are sensitive to mechanical vibration. A few manufacturers attempt to control extraneous movements by gluing these parts to the circuit boards. This method, however, will only be effective if the circuit board has been effectively decoupled from the chassis. This usually is not the case. Alternately, damping the part itself by the application of surface treatments has proved beneficial. Strips of Q-Damp or Iso-Damp are well suited to this task. If you are so inclined, experiment by placing small strips of damping material on capacitors in critical areas of the circuit. Additionally, you may want to consider isolating and/or damping the circuit board itself. This measure is especially effective in the case of tubed electronics. Note: One should only attempt these modifications if they feel comfortable with the task.

Another method often reported as effective in tubed gear involved the use of tube damper rings. These compliant rings are placed around smaller signal tubes to damp vibrations in the glass envelope. Several varieties are available, each with its own set of advantages and drawbacks. Wider designs do a good job of damping due to the large contact area. The larger contact area however, leads to increased internal envelope temperatures that may significantly shorten tube life. Smaller cross-sectional rings made of rubber avoid the heating problems, but do a poor job of damping. We have adopted a unit featuring a small cross-section, but made from high temperature silicone that exhibits good damping properties. The silicone acts as a bit of a heat sink, actually drawing heat away from the tube.

To further isolate tubes, a special isolated socket has been produced by the Canadian firm PEARL. The Iso-Socket is designed to replace existing seven and nine pin sockets with a de-coupled unit employing silicone foam or Sorbothane. These devices do an excellent job of isolating the tube from structure-borne vibrations. Their use however, does require soldering, and so should be left to qualified individuals. Additionally, this and other electrical modifications should be considered in the context of their effect on the manufacturers warranty. This procedure may void your warranty, check with the manufacturer if you have any questions.

A major factor in determining the amount of effect that vibrations will have on our components, is our choice of audio furniture. The stand or rack that we use to support our equipment can either contribute to or reduce the effect of these unwanted vibrations. A variety of designs employing many different materials are available. I personally prefer the rigid, open frame variety as they provide a very stable, rigid and relatively non-resonant support. Fully enclosed cabinets may exacerbate the problems caused by air-borne vibration by creating a resonant chamber around each component. Additionally, these units are most often made from wood, which offers and inherently less stable support. Some rather serious audiophiles have gone to the extent of providing heavy blocks of concrete, marble or granite to support their equipment. While no doubt very effective, this radical and expensive method is likely to prove impractical for most listeners. As a rule of thumb, anything you can do to increase mass and/or rigidity will reward you with sonic improvements.

The easiest way to isolate a component from structure-borne vibration is by sliding an isolation base beneath it. A host of superb products exist to reduce the effects of structure-borne vibration and dissipate internally generated vibration. These include Bright Star, Townshend, Arcici, Signal Guard, Symposium, Silent Running, etc.

Pneumatic isolation has become popular in recent years, popularized first by Townshend then by Bright Star and Arcici and the Vibraplane. These devices are extremely effective barriers to the extremely difficult to control low frequency vibrations.

In cases where the amplifier is to be located on the floor near the speakers, amplifier isolation bases are highly recommended. Tube and hybrid gear will experience the greatest improvement, but solid state equipment is likely to benefit as well. The practical aspects of improved air circulation (for better cooling) and the enhanced cosmetic appeal that these bases offer, should not be overlooked. Most use spikes to insure tight coupling to the floor.

Speakers, the component responsible for producing the vibrations we seek to quell, require careful placement techniques to insure best performance and least interference. Spikes have become the favored method of "mounting" speakers. These devices can be particularly effective when the speakers are to be placed on a concrete slab foundation. Here, the great mass of the concrete slab serves as an effective "sink" for the vibrations created by the motion of the loudspeaker enclosure. Hard-coupling speakers (using spikes) to a suspended wood floor however, can, in some cases cause problems. The floor can act as a kind of "sounding-board," set into resonance by the vibrations of the speaker. Some listeners find decoupling the speakers from the floor improves performance under these conditions. Vibrapod's are an easy solution, but some speakers are not stable once perched atop these feet. In those cases an isolation platform offers a more stable footing, to which you can spike your speakers, if desired. Any of the makes mentioned previously work very well, just be certain the platform is designed to support the weight of your speaker. For the do it yourselfer's out there, make your own isolation platform by sandwiching two pieces of rigid material like MDF (a high density wood fiber product), Corian or, for special situations, granite or marble, with a layer of damping material or Vibrapods in between.

Designers and Engineers are only just beginning to explore new methods of improving the sound quality of the equipment they manufacture through the application of vibration control. As with many other ideas, the curious audiophile is likely to find significant improvements through experimentation. Take the time to employ some of the ideas discussed here and I think you will find new levels of performance lurking within your system, just waiting to be discovered!

SUMMATION

1) Place components well away from the speakers. Do not locate equipment in comers or directly behind speakers, especially planar designs.

2) Locate components and loudspeakers on a rigid, non-resonant support. Avoid enclosing equipment in cavities that will act as resonant chambers.

3) Experiment with cones, soft decoupling feet or isolation bases under all components.

4) Consider placing floor mounted amplifiers on isolation bases.

5) Experiment with tube damper rings and/or isolation sockets on tubed electronics.

6) If you enjoy more advanced projects, consider damping internal circuit components, circuit boards and equipment chassis.