# Sticky  Principles of Mechanical Isolation and Mass-Coupling To Control Vibration In A/V Systems



## AudiocRaver

*Principles of Mechanical Isolation and Mass-Coupling To Control Vibration In A/V Systems*


Cones, dots, blocks of maple, blocks of marble, magnets, ball bearings. Do they isolate? Do they couple? Do they help? Are they a waste of time and money?

It is up to us as A/V consumers to use our noggins and apply the information seen in ads and promotions intelligently. Vibration CAN be a problem, under some circumstances, if not treated.


*Where can vibration be a problem?*

With components that are sensitive:

Turntables - the most common vibration-sensitive A/V component.
CD / DVD / Bluray drives - _sometimes,_ it depends on how well they are designed. Some can get knocked around and never give a single bit-error of an iota of jitter, others are more sensitive.
Components that use vacuum tubes, especially preamps - microphonics are to blame, vibration in the tubes can be converted directly to audio noise.
Components where low-level signals are treated or amplified (preamps) - microphonics again.
In all cases, it depends on the design, including the sensitivity level of the element that is vibration sensitive and how well noise isolation was designed into the product.

Speakers are a different animal. They are made to vibrate, so they are in a class by themselves and are handled differently.

In my experience, other than turntables, no well-designed product should be assumed to be a vibration problem unless it is found to be. A simple test can tell you a lot. With no music playing and with system volume turned up for a loud volume level, tap on the component in question, slap it a few times (gently, don't go crazy here). With a CD / DVD / Bluray player, tap it gently while playing. Does it skip or fuzz out? Does it hesitate, indicating excessive error correction? Any change from the norm indicates a possible vibration sensitivity.

*How to treat a vibration-sensitive system element:*

Understand how the vibration controller works! They may claim seemingly magical characteristics, but there are two main ways of controlling vibration:

Isolation - some isolating element makes the component in question "float" independently of the vibration source.
Mass-Coupling - a large mass is used to absorb the energy of the vibration so it is not troublesome.
With highly sensitive components, like turntables, both methods are often used together


*Speakers:*

If there is a lot of vibration in the house structure, from traffic or equipment elsewhere, then vibration getting into the speaker can be a problem. It is usually LF vibration, between 1 Hz and 20 Hz, and can affect imaging negatively. Isolating can be difficult. You are looking for something that allows a degree of "float" at those frequencies. And you need to consider all directions of isolation: "reverse cones" _might_ help in the left-right and front-back directions only, IF AT ALL (ask yourself, what is being isolated and what is being coupled and HOW???? it is usually not that hard to figure out), but NOT in the up-down direction of vibration.

Some high-end speakers go to crazy lengths to absorb and eliminate all vibration except for the vibration of the speaker cones themselves - anything else can be a disruption to image clarity. There are speaker enclosures that weigh many hundreds of pounds using materials and/or internal bracing to eliminate unwanted vibration. Here are two areas of possible benefit that I have found:

If the sweet spot is narrow and hard to set up, then imaging can be a negatively affected by enclosure vibration. Use spikes to couple the enclosure to the house structure. Or use poster putty to couple them to a marble block or stone floor, for instance. Imaging can be dramatically improved.
If bass seems soft or mushy, coupling (as above) can be beneficial to hold the enclosure in place at lower frequencies (Newton's second law - equal and opposite reaction) and bass "tightness" can improve dramatically.


*Common strategies:*


A cone tip against a hard, smooth surface *isolates* in two directions by allowing sliding action. It does nothing of benefit in the direction that the cone points toward ("chattering" is even possible, and is BAD).
A cone tip against a softer surface *couples* in all directions by digging into the softer material so they must move together.
A cone tip against a hard surface with an indentation *couples* in two directions by being locked together at the cone/indentation interface. It does nothing of benefit in the direction that the cone points toward ("chattering" is even possible, and is BAD).
"Dots" and "pads" are completely dependent on the characteristics of the material, and upon whether they have adhesive in use to stick them to the surfaces involved, and are hard to predict. At frequencies where the material is stiff, *coupling* is possible if adhesives are used. At frequencies where they are soft, some *isolation* is possible.
Poster putty (blue tack) is popular as a *coupling* element. It is sticky yet easily removed. It _might_ provide an additional benefit of some *isolation* at very low frequencies.
A rolling element (a ball bearing on a concave surface) *isolates* in two directions by allowing sliding action. It does nothing of benefit in the up/down direction ("chattering" is even possible, and is BAD).
Magnetic or air-flow levitation *isolates* in all directions. Air flow will usually introduce some vibration of its own. An electromagnet with a noisy DC driving source can couple noise into a system magnetically.
Wood or metal or stone is usually a mass to be *coupled* to for absorbing vibration. All materials have resonant frequencies depending on size, shape, and material. Resonant frequencies in the audio range are usually problematic. Greater mass generally means lower resonant frequency and better absorption of audio frequency energy.
Layers of wood or metal or stone or some combination, glued together with an isolating air pocket in between. There are elements of *coupling* and of *isolation* involved. A specific design would have to be scrutinized individually. Remember that resonant frequencies of isolators and couplers in a given design are important, and can work together to make an effective design or can work together to make a disastrous design.
There are complex suspension products recently on the market for speakers. They provide a combination of coupling and isolating protection, by using materials in a configuration that, generally speaking, *isolates* at subsonic frequencies and *couples* at audio frequencies. Some manufacturers build such a suspension into the base of their speakers. In general, I believe the approach to be beneficial, depending on the speaker design and on the presence of subsonic noise in the area from heavy equipment or traffic.

*How much is enough?*

That is really hard to judge without measurements. A good strategy is to try something on your own that is cheap and simple. Ball bearings on heavy ceramic concave dishes - this you can try for a few bucks. Do a listening test for image clarity. Measure at a pre-out with REW's RTA function, focusing on the LF noise floor (I like the RTA 1/48 octave, 65536 FFT Length, 4 averages setting).


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## Talley

Without a doubt isolation products work. But as mentioned above you must first find out if you have any isolation problem to contend with. I prefer to be overbuilt so will be placing cones/blocks/brass under my equipment and even placing heavy brass metal plates on top of all the equipment to assist in keeping internal resonance on the casing down. Brass and maple are common materials as they are widely used in the instruments that produce music. Their own inherent resonance is common to what we are accustomed to hearing when they are playing music. Hence their popularity in Isolation products.


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## AudiocRaver

Talley said:


> Without a doubt isolation products work. But as mentioned above you must first find out if you have any isolation problem to contend with. I prefer to be overbuilt so will be placing cones/blocks/brass under my equipment and even placing heavy brass metal plates on top of all the equipment to assist in keeping internal resonance on the casing down. Brass and maple are common materials as they are widely used in the instruments that produce music. Their own inherent resonance is common to what we are accustomed to hearing when they are playing music. Hence their popularity in Isolation products.


I cannot argue that sometimes a bit of overkill, when it is relatively inexpensive, is easier than going to all the trouble of finding out what is really needed. It is a common strategy.

All due respect, I am afraid I do not follow the logic that using materials common in musical instruments would be good in isolation products. For one thing, the resonant frequencies would seem to be far more dependent upon size and shape than upon the material itself. For another, the relationship between music production and isolation is, well..... I guess I do not see the relationship at all. Help me out here. Are not the two functions more like opposites than similar? If I want to absorb vibration with a block of wood, I don't want it to resonate at that frequency, that would simply tend to transmit the vibration. I want it to NOT resonate so that it absorbs and dissipates the energy. At least that is the way I see it, for a simple block of mass intended to absorb vibration energy. I am having trouble seeing the logic.


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## rab-byte

Couple all the loud things and isolate the rest.
Got it!


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