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To easily explain the principle of the Mechanical Grounding, we usually use the example of the electrical razor. Lets remind you briefly this example :
When you hold an electrical razor, you perfectly feel the vibration of the unit. If you want to cancel those vibrations, you may try to damp it by applying soft, absorbing material around the razor. But wrapped in rubber or soft towels, the razor still vibrates, even if you do not feel it as strongly : the damping isolate the vibration, it doesn’t suppress it. Now, if you gently press the razor on the side of your tub, and the tub is strongly sealed t the building, attached itself to earth, the vibration will be greatly attenuated, like “evacuated” to earth by the rigid connection you established.
This phenomenon is absolutely analog to the electrical grounding. When potential of an electrical component is floating, the noise, hum and DC offset is not stable. The chassis “vibrate” in potential. By coupling the chassis to earth, you stabilize its potential. The more the wire to connect earth to chassis is thick (rigid), the better the grounding.
When the chassis is so grounded, any potential generated inside the unit, being relative to ground, is fixed, and the signals are much cleaner. In a similar way, small mechanical movements (like cartridge following the groove) are much cleaner in a mechanically grounded component. Drivers in a speaker do not loose part of their energy to make the enclosure vibrate, they have an “absolute fixed reference” and can provide much higher dynamics.
To properly evacuate vibrations, the connection between the various elements of the mechanical structure must have certain properties. Vibrations can be “reflected” from one material to the other if some specific characteristics of the materials are not respected.
The optical analogy with light transmission in an optical system produce very interesting similarities :
When the lights travels from the air into a piece of glass, a part of the light is reflected. Between two pieces of glass, the proportion of reflection depends of the surface and of the optical characteristics of the two type of glass. If the surface is finely polished and the two pieces are made of the same kind of glass (same refraction factor), the reflection is minimum. The light travels better from slow material (high refraction, slower propagation speed of the light) to fast material (low refraction).
In mechanics, vibrations also can be reflected and not transmitted depending of the surface and kind of material. Instead of refraction factor, mechanical engineer are talking about mechanical impedance. As for optics, a vibration is easily transmitted from a slow material (soft, with slow propagation speed), to a fast material (hard, fast propagation speed). The cone material has been designed using this analogy, including the selection of its angle (the “limit refraction angle” in optics).
Intensive study of several kind of audio components by our engineers have proved that most of the audio sonic coloration’s are due to mechanical vibrations.
If this effect is quite evident for components like speakers or cartridges, the recent research made by us on electronics mechanical vibrations is less known.
As for a speaker enclosure that “vibrates”, generating frequency emphasis by re-emission, and transient blurring by energy absorption, mechanical part of an electronic circuit, including the components themselves, can vibrate and generate, usually by microphonic effect, spurious signal and coloration.
The effect is very audible in electronic tubes. When the metallic parts vibrate (and they do when the voltage applied is modulated by the signal), the resonance of the electrodes themselves becomes audible, increasing decay time of the signal (the nice “spatial effect” of tubes), and coloring the signal in some frequency bands depending of the mechanical construction of the tube (difference between a “good” and a “bad” tube).
The effect has also be detected in the past years in capacitors. The so-called “sonic fingerprint” of capacitors is mostly due to internal vibrations generated inside the capacitors between foils. The stronger the mechanical assembly is (film and foil Vs electrolytic), and the more “euphonic” the material resonance is (polystyrene Vs polycarbonate), the “better” is the capacitor for audiophiles. Thicker dielectric (high voltage) sounds better than finer. Solid aluminum electrolytic are used rather than liquid vibrating electrolytic, etc..
In an amplifier, the output transistors also generate high level of vibrations and the amps have started to isolate mechanically those from the input circuitry which can capture the vibrations by the microphonic effect of input transistors.
Mechanical grounding in speakers and turntables can also be improved by a more careful application of the same principles.
Even if most of the technology developed by to mechanically ground its line of products are patented, the general principles to apply to get a good coupling with earth are well known, and used in some other industry like in the big machine tools construction.
Again, they can be very easily deducted from the electrical and optical analogies.
First the mechanical coupling between the component and earth must be very rigid (thick wire), otherwise the coupling material itself can resonate and act as a filter (undamped cones). It will also transfer less energy (fine wire)(aluminum cones) and the vibration evacuation won’t be perfect.
More, the vibration do travel better from slower material to faster material as we have seen. Proper selection of materials going from the slower to the faster insure perfect evacuation and some limitation of vibration “re-entry” in the component. This effect has been called by the “Mechanical Diode” effect. As seen in the optical analogy, the angles of the different mechanical parts attached together have some effect on this capability of directionality. It is interesting to notice that the cone is the shape used to represent a diode in electronics…
Conical feet, mechanical diodes, strong and heavy materials for the chassis and evacuation pods, damping of the materials where the vibrations are transmitted are obvious in the Goldmund products. The Cone is a perfect example where most of the above principles have been applied in a way which is very easy to understand.
Only heavy components, built without the necessary technological knowledge cannot succeed in making a good mechanical grounding. The audio world is full of examples of designs where only a small correction could dramatically improve the sound.
