Isolation

As regards vibration, isolation means reducing excitation forces so that only a small portion of them are transmitted to the underlying foundation. A distinction is made between vibration isolation and isolation of structure-borne noise.

The isolation effect of MEGI is referred to as active interference suppression if the interference emanating from a machine is stopped before reaching the surroundings. Passive interference suppression, on the other hand, refers to the shielding of sensitive equipment from interference emanating from the surroundings. Depending on the type of vibration excitation, the interference can be periodic or in jolts.

Vibration isolation

In the case of vibration isolation, the isolating effect of rubber-metal mounts is due to the fact that above the resonance range, the force of the inert mass of the spring-mounted machine no longer vibrates in the same direction as the excitation force but counteracts it with an out-of-phase reaction. The prerequisite for MEGI 's isolating effect is thus that the excitation vibration frequencies Verr of the exciting forces and torque must be at least =1.41-fold greater than the respective natural vibration frequencies.

V_{e r r} > 1.41 \times V_{e}

The value for the isolating effect is determined using the following formula for degree of isolation n or for the isolation D.

η = 1 - \frac{1}{(\frac{V_{e r r}}{V_{e}})^{2} - 1}

D = 201 g [(\frac{V e r r}{V_{e}})^{2} - 1] d B

The above formulas apply for a single-mass oscillator. It assumes that the foundation has infinitely large mechanical driving point impedance, i.e. that it consists of an infinitely large and rigid mass. If these conditions are not met, there may be differences between the calculated and the measured values, depending on the foundation's mechanical driving point impedance.

Isolation of structure-borne noise

Structure-borne noise expands in solid and fluid media in waves. The wave is partially reflected when it hits the point where two different materials meet and it's further expansion is hindered. The larger the impedance jump p is, the greater the reflection:

p = \frac{Z_{1}}{Z_{2}} = \frac{\sqrt{E_{1} \times d_{1}}}{\sqrt{E_{2} \times d_{2}}} = \frac{c_{1} \times d_{1}}{c_{2} \times d_{2}}

Z – impedance
E – modulus of elasticity
ρ – Density
c - speed of sound

Elastomer materials generally have a low modulus of elasticity and low density. The materials used in mechanical engineering and construction, on the other hand, have a high modulus of elasticity and high densities. This explains why spring mounts composed of elastomer materials are so exceptionally effective in isolating structure-borne noise.

Assuming in the case of steel that
E = 2,1 * 105 N/mm; ρ = 7,85 g/cm³
And for elastomer material (natural rubber, 55 Shore A) that
E = 10,5 N/mm²; = 1,2 g/cm³
Then the impedance ratio p works out to
ρ = 362
And the isolation R to
R = 0,989
In other words, practically 99% of the structure-borne noise waves are reflected.

How it functions

Isolation

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Vibration isolation

Isolation of structure-borne noise