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Marsh Mellow™ Spring Dynamic Characteristics Natural Frequency
Disturbing Frequency
A spring system’s natural frequency determines the efficiency of an isolator. Effective isolators have a low natural frequency.
Disturbing frequency is the frequency of the motion which needs to be isolated. This is usually expressed in cycles per minute (CPM) or cycles per second (Hz). As an example, the disturbing frequency of a motor is the number of revolutions per minute. The lower the disturbing frequency is, the more difficult it is to isolate.
Natural Frequency (CPM) = 188 x Spring Rate (lbs / in) Load (lbs) =
188
Transmissibility
Effective Deflection (in)
Transmissibility is the amount of vibration energy which is transmitted from the vibrating source to the surrounding environment.
Natural Frequency (Hz) = 0.50 x Spring Rate (kN / m) Load (kN) =
% Transmission =
100 Disturbing Freq (CPM) Natural Freq (CPM)
[
0.50
] -1 2
Effective Deflection (m)
Isolation Isolation is the amount of vibration energy prevented from being transmitted through the isolator. % Isolation = 100% - Transmissibility This equation is illustrated in the chart below.
CPM 3000 2500 2000
FORCED FREQUENCY (ff)
99.9
25 1500 16.7 15 13.3 11.7 10 8.3
99.5 99 98 97 96 95 90
80 70 60
1000 900 800 700 600 500
Re so na nc e
HERTZ 50 41.7 33.2
P Iso erc lat ent ion
ISOLATION CHART
6.7 400 5.0 300 4.2 250
Amplification
3.3 200 2.5 150 1.7 100 30 40 50 60 80 100 0.50 0.67 0.83 1.0 1.33 1.67
150 200 2.50 3.33
300 400 500 600 800 1000 CPM 5.00 6.67 8.33 10.0 13.3 16.7 HERTZ
NATURAL FREQUENCY (fn) 8