Sean Powell
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Formulas for acoustical dampening?
Hello,
A number of years back I worked at an engineering company where we needed to isolate very large, very loud motors from transmitting sound energy into the supporting structure. We did this with a series of elastic isolators that supported the motors and frames. Based on some very simple formulas provided by the isomount fabricators we could calculate the % of sound energy dampened out for a specific frequency if we knew the mass of the motor frame and the amount of pre-deflection of the supports. For obvious reasons dampening out the lower frequencies required larger elastic pre-loads but there was a critical point for each frequency where you could set up a harmonic resonance within the isolators and accidentally get your motor frame bouncing… very bad when it’s a pair of 500hp motors and a 20ft diameter wheel running at 45mph tangential velocity.
Anyway, I have long since misplaced these formulas and don’t necessarily remember their correct application. If someone can recite the formulas or direct me to a web-page with a good explanation I would appreciate it. I now need to build a smaller machine that is essentially a hydraulic trip-hammer but it will have a variable speed setting and I need to assure myself before building it that I won’t have to pass through a dangerous amplification frequency while getting up to working speed.
Thank you,
Sean
Hello,
A number of years back I worked at an engineering company where we needed to isolate very large, very loud motors from transmitting sound energy into the supporting structure. We did this with a series of elastic isolators that supported the motors and frames. Based on some very simple formulas provided by the isomount fabricators we could calculate the % of sound energy dampened out for a specific frequency if we knew the mass of the motor frame and the amount of pre-deflection of the supports. For obvious reasons dampening out the lower frequencies required larger elastic pre-loads but there was a critical point for each frequency where you could set up a harmonic resonance within the isolators and accidentally get your motor frame bouncing… very bad when it’s a pair of 500hp motors and a 20ft diameter wheel running at 45mph tangential velocity.
Anyway, I have long since misplaced these formulas and don’t necessarily remember their correct application. If someone can recite the formulas or direct me to a web-page with a good explanation I would appreciate it. I now need to build a smaller machine that is essentially a hydraulic trip-hammer but it will have a variable speed setting and I need to assure myself before building it that I won’t have to pass through a dangerous amplification frequency while getting up to working speed.
Thank you,
Sean