Air springs are the best solution for eliminating structurally transmitted noise and vibration from equipment to acoustically sensitive areas.
Air springs support equipment with pressurized air within a thin walled rubber container, similar to, but lighter than the side walls of an automobile tire. Even high deflection steel springs cannot match the air spring’s natural frequency and provide similar vibration attenuation at the equipment’s operating speed. High frequency disturbances are another matter. In some cases high frequency noise, which is common to electrical gear and certain mechanical equipment, can travel through the steel spring wire and into the structure. With air springs, this problem is eliminated because the disturbing high frequency cannot pass through the rubber walls nor the air support.
We would like to tell you about an interesting air spring project we recently completed in New York City. A prominent securities and investment firm located on the upper west side of Manhattan needed to isolate four large emergency generators from the surrounding trading floors. Given the noise generated by the machines and the acoustical sensitivity of the surrounding spaces, the owner retained the services of the acoustical design firm, Cerami and Associates to develop the appropriate silencing systems. We were happy to help them with some of the details.
Each generator has a capacity of 2800 kW (enough electricity to power 50 homes), and weighed 63,000 lbs. These big machines could not be directly mounted on the air springs so we designed and constructed heavy steel frames between the air springs and generator. These 15,000 lbs. frames were mounted on four AS 451-20″ air springs. Each of the air mounts has a capacity of 47,100 lb. at the 150 psi operating pressure.
The four corner loads ranged from 28,000 to 44,000 lbs and were accommodated by varying the pressure per location with the use of sensitive control valves. The system worked beautifully and one of the installing steamfitters, commented that the amount of vibration on the deck of the generators as compared to the floor below was “like night and day”.
The air springs took care of the structurally transmitted noise and vibration, but Cerami and Associates still had to consider the airborne transmission of the generator’s roar. This was accomplished by surrounding the generators with a “room within a room”, or in other words, constructing two structures, separated by an air gap.
Cerami also called for a 4″ thick Mason type FSN floating floor that should knock down the airborne noise through the floor by 25 DbA. As a second precaution, they addressed the ceiling by supporting 4 layers of gyp board with 3/4″”deflection Mason type 30N spring hangers. We were honored in supplying all the required isolation and architectural material.
Please let us help with the proper materials for your acoustical design challenges. We will be pleased to work with your design group in selecting the best vibration and noise reduction systems for your project based on our 55 years of experience with the same leadership.
Happy to help you,
Best regards,
Jim Tauby P.E.
Chief Executive Engineer