Noise and Vibration Testing and Analysis
Noise and Vibration Testing and Analysis is a service that we provide to many of our industrial and commercial customers.
In many instances, the vibration of structures can result in the propagation of sound waves from the structure. This field, known as vibro-acoustics, involves the transformation of structural vibrations into sound. We encounter vibro-acoustic elements in everyday life, as loudspeakers are electro-mechanical devices that convert electrical energy into motion (or vibration) of a speaker cone. The cone then creates acoustic waves which propagate through the air to our ears. Numerous structures exhibit such behavior, and it is often necessary to address structural vibrations in order to effectively solve noise problems. Noise and Vibration Testing and Analysis is the process that allows us to develop the solutions.
It is generally not straight-forward to determine if a noise problem is rooted in vibration or acoustics. For example, a schematic of a rooftop air conditioning unit is shown in Figure 1.
If the occupants in the building are below are hearing noise, it can be a direct result of airborne sound being passed directly through the roof structure, or it could be due to structure borne sound being passed through a grounded vibration mount, or it could be due to imbalances in the rotating equipment in the air conditioner exciting vibration modes of the roof, making it act like a loudspeaker.
The solution to each of these problems would be different, depending on the root cause of the problem. Generally speaking, Noise and Vibration Testing and Analysis is the “key” to solving the problem. For example, if the noise is due to airborne sound, then the likely solution would be to install acoustic barrier and absorption materials into the roof or ceiling of the building. If the noise is due to structure borne sound, then the likely solution would be to replace the vibration mounts. If the noise is due to vibration modes of the roof, the solution might involve addressing rotating imbalances of the air conditioning pumps and fans, replacement of the vibration mounts, the use of tuned mass dampers on the air conditioner frame, or even modification of the roof structure. It is therefore important to determine if the root cause of a noise problem is due to airborne or structure borne acoustics or structural vibration before attempting to solve such a problem.
Sonic-Shield acoustic engineers are skilled in many important aspects of noise and vibration testing and analysis, which will allow us to rapidly determine root causes of problems and develop a cost-effective solution. Our capabilities include the following:
- Finite Element Analysis – For systems that are in the design stages, we can perform a computerized finite element analysis, where we can analytically determine the vibration modes and forced frequency response of a structure, knowing just the physical characteristics of the structure (i.e., mass, materials, dimensions, etc.)
- Vibration Survey – For operating systems, we can examine the power spectral density (PSD) of vibration at various points on the structure using accelerometers. These PSD functions together with acoustical measurements can help identify cause and effect relationships between vibration and noise.
- Experimental Normal Modes Analysis – For non-operating systems, we can extract the natural vibration modes by exciting the structure with a force-measuring hammer and measuring the vibration response at several points. Knowing the operating characteristics of the machinery, we can determine which of the vibration modes results in noise problems and optimize the structure accordingly.
- Operating Deflection Modes Analysis – For structures that are being excited by acoustical or mechanical inputs, we can examine the vibration response at several locations on the structure to identify the problem frequencies and obtain a graphic representation of how the structure responds to these inputs.
Sonic-Shield has an engineering staff with advanced technical capabilities and instrumentation that can assist residential, commercial and industrial customers in solving their noise and vibration problems. Not only can we perform the noise and vibration testing and analysis, we can also develop and supply the appropriate sound and vibration abatement materials and products to solve your problem.