J & A Enterprises, Inc.
Noise and Vibration Control Engineers

16 Broadway
Salem, MA 01970
01 + 978-741-1551
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Compass1.gif (1365 bytes)Engineering services relevant to noise and vibration control fall into several catagories ranging from simple review and comment on an existing design to a full array of design, analysis and precision measurment services.  Because the needs of a client will vary with their experience base, so does the level of service offered by J&A Enteprises.

We recognise that a dedicated noise control engineering staff is beyond the resources of most companies.  The engineers at J&A Enterprises are accustomed to working in functional teams on a project-by-project basis.  As we routinely participate in diverse projects, we can bring a new perspective and innovative solutions to even the most intractable noise and vibration issues.

Satisfying noise and vibration specifications requires the application of good engineering practice.  A design review can identify potential problem areas in the earliest stages of a project.   The sooner in the design/build process a problem is identified, the less costly the solution.

J&A Enterprises offers a wide range of engineering services including ...

Technical Specifications Definition and Review
The first task in any project is the definition of specifications to be satisfied.   We have found that noise and vibration issues often receive inadequate attention during the early phase of a project.  Quantifiable specifications for noise and vibration now can prevent misunderstandings later.  
Computer Aided Engineering and Design (CAE/CAD)
J&A Enterprises is committed to leveraging technology to meet the needs of our clients.  We maintain workstations for computer aided engineering and design.   We routinely work in a wide variety of formats ranging from two dimensional layouts to full featured solid models.  Chances are, we can work seamlessly within your preferred CAD format.

A 56M European built mega yacht was recently delivered with annoying generator noise levels, and an unacceptable "rumble" noise in the lower deck aft cabins. Two different noise consultants completed sea trials and made ineffective recommendations before J&A was called. J&A correctly diagnosed the problem as a very unusual structureborne noise related to vibrations of the shaft system and thrust bearing. The vibrations stemmed from the coincidence of a torsional resonance, causing unsteady propeller thrust forces to drive the resonance of an axial vibration mode involving the shaft, thrust bearing, and the bearing's foundations. The J&A theory was validated with a finite element analysis of the propeller shaft and ship's structure, and further confirmed with a brief sea trial to validate the measurements. J&A proposed a solution to the rumble noise by simply shifting the location of a flexible shaft coupling and also stiffening the thrust bearing foundation using steel box-beams and PLEXUS adhesive. When that work was being done, the shipyard also installed a J&A designed improvement to the generator isolation mounts. Both projects were successful. The generator can no longer be heard while the yacht is at anchor, and the rumble noise in the cabins was attenuated to an acceptable level.
Analysis and Prediction
J&A Enterprises can analyze your design using proprietary and commercial software tools.  The variety of methods employed at J&A ensures that an appropriate level of technology is brought to bear on every project.  Our analysis techniques range from the relatively simple practices recommended by the Society of Naval Architects and Marine Engineers to state-of-the-art dynamic finite element analysis using the latest version of MSC/NASTRAN.  
J&A Enterprises can accurately measure noise and vibration characteristics using a variety of equipment.  We can measure overall noise levels, or provide more detailed information such as noise and vibration levels in 1/3 octave and narrow frequency bands.   Other measurements employed by J&A to investigate the physical behavior of systems include frequency response, transfer function estimation, system identification and decay rate estimation (including room reverberation time).