Designing a Test Cell is a complex process. It is important to have experienced, engineering professionals help you throughout the planning and implementation process. A key factor in your success is determining the major system components and how they integrate together for a Test Cell that is safe, convenient and well-organized. Inadequate planning and design can amount in huge costs to your company leaving you with an end result that does not provide an optimal solution. In part two of this three part series, we will briefly explain the importance sound control can have on Test Cell safety.
Sound Transmission Class (STC) Ratings*
Prolonged exposure to high noise levels can lead to hearing loss. It is important to provide adequate sound control to reduce the impact of noise, whether indoors or outdoors. The walls, ceiling, windows and doors in your Test Cell should all have comparable Sound Transmission Class (STC) ratings. A STC rating indicates which assemblies are better sound insulators. The larger the number, the greater the sound control capabilities. The STC rating of your walls, ceiling, windows and doors should not vary more than approximately five STC points. For example, do not choose an engine access door with an STC-50 rating and an observation window with an STC-26 rating. The higher cost of purchasing the STC-50 door is wasted, since the sound level outside the Test Cell will still be high because of high sound transmission through the window. STC rating requirements vary by country so be sure to determine the local sound requirements for your area.
*Sound Reduction Index (SRI) is also commonly used to measure sound insulation. Please note the numbers are different than the Sound Transmission Class (STC) ratings listed above.
Walls and Ceiling
There are several types of wall construction for controlling the sound level of a Test Cell including brick, concrete block and sand-filled concrete block. All walls should be constructed using proper construction techniques. Double wall construction refers to two walls separated by 4 in. (10 cm) space. To prevent sound transfer between the two walls, there should be no physical connection between them. In most areas, double wall construction is not required unless there are very stringent sound level regulations. Wall materials are typically porous. The porosity of the wall material acts as a natural sound leak. Therefore, we recommended that interior and exterior walls be painted with a high quality sealer or paint. The STC rating of porous block can be improved from five to eight points by sealing both sides with paint. Installing acoustical perforated aluminum panels on the walls and ceiling can also help with sound control. The acoustical panels should start just above the floor and extend to the ceiling.
The personnel door(s) should be sound controlled with an STC rating comparable to the rating of the walls. The door(s) should be constructed of a thick gasketed metal with sound-deadening material sandwiched in the middle. An emergency door release must be provided on the inside. Taylor recommends that the door(s) swing inward. This is contrary to typical practice; however, balancing the Test Cell with a slightly negative pressure prevents fumes, emitted during testing, from leaking through the door and into the rest of your facility.
Typically the Test Cell is maintained at a slight negative pressure differential (vacuum) from the surrounding outside area. This pressure differential must be considered when specifying doors.
Hinged Double Doors (engine access)
Hinged double doors should be used for all interior engine access doors because they have a high STC rating. The doors should be gasketed on all four sides with a flush threshold. An emergency release lever should be on the inside of the door. These doors typically swing out so they do not take up valuable floor space within the Test Cell, and because they are not generally used for emergency exit. These metal doors should be constructed with sound-deadening material sandwiched in the middle. Because of the heavy weight of these doors, it is important that the hinge hardware and doorframe be designed to support the weight for ease of operation.
Vertical Lift and Overhead Doors (engine access)
Sound controlled doors are available in both vertical lift (telescoping) and overhead type doors. The STC rating for these doors is low because it is difficult to have good seals at the section joints and doorframe. In addition, the weight of the door must be low so it can be lifted. Most vertical lift and overhead sound controlled doors never exceed an STC-30 rating. For this reason, these doors should only be used in dynamometer applications where the door is along an exterior wall and local sound regulations permit higher noise levels to the outside of the building. These doors should have spring-loaded sound seals around the perimeter and be power-operated.
Observation Window(s), Pipes, Conduit and Ducts
An observation window(s) must be resistant to high impact because of potential engine and driveshaft failures. This usually requires bullet-resistant glass, double or triple pane. Bullet-resistant glass is multi-ply using polycarbonate, thermoplastic, and layers of laminated glass. If a total driveshaft failure occurs, the thick bullet-resistant glass offers greater protection for the operator. For additional protection, the observation window should not be located in a direct line of the driveshaft area. In a double pane installation, the glass closest to the dynamometer is tilted out at the top about 7° to reduce reflections and glares. Tilting the glass in double pane installations also helps with sound control. Windows must be gasketed on all four edges. The jambs of windows must also be sealed where they contact the wall. All pipes, conduit and ducts that penetrate the ceiling, floor and walls should be insulated and sealed to prevent sound leaks.
To learn more about Test Cell safety features or to simplify the complex challenges of the Test Cell environment, contact Taylor Dynamometer. We’ll save you time and money while ensuring safety and success. When you choose Taylor, you gain a partner who takes full responsibility for your Test Cell project. That means supporting you with everything you need to succeed – from expert advice to configuration, installation, training and lifetime product support.
Taylor Dynamometer – Everything you need to succeed. Contact us today with your testing challenges (414) 755-0040, firstname.lastname@example.org.