Noise transmission

I oise Transmission Reduction in HVACSystems. One common use of sound-absorbing treatment is to reduce noise transmission in heating, ventilating, and air-conditioning (HVAC) systems (6). The treatments ate used to reduce the transmission of fan noise and air turbulence noise through ducts into occupied spaces. Noise transmission reduction in duct systems is described in terms of insertion loss, the difference in sound power level or sound pressure level measured at a given location before and after installation of the treatment or sound attenuation, the reduction in sound power between two locations affected by a sound source. The units ate decibels. 

When the noise transmission takes place in a free field (no reflective surfaces), it is possible to calculate the pressure levels at different distances from the source. For spherical propagation, the following formula can be used ... 

The automotive industry is under continued pressure to improve the environmental performance and useful life of automotive components. S-SBR producers are responding to develop SBR grades with optimum combination of rolling resistance, wear resistance, blow-out resistance, chipping/chunking resistance, road traction under a variety of weather conditions, handling, noise transmission, and other performance properties for different tire applications. 

High rain and acoustic noise transmission Resistant to impact damage from blunt but not sharp objects. Patch repair possible - ... 

Acoustic screens Figure 20.13) are effective in reducing the direct field component noise transmission by up to 15dBA . However they are of maximum benefit at high frequencies, but of little effect at low frequencies and their effectiveness reduces with distance from the screen. 

In the office situation, if it is open plan, use may be made of barriers of composite material, porous ceiling tiles and porous flooring to reduce noise transmission and reflection. Noise can come from conversation, older style printers, telephones and so on. Well designed partitioning in closed plan offices is also effective. Serious interference by ontside noise may be coming via windows. Double glazing can reduce this. 

Noise transmission is generally controlled either through the use of barriers or sound-absorbing materials (or a combination of both), as illustrated in Figure 9.15. 

For the calculation of noise transmission into the enclosure, a simplified model shown in Fig. 4 has been chosen. A cantilever box beam is attached to two stiffeners of the discretely stiffened sidewall. A random point couple is acting at the free end of the cantilever beam. The walls at z 0 and z = d of the acoustic enclosure are treated with absorbtive materials which are represented by the point impedance model as... 

A transfer matrix procedure was developed to study the noise generation and transmission for complex stiffened and interconnected structures. It has been shown that transmitted noise levels in the interior are sensitive to the structural dynamic characteristics not only of the stiffened sidewall but also of the sub-structure to which random loads are applied. Significant differences were found in noise transmission characteristics and levels between a completely coupled case and an idealized condition where the response of a sub-structure is computed independently from the response of the noise transmitting sidewall. 

Vaicaitis, R. and Bofilios, D. A., Noise Transmission of Double Wall Composite Shells, ASME Conference on Vibration and Sound, Cincinnati, Ohio, September 1985. 

Vaicaitis, R. and Slazak, M., Noise Transmission Through Stiffened Panels, Journal of Sound and Vibration Vol. 70(3), 1980, pp.413-426. 

McDonald, W., Vaicaitis, R. and Myers, M. K., Noise Transmission Through Plates Into an Enclosure, NASA TP-1173, 1978. 

The analysis of barriers should take into account the duality availability/safety. In view of the complexity and of system automation, availability becomes a sizeable criterion when designing and implementing reliable and secure concepts. The system must be tolerated by normal and/or transient variations (noise transmission,... 

There are many noise sources that can penetrate into the eabin of an automobile, but only a few that penetrate through the primary body seals. Sources of noise transmission through primary body seals are ... 

Most current produetion automobiles use triple sealed doors, whieh comprise of a eontinuous body mounted primary seal, a continuous door mounted primary seal and a series of segmented auxiliary seals around each door. Observations at the 2006 Detroit Auto Show indicate that double sealed door apotures are only currently being nsed by U.S. manufactured trucks. The body and door mounted primary seals act as a double barrier to noise transmission and aspiration, while the auxiliary seals are for air and water management. 

Figure I. Noise Transmission Through Automotive Body Seals...

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