087

»For specific grades, see manufacturer's data; note that the term NCR, when used, is a single-term rating that is the arithmetic average of the absorption coefficients at 250, 500,1000, and 2000 Hz. Source: Reference 8.

»For specific grades, see manufacturer's data; note that the term NCR, when used, is a single-term rating that is the arithmetic average of the absorption coefficients at 250, 500,1000, and 2000 Hz. Source: Reference 8.

addition of absorbing material to the walls or ceiling will likely be ineffective. Nevertheless, the noise reduction could amount to 5 dB and thus could mean the difference between compliance and noncompliance with existing criteria.

The use of barriers near or enclosing the pump can be much more effective than environmental absorption treatments, particularly if the barriers totally confine the noise-producing components (Figure 11). Acoustic barriers simply interrupt the airborne path from the source to the listener. Such barriers work best (have the highest transmission loss) when

1. Their area density is high.

2. They are total enclosures and all joints are well sealed against air leaks.

3. They are not mechanically tied to the vibrating surfaces of the pump (that is, they are mechanically isolated).

For total enclosures, the barrier area density controls transmission loss for noise frequencies above the lowest mechanical flexural frequency of the barrier panels. Loosely sprung but well-sealed and heavy panels therefore serve this function well. Treating the interior of the enclosure with sound-absorbing material tends to reduce the apparent source strength by preventing reverberant buildups in the enclosure. Note that the use of a total enclosure around a pump may cause other operational problems that must be dealt

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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