Functional Sound Absorbers Reduce Noise Levels

This article deals with the utilization of unit sound absorbing panels - "Functional Absorbers" - to reduce background noise and reverberation in the engine generator pump room and the blower room at a waste water treatment facility in Coney Island, NY.

Introduction. Noise levels in the pump room and blower room exceeded OSHA requirements and communication between workers was extremely difficult. Part of the problem was the nature of the construction of the two large rooms. Walls and floors were made of concrete and the ceiling was metal deck, all of which are highly reflective surfaces. There were multiple pieces of equipment in each room. The average background noise levels in the pump room were 92 dBA, while in the blower room they were 87 dBA. A goal was set to reduce the level to 85 dBA or less.

In October 1995, rooms within the integrated wastewater and sludge treatment facility were evaluated as to their noise problems. Based on these studies, several rooms would need to be treated with unit sound absorbing panels

Acoustical treatment to achieve maximum noise reduction was calculated. Functional (unit) sound absorbing panels were installed on the ceilings and walls of both rooms. Average noise level in the pump room was reduced to 85 dBA and in the blower room to 82 dBA, bringing the rooms into OSHA compliance and reducing reverberation to levels that did not interfere with communication between workers.

Engine Generator Pump Room. In the generator rooms, which are 87 ft wide × 153 ft long × 41 ft high, there are four sets of 2500 HP diesel engine generators, with multiple pumps available. The generators drive 600 HP motors, which operate the pumps. In the normal running mode, one engine set is used to drive two or three pumps. A typical overload is two engine sets driving four pumps. One of the other sets of engine generators is redundant, the other is in reserve. Sound level measurements were taken at eight locations within the room at various distances from the engine generators prior to installation of Eckel's Eckoustic Functional Panels (EFPs) as shown in Figure 1. Noise control involved ceiling treatment with 6602 ft^sup 2^ (50%) coverage and wall treatment with 2069 ft^sup 2^ (10%) coverage (Figure 2). For the ceiling treatment, three-quarters of the panels were 30 in. × 10 ft EFPs; the reminder were 30 in. × 8 ft. On the walls, the panel sizes were 48 in. × 8 ft and 24 in. × 6 ft. With one engine set and three pumps running, the background noise was reduced from 92.6 dBA to 82.7 dBA after EFP treatment, a reduction of 9.85 dBA. With two sets of engine generators and four pumps running, average noise levels were reduced by 6.98 dBA, to bring the overall noise level below 85 dBA, as shown in Table 1.

Blower Room. Similar results were obtained for the blower room. A mix of panels sizes were used - 30 in. × 10 ft, 30 in. × 8 ft, 30 in. × 4 ft, and 42 in. × 5 ft - as the most efficient means of achieving the desired noise reduction. This room measures 53 × 120 × 25 ft; 2651 ft^sup 2^ of panels were adequate for effective treatment (Figures 3 and 4). With two blowers running, the average noise reduction with EFPs installed was over 5 dBA, from 86.6 dBA to 81.3 dBA, as shown in Table 2.

Conclusion. Unit sound absorbing panels offer several advantages as a method of adding sound absorption to spaces with hard reflective surfaces. They can be installed in new or existing facilities without interference with utilities such as sprinklers, lighting, ventilation, etc. They require little or no maintenance and are extremely effective in lowering background noise and reverberation in a wide variety of industrial and architectural application