Noise Curtains

by dB Engineering

A New Rotary Screw Chiller Disturbes Visitors

It was getting pretty hot at this art museum. The director of the facility decided that the best way to improve the efficiency of the museum's air conditioning system would be to install a new rotary screw chiller. The problem was that it had to be placed in the same location as the older, quieter unit, a maintenance workshop space measuring about 15'x40'. Unfortunately, it would also be adjacent to one of the museum's display areas.

The concern was that the higher noise levels generated by the new Carrier chiller would disturb visitors in the display viewing area. They were also worried that they would lose the effective use of the remaining workshop space-more than 400 square feet. Another consideration was the heat generated by the unit itself. Would it overheat the entire work room, making it impossible to work in?

An acoustical curtain enclosure was determined to be the most cost effective way to reduce noise. The acoustical curtain enclosure design would provide: accessibility, sufficient air flow for ventilation and most important, the noise reduction necessary to allow for undisturbed enjoyment of the museum's displays. The museum was delighted to learn that this kind of acoustical treatment could be fitted around the equipment to allow for use of the rest of the space. The work room would be intact.

As soon as the chiller was installed, Sound level readings were taken. Generally, the levels were 93 dB(A), with the dominate disturbing frequencies at 250, 500, and 1,000 Hz.

BSC-25 was selected to provide the required sound attenuation as well as random sound absorption within the concrete-surfaced workroom.

BSC-25 is a combination of a quilted fiberglass sound-absorption material with a loaded vinyl noise barrier septum. It is fabricated into modular acoustical curtain panels with grommets at the top, and hook and loop fasteners along each edge. Individual panels are joined together to form any configuration necessary.


After the enclosure was constructed, sound level readings were taken again.  The results were more than satisfactory.

  1. The acoustical curtain enclosure brought the work space noise levels down to 73 dB(A) - a reduction of 20 dB(A).  According to Kevin, it is now quieter than it was when the old chiller was operating!
  2. The  vent baffles were placed to duct air over the hot spots, thus causing the chiller to be properly cooled, and the work space to be at normal temperatures.
  3. The noise of the chiller in the museum viewing area is lost in the ambient background levels of the low 50's.

FIELD MEASURED NOISE REDUCTION
Octave Band Center Frequencies (Hz)

Location/Freq A 125 250 500 1k 2k 4k 8k
Loc. 1 Before
(6' from chiller)
93 74 86 89 88 82 68 60
Loc.1 After
(6' from chiller)
73 70 68 73 69 63 60 53
Noise Reduction 20 4 18 16 19 19 8 7

 

Table showing how the human ear perceives noise reduction.

Decibel Reduction Reduction Experienced by Ear
2 15%
4 23%
6 38%
8 48%
10 56%
12 63%
14 68%
16 75%
18 77%
20 81%