This Noise Monitoring Terminal by Denmark’s Brüel & Kjær is installed in the City’s financial district, immediately adjacent to the building works associated with the World Trade Center. A label on its face marks it as “Property of the Port Authority of NY & NJ” (who own much of the site) and gives phone numbers to call “for assistance.”

Carpenter, Sherwood, and Leung describe the system in an article published in the Journal of the Canadian Acoustical Association:

The monitoring system includes four (4) noise and five (5) vibration monitors placed along the perimeter of the WTC site in Lower Manhattan. ButterJAM established a web interface which queries noise and vibration monitoring databases within the off-site server. The data is automatically sent to an innovative compliance website which displays appropriate data and allows access by authorized users. The system provides e-mail alerts, warning of any noise or vibration limit exceedance or equipment malfunction. In addition, the system automatically generates reports and directly e-mails reports to authorized personnel.

Specifically of the noise monitoring portion of the system, of which this sensor is a part,

PCA chose the Bruel & Kjaer 3639 Noise Monitoring Terminal (NMT) for remote noise monitoring at the WTC site. Each NMT includes a Bruel & Kjaer Type 2250 handheld analyzer/sound level meter, a Bruel & Kjaer 4952 outdoor microphone, Bruel & Kjaer 7843 Environmental Noise Management Software, a First Power FP12170 12-V back-up battery, a Sierra Wireless Raven X V4221-V wireless modem and a digital multi-band directional antenna 489-DB. The sound level meter, wireless modem and backup battery are stored within a cabinet. Each NMT requires AC power and adequate cellular signal strength.

Type	Sensor
Owner/Administrator	Port Authority of New York and New Jersey
Manufacturer	Brüel & Kjær
Terminal Model	Noise Monitoring Terminal Plus, 3639-A-100
Data Sheet/Manual	link
Microphone Model	Outdoor microphone, 4952
Microphone Specifications	link