Location: Wilmington, Delaware
HGC Engineering was retained by Dupont to investigate noise complaints they had received from residents living nearby the Experimental Station in Wilmington, Delaware. The sound of concern had been described by the residents as a “whoosh” that is continuously audible. The source origin of the noise was undetermined despite investigative testing and measurements by others.
The Experimental Station is the largest industrial complex in close proximity to the concerned residents. Other facilities in the neighborhood include a pharmaceutical facility and a hospital. Due to the proximity and size of the Dupont Experimental Station, the residents directed their concerns to DuPont. Prior to our involvement, acoustical measurements and other investigative measures had been conducted (with oversight by the Delaware Department of Natural Resources and Environmental Control) which demonstrated that the sound levels of the DuPont facility were within the quantitative limits stipulated in the Noise Regulations of the State of Delaware. Nevertheless, as a good corporate citizen in the community, DuPont commenced a noise investigation to identify, if possible, the source of offending sound.
With permission from the concerned residents, sound level measurements were conducted at their home over an extended campaign. A sound level monitor was deployed on the property, and configured to continuously compile and log sound levels in 1/3 octave band frequencies throughout the duration of the investigation. The monitor was also configured to capture continuous audio recordings, to allow for post-processing of any acoustical events of interest.
Where access allowed, we conducted sound level measurements of the acoustically dominant sources of outdoor sound at the DuPont facility. Sound intensity instrumentation and methods were used, employing methods from ISO Standard 9614-2. Unlike simple measurements of sound pressure (e.g., with a sound level meter), the sound intensity technique uses a directional probe and sophisticated analyzer to measure both the magnitude and direction of the sound propagating from a source, and can thus accurately isolate the sound emitted by each source from any nearby sources and reject interference from background sound.
The source sound power levels, determined from the sound intensity measurements were used to develop a predictive acoustic computer model of the DuPont facility and surrounding community (including the pharmaceutical facility, nearby hospital and waterfalls, to rank the contribution of each source/facility to the sound levels at the concerned resident’s home. Attended sound level measurements completed throughout the community and in the surrounding areas around the Experimental Station, during periods of minimal interference from background sound (i.e. during overnight hours), were utilized to calibrate the acoustic model. These measurements were also utilized to quantify potential impacts from the other industrial sound sources in the community.
In addition to the sound intensity measurements and the predictive acoustic model, narrowband fast fourier transform (FFT) data was also collected at the concerned resident’s property and at various sources at the Experimental Station. FFT measurements are used to identify specific acoustic signatures from noise sources.
Through the various measurement and predictive tools, a number of specific sources were identified as potential contributors to the noise at the concerned resident’s home. The results provide direction for Dupont to modify future maintenance and replacement activities and potentially develop noise abatement for the noisiest sources.
Acoustical Engineering Services Included: