In pursuit of the Windsor Hum

There is a rumble in the air in Windsor, Ontario, Canada, or more accurately, a hum. A low-frequency, rumbling sound rattles the windows in this border community, which lies just across the river from motor city – Detroit.

Image above: View of the heavily industrialised US Zug Island from the Canadian side of the Detroit River.

Locals have described it as a steady droning sound, much like a large diesel truck idling, or a loud boom box. Whatever it is, some residents say it is driving them crazy, and that the source must be found.

Since the early ‘70s, similar phenomena have been perceived on a worldwide scale. Reports of humming, howling, and rumbling have littered the news in communities including Sydney, Australia; Taos, New Mexico; Leeds, England; and Vancouver, Canada. In each of these cases, the media have told stories of residents being kept awake at all hours of the night, subject to intermittent humming noise in their own homes and consequently disrupting their lives. With each report comes a wide range of potential sources. Predictions vary from mechanical sources (submarine activity, generators, worn industrial machines), sonar systems and radio towers, environmental features (rock faults and coastal shifts), to human traits, such as psychological problems and tinnitus. Whatever the theory is, all those affected demand a resolution be found to alleviate their discomfort.

In pursuit of the Windsor Hum

Zug Island. Copyright © Airphoto Jim Wark.

Concerned citizens
The hum in Windsor generated concern among the citizens of this industrial city to the point where the Canadian government agency for natural resources, National Resources Canada, performed a study to find the source. While they were able to confirm its existence, the study fell short of identifying the cause. However, through triangulation of ground vibration measurements, they were able to estimate the origin of the source to Zug Island, a highly industrialised piece of land on the US side of the Detroit River. This is where researchers from the University of Windsor came in, since the research arm of the Canadian Federal government did not have the technical resources to investigate further. The department of Foreign Affairs and International Trade approached the university’s Noise, Vibration and Harshness­ and Sound Quality Research Group to further investigate the source of the elusive rumble.

In January 2013, a press conference was held at the University of Windsor to announce federal government funding to locate the source of the ‘Windsor Hum’, in an attempt to protect the quality of life of Windsor’s citizens. The proposed research was separated into two phases; the first, to validate the existence and characterise the nature of the phenomenon, and the second, upon confirming these characteristics, to use advanced source identification techniques to zoom into specific areas of interest – the only methodology available to the research team without having direct access to Zug Island.

In pursuit of the Windsor Hum

Pentangular microphone array on the university research vessel.

Cloud-based noise monitoring
For the first phase, two Brüel & Kjær Noise Monitoring Terminals (NMTs) were deployed. These units are designed for permanent, mobile, or portable monitoring, where long-term, real-time, unattended outdoor noise measurement is required. The measurement data is recorded and communicated to Noise Sentinel servers, a cloud-based service where continuous noise data is remotely logged and noise level exceedances are flagged.

In this case, the communications were transmitted using 3G cellular technology, where the data is then available to the researchers through any Web interface. This way, the researchers were able to see, hear, and analyse the measured noise data from the comfort of their laboratory.

The first NMT was a permanent unit installed near the Detroit River shoreline, directly across from Zug Island. The second NMT was a portable unit that was installed and relocated to different residential areas of the city where reports of the Windsor Hum were made on a regular basis. Due to the remoteness of the deployment sites, the NMTs were powered using batteries and solar panels, remaining independent of mains power supplies.

First break in the case
While the first few months of data collection were relatively uneventful, the first real break occurred in early July with a definite recording of the characteristic hum that lasted through most of the night until approximately four in the morning. The excitement within the research team was as if they had captured a detailed photograph of the elusive Big Foot creature. Better yet, the hum continued to manifest itself every night for several weeks, usually beginning in the late evening and stopping at about the same time.

To better characterise the acoustic signature of the hum, the Windsor researchers deployed a portable LAN-XI data acquisition system with the LAN-XI Notar™ stand-alone recorder. This setup allowed the researchers to record extremely high-resolution data in the field and then perform post-processing analysis using PULSE Reflex™ back in their laboratory. From this, a very high amplitude, low-frequency tone was finally identified, which looked and sounded like the varied reports from the community.

Having found and characterised the hum signal, the next step was to locate the actual source. Because the team did not have access to the US land on the island, they again looked to their arsenal of Brüel & Kjær equipment and decided to use a pentangular array to ‘see’ the hum source. The large, 3.5-metre-diameter array, equipped with 30 microphones, uses acoustic beamforming to visualise acoustic emissions – a result which looks very much like a thermal image, where bright powerful colours represent loud sources of noise and darker colours represent quieter areas of emissions. While the pentangular array is best for sounds above 100 Hz, it still proved to be a useful tool.

In pursuit of the Windsor Hum

Under cover of darkness
The next challenge was to get the pentangular array in close proximity to the island. For this, the array was mounted in a small boat usually used to research marine life in the North American Great Lakes. Because the hum was most prominent at night, the researchers also had to take the array near to the US shore in the dark and collect their data at about 100 metres from the shoreline. This of course raised the suspicions of both the US Coast Guard and Homeland Security, who appeared out of nowhere in the darkness to investigate the researcher’s activities. Nonetheless, the team was able to collect sufficient data and make it back to the Canadian shore without spending any time in a US jail cell.

The pursuit of the Windsor Hum has gained international notoriety from prominent news reports, resulting in enquiries from people affected by similar hums around the world. Both the Canadian government and the University of Windsor researchers, armed with their Brüel & Kjær ‘noise solution toolboxes’, are dedicated to solving this mystery. A final report is expected to be reviewed by the Canadian government in early 2014 with the hope of alleviating the concerns and discomfort of the community, who only wish for a good night’s rest once again.

> In pursuit of the Windsor hum - revisited