We all agree those cicadas were loud! But just how loud were they?
Thankfully, Civiltech has a curious engineer who specializes in measuring traffic noise. Armed with a Class I sound level meter usually used for highway traffic noise monitoring, Civiltech’s Jim Woods, P.E., PTOE, first headed out into his own back yard to do some measuring. The intrigue lured him further afield, and he decided to go to the Morton Arboretum and check out the sound level there. Jim drove around the arboretum trying to ascertain the loudest spot and settled on a location near the Big Rock Visitors Station. He noted that the cicada chorus was loudest at the edge of forested areas exposed to the sun.
Jim observed that the insects were producing two different pitches. One was a higher-pitched “insect sound,” which was layered over a lower drone with more of a “sci-fi alien spacecraft” sound. Based on some research, Jim suspects that the higher sound came from the Magicicada cassini species, while the lower-pitched sound came from the Magicicada septendecim species. Both are part of the 17-year periodical emergence currently winding down in our region.
The higher-pitched M. cassini chorus was focused around the 6.30 kilohertz (kHz) frequency band, equivalent to a musical note that is well beyond the highest key on a piano keyboard. The lower-pitched and relatively quieter M. septendecim sound was in the 1.25 kHz range, like striking a piano key approximately three-quarters of the way up the keyboard. 
With respect to the sound intensity, the sustained noise level of the combined cicada chorus measured a whopping 88.5 decibels (dBA)! The cicadas’ chorus ebbed and flowed in a wave pattern, fluctuating between 82 and 89 dBA. Jim recounted that the loudest traffic noise measurement he’s taken for a highway project was approximately 75 dBA, along I-90 near the I-290 interchange in Schaumburg. The 14 dBA difference is substantial. Subjectively, most people would say the 88.5-dBA cicadas were over twice as loud as the 75-dBA traffic noise measurement. 88.5 dBA is well above the federal traffic noise thresholds of 67 for residential and 72 dBA for commercial properties. When traffic noise is above these thresholds on a highway project, noise abatement walls must be considered.
Jim verified what we all were experiencing: the cicadas were indeed loud! As the 17-year event winds down and whether you’re glad or sad to see them go, we can all agree that at least the return to peaceful and cicada-free nature sounds is welcome.