Reducing Low Frequency Noise Transmission


The negative physical health outcomes associated with high noise exposure are well-known to the soundscape community, including hearing loss, sleep disruption, and a decrease in a variety of cardiovascular health markers (Marquis-Favre, Premat, Aubrédue, and Vallet 2005: 615-616). In addition, noise exposure is associated with a variety of mental health issues, including stress, annoyance, and impaired cognitive function (Marquis-Favre, Premat, and Aubrédue 2005: 629-631; Leventhall 2009: 95).


If noise is defined simply as “unwanted sound,” inevitably some people will want a particular sound that others do not, leading to obvious conflicts when many people are within earshot of each other. For this reason, the soundscape community has historically emphasized the role of context in interpreting sound, rather than applying a generic label of “noise” to a single sound source. As the economy grinds to a halt under lockdown, many noise sources, such as traffic, industrial machinery, and workplace chatter, are greatly reduced. Yet these also have a role to play in a healthy soundscape. The routine of commuting – immersing oneself in an office, returning to a quiet home, resting, and repeating – gives rhythm and order to our daily lives. But under a quarantine, for many the only soundscape is the monotonous background noise of one's home.


In rural and suburban areas, large spaces between homes make it rare for sounds to be heard from a neighboring house. But in urban areas and most multi-unit apartment complexes, it is common for some sound to be transmitted from one dwelling into another. Over half the global population now lives in cities, and this portion is expected to increase until 2050, making this an issue whose relevance will likewise grow for the foreseeable future (Buhaug and Urdal 2013: 1).


It has been known for over a hundred years that low frequencies disproportionately transfer through insulating materials: Berger (1911) noted that transmission loss increased by 6 dB per doubling of frequency or per doubling of mass per unit area. Many older buildings which still survive were constructed for the wealthier citizens of their time and feature heavy, airtight construction which provides relatively good low-frequency insulation. Post-World War II buildings often relied on cheaper materials, allowing more low frequency sound transmission (Rindel 2007: 2). Given the limited frequency response of consumer technology at the time, this may have been acceptable, but as more of the population acquires subwoofers, this type of dwelling becomes increasingly unacceptable. 


While policy elites might hope that the average citizen might use their quarantine time to read Boccaccio’s Decameron on Project Gutenberg, or stream operas in HD from the Metropolitan Opera (which emits relatively little low frequency energy, since such high SPLs below 100 Hz were not physically or economically feasible before the advent of electronic amplification), these are niche entertainments, and it is far more likely that the average person under quarantine will stream pop music or superhero movies, which will emit large amounts of low frequency energy. This will not sound unbalanced in the room where the sound is emitted, as it is balanced by the high frequency spectrum of the sound source. But only the bass frequencies will reach neighbors, who may be exposed to repetitive and annoying low frequencies without any ambient masking noise, causing greater annoyance (Rindel 2003: 3-4; Rindel, Løvstad, and Klæboe 2017: 8-10).


This is, of course, not a new issue, and urban noise codes have been updated in the past decade to deal with the unique problems of low-frequency noise transmission (Shamoon 2012). However, such noise codes grant allowances for more noise during the day, assuming that a significant portion of residential units will be empty during business hours as residents go to work in commercial spaces. 


Indeed, many public spaces across the globe have become dramatically quieter since quarantines were imposed. Just as underwater silence can indicate ecological problems in a coral reef, so too the new silences caused by the coronavirus are a sign of damage to the complex soundscape of urban ecosystems (Atkinson 2007: 1905-1917). Additionally, we should keep in mind that increases in bandwidth and signal-to-noise ratio have created a more “hi-fi” environment in the context of Murray Schafer’s original conception of the soundscape (1977).


However, in private dwellings the situation is dramatically worse during a pandemic: a months-long quarantine in urban areas will likely mean that high-strung professionals working from home find themselves adjacent to unemployed people distracting themselves with a movie in the middle of the day. Extroverts, who may feel drained of energy from seclusion, may pump EDM playlists through their subwoofers while the introvert next door is much more likely to be highly sensitive to repetitive bass lines from which they cannot escape (Aron and Aron 1997: 345-368).


While the psychoacoustics literature has typically focused on the negative impacts of noise transmission, in-depth interviews by soundscape researchers have also shown that lonely people sometimes find their neighbors’ music to be a source of comfort (Waldock 2011). However, the very personal nature of such an interpretation suggests that it should not be generalized into public policy. There are many existing technological means to introduce wanted soundscape elements into one’s home, which will be covered in more depth in the second half of this essay. Indeed, the special nature of “home” sets this space apart from public or corporate spaces in which we take part, acknowledging someone else’s primacy over the soundscape. Being forced to stay inside one’s dwelling by law and then being repeatedly exposed to unwanted sound is the beginning of what Steve Goodman has termed “sonic warfare” and indeed bears some similarity (albeit at a lower sound pressure level) to the strategy imposed by the US government on Manuel Noriega as he hid in the Vatican’s embassy in 1989 (Goodman 2010: 59-62).


Both total noise exposure and conscious attention of the listener are correlated with people who are “highly annoyed” by their acoustic environment (Schultz 1978: 377-405), and both of these conditions are likely to be present throughout a lockdown. Introduction of a new noise source is generally perceived as more annoying than one that is part of an individual's routine already, so going into lockdown could exacerbate annoyance at noise from neighboring units. Given the already significant mental health risks from being indoors for so long, additional long-term exposure to annoying noise transmission will make a long quarantine even more intolerable.


Though the best solution is to construct high-density housing with good low frequency sound insulation, this is also expensive and obviously cannot be done as a rapid response to a crisis. To paraphrase the former US Secretary of Defense Donald Rumsfeld, we go into a lockdown with the apartments we have, not the ones we would like to have. It is not cost-effective to purchase noise-cancelling headphones for every urban inhabitant who might need them, not to mention that even noise-cancelling circuits only remove airborne sound at the ears, not the visceral feel of bass frequencies, whose resonance can be felt in multiple cavities in the chest and head. However, there may be some policy solutions (both bottom-up and top-down) that can be implemented quickly upon the introduction of lockdown procedures.


Voluntary solutions might stress the importance of being a good neighbor during a pandemic: in the midst of the crisis, many are already stressing the importance of wiping down doorknobs and assisting those who are immunocompromised. In the same way, the soundscape community ought to emphasize minding one's own sound production during a lockdown. The average citizen, most likely being unaware of the nonlinearity of human hearing or sound transmission at low frequencies, is probably not aware of how loud their music sounds to their neighbor. Simple explanations of these phenomena in media outlets could help cultivate greater social responsibility about one's use of sound. 


There are also possibilities for top-down solutions in the midst of such a crisis: since an increasing amount of music and television consumers get content through streaming rather than ownership, this could be implemented via a moderate high pass filter at 100 Hz by companies like Netflix, Hulu, or Spotify. Theoretically, such a change could be applied voluntarily, as with a button labeled “Good Neighbor Mode” with a bit of explanation for the change. However, as humans become more sensitive to spectral changes when they can toggle the option on or off, this might simply draw more attention to the filter, making it less likely to be chosen. A better (top-down) solution might simply be to use location data to infer which users are listening in apartment buildings and apply the filter automatically until the crisis is over, perhaps only during nighttime hours when stricter noise codes would be in effect. Granted, this will not affect users who own their own music, but it would be a significant nudge toward more neighborly acoustic behavior.