In a previous post I discussed the influence of shop doors on the acoustics of the space. The basis analysis and methodology will be published in a forthcoming edited volume (hopefully in June). Recently, I have been exploring the acoustics beyond the facade or shop front and looking at street noise. Much of the methodological approach remains the same; dimensions and construction material form the baseline of the acoustic analysis. However, certain elements are missing in street canyons that mean sounds react in different ways to the space.
First, the lack of covered or enclosed space means that large areas will not reflect sounds. It is a basic feature of streets that they are open to the sky and rarely covered. In acoustic terms, this means that much of the sound will dissipate over distance, as opposed to being absorbed by the physical walls or ceilings, as happens in enclosed rooms.
Despite the lack of covering, the pavement and building facades will reflect and absorb the sounds and noises of the street. In contemporary acoustic design, traffic noise is the primary nuisance, which acoustic designers and architects try to limit. It was, in fact, the high levels of traffic noise that began the search for standard acoustic measures. Emily Thompson has a fantastic book, *The Soundscape of Modernity*, that charts the history acoustics as a field in the start of the modern period.
In terms of ancient streets, in a similar manner to enclosed spaces the types of materials can be assessed for their absorption coefficient, a standard measure of a materials ability to absorb sound. These basic elements can again be plugged into a predicative equation to measure the absorption.
The second deficulty with streets is the complexity of the arrangements. Even building facades present a complex sound field with various surfaces, materials and architectural features. In Ostia, several buildings have monumental entrances with pillars, columns, or pedestals and some times all three. These features will change the way the sound reflects off the surface. Even more problematice, although I do really like the challenge, is the widespread use of colonnades or porticos. The space of the portico is, again, partially covered and partially open. This means that sounds from the street can fill the portico, as well as sounds within the portico only being heard in close proximity to the space. The nature of porticos present their own acoustic character, quite unlike other street spaces.
It has been fun to explore the ways these acoustic features of streets, and porticos, can help us to better understand the street as a social space. I have just begun to map the effects of conversation noise in certain streets in Ostia and I will post an update as I write more about the street space. I will be presenting some of these findings this weekend in Umea, Sweden.