Lauren Ronsse - lronsse@ku.edu
University of Kansas
Lawrence, KS
Popular version of paper 2aAA2
Presented Tuesday morning, November 16, 2004
148th ASA Meeting, San Diego, CA
The relationship between the location of rock art and the acoustical properties of its immediate environment has been a source of previous investigation. This topic, known as rock art acoustics, involves the study of rock art that has been placed in locations with strong discrete echoes or flutter echoes. Previous research has shown that often ancient rock art was placed on surfaces or in locations that echoed, whereas locations without such echoes were undecorated [S.J. Waller, 2002 Rock Art Acoustics in the Past, Present, and Future. 1999 International Rock Art Congress Proceedings 2:11-20]. This study examined six rock art sites located in Ellsworth County, Kansas to determine if a similar pattern exists in the Mid-American Plains.
All of the sites that were examined are located in an eleven-square-mile portion of southeastern Ellsworth County. At each site, the rock art is located on yellow Dakota sandstone outcroppings ranging from 30 to 70 feet high. The specific topography of the different rock art sites affected the acoustical properties observed at each site. At the various sites tested, the rock art was located in a topographic bowl. Such bowls create areas that are conducive to acoustically rich environments. It was found that often the rock art was located near the center of a concave rock face. In other cases, the decorated rock face was part of a larger concavity in the landscape. At each site, strong echoes were perceived to be emanating from the rock faces containing the rock art. Similar methods and items of equipment were used to analyze the acoustical properties of the several rock art sites. At all sites tested in this study, impulses were created to energize the space. The impulses included a human shout, a clap, the popping of a round 16-inch-diameter balloon, and the firing of a 22 short black powder blank from a North American NEF starter's pistol. Using these various impulses allowed for both a recreation of the sounds the Native Americans would have heard and a standardized noise that could be repeated at each site. The impulse and impulse response were recorded using an instrumentation type condenser microphone cable-connected to a USB audio device and a PC notebook computer. At one site, recordings were also gathered while generating an MLS signal as well as a sine wave sweep. See Figure 1 for an image of a typical equipment setup. Using the combination of these methods and equipment provided an effective, portable means of conducting the study.
An example of the equipment setup and results obtained at one of the rock art sites studied is described. At Alum Creek Bluff, two different rock faces containing rock art were tested. The rock faces in this area are yellow Dakota sandstone, now covered with foliage in many areas. Alum Creek runs along the face of a bluff embanked on the opposite side by an 8 feet high dirt ledge. At the first testing location, the exposed rock face is about 40 feet wide on a 70 feet high bluff. The petroglyphs at this site are 2.5 feet above the base of the rock face near the center of a concavity in the bluff approximately 200 feet wide. The rock art includes a zoomorphic, arrow, and rectilinear glyphs. See Figure 2 for images of the petroglyphs.
The impulses and impulse responses were recorded 140 feet north of the rock face. The recording location was positioned just before the ground drops off to the creek below. At the recording location, an echo could be heard off the decorated rock face after each impulse from the balloon, shout, clap, and pistol was created. Impulse responses are shown of resulting data in Figures 3 and 4. The balloon recording is shown in Figure 3 at 250 Hz. The echo peak occurs 270 ms after the initial impulse peak. The shout recording is shown in Figure 4 at 400 Hz. The impulse and impulse response peaks on this graph are separated by about 295 ms. Since the recordings were taken 140 feet from the rock face, the estimated time that should have elapsed between the initial impulse and first impulse response was approximately 280 ms. Therefore, an observable echo did occur, which was most probably reflected by the decorated rock face.
Similar echoes were found at the five other rock art sites tested. This study found that the echoes occurring at the decorated sites were noticeably louder than any reflection of sound observed in the surrounding areas. The occurrence of echoes at the rock art sites indicates that the early peoples in this area may have been aware of their acoustical environments. The objective of this study, however, was met by obtaining descriptions of the rock art acoustics of six different sites.
This study was conducted under the instruction of Professor Robert Coffeen. The equipment used was provided by Professor Coffeen and the University of Kansas. Martin Stein at the Kansas State Historical Society provided the rock art site descriptions and maps. Ronald K. Rathbun provided access to and descriptions of the petroglyphs on his land. All of the sites were visited and recordings were made with the help of the author's father, Peter Ronsse. His continued enthusiasm allowed for the success of this project.