Page 35 - Jul2009

Fig. 8. Geophone positioned on the metal grating in the service stairwell under- neath the summit. Credit: France Languérand.
Fig. 6. Another view of the sub-basement equipment with a portion of the large orange accumulator on the left. Credit: France Languérand.
tenance staircase surrounded by the open geometric pattern- ing of iron that forms the structure. There again, the binaur- al recording method was limited to the staircase, but what was captured by both the geophones and binaural micro- phones was remarkably dynamic: regular metallic clattering of the ascending and descending elevators, second harmon- ics of the wind through the infrastructure, and of course the occasionally radical changes in noise as wind screens were blown off by gusts (Fig. 9, Clip 6).
On a clear day the summit provides spectacular views of the city—up to 40 miles away. That day, however, there was a taxi protest so when we looked down we saw the taxis lining the streets for hours protesting for a wage increase. While we were told that this was not that unusual, the semi-constant tones of French taxi horns were fleetingly picked up, even miles away and 300 meters up, underneath the more local sounds of the wind, rain and of course human voices. One of the more interesting moments sampled was a group of chil- dren seeing the Eiffel Tower for the first time. Their enthusi- asm was contagious (Fig. 10, Clip 7). In this clip you will also hear the geophone recording of the high-pitched whistling of the wind. This is an exciting example of the wind’s energies sending waves and vibrations through the tower’s structure.
How does recording beyond the normal sonic range change how we understand sound?
Vibrations are anywhere there is energy and a medium to transfer it. The sources are from the forces of the wind, rain and snow, the machines that operate in or around the structure, and from people moving through the space. Materials used in the construction of structures respond differently to these sources, and although we do not hear them all, it is the vibrations that create the total sound field of a structure. To experience and perceive this full range, we need to extend our own sensory range and bring those below (or above) it into the realm of human experience.
At a practical level, as the goal of this project was to cre- ate a sound art/musical piece, I needed to be sure that the entire range of acoustic signals, even those below the nor- mal range of human hearing (not to mention speaker per- formance) would be audible to listeners. While the geo- phones picked up sounds in the range of 1-40 Hz, analysis and editing software showed some of the more interesting vibrational signals were, as expected, well below 20 Hz. To bring these sounds into the listener’s range, I inverted a method from bioacoustics that allows humans to listen to ultrasonic bat signals and used a pitch shifting algorithm to bring the lowest frequencies into the audible range.
A good example of the usefulness of extending our acoustic range can be found in the seemingly unrelated field of animal behavior. Animal behavior has often been studied by using the most basic (and useful) of tools—our own eyes
Fig. 7. Placement of the geophone on the railing with a view of the Champ de Mars below. Credit: Seth Horowitz.
34 Acoustics Today, July 2009