“The whole room may be mapped out into regions in which the sound is loud and regions in which it is feeble.” –Collected Papers on Acoustics, Wallace Clement Sabine
Resonant frequencies occur in every enclosed space. The frequency of each resonance is directly related to the room's dimensions. When a sound is played having the same frequency as a natural resonance of the room, that note will sound much louder as a result of constructive interference, or weaker due to destructive interference, depending on the listener's physical position within the space.
Wallace Clement Sabine describes this phenomena in The Collected Papers on Acoustics using the image below.
This image describes the distribution of sound intensity at the head level of the Congregational Church in Naugatuck, Connecticut. This particular space has a barrel-shaped ceiling with the center of curvature on the floor level. It should also be noted that the sound source in this study when Sabine conducted it was placed in the center of the space. The distribution of sound intensities are expressed using the language of a topographical landscape map.
I am interested in deliberately exposing this specific property of enclosed spaces in order to make the occupant aware of the fundamental relationship between body position, built environment and aural experience.
A cubic room will exhibit three resonances at the same frequency since its dimensions are all equal. I propose that a room is constructed with the dimensions of a cube, 3m x 3m x 3m. Built within a controlled setting (interior space?), the construction should be made of masonry or of otherwise massive and reflective material with a smooth interior surface. The standing room modes for this volume are calculated using the room mode calculator and visualization tool found here.
The dark regions are areas of high sound pressure and are therefore louder in intensity. As you can see, interference alters the distribution of sound in the room "causing the intensity of any one pure sustained note to be above or below the average intensity at near points." (Collected Papers on Acoustics) This phenomena is constant so long as the source of sound is continued.
Axial modes at 57Hz, 115Hz…
Tangential modes at 81Hz, 128Hz…
Oblique mode at 99Hz…
Within this 3m x 3m x 3m cubic room a sound signal will be placed in the center of the space and will excite the axial frequencies (since they are the most pronounced). Later perhaps, other frequencies and/or complex signals can be employed to further study the relationship between the interference system within the given space.
This construct will serve as an experimental environment within which the properties of a sound signal can be experienced in direct relation to an enclosed space. As the visitor moves throughout the space he will encounter areas of uncomfortably high sound intensity and practically inaudible sound intensity which will encourage a new understanding and awareness of the space one occupies.
The natural resonant frequencies of an enclosed space can be determined using the 20Hz-200Hz swept sines found here.
Michael Brewster is an artist that employs the phenomena of standing waves in his work. As part of his "See Hear Now" exhibit, Brewster works with synthesized sounds which are amplified in a specifically constructed room (14'wide x 28'long x 14'high) in order to create a kind of sculptural experience using the resulting standing waves. A link to his website which includes some sound clips is posted below:
ReplyDeletehttp://acousticsculpture.com/