Page 15 - Summer 2007

Creation of acoustical models
Using the collection of architectural, photographic, and acoustical details the task of constructing an acoustical model for study and subsequent auralization was possible. As the room had undergone various architectural and acoustic modifications, the goal was to have valid models for the var- ious phases. The process adopted was to create a sequence of models, each linked to the previous one, covering the major changes. The primary goal was to arrive at the 1895 and 1898 conditions, those on which Sabine actually worked. In total, three conditions have been considered here: 1895 (pre- Sabine), 1898 (post-Sabine) and 1972, in which the 1912 remodeling, the c.1930 acoustic treatment, and the c.1965 carpet are included. The 1972 canopy has not been included.
Among the general assumptions necessary to make the transition from ink drawings to computer model, the lack of a lateral section and reflected ceiling plan made creation of the dome and skylight areas difficult and posed many questions. In addition, the majority of photos taken during the 1973 measur- ing session do not show the ceiling or higher elevations or were taken with the large canopy in place, masking the dome and arches. For this part of the model, the 1898 photo (Fig. 3) was the only real source of information. A great number of assump- tions have been based on careful analysis of this photo.
Conflict between drawings
Several discrepancies were found when comparing the various section drawings (see Fig. 1 and Fig. 2). First, regard- ing the curvature of the dome and arch above the platform; in Sabine’s drawings these curved surfaces are circular. In contrast, Fig. 2 shows a composite curve. While the authors have great respect for Sabine’s acoustical work, they have more faith in the architectural study in terms of determining the actual geometry of the room. Inspection of Fig. 3 sup- ports the non-circular form.
The second major discrepancy was the determination of the height of the room. In using Fig. 2, it was found that the noted height was inconsistent with the other dimensions of the room, being 9% smaller. As Sabine’s drawing did not include dimensions, a calibration between the drawings would be necessary. Comparisons of other dimensions on the drawing showed the single inconsistent dimension was the height. This was shown as referenced to an external measure on the outside of the building. A final comparison was per- formed using photographs taken during the 1973 measure- ment sessions. These supported the hypothesis that the height was erroneously labeled and it was decided to dis- count this single noted dimension. These decisions result in the final model being based on a combination of dimensions from drawings of various sources.
Geometrical model 1972
A base model was created which contained architectural elements constant between the eras: the platform wall and arc and the dome. Most of the model was parameterized using cir- cle and ellipse equations approximated from the architectural drawings. The dome section also has rotational symmetry, so there was need for only one “pie slice” to be modeled, than sim-
Fig. 3. Interior photo of lecture-room after 1898. Courtesy of Fogg Art Museum, Harvard University.
light on the Fogg Art Museum.
To summarize, the lecture room can be characterized as
having gone through two architectural modifications since its completion in 1895: in 1912 (volume reduction, flat floor) and 1972 (addition of canopy). In addition, there were three purely acoustic modifications: 1898 (Sabine’s acoustic treat- ment, partly removed in 1912), c.1930 (acoustic panels added on lower portion of rear wall) and c.1965 (floor carpeted). It is likely that successive paintings of the fabric covering in the lunettes gradually reduced their absorptive characteristics. Drawings of the various renovation stages can be found in
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Acoustical measurements
What has become a historical study of the Fogg Art Museum was not foreseen at the outset. A newspaper article on the planned demolition of the building simply prompted an interest in making some final acoustical measurements before the building ceased to exist. However, a subsequent New York Times article by the distinguished architectural critic Ada Louise Huxtable, deploring the loss of one more historical building, indicated the importance of reporting the measurements.
Demolition was scheduled for 16 June 1973, the end of the academic year, so measurements had to occur in the interval between the end of classes and that date. With the support of several University departments, acoustical meas- urements were made on two occasions. On 5 June, with the room in its final configuration, tape recordings were made of sound decay, impulse response, and sound distribution using noise bursts (1/3rd octave) and balloon bursts. Then the canopy was substantially demolished and on 15 June the measurements were repeated.
However, since the summer administrative staff had not been made aware of this study, permission to make the sec- ond set of measurements had to be renegotiated that evening at the campus gates, so they came perilously close to not tak- ing place at all.
Architectural Acoustics.
Fogg Art Museum 13