Masch 20, 1908] 



SCIENCE 



467 



Memorial Hall, February 17, 1908. Dr. L. A. 

 Bauer presided. 



Professor Wallace 0. Sabine, of Harvard 

 University, delivered an address on " Some 

 Phases of Architectural Acoustics." 



The lecture hall of the Fogg Art Museum 

 erected in 1895 was modeled after Sanders 

 Theater in Cambridge, but failed to duplicate 

 its excellent acoustic properties. This mis- 

 fortune led the corporation of Harvard Uni- 

 versity to request Professor Sabine to investi- 

 gate the matter and propose changes to remedy 

 the difficulty. 



It has been claimed by some that to secure 

 good acoustic properties the dimensions of 

 the room should be as 2:3:5 or similar pro- 

 portion, or that the room should be elliptical, 

 but the best and the worst auditoriums in 

 Cambridge are both semicircular, indicating 

 that it is by no means a matter of proportion 

 or shape alone. 



The acoustic properties of a hall involve 

 four principal factors : distributed loudness, 

 reverberation, resonance and interference. To 

 adjust these four physical characteristics there 

 are two variables, the form of the auditorium 

 and the material of which it is constructed. 

 The essential features of the material are its 

 absorbing and reflective powers. Through a 

 measurement of the reverberation it is possible 

 to determine the absorbing and therefore the 

 reflecting powers of a wall surface. The 

 method of so doing was explained at some 

 length, and the results of such measurements 

 given. 



With an organ pipe as a constant source of 

 sound and a chronograph to record its dura- 

 tion after the wind was cut off, the audibility 

 of the residual sound, the reverberation, in 

 the lecture hall of the Fogg Museum was 

 found to be 5.62 seconds — a condition which 

 rendered the room intolerable as an audi- 

 torium. By putting Sanders Theater cushions 

 upon the seats, floor and part of the wall of 

 the lecture hall, the duration of the residual 

 sound was reduced to 1.14 seconds. The ab- 

 sorbing power of these cushions was ultimately 

 compared with that of an open window. The 

 absorbing power determined for a few of the 

 kinds of wall surface and of an audience are 



given below, expressed in square meters of 

 open window.' 



Hard pine wood sheathing per square meter . .061 



Plaster on wood lath per square meter 034 



Glass — single thickness — per square meter . . .027 



Audience per square meter 94 



Isolated woman 54 



Isolated man 48 



Cretonne clotli per square meter 15 



Hair felt 2.5 cm. thick and 8 cm. from wall 

 per square meter 78 



As a result of two years' investigation felt 

 was placed on particular walls of the lecture 

 hall in the Fogg Museum; so the room was 

 rendered, not excellent, but entirely service- 

 able and has since been used without com- 

 plaint. 



With a number of given and determined 

 factors Professor Sabine treated the subject 

 mathematically and showed that knowing the 

 absorbing power of the wall bounding surfaces 

 and the dimensions of the auditorium it is 

 possible to calculate with accuracy the re- 

 verberation if need be in advance of construc- 

 tion. Several examples of such calculations 

 were given. The paper up to this point hav- 

 ing dealt entirely with middle C, was then 

 extended to a discussion of the whole range 

 of the musical scale. Examples were given 

 showing the absorbing power of wall surfaces 

 for notes of high pitch. 



Mr. Bernard E. Green, discussing the paper, 

 remarked upon the difficulty of killing echoes 

 and inquired as to the facts concerning the 

 Mormon Tabernacle. 



Professor Sabine replied that he had made 

 a special journey to Salt Lake City to study 

 the acoustic properties of the tabernacle, and 

 found that its excellence in that respect was 

 not a matter of " inspiration." When first 

 built the acoustic properties were very poor. 

 Attempts were made to remedy the difficulty 

 by stretching wires across the room and hang- 

 ing curtains, but they were of no avail. 

 Finally, the increasing size of the congrega- 

 tion necessitated the construction of a gallery, 

 which unexpectedly corrected the acoustic 

 defects. 



'^Americaii Architect and Building News, Vol. 

 68, pp. 3, 19, 35, 43, 59, 75 and 83. 



