56 PROCEEDINGS OF THE AMERICAN ACADEMY. 



at each reflection. In either case it is called reverheration. It is some- 

 times called, mistakenly as has been explained, resonance. The rever- 

 beration may be expressed by the duration of audibility of the residual 

 sound after the cessation of a source so adjusted as to produce an aver- 

 age of sound of some standard intensity over the whole room. The 

 direct determination of this, under the varied conditions of this experi- 

 ment, was impracticable, but, by measuring the duration of audibility 

 of the residual sound after the cessation of a measured organ pipe in 

 each room without any cushions, and knowing the coefficient of absorp- 

 tion of the cushions, it was possible to calculate accurately the rever- 

 beration at each stage in the test. It was impossible to make these 

 measurements immediately after the above experiments, because, al- 

 though the day was an especially quiet one, the noises from the street 

 and railway traffic were seriously disturbing. Late the following night 

 the conditions were more favorable, and a series of fairly good obser- 

 vations was obtained in each room. The cushions had been removed, 

 so that the measurements were made on the rooms in their original 

 condition, furnished as above described. The apparatus and method 

 employed are described in full in a series of articles in the Engineering 

 Record and American Architect for 1900. The results are given in the 

 accompanying table. 



The table is a record of the first of what, it is hoped, will be a series 

 of such experiments extending to rooms of much larger dimensions 

 and to other kinds of music. It may well be, in fact it is highly 

 probable, that very much larger rooms would necessitate a different 

 amount of reverberation, as also may other types of musical instru- 

 ments or the voice. As an example of such investigations, as well 

 as evidence of their need, it is here given in full. The following ad- 

 ditional explanations may be made. The variation in volume of the 

 rooms is only threefold, corresponding only to such music rooms as 

 may be found in private houses. Over this range a perceptible varia- 

 tion in the required reverberation should not be expected. The third 

 column in the table includes in the absorbing power of the room 

 (ceiling, walls, furniture, etc.) the absorbing powers of the clothes of 

 the writer, who was present not merely at all tests, but in the meas- 

 urement of the reverberation the following night. From the next 

 two columns, therefore, the writer and the effects of his clothing are 

 omitted. The remarks in the last column are reduced to the form 

 "reverberation too great," "too little," or "approved." The remarks 

 at the time were not in this form, however. The room was pronounced 

 "too resonant," "too much echo," "harsh," or "dull," "lifeless," 

 " overloaded," expressions to which the forms adopted are equivalent. 



