John S. Parkinson

A Method for Evaluating Compliant Materials in Terms of Their Ability to Isolate Vibrations

A method is given for evaluating by dynamic means the stiffness and resistance of a vibrating system. By using this method, compliant materials not readily evaluated by static means may be investigated. The actual efficiencies of isolating systems are compared with the efficiencies predicted from a theoretical one‐degree‐of‐freedom treatment. The comparison is favorable, but certain limitations of the theoretical treatment are discussed.

The Adaptation of Acoustical Materials to Auxiliary Functions

With the increasing use of acoustical materials for purposes of interior finish, a number of additional uses have been found for these products. Cases are cited where the acoustical treatment has been made an integral part of the air conditioning system. The adaptation to improved lighting methods is discussed. Certain materials have such inherent architectural value that they are used primarily as interior finishes, with the acoustical function secondary. In the summary, suggestions are made to assist the architectural profession in taking advantage of these various adaptations. Details and photographs will be included.

Sound Insulating Properties of Certain Building Materials

Transmission loss data obtained in the Johns‐Manville Laboratories on various building constructions are reported. Almost all this data has been obtained on “room size” floors and partitions. The relation between such tests and “panel” tests is given where data is available. Detailed studies of the vibrational properties of various constructions are also reported which show the response characteristics at various frequencies, the degree of structural isolation obtained in various double constructions, the relative importance of damping, etc.

Facts Developed in the Design and Construction of the Johns‐Manville Acoustical Laboratory

A brief description of the Johns‐Manville Acoustical Laboratory is given, with test data on the efficacy of various constructions employed and a description of certain modifications in test procedure.

Experimental Judgments of Relative Loudness by a Number of Observers as Related to the Decibel Scale

A large number of experiments were made, both on trained and untrained observers, to determine the factors which influenced individual judgments of the relative loudness of tones. These experiments included a considerable range of levels and a number of different frequencies. The results show a marked uniformity but do not appear to be related directly either to the intensity or the loudness levels as measured in decibels.

Area and Pattern Effects in Absorption Measurements

The coefficient of absorption of an acoustical material as obtained by the reverberation chamber method varies with the area tested and the shape of the sample. A theoretical explanation of this phenomenon is outlined, showing that the results cannot be attributed entirely to edge affects, and explaining the discrepancies which appeared when the diffraction theory was applied to the tests.Test results show the efficiency of various patterns and arrangements of treatment. It can be shown that the absorption coefficient isproportional to K(p/A)where p is the perimeter of the individual sample and A the area. It can be shown also that the absorption per square foot of total pattern area is always proportional to the ratio of treated to untreated area, regardless of the pattern arrangement. This relation is formed to hold good for all frequencies with the same material, but not for different materials. Typical questions of construction and design can be answered as a result of the data.

Part III. Noise Reduction

A summary is given of the results of noise surveys, including new measurements as well as certain material previously available. The report treats of noise out-of-doors, in buildings and in conveyances, and discusses noise levels and characteristics, noise sources, and noise reduction.