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It has been shown recently that microphones and contiguous amplifiers distort the sound field in which they are placed by reason of their size and the cavity external to the diaphragm of the microphone. For frequencies such that the size is large compared to the wave‐length of perpendicularly incident sound, reflection causes the actuating pressure to be double that which would exist in the undisturbed field. If the direction of the incident sound be along the plane of the diaphragm, the increase of pressure due to reflection is not as great; but there may be a substantial reduction in effective pressure due to differences in phase across the diaphragm. In addition, cavity resonance produces an increase of pressure at frequencies usually within the working range of the microphone. This paper describes a laboratory model of a Wente‐type condenser microphone of high efficiency and an associated coupling amplifier which are of such small size that reflection and phase‐difference effects are of negligible importance within the audible frequency range; while the cavity is so proportioned that its resonance effect is an aid rather than a detriment to uniformity of response in a constant sound field.

Synopsis: This paper deals with an analysis of the general requirements of recording and reproducing sound without appreciable distortion. The storing or recording of sound requires, first, a mechanical system which will respond faithfully to the sound waves which are to be recorded. Then there is required some material in or on which this sound may be recorded and an intervening system which permits the sound waves to make the record in this material. In the usual case, and in that which is particularly discussed, there is a mechanical system which will vibrate in response to the sound which is to be recorded and directly through some mechanical linkage, or less directly through an electrical linkage, drives a cutting mechanism which will impress a wax record. The amount of power available to operate the recorder directly from the sound in the recording room is so small as to make the use of high quality electrical apparatus with associated vacuum tube amplifiers of very distinct advantage over the acoustic method. Where the question of reproduction is concerned, the same two alternatives mentioned for recording present themselves, namely, direct use of power derived from the record itself vs. the use of electro‐mechanical equipment with an amplifier. In this case, however, the situation is materially different since the power which can be drawn directly from the record is more than sufficient for many uses. It is, therefore, generally simpler to design one single mechanical transmission system than it is to add the unnecessary complications of amplifiers, power supply and associated circuits. In cases where music is to be reproduced in large auditoriums, the power which can be drawn from the record may be insufficient and some form of electrical reproduction using amplifiers becomes necessary. The paper points out, at length, how many of the heretofore unsolved fundamental problems of sound recording and reproduction have been readily solved by the application of a detailed knowledge of telephone transmission theory. The advances which have been effected in telephone transmission theory and in related electrical measuring apparatus in the last few years, have been so great as to surpass previous knowledge of mechanical wave transmission systems. The result is, therefore, that mechanical transmission systems of the type here considered, and perhaps other types, can be designed more successfully if they arc viewed as the analogs of electric circuits. A detailed analysis is here made of the analogies between electrical and mechanical systems in the voice frequency range and a discussion of the resulting mechanical design is presented.

A procedure, developed for the study of volatile glaze constituents, consists of heating the glazes beneath an absorbing medium which is subsequently tested by the spectrograph for the volatilizable constituents evolved. Data are presented showing temperatures at which certain important glaze constituents begin to volatilize, the order in which they leave the parent glaze, the influence of glaze composition on the volatilization temperature of each volatilizable constituent, and the effect of heat treatment on the volatilization temperatures.

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