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Feb., 1930] LOUD SPEAKERS 171
measurements as ordinarily made are hardly a satisfactory basis for estimating efficiency because of the concentration of sound in a beam. The efficiency is not a complete measure of utility; the beam intensity may be a better measure of Utility than total sound radiated. Both factors come in, their relative importance depending largely on room acoustics, but when we talk about efficiency, we have to base it on the total sound radiated, and it is difficult to make a comparison.
MR. TOWNSEND: I am wondering about the same thing that Mr. Crabtree spoke about with regard to the amount of power required. I use an amplifier in my home which has an undistorted output of approximately 15 watts. I don't use that for loudness but for quality. If we go down to one watt in even a small theater it appears to me that the quality of sound would be rather poor. The theater with which I am connected happens to have six dynamic speakers, and six air column horns with dynamic units.
I can switch from the horns to the baffle type speakers and as nearly as the ear can follow, either will give the same volume in the theater. It is impossible to get any difference in volume between those two sets of speakers connected to the same output transformer and using the same gain. It has been a puzzle to me to find out where the difference in efficiency really is.
MR. BLATTNER: Referring to Mr. Kellogg's remarks, we agree that efficiencies of 8 or 10 per cent can be obtained with baffle speakers over a limited frequency range. Our figure of 3 per cent refers to the overall efficiency for a broad band and checks satisfactorily with the difference between the generally accepted efficiency figure for the better grade of horn type speakers and the difference in loudness between the two types as observed throughout the theater auditorium. I believe we have adequately covered the question as to relative high frequency response and directivity in the paper.
As for Mr. Townsend's remarks I am unable to explain the lack of difference in performance in his two types of speakers. To do so, it would be necessary to know the characteristics of the particular device that he uses. There is a considerable range in the merits of the device of both types generally available in the market. The discussion in the paper applies to what we termed "well designed" devices of the two types.