A Method of Measuring the Total Output of Speakers

This paper presents a method of measuring the total output of speakers, which is analogous to the globe photometer method of measuring the total light flux from a lamp. The speaker is placed inside a hollow sphere with the measuring microphone located in a small hole in the wall of the sphere. A single measurement at the microphone window gives a value proportional to the total output of the speaker. In order to break up standing wave patterns which form in the sphere the frequency of the oscillator used to drive the speaker is wobbled above and below the steady value. Theory is developed to show that in order to smooth out standing waves a constant frequency deviation is required regardless of the fixed frequency instead of a certain percent of the frequency at which the measurement is made. Data are given comparing this method with measurements made out of doors on a speaker.