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104 EDWARD W. KEU.OGG [J. s. M. p. E.
ever directive device is employed, would have to be much larger than those used in the usual public address system. It may be desirable to impart directive properties to the sound pickup or microphone system as well as to the loud speakers. With the retention of low frequency components of voice and music it may develop that increased attention will have to be given to the sound deadening of the auditorium to low frequency sounds. In his paper already referred to, Dr. Sabine mentions the difficulty of securing large absorption of low frequency sounds, but progress is steadily being made in this direction.
The use of a high quality reproducing system will go far toward reducing feedback difficulties especially if the auditorium is adequately damped. High quality systems must amplify all frequencies within the essential acoustic range nearly equally. Systems which are more imperfect amplify certain frequencies much more than others. It is these resonance points where the amplification is high that always start the "singing" or feedback. Even though the amplification is held below the singing point, regeneration causes an exaggeration of those frequencies for which the amplification is already too high and distortion becomes intolerable unless the amplification is held far below the singing point. The more nearly uniform the amplification of the system the closer to the singing point it is possible to work without objectionable distortion. The objection that by employing a public address system we shall necessarily lose the fine quality of voice or instrument is therefore unfounded. Let us assume, however, that a system having perfectly uniform amplification is not employed and distortion results. Will the artist have a right to object? The alternative would be to go back to the reverberant auditorium. What does this do to voice quality? Not only does it give the overlapping and resultant blurring which is objectionable, but it results in great inequalities in the loudness of the various frequencies present in the voice. The high quality amplification system does no worse. There is one form of distortion which the auditorium in general does not produce ,. namely, what is known as non-linear distortion or the production of overtones not present in the original sound. An electrical system may give rise to non-linear distortions, but here again the question is only one of proper design and adequate power in order to eliminate such effects.
Given a high quality amplification system, a small amount of