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226 IX. SOUND-RECORDING EQUIPMENT AND ARRANGEMENT
sidered proportional to the cosine of the angle between the plane of the ribbon and the direction of approach, with maximum response occurring normal to the plane of the ribbon. There is very little frequency discrimination with change in angle of incidence of the approaching sound ; the directional characteristics of the ribbon microphone are quite uniform for all frequencies in its design range. The 44BX microphone is capable of substantial output to 20,000 cps; its weight is about 8 1/2 pounds and its length (including the cushion mounting) is about 12 inches.
As the energy response of the ribbon microphone to randomly reflected sound is but one-third that of a nondirectional microphone, it is possible to increase the distance between the sound source and the microphone for the same "quality" (ratio of direct sound to randomly reflected sound) as that obtained with a nondirectional microphone. The ribbon microphone is excellent for the recording of music because of its smoothness; it is also very good for the recording of speech — provided the speaker is at least 2 feet from the microphone. When the speaker-tomicrophone distance is less than 2 feet, the recorded speech sounds unnatural and tubby; ordinarily no simple form of equalizing is capable of satisfactorily correcting for the deterioration in quality that results. Some RCA 44 type microphones are provided with a voice tap connection at the microphone terminal board ; when the voice tap is connected, the response of the microphone is attenuated in the low-frequency range by some 6 db at 100 cps.
Cardioid Types of Microphones
For years designers have been trying to make a unidirectional microphone that is as small and light as the smaller pressure-operated microphones (about 3 inches long and weighing not more than 1 pound) ; such a microphone should have the sensitivity of a pressure-operated type such as the Western Electric 633A, it should pick up sound from one side only, and it should be equally directional for low and for high frequencies. Such a microphone would make it possible to discriminate against noise and extraneous sound such as camera noise that originate in a direction different from that of the sound source to be recorded ; in addition, the ratio of the direct sound picked up by the microphone to the reflected sound could be increased, thereby materially improving the quality of the recording. Small size is desired because a microphone casts a shadow when it is used on an illuminated set, and the smaller the microphone, the smaller is the shadow. Light weight is desired because the micro