The Model 644 is a highly directional dynamic microphone utilizing a com­bination of cardioid and distributed front opening designs. This gives greatly extended frontal pickup on the microphone axis, extending working dis­tance over 2.5 times compared to present non-directional type micro­phones. Above 700 cps cancellation of sound at the rear and sides exceeds 20 dB providing unequalled rejection of random noise, reverbera­tion and feed­back without sacrifice of frequency response. The Model 644 allows much greater latitude in loud­speaker place­ment and will solve many specialized problems where micro­phones cannot be placed near the source of sound.