Even in a very noisy environment, Model-139B still has the ability to determine quickly and precisely the positive and negative polarity of a loudspeaker headphone receiver and every single unit in a loudspeaker system. Model-139B also includes 3 sets of external input terminal and selector which can be used to combine with other instruments, in order to measure the other features of a loudspeaker simultaneously. It is quite suitable for 100% Q.C. testing for loudspeakers in the production line. Loudspeaker Polarity Tester 139B Technical specification: (1) Pulse measuring method. (2) Polarity indicator : (a) Green indicator: Positive polarity with beep sound. (b) Red indicator: Negative polarity with no sound at all. (3) Five touch switches : (a) WF range: Suitable for measuring the polarity of the woofer. (b) M & T range: Suitable for measuring the polarity of midrange and tweeter. (c) EXT.1 to EXT.3: Used to select the instrument connected to the external input terminal. (4) Model-139B can be connected with Model-7116C, to measure the buzz, and rattle of a loudspeaker. Only one operator is needed. (5) Measuring distance: 2 to 4 Cm. from the center point. of the dust cover of the pre-measure loudspeaker. (6) Measuring sensor: Uses ECM. (7) Dimension ( m / m ): 85 ( height ) x 205 ( width ) x 280 ( depth ). (8) Weight: 2.3 Kg. SUNLIGHT AUDIO SWEEPER 7116C Loudspeaker Polarity Tester 139B NOISE GENERATOR 8121C GAUSS METER 138 IMPEDANCE METER 152A DIGITAL HIGH-SPEED Fo METER 7117 C.