Tube mic Connecting the capsule 2

Posted on Feb 4, 2014

Connecting a condenser capsule to the grid of a tube amplifier, in order to build a tube mic. In this part we consider how to connect a capsule with two diaphragms in order to get a multi-pattern mic. First let`s examine the different pickup patterns available. There are three extremes: Omni, where the microphone hears sounds equally in all directions. Cardioid (heart shaped*), where sensitivity is greatest in the

Tube mic Connecting the capsule 2
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direction in which the microphone is pointing, falling off to a null point behind. And Figure-of-Eight, with equal (but opposite) pickup in front and behind, and null pickup to the sides. To complicate things further, the pickup pattern may depend upon the frequency, and some mics will have good directionality at higher frequencies, but become less directional as the frequency drops. But what if we want a microphone with selectable pattern This can be achieved by arranging a pair of cardioid capsules back-to-back, and combining there signals in different ways. We`ll call these capsules front and back, although of course they could be pointing in any direction. If we require a cardioid signal, we just take the front capsule and for omnidirectional pickup, we mix both signals equally. If we want figure of eight, we subtract the output of the rear from the front: where the signals overlap at the sides of the microphone, they cancel each other out producing null points. Other patterns such as hyper-cardioid and super-cardioid may be considered as in-between positions of these extremes. So, what is the best way to achieve this practically in our hypothetical tube microphone Two of the earliest commercial mics with more than one pattern were the Neumann U47, which offered cardioid and omni, and the U48, with cardioid & fig. 8. Let`s look at the U47, as this is probably the simplest way to combine the two capsules. In the U47 the...

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