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596 RICHARDSON'S BLUEBOOK OF PROJECTION
lost. Consequently speakers are "poled" or "phased" — that is, connected in the same polarity. Both voice and field lines must be poled. All voice contacts are marked, often with numbers. All the number 1 terminals should be connected to the same side of the output transformer secondary; number 2 terminals to the other side. Sometimes the wires are not numbered, but color-coded. Field coil terminals are commonly polarized + and — , and should be so connected to their pow^r sources.
When speakers of different manufacture are used together reliance on marked terminals may not prevent incorrect poling, and it may be necessary to experiment with reversing polarities to determine which connection gives the best results. When the correct arrangement has been found the speaker terminals and connecting wires should be tagged accordingly.
Whenever a speaker unit is replaced care must be taken to pole the new unit correctly. The connecting wires are tagged for this purpose, and the speaker markings or color code consulted. Of course, where only one stage speaker is used, poling doesn't matter.
On rare occasions a speaker that has been incorrectly poled escapes factory inspection. When such a unit is wired in properly, according to the lettering of its terminals, or to its color code, the resulting loss of volume, especially in the space between the speakers, will reveal the fault at once. To determine which is the winding that was incorrectly marked, reverse connections, first to the voice coil and then, if the change, has not increased the volume between speakers, restore the original voice coil connections and reverse those to the field coil. A tag bearing the proper information should then be attached to the speaker, for future reference.