[Al Skierkiewicz]

Unlike an AC motor, the number of poles does not have a direct effect on output power or RPM nor can you say it is more efficient. The number of poles are optimized for motor function. You can say that the higher the number of poles, the greater the starting torgue or starting RPM under load. In general, the higher the number of poles the greater the output power at low RPM. There are always tradeoffs, cost goes up as you add windings, construction becomes more complicated, balance is more difficult to obtain, etc. The motor designer must choose from their box of tricks which variables to optimize and which to suffer with.