But if the goal is to reproduce sounds accurately, then a speaker must be either an acoustic point source (monopole, omni-directional) or an acoustically small bi-directional source (dipole).

但是，如果目标是精确的重放声音的话，一个扬声器必须是声学上的点声源(单极点，全向响应)，或者是一个声学上小的双向源(偶极)。

youdao

The presumably arise from small changes in either of the two Processes, which give the dynamo action, or both, decay time for the main dipole part of the geomagnetic.

这种变化当是起因于能产生发电机活动的这两个过程之一。或者是两个过程中的小变化。

youdao