Building for Clarity
When one stop per pitch level does not produce enough volume, you might consider ADDING a stop at a particular pitch level, beginning with the 8' level. Each stop that you add in this manner does increase volume. However, ideally a rank of pipes is voiced by the builder to speak at its optimum volume level for the nature of that stop in its designated space. If your combination needs more volume, you should first try substituting a single stop that is louder by its very nature. For example, if an 8' flute is not loud enough, try an 8' principal instead.
Only after you are sure that you cannot increase the volume by simply changing to another stop should you consider adding another stop. Adding a stop will move you in the direction of richness and away from clarity.
