This calculator is intended to help you design an "L-pad" type circuit. It can be useful if you need to attenuate (reduce) the sound level of one speaker so that it will match the output of another driver.
This circuit is commonly used on tweeters because they are generally more efficient (higher sensitivity) than woofers. It can also be applied to the "rear fill" speakers in a mobile audio application. It is very undesirable to have the soundstage in the rear of the vehicle (which will happen if your rear speakers are too loud).
Note : You can accomplish this using only 1 resistor in series with the driver, however, the impedance load presented to your amplifier will be increased. When you use a L-Pad, the impedance load stays the same as it was before.