Mackie’s SRM1801 subwoofer includes a switch that allows you to quickly invert the polarity of the subwoofer’s output relative to the input signal it is receiving from the mixer or other sound source. But what exactly does that mean? A subwoofer works by literally pumping air as the woofer cone moves in and out with respect to the cabinet in which it is housed. It does so according to the
The woofer cone is simply following the waveform as seen in the sine wave in Figure 1. As the sine wave rises, the woofer cone pushes out. Likewise, as the sine wave falls, the woofer cone pulls into the cabinet. A musical signal is much more complex, of course, but the same principle applies. Movement of the woofer cone causes air pressure changes that we perceive as sound.
When the Polarity Invert switch [6] is engaged, the original waveform is simply reversed 180º (see Figure 2). Again, the subwoofer cone follows the waveform.
However, this time the woofer cone starts by pulling into the cabinet followed by the woofer cone pushing out. If you have ever experimented with a subwoofer polarity switch, you may not have noticed any changes to the sound regardless of its position, especially if you are listening to just the subwoofer. This is normal, as our ears perceive them both as the same.
The polarity invert switch comes into play when the SRM1801 subwoofer is paired with a loudspeaker. Ideally, the woofer cones of the subwoofer and
Listed below are some recommended configurations for pairing a Mackie SRM1801 subwoofer (using the
•SRM450v2
•
In alternate setups where the
< - - T i m e - - > | < - - T i m e - - > |
Amplitude | Amplitude |
Figure 1 | Figure 2 |
11