Mackie Thump18s Owners Manual - Page 12

Thump18S Powered Subwoofer Placement The Ins and Outs of Polarity The Thump18S subwoofer is designed to sit on the floor or stage. It is not designed to be pole-mounted or suspended. When pole-mounting loudspeakers, be sure that the Thump18S subwoofers are stabilized and secured from falling over or being accidentally pushed over. For stacked scenarios, it is highly suggested that straps are utilized. Failure to follow these precautions may result in damage to the equipment, personal injury, or death. The cabinet has no rigging points and is not suitable for rigging. NEVER attempt to suspend an Thump18S subwoofer by its handles. As with any powered components, protect them from moisture and extreme cold and follow the other Care and Maintenance suggestions below. Care and Maintenance Your Thump18S subwoofers will provide many years of reliable service if you follow these guidelines: • Avoid exposing the subwoofers to moisture. If they are set up outdoors, be sure they are under cover if rain is expected. • Avoid exposure to extreme cold (below freezing temperatures). If you must operate the subwoofers in a cold environment, warm up the voice coils slowly by sending a low-level signal through them for about 15 minutes prior to high-power operation. • Use a dry cloth to clean the cabinets. Only do this when the power is turned off. Avoid getting moisture into any of the openings of the cabinet, particularly where the drivers are located. Thump18S subwoofers include 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 low-frequency portion of the signal it receives from the sound source. 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 normal/invert [polarity] switch is engaged, the original waveform is simply reversed 180˚ [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 at the same time. The normal/invert [polarity] switch comes into play when the Thump18S subwoofer is paired with a loudspeaker. Ideally, the woofer cones of the subwoofer and full range loudspeaker would work together by pushing and pulling in unison. Thump18S subwoofers are designed to be used in a broad range of applications. The flexibility provided by the polarity switch is necessary to ensure that you are receiving the best possible sound from your system, regardless of your setup. Polarity Waveforms Figure 1: Normal [0˚] Figure 2: Invert [180˚] Amplitude Amplitude 12 Thump18S Powered Subwoofer