Alesis RA500 User Manual - Page 22

Connections: Chapter 2 THE IMPORTANCE OF SPEAKER POLARITY The speaker cone's motion should mimic the instrument it's reproducing. For example, a kick drum pushes air toward you on the initial transient, so a speaker reproducing a kick drum should have its cone push air toward you. If the polarity is reversed, the cone will suck air away from you. Even though the same amount of air is moved in either case, many listeners report superior sound with proper polarity as opposed to reversed polarity. An additional problem occurs if the polarity of one speaker is reversed with respect to the other. This can cause phase-related problems such as thin bass, poor stereo imaging and frequency response anomalies. With the RA150/300/500, polarity is a function of correctly hooking up the output cables. Usually, for proper polarity, the tip of the output phone plug or the red terminal of the output connector must connect to the speaker's positive (+) terminal. This will ensure that polarity from the RA150/300/500 input to speaker cone motion will be consistent. Check your speakers' polarity, however, because not all brands follow this wiring convention. Please note that polarity reversal can occur in devices (such as mixers or effects units) "upstream" of the RA150/300/500. To test for proper speaker and system polarity, see page 22. OUTPUT CONNECTIONS FOR BRIDGED OPERATION Instead of using the RA150/300/500 as a stereo 2channel amplifier, it is possible to use it as a mono amplifier with twice the power. This uses both sides of the amplifier in a push-pull configuration, so the speaker must be wired to the amp differently. However, note that the minimum load impedance is 8 ohms, instead of the 4 ohms in stereo operation. To connect a speaker in bridged mono mode: Following the instructions on the previous page for binding post or crimp-on connection, connect the "+" wire to the red binding post for the Channel 1/Left and the "-" wire to the red binding post for Channel 2/Right. You may use a dual banana plug in this situation. If present, remove the protective caps from the top of the binding posts for the two red terminals. Plug the banana connector into the two center red terminals with the ridged/GND side on Channel 2/Right. The single input is connected ONLY to the Channel 1/Left input jack, and the stereo/mono switch under the right input connector should be set to BRIDGED MONO. Don't plug any input into the Channel 2/Right input jack, and leave the Channel 2 volume control all the way down. Should you use bridged mode? In a typical PA system with two speakers, in most cases you'll be better off running the RA150/300/500 in stereo mode, because most speakers are 8 ohms and if they were wired in parallel the total load would be 4 ohms, too low for bridged mode. In any case, the total system volume doesn't rise if you were to connect 2 speakers to a single 500-watt amp instead of to two 250-watt amps. But if you are connecting to a single speaker (such as a subwoofer) in a biamped or triamped setup, bridged mono mode will give you the chestthumping headroom you need. 20 RA150/300/500 Reference Manual