MPA-45 (320-2035) Connecting Speakers Faxback Doc. # 15699 For the best results, use speakers that are rated at 4 to 16 ohms. For speaker connections, use 18-gauge speaker wire for lengths up to 25 feet- 7.5m. Use 16-gauge wire for lengths over 25 feet-7.5mm. We recommend that you use the shortest length of wire possible. To prepare the speaker wire, remove about 1 inch-2.5 cm of insulation from the end of the speaker wire you intend to connect to the amplifier. Then, twist the exposed wire to secure all of the wire strands. To connect speaker wire to the amplifier, press down the appropriate push terminal lever on the amplifier and insert the end of the wire into the terminal's hole. Then, release the lever to secure the wire. You can connect two or more speakers with or without transformers. DETERMINING SPEAKER POLARITY Most speaker terminal are color-coded or have a mark that indicates the terminal's polarity. Usually, terminals with positive polarity are red or have a plus symbol (+), and terminals with negative polarity are black or have minus symbol (-). If your speakers' terminals do not indicate their polarity, you must determine the polarity yourself to ensure that the speakers are properly phased. Proper phasing is important when you use more than one speaker in the same room or area. Speakers are in-phase when their cones move in the same direction when an equal signal is applied to the speakers. Speakers that are out-of-phase can lose up to one-half of their potential volume, and can have a decreased bass effect. Follow these steps to determine the polarity of the speaker terminals. 1. Connect one end of a 1.5-volt flashing battery to one of the speakers terminals. 2. Briefly touch the opposite end of the battery with the other speaker cone moves in or out. If the cone moves in, the terminal connected to the battery's negative side is positive. Mark the positive terminal with a plus (+) sign. 3. Repeat Steps 1 and 2 for each speaker. CONNECTING ONE SPEAKER Connect the speaker's negative (-) terminal to the amplifier's COM terminal. Then, connect the speaker's positive (+) terminal to the terminal that matches the impedance of the speaker. The following example shows an 8-ohm speaker connected to the amplifier's 8-ohm terminal. NOTE: We recommend 18-gauge speaker wire if the length of wire is 25 feet- 7.5m or shorter. For the best results, we suggest you use the shortest length of speaker wire possible. CONNECTING SPEAKERS WITHOUT TRANSFORMERS If you connect speakers without transformers, the lengths of speakers wire should be no longer than 50 feet-15 m. For lengths up to 25 feet-7.5 m, use 18-gauge wire; for lengths from 25 to 50 feet-7.5m to 15m, use 16-gauge wire. To ensure equal volume from each speaker, all the connected speakers should have the same impedance rating. The following examples show 8-ohm speaker, which are the most common type sold by your local Radio Shack store. CONNECTING SPEAKERS IN SERIES Before you connect speakers in series, determine the total impedance for the speakers. To do so, add the impedance of all connected speakers. For example, if you connect two 8-ohm speakers, add 8 (impedance of one speaker) for a total impedance should match one of the amplifier's terminals (4-ohm, 8-ohm or 16-ohm). CAUTION: The total impedance must be at least 4 ohms but most not exceed 16 ohms. CONNECTING SPEAKERS IN PARALLEL Before you connect speakers in parallel, determine the total impedance. To do so, divide the impedance of one speaker by the number of speaker. For example, if you connect two 8-ohm speakers, divide 8 (impedance of one speaker) for a total impedance of 4 ohms. The total impedance should match one of the amplifier's terminals (4-ohm, 8-ohm, or 16-ohm). CAUTION: The total impedance must be at least 4 ohms but not exceed 16 ohms. COMBINING SERIES AND PARALLEL CONNECTIONS Before you connect speakers in parallel, determine the total impedance. To do so, divide the impedance of one speaker by the number of speaker. For example, if you connect two 8-ohm speakers, divide 8 (impedance of one speaker) by 2 (the number of speaker) for a total impedance of 4 ohms. The total impedance should match one of the amplifier's terminals (4-ohm, 8-ohm, or 16-ohm). CAUTION: The total impedance must be at least 4 ohms but not exceed 16 ohms. If you connect more than two speakers using only series or only parallel connections, the total impedance might exceed the amplifier's maximum impedance (16 ohms) or fall below its minimum impedance (4 ohms). For example, if you connect four 8-ohm speakers in series, the total impedance is 32 ohms (8+8+8+8=32). Or, if you connect four 8-ohm speakers in parallel, the total impedance is 2 ohms (8 divided by 2 =2). CAUTION: A total impedance that is too high or too low can damage your amplifier or speakers. You can arrive at a proper total impedance by combining series and parallel connections. In the following example, we show the connection of four 8-ohm speakers. First, connect each pair of speakers in series. Each pair has a total impedance of 16 ohms ((6+6=16). Next, divide 16 (the impedance of one pair of speakers) by 2 (the number of pairs) for a total impedance of 8 ohms. After you determine the total impedance, connect the two pairs of speakers in parallel. CONNECTING SPEAKERS WITH TRANSFORMERS If you connect two or more speakers in you system, you can use a line transformer (Cat. No. 320-1031) for each speaker. Transformers offer these advantages: You can use speakers that have different impedances without causing differences in output between the speakers. You can add or remove a speaker from the system without having to recalculate the impedance for the entire system. You can reduce signal loss when you use runs of speaker wire over 50 feet-15m long. NOTE: Use 18-gauge speaker wire for lengths up to 25 feet-7.5, and use 16-gauge wire for lengths more than 25 feet-7.5m. Line transformers have several connectors called taps. The primary taps are on one side of the transformer, and are marked as 10,5, 2.5, 1.25 and 0.62 watts. The secondary taps are on the other side of the transformer, and are marked as 4, 8 and 16 ohms. CONNECTING THE PRIMARY TAPS Before you connect speakers, be sure the total wattage of the primary taps you intend to use does not exceed the amplifier's power rating of 35 watts. In the following example, the total wattage is 8.75 watts. 1. Connect the desired primary taps to the amplifier's 70V terminal. NOTE: Usually, each speaker in a system uses the same wattage. If you want a particular speaker to have a higher volume level, use a higher wattage tap on its transformer. 2. Connect the C (common) taps on the transformers' primary side to the amplifier's COM (common) terminal. CONNECTING THE SECONDARY TAPS To connect the secondary taps of each transformer, follow these steps. 1. Connect the speaker's positive (+) terminal to the transformer's secondary tap that matches the speaker's impedance. 2. Connect the speaker's negative (-) terminal to the C (common) tap on the transformer's secondary side. SPEAKER PLACEMENT Finding the best speaker placement requires some experimenting. For the best result, point the speakers toward the listeners, and mount the speakers slightly above the level of the listeners' heads. The following drawings show recommended speaker placements for typical, narrow, and wide sound coverage. Hint: If you need to place speakers far apart, point them toward the main listening area so that the speakers' coverage areas overlap. This helps prevent dead spots (areas not covered by the speakers' sound). (SP/all-06/28/95)