Radio Shack MPA-125 owner manual Connecting The Speakers, Determining Total Speaker Impedance

32-2003.fm Page 8 Tuesday, March 28, 2000 10:45 AM

CONNECTING THE

SPEAKERS

You can connect one or more 4-, 8- or 16- ohm speakers to the amplifier, with or with- out transformers. To ensure equal volume from each speaker, all connected speakers should have the same impedance rating.

Proper phasing is important when you use more than one speaker in the same room or area. Out-of-phase speakers can lose up to one-half of their potential volume, and can have a significantly decreased bass effect.

Most speaker terminals are color-coded or have a mark that indicates the terminal’s po- larity. Usually, terminals with positive polarity are red or have a plus symbol (+), and termi- nals with negative polarity are black or have a minus symbol (–). Phasing is correct when you connect + to + and – to –.

Determining Total Speaker Impedance

Before you connect speakers to the amplifi- er, you must determine the total speaker im- pedance.

Caution: A total speaker impedance higher than 16 ohms or lower than 4 ohms can damage your amplifier or speakers.

In determining the total speaker impedance, you must first determine if you are connect- ing the speakers in series, parallel, or a se- ries/parallel combination.

Note: For the best results when connecting speakers (in series or parallel), only use speakers that have the same impedance.

•Speakers are connected in series when the first speaker’s positive terminal is connected to the next speaker’s nega- tive terminal.

Determine the total impedance of speakers you want to connect in series by adding up the individual impedances of all the connected speakers. For example, if you want to connect two 8- ohm speakers in series, add 8 (the impedance of one speaker) plus 8 (the impedance of the other speaker) for a total speaker impedance of 16 ohms (see “Connecting Two Speakers In Series” on Page 9).

•Speakers are connected in parallel when all the speakers’ negative termi- nals are connected together and all their positive terminals are connected together.

Determine the total impedance of speakers you want to connect in parallel by dividing the impedance of one speaker by the number of speakers. For example, if you plan to connect two 8- ohm speakers in parallel, divide 8 (the impedance of one speaker) by 2 (the number of speakers) for a total speaker impedance of 4 ohms (see “Connecting Two Speakers In Parallel” on Page 10).

•If you are connecting more than two speakers using only series or only paral- lel 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). This exceeds the maximum rating.

•In parallel, the total impedance is 2 ohms (8 divided by 4 = 2). This falls below the minimum rating.

8 Connections