Radio Shack MPA-50 owner manual Speakers, Speaker Phasing, Determining Total Speaker Impedance

32-2002.fm Page 6 Friday, February 11, 2000 11:36 AM

ˆSpeakers

SPEAKER PHASING

Phasing is the direction the speaker cone moves with reference to the polari- ty of the connection wires. Proper phas- ing 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.

Speakers are in phase if all the speaker cones move in the same direction when an equal signal is applied. Phasing is correct if you observe the correct polari- ty (+ to + and – to –) when connecting the speakers.

Most speaker terminals are color-coded or have a mark that indicates the termi- nal’s polarity. Usually, terminals with positive polarity are red or have a plus symbol (+), and terminals with negative polarity are black or have a minus sym- bol (–). If the speaker terminals are un- marked, follow these steps to determine their polarity.

1.Remove about 1 inch of insulation from both ends of a short piece of wire (available at your local RadioShack store). Then twist the exposed wire to secure all its strands.

2.Connect one end of the wire to one of the speaker terminals.

3.Touch the positive end of a 1.5-volt flashlight battery to the speaker ter-

minal that does not have the wire attached to it.

4.Touch the negative end of the bat- tery with the lose end of the wire attached to the other speaker termi- nal. Note the direction of the cone movement — inward or outward.

5.If the speaker cone moves outward, the speaker terminal where you touched the positive end of the bat- tery is positive. Mark that terminal with a + and mark the other terminal with a –.

If the speaker cone moves inward, the speaker terminal with the wire attached that touched the negative end of the battery is positive. Mark that terminal with a + and mark the other terminal with a –.

6.Remove the wire.

Repeat Steps 2–6 for each speaker with unmarked terminals you plan to connect to the amplifier.

DETERMINING TOTAL SPEAKER IMPEDANCE

Caution: A total speaker impedance that is higher than 16 ohms (Ω) or lower than 4 ohms can damage your amplifier or speakers. Be sure to make the proper connections.

Before you connect speakers to the am- plifier, you must determine the total speaker impedance. In determining the total speaker impedance, you must first

6 Speakers