Multi Zone Amplifier

The speaker selector is not just a piece of pretty accessory in the audio system. Please be warned that multiple sets of speakers usually can not be hooked directly to a standard audio amplifier without some sort of impedance

matching device. This article is written specifically for those of you who still wants to use your old amplifier to distribute multi zone sound instead of investing on a new multi zone amplifier. Bear in mind, if several sets of speakers are run from one set of speaker terminals the amplifier will usually overheat and shut down, and may blow the output stage.

The correct solution is to use either an impedance matching speaker selector with the protection-mode enabled. Curiously, most speaker selectors are made with a dangerous feature: a switch located right in front, to disable the protection. If the protection is accidentally switched off while running multiple pairs of speakers the amplifier will shut down, may blow output fuses, and very well may damage the output stage of the amplifier. As a result, I would advise you to always leave the switch on, irregardless.

One rule of thumb, only put one speaker per pair of terminals (usually red and black) on the amplifier. Do not try to use a surround amp to feed several rooms with one room on the center, one room on the rear surrounds etc. This is due to the way a surround receiver distributes the sound as you may end up with only the voice in one room and only the music in another! The correct hookup for a surround receiver puts surround sound in the main room and sound from the left and right main speakers is distributed.

One recommendation for wiring up a surround receiver is as follows. Run the speaker selector from the front left and front right outputs on the amplifier. Hook your front left & right speakers to the first speaker switch on the speaker selector. You will need to rebalance your surround system by running the pink noise test as the speaker selector will decrease the output to the left and right speakers by a small amount. This allows running the main speakers & the other speakers connected to the speaker selector without one set being louder than the others. If your speaker selector has volume controls, you need to make sure when you use your surround system for movies the volume control is at the same setting it was when doing the pink noise test. You may hook the speaker selector to the ‘b’ speaker switch on the amplifier if speaker volume balance between your main left & right speakers and the rest of the speakers is not an issue.

Another variation is amplifiers with a direct speaker output for zone 2, 3, etc. These are set up to drive 1 pair of speakers, and must be used with impedance matching if more pairs are to be used. The zone outputs allow a second (or third etc) source, for example CD in one room and radio in another.

An impedance matching speaker selector provides multiple outputs from one input, and protects your amplifier from damage. Speaker selectors come with 4-12 outputs. As long as your amp has enough power, you can push as many sets of speakers as you want. Simply connect the speaker selector to your ‘A’ (or ‘B’) outputs and the rest of your speakers on the speaker selector. You can purchase speaker selectors with volume controls for each individual speaker. Another option is in wall impedance matching volume controls, which require no speaker selector. Most of these are set with jumpers at install time, providing the correct matching. If you want to run more pairs of speakers than the speaker selectors or volume controls are made for (usually 12 pairs max. depending on the hardware) you probably want a second amplifier to run the second set of volume controls (or speaker selector) from.

The music signal to your speakers is called alternating current (or AC), because it varies polarity and voltage. This is in comparison to a battery, for example which produces a steady, or DC current. You may picture current as the amount of water flowing in a pipe (the wire) and voltage as the water pressure. AC current can be imagined as a flow that reverses direction and DC as a steady flow in one direction. The analogy is not exact but is close enough to get a picture of what is happening. Standard house current in the US reverses direction (polarity) at an interval (or frequency) of 60 times per second, measures as 60 Hz (Hertz).

Your speakers have a certain amount of resistance to current. Imagine the resistance as a constriction in the pipe, limiting the  flow. They have a DC resistance, termed the voice coil resistance, and resistance to AC is called impedance. Resistance and impedance values  are measured in Ohms. Impedance is a complex sum of dc resistances, plus the resistance to various AC frequencies caused by capacitance and inductance (normal properties of electrical and electronic devices).

It is usually specified for speakers as nominal impedance, and is referenced to particular frequencies . However, just think of it as resistance to AC for practical purposes. This is usually rated at either 8 or 4 Ohms. Most home amplifiers prefer an 8 ohm impedance. Each time another speaker is added in parallel the impedance is reduced. Visualize several pipes connected together to the same pump, obviously the flow from the pump increases (up to the limit of the pump’s capability). The amplifier is the pump. Two  8 ohm speakers reduce the impedance to 4 ohms, four 8 ohm speakers reduce the impedance to 2 ohms, and so forth.

An amplifier expects (most require) a certain amount of resistance to current flow. The lower the impedance, the more current flows through the output stage of a typical amplifier. This usually flows directly through a transistor (or other amplifying device) and damages the transistor or protective resistors in the output stage. If you get lucky it only blows an output stage fuse. The moral of the story is always use an impedance matching speaker selector, (or volume control) and your amplifier will always see a safe impedance load.

Source: www.smartbuyspeakers.com