This is straightforward, but before I describe how to do it, I believe I should issue a caution. An impedance-matching device is usually required when connecting multiple speaker systems to a single audio amplifier. This is for the benefit of folks considering installing speakers in various locations simultaneously (distributed audio). Overheating and shutting down of the amplifier and possible damage to the output stage are typical results of connecting many speaker systems to a single set of speaker terminals (see footnote 1). Special speakers with transformers are needed for PA-style amplifiers with 25 or 70-volt outputs. Therefore my comments do not apply to them.
The best option is to install impedance matching in the wall volume controls or utilize a speaker selector with protection enabled. Please take note of the highlighted portion of the phrase above. This is because most speaker selectors include a button on the front that may be used to bypass the safety features. It would be preferable if the switch were placed in the speaker’s rear to prevent accidental activation of the safety feature. The amplifier will shut down, blow output fuses, and destroy the output stage if the protection is accidentally turned off while operating numerous pairs of speakers. This switch should be off if impedance-matching volume controls are being used on ALL pairs of speakers. There’s also no need for impedance matching if you only use a single set of speakers. In this case, the sound quality will barely change if the protection is left on. Thus, there’s no reason to turn it off.
Remember that each set of amplifier terminals (often colored red and black) should only ever connect to a single speaker. Avoid connecting a surround amplifier to a system where just one room uses the center channel; another uses the rear surround, and so forth. This is because a surround receiver separates the audio tracks, which can result in you hearing only the voice in one room and the music in another. Surround sound should be played in the central area, with the left and right main speakers distributing the sound. This is how I would suggest connecting a surround sound system. The speaker selector should use the amplifier’s front left and proper channels. Connect the left and right front speakers to the speaker selector’s first switch. Since the speaker option lowers the output to the left and right speakers, you’ll need to re-balance your surround system by playing the pink noise test. This allows for the main speakers and any additional speakers to be played through the speaker selector without any distortion in volume. If your speaker selection includes volume controls, remember to utilize the same volume level when watching movies with your surround system as when you tested it with pink noise. You can connect the speaker selector to the amplifier’s ‘b’ speaker switch if you don’t care about maintaining a consistent volume between the front left and right speakers and the rear surrounds.
Amplifiers with separate speaker outputs for zones 2, 3, etc., are another variant. These are designed to power a single set of speakers and require impedance matching if more than two sets of speakers are to be driven. Thanks to the zone outputs, you may play a CD in one room and the radio in another.
A speaker selector with impedance matching allows for many outputs from a single input and safeguards your amplifier from overheating. Inputs range from 4-12 on speaker selections. If your amplifier has good juice, you can connect as many speaker systems as you like. Connect the rest of your speakers to the speaker selector and the ‘A’ (or ‘B’) outputs on your amplifier. You can have speaker selectors that include individual volume controls for each speaker. Speaker selectors aren’t necessary with in-wall impedance-matching volume controls. The majority of these are matched at the time of installation through jumpers. Depending on the hardware, most speaker selectors and volume controls can only handle up to 12 pairs of speakers at once, so if you need to use more than that, you’ll need a second amplifier to power the extra speakers.
Impedance and impedance matching—what are they, exactly? (Caution, some moderately technical language ahead.)
Alternating current (AC) refers to the voltage and polarity fluctuations in the audio signal sent to your speakers. This contrasts with a battery’s steady, or direct, current. Present may be thought of as the volume of water flowing through a pipe (the wire), and voltage as the pressure of the water. One way to see the difference between direct and alternating current is as a river constantly switches directions. Although this isn’t a perfect example, it does help paint a picture of the situation. In the United States, standard household current is measured in Hertz (Hz) and cycles back and forth between positive and negative 60 times per second. This essay and accompanying diagrams are available entirely if you visit our site.
There is a certain amount of current resistance in your speakers. Think of the resistance as a conduit bottleneck preventing water flow. The voice coil resistance measures their DC resistance, while impedance measures their AC resistance. The Ohm is the standard unit of measurement for resistance and impedance. An electrical circuit or electronic component impedance is the complex sum of its dc resistances and the inductance and capacitance that result from operating at alternating current (AC) frequencies. Nominal impedance is a frequency-referenced specification typically used for speaker design. For now, though, you can think of it as AC resistance. Usually, this will have an 8 or 4 Ohm rating. The standard for residential amplifiers is 8 ohms. When more speakers are connected in parallel, the impedance drops. Imagine several pipes all leading to the same pump; the flow from the pump will rise (up to the pump’s capacity). That pump is the amplifier. If you use two 8-ohm speakers, the impedance drops to 4 ohms; if you use four, it falls to 2 ohms, and so on.
For an amplifier to function correctly, some current resistance is expected. In a conventional amplifier, the current flowing through the output stage increases as the impedance decreases. The output stage transistor or protection resistors can be harmed when this runs directly through the device. If you’re lucky, only the fuse protecting the output stage will blow. Use a speaker selection (or volume control) with built-in impedance-matching features, and your amplifier will always perceive a safe impedance load.
1. (See Note 1)
The output stage of the amplifier has failed. This is because of how a regular amplifier works. An amplifier does not, contrary to popular belief, increase the size of the input signal. It takes the input signal and outputs a bigger (more significant current and voltage) version to the speakers. It replicates the AC voltage from the wall outlet, from which the power supply draws electricity. This present needs to be rectified into a DC voltage first. The amplifier will hum inefficiently (since it doesn’t understand the words). The amplifier functions like a valve regulating the output voltage and current. Input signals operate these valves (often transistors but possibly integrated circuits, vacuum tubes, and other devices). An amplifier takes an input signal and replicates it at the output by adjusting the current (and voltage) it permits to pass through it. A low output impedance (see the preceding text for an impedance description) is required for an amplifier to be compatible with most speakers. The frequency response will change depending on the impedance of the
speakers if the output impedance is too high. This means that individual speakers will have different degrees of emphasis on different sounds, and thus the overall impact will be variable from system to system. In practice, this implies that the typical circuit design requires nearly all of the available current from the power source to flow through the transistor (or other device) while it is entirely on. It gets complicated now. The linked speakers’ impedance greatly determines the current flow. Although most amplifiers are rated for 8-ohm speakers, some may function adequately when connected to 4-ohm speakers. Some so-called high-current amplifiers might even be usable in a 1-ohm load. The amplifiers are constructed so that while the output transistors are passing the maximum current and voltage they are rated for, they are doing so against an impedance that is expected to be there. Too much current is allowed to flow through the amplifying device when the connected speakers’ impedance (ac resistance) drops below a certain threshold. Either it completely disintegrates, burns out, bursts a fuse, or destroys the emitter resistors. Most of the time, fuses can’t preserve a circuit because of how slowly they react. Then why aren’t all systems built to function with low impedance?
Without getting too technical, this can have significant financial implications. For most modern speaker systems, an amplifier’s power should be increased by a factor of two for every half-point drop in impedance. For example, suppose an amplifier is rated at 100 watts into 8 ohms. In that case, it must be able to produce 200 watts into 4 ohms, 400 watts into 2 ohms, and 800 watts into 1 ohm (keep in mind that this is the theoretically ideal case, and in practice, very few amplifiers can achieve an actual doubling of power for a halving of load impedance).
The output impedance of most modern amplifiers is much below. Five ohms allows them to work well with speakers exhibiting low impedances at specific frequencies. For our hypothetical amplifier to function into an a. 5-ohm load, it would require an output power of 1600 watts per channel. You may probably guess that a high-quality amplifier with those capabilities would come at a hefty price. Now consider this: With 8-ohm speakers and this big amp, the typical user will only experience an average output wattage of 100 watts RMS (RMS stands for Root Mean Square and is a middle power measurement of roughly 70 percent of peak power). This puts the amp out of reach for the vast majority of consumers. Some amplifiers are constructed to this specification because some speakers have impedances as low as one ohm and benefit significantly from being powered by a high-current amplifier. The Krell Evolution One is a monoblock that fits this description. Two of them are required for stereo sound. Each one will cost you roughly $25,000. Those who doubt me can check the going rate for Krell monoblocks online.
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