A Guide to Connecting Multiple Speakers to a Single Stereo or Home Theater Amplifier

Though straightforward, I feel compelled to issue a cautionary note before detailing the steps. It is not common practice to connect multiple speaker systems to a single audio amplifier without using an impedance-matching device. This is for the benefit of folks considering installing speakers in multiple 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 correct answer is an impedance-matching speaker selector with the protection turned on or impedance-matching in-wall volume controls. The above-underlined sentence is significant, so keep it in mind. This is due to the fact that 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 device’s rear, away from curious fingers. Disabling the protection while powering numerous speakers will cause the amplifier to shut down, possibly blow output fuses, and almost certainly harm the amplifier’s output stage. 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. Leaving the protection on, in this case, will slightly alter the sound; thus, there’s no reason to turn it off.

Remember that the amplifier can only handle one speaker connected to each set of terminals (often red and black). 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 channels, 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. Here are the steps I take when installing a new 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 cuts some power from the left and right speakers, you’ll need to conduct the pink noise test to re-balance your surround setup. This allows the main speakers and any additional speakers to be played through the speaker selector without distortion in volume levels. If your speaker selector has volume controls, remember to utilize the same volume level when watching movies with your surround system as you did when you ran the pink noise test. If the volume difference between your main left and right speakers and the rest of the speakers is not a problem, you can connect the speaker selector to the amplifier’s ‘b’ speaker switch.

Amplifiers with a dedicated speaker output for Zones 2–5, etc., are yet another possibility. If you want to use them to power more than one set of speakers, you’ll need to ensure their impedance matches. The zone outputs let you play a different audio source in each zone so you can listen to a CD in one room and the radio in another.

An impedance-matching speaker selector prevents your amplifier from being harmed by having many outputs from a single input. Some speaker selectors have as many as 12 channels. You can connect as many speaker systems as your amplifier can handle. To use the speaker selector, link the ‘A’ (or ‘B’) outputs to the remainder of your speakers. A speaker selector with independent volume settings is available for purchase. In-wall impedance-matching volume controls are another viable alternative; these can be used without a speaker selector. The majority of these are matched at the time of installation through jumpers. You will need a second amplifier to power the second set of volume controls (or speaker selectors) if you want to use more than the maximum number of speaker pairs the hardware supports (often 12).

So, tell me, what is impedance and how is it matched? (Slightly technical information ahead.)

The voltage and polarity of the signal sent to your speakers alternately, hence the name “alternating current” (AC). This contrasts with a battery’s steady, or direct, current. Current may be thought of as the volume of water flowing through a pipe (the wire), and voltage as the pressure of the water. Direct current is a constant flow in one direction while alternating current flows in one direction and the other. Although this isn’t a perfect example, it does help paint a picture of the situation. The frequency of 60 Hertz (Hz) refers to the number of times per second that the polarity of standard household electricity in the United States is reversed. This essay and accompanying diagrams are available entirely if you visit our site.

Your speakers have some degree of electrical resistance. Visualize the obstruction caused by the resistance as a narrowing of the pipe. The voice coil resistance measures their DC resistance, while impedance measures their AC resistance. The unit of measurement for resistance and impedance is the Ohm. Impedance is the combined DC and AC frequency resistances from standard electrical and electronic device features like capacitance and inductance. Nominal impedance is a frequency-referenced specification typically used for speaker design. For now, though, you can think of it as AC resistance. Typically, this is given an Ohms rating of 8 or 4. An 8-ohm impedance is ideal for most household amplifiers. When more speakers are connected in parallel, the impedance drops. Imagine several pipes all leading to the same pump; the flow rate will grow (up to the pump’s capacity). The pump is the amplifier. When using two 8-ohm speakers, the impedance drops to 4 ohms; when using four 8-ohm speakers, it drops to 2 ohms, and so on.

For an amplifier to function correctly, some current resistance is expected. In a standard amplifier, the current through the output stage increases as the resistance decreases. This commonly occurs in the output stage, when it flows directly into the transistor (or other amplification device) and causes damage. A fuse in the output stage may be all that is blown. Use a speaker selection (or volume control) with impedance-matching capabilities to ensure your amplifier continuously detects a safe impedance load.

1. (See Note 1)

What causes the output stage of the amplifier to fail? This is because of how an ordinary amplifier works. Contrary to popular belief, an amplifier does not increase the size of the input signal. It takes the original signal and makes a more extensive (more significant current and voltage) version, which is then sent to the speakers. The AC from the wall outlet generates the voltage used to make the copy. This current needs to be rectified into a DC voltage first. The amplifier will hum inefficiently (since it is unaware of the words being played). The amplifier functions like a valve regulating the output voltage and current. The input signal regulates the operation of the valves, which are often transistors but could also be integrated circuits, vacuum tubes, or other devices. The output of an amplification device is proportional to the amount of current (and voltage) allowed to flow through it in response to the input signal. A low output impedance (see the preceding text for an explanation of impedance) 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 some speakers will have varying degrees of emphasis on various sounds, while other speakers will play them at lower volumes than they should. 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. This is when things become complex. The linked speakers’ impedance has a significant effect on the current flow. Most amplifiers are optimized for use with 8-ohm speakers but can often be made to function adequately with 4-ohm loads. The input impedance of some so-called high current amplifiers may be as low as 1 ohm. In other words, the amplifiers are constructed such that the output transistors are operating into an expected impedance value while transmitting the maximum current and voltage to which they are rated. If the speakers’ impedance (ac resistance) is too low, then the amplification device will be overloaded. Either it completely disintegrates, explodes a fuse, destroys the emitter resistors, or does other harm. Unfortunately, fuses don’t always react quickly enough to save the circuit. Why don’t we build everything to function well with low impedances? Without getting into the nitty-gritty, this might cause significant price hikes. For most modern speaker systems, an amplifier’s power should be increased by a factor of two for every half-point drop in impedance. So, suppose it puts out 100 watts into 8 ohms. In that case, it needs to put out 200 watts into 4 ohms, 400 watts into 2 ohms, and 800 watts into 1 ohm (remember, this is theoretically ideal, and nearly no 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 a. 5-ohm load, it would require 1600 watts per channel output power. You may probably guess that a high-quality amplifier with those

capabilities would come at a hefty price. Consider the following: A typical user of this enormous amp will only see an average output wattage of 100 watts RMS when driving 8-ohm speakers (RMS stands for Root Mean Square and is an average power measurement of roughly 70% of peak power). This puts the amp out of reach for the vast majority of consumers. Because some speakers with impedances as low as one ohm benefit significantly from being powered by a high-current amplifier, some amplifiers are designed to accommodate such loads. A monoblock model like the Krell Evolution One is one such instance. For stereo sound, you’ll need a pair of them. 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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