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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 first using an impedance matching device. This is for the benefit of folks who are considering installing speakers in multiple locations simultaneously (distributed audio). Overheating and shutting down of the amplifier, as well as possible damage to the output stage, are common 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. Either an impedance-matching speaker selector with the protection turned on, or impedance-matching in-wall volume controls, is the correct answer. The above underlined sentence is of particular importance, 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 rear of the device, away from curious fingers. Accidentally disabling the protection while powering numerous sets of speakers will cause the amplifier to shut down, possibly blow output fuses, and almost certainly harm the amplifier’s output stage. If impedance matching volume controls are being used on ALL pairs of speakers, this switch should be off. There’s also no need for impedance matching if you’re only using a single set of speakers. Leaving the protection on in this case will just slightly alter the sound, thus there’s no reason to turn it off. Keep in mind 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 in which just one room uses the center channel, another uses the rear surrounds, and so forth. This is because of how 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 main 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 amplifier’s front left and right channels should be used for the speaker selector. 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 for the main speakers and any additional speakers to be played through the speaker selector without any 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 make sure 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 much 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 that the hardware supports (often 12 pairs). 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 is in contrast to the steady, or direct, current produced by, say, a battery. 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 alternates between flowing 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, together with accompanying diagrams, is available in its entirety 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 resistances 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 the time being, though, you can simply 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 a number of 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. In order for an amplifier to function properly, some level of 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 that your amplifier always 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. An amplifier does not, contrary to popular belief, increase the size of the input signal. It takes the original signal and makes a bigger (greater current and voltage) version of it, which is then sent to the speakers. The AC from the wall outlet is used to generate 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 in that it regulates 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/or voltage) that is allowed to flow through it in response to the input signal. A low output impedance (see to the preceding text for an explanation of impedance) is required for an amplifier to be compatible with the vast majority of 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 fully 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 value of impedance while they are transmitting the maximum current and voltage to which they are rated. If the impedance (ac resistance) of the speakers is too low, then the amplification device will be overloaded. Either it completely disintegrates, explodes a fuse, destroys the emitter resistors, or does some other type of harm. Unfortunately, fuses don’t always react quickly enough to save the circuit. Why then don’t we build everything to function well into 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, if it puts out 100 watts into 8 ohms, 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 actually achieve an actual doubling of power for a halving of load impedance). The output impedance of most modern amplifiers is much below.5 ohms, allowing them to work well with speakers that exhibit low impedances at certain frequencies. In order for our hypothetical amplifier to function into a.5 ohm load, it would require the 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. 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 essentially an average power measurement that is 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 greatly 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. Licensed from: Seafawn Enterprises, LLC (2006-2008) You are welcome to copy whatever you find here as long as you include the link. Shop for audio equipment for your home theater Gary Seaman [http://www.smartbuyspeakers.com] Dependable, Uncomplicated, Prompt, High-Quality Product Offerings. To purchase home theater speakers and in-wall audio components, please click the above link.

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