Knowledgebase: Speaker
"Chaining" or "piggybacking" multiple monitor speakers in parallel
Posted by Rick Shao on 13 November 2015 05:48 AM

Q: Chaining or piggybacking multiple monitor speakers in parallel is a common and convenient practice. What does that do to the power amp that drives them? How many such speakers can we chain together?

A: This is an important issue that, understood properly, can keep you from burning out an amp. Speakers - monitor type as well as mains - are rated according to their wattage output power into an impedance or electrical resistance measured in ohms. The most common speaker cabinet impedance is probably eight, while one also encounters four-ohm and sixteen-ohm speakers. A fact of electrical/acoustical physics is that when each additional speaker is chained in parallel, the net impedance in that channel or circuit is reduced.

The formula for that reduction is: RT = 1/(1/R1 + 1/R2 + ... + 1/RN) where R represents each speaker boxs impedance, and RT = the total combined impedance. Accordingly, two piggybacked eight-ohm monitors present a four-ohm load to the power amp channel to which theyre connected. (If you work these examples through the formula, you are guaranteed to learn the principle.)

When this impedance is cut in half, the power load on that amp channel increases by approximately one-half (i.e., a 300-watt amp would run at about 450 watts). The addition of a third chained eight-ohm monitor cuts the combined impedance to 2.7 ohms. A four-speaker chain of eight-ohm speakers presents a two ohm combined impedance. Into a resistance of two ohms, the same power amp would crank at about 700 watts (~450 x 1.5). If the amp isnt rated as capable of enough power to operate at these wattage output levels, it is likely to overheat, and will probably fail prematurely.

Tip: Understanding the inverse relationship between load impedance and power levels will ensure that the number of speakers you chain into an amp channel is properly matched with the amp that drives them. A safe habit is to deploy your monitors in equal numbers on either right or left channel of your power amp, so that the output load is matched, or at least approximately

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