How to Choose an Amplifier for Speakers

Selecting the right amplifier for your speakers can be a bit tricky. But it would be best if you did proper research on your options before making a choice. The wrong choice may get you stuck with poor sound quality, or you could damage both the amplifier and the speakers.

This article will explain everything about speakers, amplifiers, impedance, power rating, and sensitivity. You will also learn how these parameters can help you choose a suitable amplifier for your speakers. We will also explain how to connect speakers in parallel or series to alter the impedance.

Now, before we dive into the details, here is a summary of the entire process:

The Matching Process

the matching process on choosing an amplifier for speakers
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To put it simply, all you need to do when selecting an amplifier for your speakers is to find one with suitable impedance and power ratings. Do not worry if you are unfamiliar with these technical terms, as they will be explained later.

For now, all you need to know are these two basic rules:

1.   Amplifier Power Rating Should Be Slightly Above That of the Speaker

amplifier power rating should be slightly above that of the speaker
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The power rating of your amplifier’s output channel should be between 1.2 and 2 times the power rating of your speaker. So, if you have a 50-watt speaker, you should go for an amplifier with a power rating somewhere between 60 watts and 100 watts.

The recommended gap gives your amplifier enough room to power your speakers to their full potential. But, too large of a gap means that the amplifier could feed the speakers with a too high signal. This will cause the speaker to produce a sound of terrible quality due to clipping (another technical term we will explain later).  Also, an amplifier could feed a speaker with a strong signal to damage it in some cases.

On the other hand, if the amplifier’s power rating is less than the speaker’s, the sound produced may be too low. This is also an undesirable outcome.

So, before you go shopping for an amplifier, take note of your speaker’s power rating. This parameter is usually stated in Watts (W). And in most cases, you will find this information written somewhere at the back of your speaker. The amplifiers also have their power rating printed at the back of the appliance. It would typically be stated as X Watts or XW (where X is a number).

2.   Amplifier Impedance Should Be Equal To or a Bit Less Than That of the Speaker

Amplifiers usually have an impedance range instead of just a specific impedance rating. Therefore, when matching an amplifier to speakers, you should consider the lower range of amplifier impedance. For example, if your amplifier is for speakers with an impedance of between 4 ohms and 8 ohms, the number that concerns you is the lower range (4 ohms).

All you need to do is make sure you pick an amplifier whose impedance rating has a lower range, equal to or a bit less than that of the speaker. So, if your speaker has an impedance of 6 ohms, you will need to choose an amplifier with a lower range of 6 ohms or 4 ohms.

If you should do the opposite, like trying to power a 6-ohm speaker with a 16-ohm amplifier, make sure you have a fire extinguisher nearby. Okay, that was a joke (partly). But on a serious note, powering a speaker with an amplifier whose impedance rating is higher could fry the amplifier’s internal components.

On the other hand, if your amplifier impedance is far lower than the speaker’s, you could have a barely audible sound.

Like power ratings, the manufacturers print the impedance at the back of these appliances. If you cannot find this information on a device, you can check its manual. You can also search for the model number of the appliance on Google. This will give you links to web pages with all the technical information you need.

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What Do These Technical Terms Mean?

Now, just in case you are not familiar with some of the technical terms used, we will explain their meanings:

Power Rating

For most appliances, the power rating given by the manufacturers is an estimation of the rate at which the appliance consumes electric energy during normal operations. As we mentioned earlier, the unit for power rating is Watts (W). For the output channel of an amplifier, the power rating is the amount of electric power that the output channel can feed to the speakers.

An amplifier’s output channel connects and feeds sound signals to your speaker. It can have more than one output channel. And in most cases, all the output channels of an amplifier will have the same impedance and power rating.

Now, coming back to the term under consideration, an amplifier’s output channel will sometimes have two different power ratings printed on the back. Do not let this confuse you. These are the “continuous power” and “peak power” ratings.

The peak power rating is the highest level of electric power that the output channel can feed to a speaker momentarily. When choosing an amplifier, this is not the power rating you should be concerned with. The one you should take note of is the continuous power rating. That is the one we have been referring to since the start of this article. The level of electric power the amplifier’s output channel can comfortably feed to a speaker over an extended period.

For a speaker, the power rating is the level of electric power it takes to operate at its loudest without distorting the sound. And as we mentioned earlier, your amplifier should be capable of supplying power higher than the speaker’s power rating.


balanced sound waves and impedance
Image by mtmmonline on Pixabay

Impedance measures the resistance to the flow of an alternating current (or signal). For this article, we are giving an oversimplified description of the term. The full details are way too technical, and there is no need to go into all of that. This property is measured in ohms, and every appliance has it. That is to say that every single appliance presents some level of resistance to the flow of electric signals.

However, the impedance printed at the back of an amplifier is not necessarily the impedance of the amplifier itself. Instead, it is the recommended impedance of speakers the amplifier can power. So, if you see “4 ohms” printed on the back of an amplifier, the manufacturers recommend using the amplifier with a 4-ohm speaker. And if you see a range of 8 ohms to 16 ohms, the manufacturers recommend you connect the amplifier to a speaker with an impedance of between 8 ohms and 16 ohms.

The impedance printed at the back (or in the manual) is the speaker’s actual impedance for a speaker. However, there is a slight complication. In reality, the impedance of a speaker varies according to the frequency of the signal it receives. Therefore, it does not remain constant while the speaker is in use. But the manufacturer’s impedance rating is a good approximation of the speaker’s average impedance level during regular operation.


Clipping is the distortion when a signal has an amplitude (level) too high for an appliance. This distortion occurs as the appliance attempts to forcefully limit the amplitude by cutting off the excess (or clipping). For appliances like an amplifier and a speaker, the signal’s amplitude is proportional to the loudness of the sound produced. In other words, the higher the amplitude, the louder the sound.

For example, appliances like amplifiers and speakers are designed to handle signals below a certain level. Anything higher than that specific level will get clipped. This results in a distorted sound.

As we mentioned earlier, this happens when your amplifier’s power rating is many times higher than the speaker’s. As a result, the amplitude of the signals sent to the speaker would be too high. So, the speaker would clip the excess amplitude, resulting in a distorted sound.

Clipping could also occur when the power rating of your amplifier is considerably less than that of the speaker. In this case, the sound would be too low. But in a futile attempt to make it loud enough, most people would raise the volume settings too high. In this case, the amplifier does the clipping as the signal amplitude rises above the level it can handle.

Speaker Sensitivity

You would assume that the higher the speaker’s power rating, the louder the sound it produces. But this is not necessarily so. While the power rating does determine the loudness of a speaker to some extent, it is the sensitivity that counts. For example, a sensitive 10-watt speaker could be louder than a 20-watt speaker that is less sensitive. So, do not let the power ratings deceive you – it isn’t all that matters.

Conventionally, a speaker’s sensitivity is how loud (in decibels) a speaker can get when powered by 1 watt of electric power and observed from 1 meter away.

How to Match an Amplifier to Multiple Speakers

how to match an amplifier to multiple speakers
Photo by Thomas Litangen on Unsplash

If you have several speakers, you could connect more than one speaker to each channel of an amplifier. Doing this can alter the effective impedance of your speakers. The good thing is that this gives you more options when choosing an amplifier.

Here is an example to explain how this works:

Let us assume you have eight speakers. And each one of them has an impedance of 8 ohms with a power rating of 16 watts. If you know how to connect these speakers correctly, you will have more options when choosing an amplifier.

Using the previous method, you would need to go for an 8-ohm amplifier with a 20 to 32 watts power rating. You can also creatively connect the speakers in parallel or series in either a 2-ohm, a 4-ohm, or even a 16-ohm amplifier instead. The amplifier only needs to have a power rating higher than the sum of the power ratings of all connected speakers.

Now, let us explain how this can be done. But before we proceed, be warned that this involves some mathematical calculations. If you hate equations and calculations, you may want to stop right here. Also, connecting multiple speakers to a single amplifier output channel must be done with extreme care. If you find the following details confusing, do not try this. This should only be attempted by someone who knows what they are doing. If you do not get it right, you could end up permanently damaging your appliances.

But if you can get it right, it allows you to use just about any amplifier with your speakers. It expands your list of options.

So, this is how it is done:

If you want to use an amplifier with a considerably less impedance rating than your speakers, you connect the speakers in parallel. Doing this reduces the effective impedance of the speakers as a whole. This brings the impedance down to the level that matches the amplifier.

On the other hand, if you want to use an amplifier with an impedance rating that is too high for your speakers, you connect the speakers in series. This increases the effective impedance of the speakers so they can match that of the amplifier.

Next, we will explain what it means to connect speakers in parallel or series. And we will show you how this reduces or increases the effective impedance. We will also show you how to calculate the impedance of a group of speakers connected in series or parallel.

Connecting Speakers in Series

connecting speakers in series
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When you connect speakers (or any component) in series, you increase the impedance. The resultant impedance is simply the sum of the impedances of all the individual speakers. For example, if you connect one 6-ohm and two 4-ohm speakers in series, these speakers will have an impedance of (6 + 4 + 4) ohms. That is 14 ohms.

To connect a group of speakers in series, you line them up and link them in a chain-like formation. For example, if you want to connect speakers A, B, and C in series, you connect the amplifier output’s positive terminal to A’s positive terminal. Then, you link the negative terminal of A to the positive terminal of B. Similarly, you also link the negative terminal of B to the positive terminal of C. Finally, you link the negative terminal of C, the last speaker in this chain formation, back to the negative terminal of the amplifier. So, the amplifier output’s two terminals are connected to the first and last speaker in the chain while the speakers link up with each other.

Remember, you should do this when you want to increase the impedance to match the amplifier. Also, the total power rating of these speakers would be the sum of the power ratings of the individual speakers.

Finally, if you want to connect speakers in series, it is recommended that they all have similar impedances. For example, do not link a 16-ohm and a 2-ohm speaker in series. If you do, you will likely damage the one with the higher impedance.

Connecting Speakers in Parallel

Now, this is where it gets complicated. When you connect speakers in parallel, the inverse of the resultant impedance is equal to the sum of the inverses of their impedances.

For example, three speakers are linked in parallel, and their impedances are represented by the letters X, Y, and Z. Also, the resultant impedance is represented by the letter R.

Then, 1/R = 1/X + 1/Y + 1/Z

There is no need to dive deeper into this equation. However, it would be best to remember that the resultant impedance (R) is always smaller than all the individual impedances when connected in parallel.

Also, if speakers with the same impedance, X, are connected in parallel, the resultant impedance is X divided by the number of speakers. For example, if you connect four 8-ohm speakers in parallel, the impedance is 8 ohms / 4 = 2 ohms.

And just like speakers connected in series, the power rating of speakers connected in parallel is also the sum of the individual power ratings. So, you only need to select an amplifier with a power rating high enough to carry all the speakers.

As we stated earlier, you connect speakers to an amplifier in parallel when you want to reduce the impedance of the speakers to match that of the amplifier.

To connect speakers to an amplifier output channel in parallel, the positive terminal of the output must be linked directly to the positive terminal of all the speakers. At the same time, the negative terminal is also connected directly to the negative terminal of the speakers.

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In conclusion, you must adhere to all these recommendations when choosing an amplifier. Remember, if you get it wrong, you could damage both the amplifier and the speakers.

In this article, we have carefully explained two different ways one can go about selecting an amplifier. The first is finding an amplifier with a power rating and impedance that matches your speakers.

The second is to expand your options by mastering the art of connecting speakers in series or parallel. This would save you the trouble of having to search for an amplifier that strictly matches your speakers. Also, understanding the mathematical equations that govern series and parallel connections will help you calculate the exact impedance and power rating options that can work.

Some of the technical details here may be hard to understand. But if you can grasp them, you will enjoy the benefits. These benefits include superior sound quality and a longer life for your appliances. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to