How to choose amplifier for speakers: Complete buying guide

One of the most confusing and difficult-to-comprehend subject in the audio world is to understand the amplifier for a speaker. It is the most common question that every music lover asks and Google for hours in search of an ideal amplifier to pair with their speaker.

Why is it confusing? The terms, especially the power of a speaker varies from model to model. So among several technical terms and specifications, it is difficult to get an overall idea. In this article, I will talk about amplifier, power rating on how to match the amp with your speaker.

While selecting the right amp for your speaker the nominal impedance, power, and sensitivity are some of the crucial factors. Once you understand the technical terms you can choose one for your speakers by yourself with confidence.

What is an amplifier?

The role of an amplifier is to take in the audio signal, boost it up with power, and send it to the speaker so that it can play the track.  The amplifier doesn’t affect the audio quality directly via coloration if the specifications match with the speaker.

Types of amplifier

An amplifier can be divided into two types:

Power amplifier

This type of amplifier can only enhance the audio source in terms of power, voltage, and current and forward it to the speakers.

Integrated amplifier

This type of amplifier consists of a preamp and a power amplifier. The preamp consists of the volume control, input switching, phono preamp, tone controls, etc.

Although I wanted to keep things simple, this topic is not as easy as that. And the main purpose is to make sure at the end of the article you understand it all.

List of 5 best amplifiers:

Onkyo A-9150

Marantz PM6006

NAD Electronics D3020 V2

Yamaha A-S501

Cambridge Audio CXA61

Things I considered while choosing an amplifier

Impedance

What is the impedance?

Speakers and amplifiers usually have a rated impedance. Generally, the speakers are rated within 4, 6, or 8 ohms and the amplifiers can vary within 4 to 16 ohms. Impedance means the factor that resists the electric current through a circuit.

What is the difference between resistance and impedance?

Resistance is a factor that tries to prevent the current (DC) circulating through the circuit.  In Impedance the circuit uses AC current and it changes with frequency. When we talk about output impedance we mean the speakers because amplifiers don’t this feature. The term that you see in the user manual or datasheet as impedance for an amplifier, is the highest value of speaker impedance that a specific amplifier can handle.

Guideline

How to match the impedance of the speaker and the amplifier? You can pair an 8-ohm speaker with an amplifier than has 4-ohm impedance. However, a speaker of 4 ohms cannot be connected to an 8-ohm amplifier.

To summarize, the impedance of the speaker should be more than the speaker.

A word of caution: Consider a case when you connect a 4-ohm speaker to an 8-ohm amplifier and adjust the volume to maximum, the amplifier will face less resistance so it will allow more current and power to flow to the speaker.

The amplifier will shut down before it sends the excess power. In some cases, the speakers might be damaged before the amplifier can act. You can still connect a 4-ohm speaker to an 8-ohm amp, and they will work fine if you control your volume knob. But to keep things safe, we don’t want to do that.

Power

One of the haziest terms in the audio world is the power specification. Different manufacturers list the power in different ways and most of them want to give a bigger number because bigger sounds better.

What is a speaker’s power rating?

To learn more about speaker and amplifier power ratings we need to know that only amplifiers can generate power. The power specifications found in the speaker manual represents the value the speaker can handle without being distorted.

If the speaker is fed with more power than it can handle, it will start to distort and become hotter which might cause damage to the drivers and the speaker.

Manufacturers list the power of the speakers as Power output, Power handling, RMS, Peak, Maximum output, maximum input power, etc.

What is the amplifier power rating?

Amplifier power rating is a measure of the power the amp sends to the speaker. Here, we will always look for power watts per channel.

Quality of an amplifier

How can you understand which amplifier is the best? The following criteria are crucial to measuring the quality of an amplifier:

Damping factor

It is the ratio of loudspeaker impedance to the output impedance of the amplifier. Ideally, the output impedance should be smaller so the damping factor has to be higher. The higher the damping factor the better the amplifier can control the speaker drivers under 150Hz. It also means the system will be stable and have good bass.

THD

This is Total Harmonic Distortion that measures the difference between input and output signal. It is a measurement in various points in terms of percentage. THD should be less than 0.5%.

SNR

The signal-to-noise ratio means the ratio of amplifier noise given while boosting/amplifying the audio signal. If a speaker has an SNR of 110db it means that the sound signal level is 110dB greater than that of the noise signal. So if a speaker has SNR 90dB and another has 110dB, the latter is better.

The picture above shows the datasheet of the Marantz PM8006 Integrated Amplifier. Here we can see the THD is 0.02% and the damping factor is 100. So based on our definition the values are good.

The image above is the datasheet of NAD 3020. Here we see the Damping factor is 55, SNR is 75, and 110dB and THD are 0.02%. While the THD is good, the Damping factor and SNR could be improved.

How to match the speaker and amplifier power?

At first search for the amount of power the speaker is designed to deal with, let’s say the speaker can handle 150 W with 8ohm impedance, then it is better to pair it will an amplifier that has 200W per channel into 8 ohms.

If the speaker has a rating of power handling: 75W RMS /130W peak, then you can take the RMS value into specific impedance and compare it with the amplifier output per channel into specific impedance. That this, similar power has to be compared, with the RMS to RMS or Peak to Peak along with impedance, and the amplifier should be power per channel.

What happens if you do a mismatch, will the speaker immediately burst out? The answer is no.  For home uses, most of the time the mismatch doesn’t make damages given that you don’t play with the volume control too much.

If a speaker with 150W and 8ohm is paired with an amplifier that has 150W per channel into 8ohms, the speaker will still work but if you turn the volume up, there might be distortion. Similarly, a 100 W speaker with 8ohms can be connected to an amplifier rated 75W per channel into 8ohm. It will work but the volume has to be within a limited range.

Guideline

  • It is better to have an amplifier more powerful than the speaker so that if the volume is at maximum and the speaker needs more power, the amplifier can still provide it.
  • Match RMS to RMS or peak to peak along with impedance. The minimum value for the amplifier should be the rated RMS of the speaker, or higher.
  • Amplifier recommended power: oftentimes ‘recommended amplifier power’ is listed in the speaker datasheet. For example, an 8Ohm speaker has a recommended amplifier power of 400-750W per channel. Here an amplifier has to be selected that has the power within 400-750W.
ABC
450 W 320 W450 W
4 ohm8 ohm8 ohm

Let’s say the table above shows you the list of amplifiers you can choose from. Also, A and C are suitable in terms of power range we can’t choose ‘A’ because the amplifier has lower impedance.

DEF
300 W375 W525 W
8 ohm8 ohm8 ohm

Which one will you choose from the table above? Both E and F are compatible with the speaker that has 350-700W recommended amplifier power into 8ohms for each channel. Well, you can take any one of them but the ‘F’ might be more expensive and if you don’t have budget issues you should go with ‘F’.

This is because a more powerful amplifier will have more ‘headroom’. That indicates that the amplifier can play audio within a greater dynamic range so that when there are sudden bursts of sound when you are playing it loud, the amplifier can handle it without clipping.

  • If the speaker doesn’t specify the amplifier power range, you can look for the Power RMS of the speaker. If the Power RMS is 300W, then the range will be within the RMS and double the RMS value.

So here the recommended amplifier power will be 300-600W per channel into 8ohms. Since now you know the range you can easily find a match.

Sensitivity

What is the sensitivity of a speaker?

Sensitivity is measured in decibels or dB. It measures how loud a speaker can get. The sensitivity is measured when 1W input power is given as input and the listener is sitting 1 meter away.

Such as, if the speaker has 88dB sensitivity, this means if we are 1 meter away from the speaker, and we give 1W input to it. This is measure by Sound Pressure Level or SPL.

For the sound to be ‘twice as much’ it has to be 10dB more, this means if one speaker has 88dB and another has 98dB, the latter is twice as loud as the previous one. 88dB sensitivity is not that loud. Speakers with a sensitivity of 90 and above are considered to have good sensitivity.

For an increase in 3dB the power has to be doubled. This means if it needs 3W to deliver 88dB sensitivity, then the power has to be increased to 6W to achieve 91dB and an increase in 3dB isn’t noticeable. Also, the loudness will decrease by 6dB if you double the distance of your listening position.

How much loud should the speaker be?

Usually larger rooms need powerful speakers and amplifiers compared to smaller ones. Speakers with a sensitivity of 90 and above are considered to have good sensitivity.

Why should you choose a speaker with higher sensitivity? Well, if speaker A has efficiency 88dB and B has 92dB then B will need less power to achieve the THX reference level. The THX reference level is the 105dB peak for a given channel.

86 @1W88dB @1W92 [email protected]
89dB=2W91db=2W95dB=2W
92dB=4W94dB=4W98dB=4W
95dB=8W97dB=8W101dB=8W
98dB=16W100dB=16W104dB=16W
101dB=8W103dB=32W107dB=32W
104dB=16W106dB=64W111dB=64W
107dB=32W109dB=128W113dB=128W
110dB=256W112dB=256W116dB=256W
113dB=128W115dB=512W119dB=512W

From the table, we easily understand that the speaker with the highest efficiency, 92dB needs less amount of power from the amplifier to reach the THX level. So the higher sensitivity speaker doesn’t need larger amplifiers which will be expensive. In the example above, with better sensitivity, you can easily go with amplifier E rather than F.

Room arrangement

This is the most neglected factor while choosing an amplifier but has a significant effect on the speaker and amplifier. As mentioned earlier, larger rooms will need a more powerful speaker and amp. To achieve the best audio from the speaker, a general rule is to keep the speakers 1.5-2.5 m apart and make an equilateral triangle with your listening position. The speaker should be placed such that it is parallel to your ear level.

Once you know your room size and listening position, decide how loud you want your speakers to be. For most people, 85to 88dB is enough for listening to music. 90dB is quite loud and as the value increases, the audio becomes crazy-loud. For human beings, prolonged exposure to the audio above 90dB is harmful.

Audio quality

If you have a speaker that has a bright sound that may come from horn drivers or metal-made drivers then you don’t want to add another bright amplifier.  The bright audio will seem harsh and cause ear fatigue if you listen for a long time.

The tonal characteristics of an amplifier are important.  How to measure it? The only way is to listen to the sound or consult with a retailer/dealer to describe the audio characteristics. So if you have a bright speaker you have to choose a warm sounded amplifier. Warm sound means it is mellow, soft, or pleasant.  This balance is important as well as other factors.

FAQs: How to choose amplifier for speakers

You may be the type of person who loves to ask a lot of questions. For those that are, this is your lucky day! The FAQ section will answer some important and popular questions you might have about this matter so that we can help make it easier for you to learn more and better understand what we’ve talked about.

Should the wattage of the speakers be higher than the AMP?

The speakers should be rated for the same amount of power as the amp; otherwise, you risk damaging them by overdriving them.

Is it true that more watts are better for speakers?

Many artists solely evaluate the amplifier’s power or wattage rating when it comes to “volume,” and more watts does mean “louder” in general. While wattage is essential, the efficiency of the speaker(s) connected to the amplifier is also important in the loudness equation.

Is it possible for AMP speakers to be overly powerful?

Speakers can be overpowered by amplifiers. The amount of electrical energy that speakers can convert into audio is restricted. If the amplifier generates more electrical energy than the speakers can handle, distortion or clipping may occur, although damage is unlikely.

Conclusion: How to choose amplifier for speakers

If you ask which amplifier will go for my ‘X’ speakers? There isn’t one correct answer. So you need to comprehend the specifications and figure out which amplifier will be the best.  For home systems, a slight mismatch will not burn your speakers immediately so you can relax.

While choosing an amplifier, the amplifier should be more powerful in terms of power compared to your speakers. Also, the speaker impedance should always be more than that of the amplifier. You should also keep an eye on the damping factor, THD, SNR of the amplifier as they represent the quality of it.

Another thing is, you should always buy speakers and amplifiers based on room size, your loudness expectations. The higher the sensitivity of the speaker, the less power it needs to run or achieve higher volume.

I hope now you have a clear understanding of the amplifiers of speakers and how to choose them correctly.

For more information, you can visit our comparison article about Preamp and Amp.

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Power Amplifier vs Integrated Amplifier

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