How Many Watt Amplifier Do I Need? The Math Behind

How Many Watt Amplifier Do I Need
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Among the most common questions we get is this: how many watt amplifier do I need? Someone with absolutely no knowledge of wattage will just assume that the higher the watt rating, the better. There are also some who make a decision based on the meaningless amp and speaker output specs.

As you can see, this is indeed a very confusing subject, which is why we decided to set the record straight once and for all. In this article, we will tell you just how many watts are required for your speaker to work at its best.

What Exactly Do the Specs Tell You?

On just about any speaker you own, you will notice that there is a rating for the amount of power that the speaker can handle. Let’s just say right away that this number is pretty much meaningless. More often than not, this number is the maximum power, but there is no explanation as to how and why it was derived.

You see, there are some obvious questions that arise with this. Is this number the maximum continuous level? Is it the peak level? Is it the average level? How long can this be sustained?

You will find several high-end speaker brands talking about different and often conflicting standards to measure how much power a certain speaker can handle. This is one of the main reasons why people are so confused.

To make matters worse, not even the manufacturers themselves follow these standards. Unfortunately for us, all they do is make an educated guess.

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How Big Is the Room?

Another factor that needs to be addressed before we talk about power is how big the room is or whether or not it is at a large venue. It also needs to be determined whether or not you are looking to power a small home theatre or some loud and massive outdoor speakers.

These questions, to a certain extent, will also help in determining the amount of power your speakers need from the amplifier.

Amplifier Power vs. Volume Settings

In most cases, an amplifier running on a 200-watt motor will put out the same power as an amplifier with a 10-watt motor. This is because most of the listening will occur at average levels where lesser than a watt is more than enough power for the speakers.

In order to a load a given speaker at a particular volume, any amplifier will deliver the exact same amount of power. That is, as long as they can deliver that much.

So, in that sense, it is pretty much the volume that matters and not the power of the amplifier. If you never listen to your speakers at volumes where it tends to get uncomfortable, the amp may not even put out more than 10 or 20 watts.

What does this mean? It means that you will be able to connect even a 1000-watt amplifier to a tiny two-inch speaker. But then again, you are advised not to raise the volume beyond the point where the speaker is unable to handle it.

This also means that you should not be connecting an amplifier with a low power model (such as a 10- or 20-watt model) and into a regular speaker and turn the volume at the loudest. The amplifier with the low watt rating will end up clipping, and this is a common reason for speaker failures.

If the amplifier does clip, it basically outputs a high-level of DC voltage right into your speaker. This will burn out the voice coils on your speaker drivers in an instant.

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How Many Watt Amplifier Do I Need?

We agree that all this appears to be very confusing. However, it is quite easy to calculate how many watts you need. In fact, you can do all of this in your head.

While it will not be perfect as you will rely on the specifications from the amplifiers and the speaker, which are both vague, it surely will give you a number that is quite close enough to it.

This is how you do it:

  • Begin by taking note of your speaker’s sensitivity rating. This will be expressed in decibels or dB at one-watt/one-meter. If this is listed as an in-room or half-space spec, you can use that same number.

On the other hand, if it is an anechoic spec, then you will need to add about three decibels to it. Whatever number you ultimately have will be able to tell you to a certain extent how loud the speaker will play with a one-watt audio signal.

  • What the goal is, is to find the power that is required to reach at least 102 decibels. This is typically at a level where most people tend to enjoy. Not sure how loud that is? Think of a very loud movie theatre. 102 decibels make a perfect target.
  • Here is the last thing you need to know. To get that extra three decibels, you will need to double your amplifier power. So, a speaker with a sensitivity rating of 88 decibels is at one-watt; two-watts will get you 91 decibels, and four-watts will get you 94 decibels and so on.

So, by that logic, you require an amplifier that comes with a rating of 32 watts. However, no one really makes that, which means that you can end up settling for an amplifier that has a 40- or 50-watt rating.

That being said, if there's a particular amplifier you are interested in that can possibly put out about 100 watts, you don’t need to worry about it. That’s because at average listening levels with a regular speaker, the amplifier puts about just a watt anyway.

Conclusion

Knowing how many watt amplifier do I need is something you do not honestly need to worry about. This is because you will find countless entry-level amplifiers and AV receivers to provide more than enough to power regular home speakers.

For outdoor applications or larger rooms, you can use a dedicated amplifier or a high-end surround system receiver with dedicated zone 2/3 amplifiers. We recommend that you do not waste money buying amplifiers that are evidently an overkill for your speakers.

That being said, do not cut costs by buying amplifiers with low wattage because, more often than not, they will end up frying your speakers.

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