If you’re just getting started with building your system, there are a couple of tips you’ll want to know. For example, how do you choose the right amplifier for your speakers? When you’re new to a topic, it can be overwhelming to know all the little details that will help you out. Luckily, we’ve got you covered.
A good rule of thumb is to choose an amplifier that delivers at least the same amount of power as the RMS or continuous (program) power that the speaker can handle. It is a better practice to choose an amplifier that is twice the RMS or continuous power because that way, you will have more headroom.
There is more to it than just selecting the number of watts. Follow along, as I’ll explain the concept in more detail, and you’ll find exactly what you’re looking for to get started with your setup.
Matching the Right Amplifier to Speaker’s Wattage – Speaker Impedance Matching
Covering Basic Terminology
Let’s look at the basic terminology used with amplifiers as it will help you understand the concept better.
- Watts: Watts measures power. In this case, our power is amps x volts.
- Ohms: Ohms measures resistance. We’re keeping this as simple as possible, without throwing in equations, but it relates to Ohm’s Law.
- Speaker Impedance: It’s measured in Ohms and refers to the resistance that the speaker presents to the amplifier. It’s not a constant value, and it changes depending on the frequency of the signal applied to it.
- Sensitivity: To keep this simple, the higher the sensitivity, the less power you need.
Why Matching the Right Amplifier to Speaker’s Wattage is Important
When you jump into audio forums and message boards or check articles on how to set things up, it can get confusing quickly with all the fancy jargon and equations thrown at you. It’s easy to get overwhelmed when all you wanted to know was, should speaker wattage be higher than amps, or vice versa? Am I right?
The first question to ask is, why do you need to match your speakers and amp? There are two reasons.
- By matching your speakers and amp, you won’t damage your speakers or amplifier.
- By matching your amp with your speakers, you’ll get a rich, clean sound without awkward distortion.
What else do you need to know?
- Your amp is an electrical unit that helps you increase a signal.
- Your speakers take the electrical signal from the amplifier and turn it into sound energy.
So, you need an amp for power. You need speakers to push the sound out. Watts measures power, Ohms measures resistance. You match these up, so you get a clean, rich sound without damaging any component.
Let’s move on to the next part, which explains how to match them by choosing the right amplifier for your system.
READ: Speaker Wattage Explained
How to Choose Amplifier for Speakers
I always recommend checking the specifications from the manufacturer before attempting to match amplifiers to speakers. If possible, use the same manufacturer for both units and see what their recommendations are.
Okay, so, let’s talk about matching your amplifier to your speaker’s wattage.
When you’re matching amps to a speaker’s wattage, you want an amp that can push two times the amount of power the speaker can handle continuously. That way, you have more headroom, and you don’t have to drive the amplifier to its limits.
Be careful not to increase the volume on the amplifier all the way up, because if it delivers twice the power, a speaker can handle it could easily burn the coil. Run the amp at about 60 to 70% of the total power, and you will get rich, clean sound without any distortion. That way, your speaker will run happily as well as your amplifier.
If you don’t feel comfortable connecting your speakers to an amp that is twice as powerful fearing that they’ll burn if you don’t have control over the volume, then the best option for you would be to choose an amplifier that delivers at least the same amount of power as the RMS or continuous power that the speaker can handle.
For instance, if you have 300 Watt speakers, what size amp should you choose? The answer is, ideally, an amplifier that delivers 600 Watts, running it at 60 to 70% of its maximum volume. You also have the option of using an amp that provides at least 300 Watts, but you have to make sure not to run the amplifier at its clipping point.
Recommended Amplifier Power for Speaker Chart
| Speaker RMS Power Rating | Minimum Recommended Amplifier Power (RMS) | Ideal Recommended Amplifier Power (RMS) |
|---|---|---|
| 50 Watts | 50 Watts | 100 Watts |
| 100 Watts | 100 Watts | 200 Watts |
| 200 Watts | 200 Watts | 400 Watts |
| 300 Watts | 300 Watts | 600 Watts |
| 500 Watts | 500 Watts | 1000 Watts |
| 1000 Watts | 1000 Watts | 2000 Watts |
Amplifier Headroom
Another essential fact to keep in mind when choosing the right amplifier for loudspeakers is the headroom. Oh yeah, and what’s headroom?
Headroom is a term used to describe the amount of power your amplifier can continuously deliver before distorting the sound. In other words, the ability to provide enough power without driving the amp into its clipping point.
When it comes to audio speakers and amplifiers, if your amp can’t deliver enough power to the speaker, it will start to distort before providing the energy needed to make the speaker work to its full potential.
Think about this…you see a tall guy walking toward a doorway. You know he’s got X amount of clearance to get through without hitting his head. An average doorway is 6.6’ – so what happens when basketball player Yao Ming walks toward that door, who happens to be 7.6’? Right, he meets resistance.
Same thing with headroom in audio. You have X amount of power available from the amplifier; if the speaker needs more to work to its full potential, then it doesn’t matter if the amp is at its maximum, it wouldn’t be able to deliver enough output level.
You always want to have enough headroom so that the amp works within its ideal area.
Matching the numbers of watts is only half of the story; you also need to match the impedance between the amplifier and speaker as well.
Okay, now let’s go deeper into impedance. Keep reading to find out how it affects the amplifier’s power.
The Speakers’ Impedance is Key When Choosing an Amplifier – Speaker Impedance Matching
So, what is speaker impedance, and how does it affect the amplifier’s power? Well, we learned earlier that impedance is the measure of the resistance that the speaker presents to the amplifier.
Why is it important to know? Because mismatching the impedance between speakers and amps can create too much of a load for the amplifier, causing it to overheat and stop working.
Let me give you a visual. The little creek down the way is happily flowing along, but then a beaver builds a dam and starts to slow the water’s flow down. This is the same thing as your energy resistance with ohms.
Your signal is moving along happily, and then it meets resistance. You don’t want too much friction; you’d prefer a clean flow of water without it. It’s a happy balance. That’s why matching an amplifier to the speaker’s impedance is so essential.
Connecting Speakers in Parallel
Speakers can be connected in parallel (the most commonly used) and series (rarely used). It is always recommended to connect speakers of the same impedance to avoid mismatches.
When connecting speakers in parallel, the total impedance will be decreased each time another one is added to the amplifier. The most common speaker impedances are 16 Ohms, 8 Ohms, and 4 Ohms.
When connecting speakers in parallel, the connection goes from the positive terminal of the first speaker to the positive terminal of the second speaker. And the negative terminal of the first speaker to the negative terminal of the second speaker, and so on depending on the number of speakers you want to connect.
The following diagram illustrates what I explained in the previous paragraph.
Ready for an example?
Let’s say that you have two 8-Ohms speakers. If you connect them in parallel, you will end up with 4 Ohms of total impedance. If this is the case, then your amplifier should be capable of handling 4 Ohms at the RMS value of the loudspeakers.
Let’s do it again. This time let’s say that you want to connect four 8-Ohms speakers. After connecting them in parallel, you will end up with a total impedance of 2 Ohms.
Basic math, forget all the fancy equations the internet throws at you, and keep it simple. But instead of getting into more details, I’ll leave you with this handy chart.
Quick Reference Chart for Speaker Impedance Matching
| Number of Speakers Connected in Parallel | Rated Impedance of Each Speaker | Total Impedance as Seen by the Amplifier |
|---|---|---|
| 2 | 4 Ohms | 2 Ohms |
| 2 | 8 Ohms | 4 Ohms |
| 2 | 16 Ohms | 8 Ohms |
| 3 | 4 Ohms | 1.33 Ohms |
| 3 | 8 Ohms | 2.67 Ohms |
| 3 | 16 Ohms | 5.33 Ohms |
| 4 | 4 Ohms | 1 Ohm |
| 4 | 8 Ohms | 2 Ohms |
| 4 | 16 Ohms | 4 Ohms |
Here’s a key to understand
How much current flows, but there’s a pesky detail to throw in here… because the resistance is actually with the speakers, the numbers you see on the amp are really about how they work with the speakers (usually in the form of speaker range) and what’s optimum to work with. But to continue the concept of flows, keep these basic thoughts in mind.
- An amplifier connected to a low impedance speaker (4 Ohms or 2 Ohms) needs to put out a higher current, that’s why lower impedance speakers are harder to drive and consume more power.
- The same amplifier connected to a higher impedance speaker (8 Ohms or 16 Ohms) puts out less current to drive the speaker.
So, when passing a signal from the amp to the speaker, you want those numbers to match as closely as possible. So, you’re aiming for equal.
Remember our chart of the common speaker loads in parallel configuration? By selecting a speaker configuration with a specific impedance and making sure that the amplifier can deliver the amount of power at that impedance will create an easy flow of power exchange between the two units.
This is why the loudness of a sound system should never be deduced from the amount of power a speaker can handle or the power an amp can deliver. Loudness is an entirely different story.
It’s measured in dB (Decibels), and it’s referred to as SPL (Sound Pressure Level). Check out what SPL is in audio and why you need to pay attention to this metric when defining the efficiency of a loudspeaker or amplifier.
READ: Best PA Systems For Live Bands
Final Thoughts
All of that to say, don’t stress yourself out. When it comes time for matching amplifier to speaker’s wattage, remember the basics and don’t get caught up on, he said/she said on all the different audio forums.
Learn the foundation of these details first, because once you understand them, you’ll be a step ahead of those left scratching their heads from getting too many different answers. And when it comes time to figure out how to choose an amplifier for speakers—you’ve got this.