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Matching amps with speakers: Ohms, watts, and decibels

The synergy between your loudspeakers and stereo amplifier is perhaps the most crucial aspect to consider when setting up your hi-fi system. As a result, it’s also one of those decisions that require deep research and multiple trials if you want to reach optimal results.

If you have just started delving into the world of audio systems, you might feel overwhelmed when reading reviews mentioning impedance, ohms, sensitivity, and other jargon you’ve never heard before. And while that’s absolutely normal, getting a grip on what these terms mean will help you create the best hi-fi for your budget, environment, and needs.

This article will guide you through the best practices when buying a power amplifier to match your speakers, explain the terminology involved in simple terms, and help you choose compatible audio gear with confidence.

Let’s dive in!

Behind the insights

Marco Sebastiano Alessi, author and contributor at Higher Hz

I’m a music producer and audiophile obsessed with the intricacies of the aural experience and a trained ear that scrutinizes every sonic layer.

Having been immersed in music my entire life, my mission is to inform you about the beauty and complexity of sounds through articles that highlight products and techniques to enjoy every medium with audio fully.

What’s a power amplifier?

First, let’s zoom out a little. What’s a power amplifier? Simply put, it’s a device placed between the audio source and the passive loudspeakers, which allows you to raise the signal’s volume until it can fill the room.

Without getting too much into detail, the line-level signal received by audio sources is often too weak to drive a speaker, which is why you need a device to amplify that signal to the speaker level. Enter the power amplifier!

vintage stereo power amplifier

Amplifiers come in many different shapes and forms, but one of the most critical features is the number of channels they provide. For instance, a mono power amplifier offers only one channel, while a stereo amp will have two channels.

You can even get a power amplifier with more channels, but if this is your first amp, I’d recommend going for a two-channel stereo amp.

A power amplifier will have multiple controls to adjust the output, including a volume control which will allow you to increase the volume of the audio signal.

Matching your gear

To find out whether loudspeakers and a power amplifier can deliver optimal results, there are certain specifications we need to understand and analyze.

Especially when creating a hi-fi system using multiple brands, it’s fundamental to pay attention to these specs, which you can always find in the tech specs of loudspeakers and power amplifiers.

1. Impedance

Impedance is the electrical resistance of your audio gear and is measured in ohms (Ω). As a rule of thumb, it’s good practice to choose a power amplifier whose impedance is equal to the total impedance of your loudspeakers. Power amps feature an impedance of 4, 8, or 16 ohms.

It’s still OK to connect a power amp with an impedance lower than the loudspeakers’ (so long as you don’t have to crank up the volume to the amp’s limit), but the opposite will send too much heat energy to your speakers and damage them.

These days, most amplifiers come with a list of compatible ohms, making it easier to match them with loudspeakers without worrying about impedance.

2. Power

Power, measured in watts (W), determines how much power an amplifier can send to the speakers and how much power the speakers can sustain. However, we need to get more into detail as there are different types of “power” you need to be aware of when choosing a power amp.

Peak power is the maximum power a speaker can sustain without getting damaged. Continuous power is, you might guess, the power a speaker can sustain during regular operation.

You’ll find both specs on your amplifier, so matching the power of speakers and the amp will allow you to get the most out of your hi-fi system.

A common misconception is the belief that wattage is what defines the system’s loudness, but that’s actually determined by sensitivity, which is not strictly connected to power.

3. Sensitivity

The sensitivity of a speaker will indicate how loud it can get with a one-watt input and measured from one meter away. Sensitivity is measured in decibels (dB).

Essentially, higher sensitivity means speakers will require less power from the amplifier to sound louder. Amplifiers provide more than one watt because their power output has to double to increase the sound pressure of 3 dB.

Furthermore, the distance from the loudspeakers decreases the sensitivity dramatically, meaning you’ll need more power depending on the environment’s size.

Disposition

Having a dedicated space for your hi-fi system not only makes it look cooler but might also improve the sound quality.

If you’re into vinyl, bear in mind that if every part of your hi-fi system is placed on one surface, the vibration caused by each component might impact the vinyl player and disrupt reproduction.

Amplifiers need some breathing space behind them as they tend to get warm, so make sure you don’t place it right on the wall as it might overheat.

matching amplifiers and speakers

A wooden hi-fi rack is ideal because it’s solid and gives the sound a warmer feel. Finally, keeping each part of your audio gear separated makes it easier to clean and maintain your hi-fi system.

Final thoughts

Let’s summarize the most critical aspects discussed in this article.

A power amplifier makes the line-level signal louder and is placed between the audio source and the passive loudspeakers.

There’s no one-size-fits-all solution when it comes to matching amplifiers and loudspeakers. However, there are specific parameters to follow to ensure they’ll work well with each other and you won’t damage audio gear: impedance, power, and sensitivity.

All specifications are included in both loudspeakers’ and amp’s tech specs, so make sure they’re compatible before purchasing them.

The speaker’s continuous power rating plays a crucial role here, and I’d recommend you get an amplifier that can provide twice that much power per channel, which will leave enough headroom for peaks and won’t cause distortion.

Choose a power amplifier and loudspeakers that’ll fit the environment they’re placed in. If your hi-fi system is in a large room, but you’re using an underpowered amp, your gear will overheat, and you’ll start hearing clips and distortion.

On the other hand, if the amp is too powerful, the speakers will not be able to sustain the heat energy and get damaged.

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