This article should give you all you need to know about power, sensitivity, and impedance to help you understand how these numbers could affect your home audio or home theater buying decisions.

You’ve probably seen these three terms when shopping for speakers, but did you know they also should be considered when you are choosing what component will power your speakers.

We will go over all of these in simple terms to help you understand what numbers really matter and how you need to think about the relationship between speaker specifications and your amplifier or home theater receiver.

Speakers

First, let’s take a look at speakers. When you are shopping around for speakers, you’ll find several numbers in their specification section. These are usually the minimum and maximum recommended power, sensitivity, and impedance. One thing that makes these numbers a little tricky is there is no world wide rule speaker manufacturers have to follow when publishing their specifications. This is where our team of passionate audio and home theater experts' advice can be invaluable to you. We are just a phone call or chat away to help you decide if the components you are looking at match up well together and work for your room.

Most speaker manufacturers state the minimum recommended power needed to get decent volumes out of that particular speaker in an average sized room. The maximum figure listed is the power level they can withstand continuously without sustaining damage to the speaker components. But these numbers usually come from steady test signals, not the full dynamics of actual music.

But for many music lovers just getting into this, these numbers can lead to a bad decision. Normal logic would tell you that just like driving where going far too fast can lead to an accident, too much power could damage your speakers. It turns out the opposite is true. Music is very dynamic with swings from extremely quiet to super loud. When those loud peaks occur, the demand for amplifier power goes way up. If you are playing at a pretty loud level when a peak hits and your amplifier does not have enough power for that peak, the amplifier will do what is called clipping. This sends a distorted signal to your speakers, which in most cases either partially damages or fully blows the tweeters in your speakers. In all of our years of experience, when we see damaged speakers come into our shop, it is always due to someone trying to play too loud with too little power, not too much. Sure, with a huge amplifier that you played wide open for a long time, you might damage your speakers, but that is extremely rare. As a matter of fact, we prefer you to have as much power as possible and don’t really worry about the maximum power rating too much. When a dynamic passage comes, your amp will sail through it with no strain to the music or your ears.

Sensitivity

Then the question is, how much power do you really need? Well, that depends on another spec called speaker sensitivity, the volume of your room, and your listening tastes. You’ll see sensitivity numbers like 89 dB, 91 dB, 93 dB, and more. This is technically supposed to be the measured decibel level with a microphone one meter from the speaker with pink noise playing, which is basically all the audio frequencies at one time. The catch is that some speaker companies measure their speakers in a room that adds some reflections, which will raise this number somewhat, while others use an anechoic chamber to give a very honest result.

The higher the sensitivity spec, the less power it will take to drive your speakers. This means you can get by with a smaller amplifier if your speakers have a high sensitivity rating. But what numbers show high sensitivity? Well, most speakers fall in the 88 to 90 dB range which we would consider medium sensitivity. If you are looking at speakers with sensitivity specs below 88 dB, you will want to have an amplifier that can deliver pretty serious power. When you start getting to 93 dB and above, those speakers are entering high sensitivity territory. Now, bear in mind, a 10 dB difference is perceived as twice as loud to the human ear and you have to double amplifier power for each 3 dB increase. This means there is a pretty big difference in what you’ll experience between a speaker with 90 dB sensitivity and one with 96 dB or greater. Many horn-type speakers have an extremely high sensitivity number, and you’ll see owners of those speakers using small 5 or 10 watts per channel tube amps on them and be able to drive them to very loud levels.

Some music lovers also contend the higher the sensitivity of a speaker, the better it can portray the dynamic contrasts of music, while others will swear by a medium sensitivity speaker and a massive McIntosh high power amplifier that can provide those same dynamics due to all the extra power on board.

The size of your space also plays a role in this. It's going to take much more power to fill up a very large space compared to a smaller room given the same pair of speakers.

So as a general rule, the lower the sensitivity number and/or the larger your room, the more power you will need.

At this point you may have figured out, that more power is always a good thing, even with high-sensitivity speakers. We like to make this analogy. Imagine you are driving a high-performance sports car with an 8 or 12 cylinder gas engine. You are cruising along at 65 and need to pull out to pass. With a stomp on the gas pedal, you zoom around the other car in no time. That act of passing is akin to a dynamic passage in music. With all that extra power on board, the car, and amplifier sail through it.

Impedance

Now we come to the final number, you might be curious about, speaker impedance. Speaker impedance is measured in ohms and it is essentially the load the speaker presents to the amplifier. You will usually see numbers here of 4,6 and 8 ohms. Technically, a well made amplifier will put out more power into a 4 ohm speaker load, but here is where the specs can get tricky. The problem is there is no universal way to measure speaker impedance. This is an issue as no speaker is just 4 or 8 ohms as the resistance a speaker shows an amplifier changes with frequency. Some may dip down as low as 2 ohms at lower frequencies and go above 16 or even much higher as the frequency increases. If you see the word “nominal” with the impedance number, that usually means it is a more honest spec of the average load the speaker presents an amp.

So, while one brand may rate their speakers at 8 ohms, if another brand tested that exact same speaker, they might rate it with a nominal impedance of 4 or 6 ohms. Manufacturers like to show an 8 ohm rating as it is more the standard but this does not mean their speaker never dips below 8 ohms.

If you are powering one pair of speakers off two channels of an amplifier, if the amplifier is of decent quality, we feel you really do not need to worry much about the impedance number. But, if you have an amp that has 2 pairs of speaker connections you see on some integrated amps, like a speaker A and B, and the speakers you want to use have a spec of 4 ohms, you might overheat your amplifier when you are playing both at the same time.

The other case where impedance matters is with a tube amplifier that has different speaker connections for a different impedance. Most tube amps have 4,8, and 16 ohm taps. Here, if your speaker is rated at a simple 8 ohms with the word nominal, we suggest you try both and see which sounds better. If it's rated at 4 ohms, you should use the 4 ohm tap, and if it's 8 ohms nominal, it will probably sound better on the 4 ohm tap. 6 ohm speakers will definitely need to be tested on both taps.

So far, we’ve learned the more power, the better but you will need less with very high sensitivity speakers. And the impedance spec may not be that big a deal for your needs.

Amplifier Power

But before we end this article, let's talk a bit more about amplifier power, as those numbers need digging into. First, it's important to understand an amplifier has a far easier time driving a higher frequency than a low frequency. This means if you just played a test tone into an amp, it might produce 50 watts at a low frequency before it went into serious distortion but 200 watts into a higher frequency. When you look at the fine print, you’ll find some amplifiers and home theater receivers rated at X watts per channel at 1000 Hz, a much easier to drive load, and others rated at X watts per channel from 20 Hz to 20,000 Hz, a much more honest spec. This has been a major point of confusion, especially in the soundbar realm, where you could see tiny soundbars claiming to have 500 watts or more of total power inside.

The great news is on June 5th, 2024, the Federal Trade Commission said enough is enough and set a standard all companies must follow for home entertainment amplifier ratings. They now have to warm up the amp, then test it from 20hz to 20,000hz for a full five minutes to come up with their power rating. And better yet, as some fudged on this, at no time can the distortion be more than 1%. We are sure this will bring down some exaggerated power ratings and allow music lovers to make an easier decision on the quality of the amplifier they are considering.

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