This can feel like a complicated and overwhelming question when putting together your home theater. With specs from wattage, speaker sensitivity, decibels and more, it can feel like some really difficult math homework. Luckily, figuring out how much power your speakers should have doesn’t need to be difficult.
Most people enjoy media at about the same maximum volume. Nearly every amplifier is going to provide enough power for your speakers. Amplifiers capable of putting out 10-20 watts of power will be capable of making your system fully functional at a normal listening volume. More specifically, if you have an average sized room (about 12 feet) and listen at an average volume, you will likely only need 50 watts of power for your speakers.
There are dangers, however, to miscalculating and misusing your equipment. You can damage speakers or the amp even if they will work together. For example, regardless of if you are using a 10-watt amplifier or a 1,000-watt amplifier, you can ruin your speakers if you turn the volume up too high. To understand why this happens, we need to understand a little about how speakers work.
Speaker Specs Explained!
It’s important to note that these specs are specific to speakers, and don’t fully apply to soundbars. If you are interested in learning about these specs for soundbars, you can read about that here.
A speaker’s sensitivity is a measure of how efficiently it creates volume from the power it draws. You will measure the power in watts, and the volume produced in dB, or decibels. Sometimes speakers will have this listed as the SNR, or Signal to Noise Ratio. You may also find it listed by SPL (sound pressure level), dB, and dba.
To find the sensitivity of a speaker, measure the volume of the speaker from 1 meter away, with 1 watt of power. So if you stand one meter from your speaker and input 1 watt of power from your amplifier, and this results in 85 dB of sound, then the speaker sensitivity is 85dB.
Doubling the wattage input into the speaker will result in approximately 3dB of volume increase. In this case, 2 watts of power results in 88dB, 4 watts of power will produce 91dB, and so on. At 10 watts of power, you would be producing about 96dB of volume. That’s about as loud as a jackhammer from 50 feet away.
The table below is a helpful tool for calculating volume based on speakers with 85dB and 90 dB sensitivity rating. Remember to take these decibel measurements at 1 meter from the speaker. You will lose approximately 6 dB of sound every time you double the distance between yourself and the speaker.
Impedance, Resistance, or Ohms
These three terms are largely interchangeable and are terms for the measurement of that speaker’s ability to restrict the flow of electrical current. Typically speakers will be rated for 4, 8 or 16 ohms. The resistance is called ‘nominal impedance’ for speakers, as the actual impedance changes based on the frequencies of sound you are playing at the time.
A good way to think about wattage and impedance is to think of it like a garden hose. Impedance is like putting your thumb in the hose while water is flowing through. The voltage is the pressure of the hose, the flow is the current, or how much water is coming through, and the ohms are the resistance, or how much of the opening is covered by your finger. The basic formula is: current = voltage/impedance.
The most important thing to remember is the lower the ohms the more current is coming through. If you have a speaker output that is labeled for a “minimum of 4 ohms,” you can connect one 4-ohm speaker or two 8 ohm speakers to that output. If you were to connect two 4-ohm speakers to that output, it would overload the amplifier and likely destroy it.
Power from the A/V Receiver or Amplifier
The power rating that an A/V Receiver or Amplifier manufacturer advertises can be confusing and misleading. It might be advertising the total power output, the power output per channel, or the power output when using two channels. For our purposes, we are going to use the ‘Wattage-per-channel’, or WPC measurement.
Just like it sounds, the WPC of an amplifier is a measure of how much power that amplifier can deliver to each channel of its system. Much like speaker sensitivity, the volume amplifiers can deliver based on its wattage is not linear. You would think that a 20-watt amplifier would deliver twice the volume of a 10-watt amplifier, but that is not the case. To double the volume output of a 10-watt amplifier, you would a 100-watt amplifier. It takes 10-times the power to double the volume.
Calculating Amplifier Power Needs
Remember that formula we went over before? A speaker with a Sound Pressure rating of 85dB will put out 85 dB of sound to a person 1 meter away with 1 watt of power. If this were the rating for your 75 Watt speaker, then this means that person would be experiencing about 104dB of volume with your speaker receiving 75 Watts of power.
104dB is well into the maximum volume for enjoyable listening for most people. So that’s great! Why would you ever need more? The answer is simple: That’s at 1 meter away. With no other interference, sound decreases about 6dB every time you double your distance. So at two meters away, that 104dB becomes 98 dB, and at 4 meters away it becomes 92 dB. At 8 meters that 104dB will become 86 dB, which is approximately the volume you hear dialogue in a movie theate.
86 dB is still fairly loud, but as you can see, filling a large room with a lot of sound can quickly become an issue, especially since the above scenario is using the maximum wattage your speaker can handle.
You can get an even more in-depth look at amplifier specs in this article.
The size of the speaker enclosure (also called a cabinet) itself can have its own effect on sound quality. This doesn’t mean that bigger size automatically means better audio. Bigger speakers can have different drivers, components and high-quality materials. It’s also possible to create a big speaker with cheap components and poor sound quality.
When engineering a speaker, companies need to take thousands of factors into consideration. Mounting the drivers and other speaker components inside of a cabinet can automatically create its own set of problems. It’s the engineer’s job to make sure that the speaker components work in tandem with the cabinet that contains them to create the best possible speaker.
There are a few peculiar speaker designs, however, that don’t have cabinets at all, and they are quite expensive. These speakers are called ‘electrostatic speakers,’ and can cost tens of thousands of dollars. If nothing else, they are a testament to the fact that with great engineering, the speaker cabinet can be skipped entirely.
So how does cabinet size impact sound quality? As a general rule, a larger speaker will likely sound better because it has more room for materials. It will be engineered better, and have more weight, which will reduce any unwanted vibrations while the speaker is in use.
With that said, bigger doesn’t necessarily mean better. A well-engineered speaker may be smaller yet produce much better results than a larger speaker – but that smaller speaker will likely cost significantly more. Check out another article from us for more information on speaker quality in relation to size.
Can Too Much Power Damage Speakers?
Too much power absolutely can damage your speakers. Connecting a 100 Watt amplifier to 75-watt speakers won’t inherently cause any issues. In fact, under most normal listening conditions, pairing a 100-watt amplifier to a 75-watt speaker is entirely okay. The problem occurs when you turn the volume up high enough that your amplifier is sending more than 75 watts to the speaker.
It is likely that you will start to experience heavy distortion well before speaker damage actually occurs. However, once your amplifier starts sending more power than the speaker can take, it will blow out the speaker and damage the components.
On the other hand, If you are using a low wattage amplifier and turn the volume up all the way, then you are actually sending voltage straight through to the speaker. This will quickly burn out the driver and ruin the speaker. Many people think this is the speaker being unable to handle the volume, but that’s not true. This is actually because the amplifier itself cannot handle the signal it’s trying to send and sends
Can Speakers Draw Too Much Power from the Amplifier?
Speakers can draw too much power from an amplifier and damage the components inside an amplifier. This doesn’t happen because the speaker itself is drawing too much much, but instead because there are too many speakers or because the impedance of the speakers is too low.
If you use a speaker with an resistance rating that is lower than the output jack it’s connected to, then the speaker the amplifier will have trouble sending the proper current. If we go back to our garden hose analogy, it’s almost like the water getting so backed up in the hose that it springs a leak.
You also might think that a simple solution all of this would just be to add extra speakers. Unfortunately, if you splice together speaker wire to rig additional speakers into your amplifier, then each speaker will be drawing equal power from the amplifier.
Let’s say you have a 50-watt amplifier and have the volume turned up enough to be using 20 watts. Then you splice together speaker wire to add an additional speaker to that channel. Each of those speakers will be drawing 20 watts of power. Now, if you splice together a third speaker into that output jack, you are demanding 60 watts of power from a 50-watt amplifier.
Remember how we talked about doubling your wattage to add 3 decibels of sound? That’s exactly what happens when you add additional speakers. You may be doing so in an attempt to double the volume coming out of your system. Unfortunately, adding another speaker, just like turning up the power, will only add 3 dB of volume.
This is an absolute rookie way to destroy your entire home theater system. You can damage the amplifier and the speakers if you connect the system this way while the volume is too high.
So, How Do I Calculate the Power I Need?
The first thing you want to look at is the sound pressure level of the speakers themselves. Let’s take this model as an example, which has an SPL of 88. We will call that S. Next, we will look at the actual room that we will be setting up our entertainment center in.
We are going to aim for a maximum decibel rating of 102 dB, which is louder than most people would enjoy. To get 102dB at 1 meter away, we will start with 88 dB at 1 watt, and add 3dB for every time we double the wattage. If we refer back to that earlier table, we will see that we need 16 watts to reach 102 dB.
However, if you move back another meter, you will lose 6dB. Then you would need to double the wattage two more times to make up for it. That would mean that we need a 64-watt stereo system. Since 64-watt stereo systems don’t exist, you would need a 75 or 100 watt per channel amplifier.
If you plan to have surround sound, then you also need to factor in each speaker. Assuming the speakers are all the same, then each speaker will produce 3 more dB of sound. In this scenario you could, for under $1,000 to pair this 80 watt Denon Amplifier with these 130 watt Onkyo speakers.
We have spent countless hours testing and researching different speakers out there. Here is a list of some of our favorite home theater speaker choices!