RMS stands for Root Mean Square. RMS is a mathematical calculation done by engineers to determine the suitable continuous power output or handling measure of a device over a specific period without damaging the device.
In terms of speakers, RMS refers to the power a speaker can handle for a prolonged period without blowing up. RMS values are vital when purchasing a speaker and also when matching it with an amplifier.
So if you have ever invested in a speaker and an amplifier only to be disappointed by the sound quality or output volume, then you must have ignored the power measures indicated on the specifications sheet or packaging box.
Incorrect amplifier and speaker RMS power matching leads to poor sound quality or distortions. In the worst case, such a mistake can damage the voice coil. Speaker and amplifier manufactures indicate the power handling or output capability of their devices in either RMS power or peak power.
What is Peak Power?
Peak power refers to the amount of power a device can output or handle over a short period of time. If an amplifier or speaker was to output or receive power at its peak power rating for an extended period, they would get spoiled.
Unfortunately, numerous speaker and amplifier manufacturers prefer inscribing the peak power on their manuals or packaging boxes to increase sales. Power is measured in Watts. Peak watts are usually greater than RMS watts and most customers think more is always better.
When it comes to buying speakers and amplifiers, more peak power is not always better unless you are talking about RMS power. The more RMS power the amplifier can produce and the speaker can sustain, the greater the sound quality and volume output you enjoy.
Example: A speaker with a peak power of 1060 W and RMS of 750 W would have better sound quality than one with an RMS of 400 W and peak power of 566 W. In case of a power surge from the amplifier, the speaker with a 1060 W peak power is more likely to survive. That is why you must know how to select a compatible amplifier for your speaker to protect it.
Since speaker and amplifier makers rarely highlight both RMS and peak power, this post will arm you with the formula you need to calculate RMS power from the peak power value and a thought-out process to determine the compatibility of a speaker and amplifier based on the RMS value.
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How to Convert Peak Power to RMS Power and Vice Versa
For every speaker or amplifier you purchase, the peak power or RMS power value must be written on the manual or packaging material. In case the manufacturer does not include both power measurements, you can use one to find the other.
Keep in mind that the most vital measure is the RMS and you cannot afford ordering for a speaker or amplifier without knowing the RMS. You should also be able to calculate the peak power to know the maximum power input or output a speaker can receive or amplifier can provide.
Conversion methods
1. Use an RMS or Peak Wattage Calculator
You can download an electrical calculator application to calculate the RMS or peak wattage. Also, you can opt for an online peak wattage or RMS wattage calculator. You are only required to key in either of the values to get the desired result.
2. Multiply the peak watts by 0.707
In case you know the peak wattage of a speaker or amplifier, multiply that value by 0.707.
Example: When the peak wattage of a speaker is 566W, you would multiply this by 0.707 to get 400.162, rounded off to 400 W.
Matching the RMS of a Speaker to that of an Amplifier
There are different types of speakers, each with their peak and RMS power rating and each of them have different specifications that determine the sound experience you would get. For example, an electrostatic speaker would have superior sound quality compared to a cone or stereo speaker. But, the rule of matching an amplifier to a speaker by referencing the RMS rate applies to all speaker types.
The RMS of an amplifier does not have to correspond to that of the speaker. For example, if you are planning to buy a speaker with an RMS rate of 60W, you do not have to purchase an amplifier with an RMS of 60 W. Speakers need about 30% an amplifiers’ RMS rate to function properly.
Although you can save on cost and buy a lower powered amplifier, note that the sound pressure level (SPL) would be low too. Sound pressure level denotes the loudness of a speaker. Therefore, if you want to have a loudspeaker around, you should get an amplifier whose RMS is close to that of the Speaker.
Here is a table of reference to help you settle on a favorable RMS rating for a speaker and amplifier.
| Number of speakers (C1) | RMS of each speaker (C2) | Total speaker RMS(C3) = (C1) * (C2) | Suitable amplifier RMS power range (C4) = (30%*(C3)) to (C3) |
| 1 | 150 watts | 150 watts | 45 – 150 watts |
| 2 | 150 watts | 300 watts | 90 – 300 watts |
| 3 | 150 watts | 450 watts | 135 – 450 watts |
| 4 | 150 watts | 600 watts | 180 – 600 watts |
| 5 | 150 watts | 750 watts | 225 – 750 watts |
What is the Best RMS for Speakers?
Selecting a speaker with at least 100 W peak power and 80W RMS would be a great choice as it delivers a powerful and rich sound without unwanted distortion. As a rule of thumb, opt for a speaker with a higher RMS value as it performs well and gives you a better music experience.
The best RMS for speakers is one that aligns with the RMS of a selected amplifier without compromising either of the two devices.
Amplifiers supply speakers with the needed power and a simple RMS mismatch would lead to a breakdown in either the speaker or amplifier. Why? If the power source connected to the amplifier supplies more power than the RMS and peak power rating, it would still be damaged.
The best RMS rating is one that also allows you to have a better music experience without any hiccups. If you want to be louder, you can go ahead and do so. To achieve this, you must carry out the correct RMS calculations.
Finally, the best RMS should also suit the space in which you have placed the speakers. If the area requires loud music, then the RMS power should be greater and vice versa.
