What is RMS? What is RMS power rating mean in Speaker

Last Updated on November 6, 2022 by Devon

What does RMS stand for in speakers?

RMS Power Ratings: The RMS power meaning is defined as Root Mean Square which is a statistical way of representing DC voltage or AC voltage. Instead of using peak values, it uses average values thus giving you a better idea about its true performance and power handling capability.

What does RMS mean in Speakers?

What is RMS? What is RMS power rating mean in Speaker

RMS in speaker means, power refers to how much continuous power the speaker can handle. For example, a 50W RMS rating but 70W peak means that the speaker can comfortably run with 60 watts of continuous power, occasional bursts up to 100 watts.

More often than not an amplifier’s RMS power ratings are grossly inferior to what it can actually handle. This is because manufacturers would want you to think that their amplifier has a maximum input power rating of, say, 1000 watts which may just be the peak or transient power it can handle. Manufacturers often measure RMS voltage by using a “burst” signal consisting of an extremely short duration (usually 10 ms or less) sine wave.

Such a signal will be able to produce higher output than a sustained sine wave, but only for a fraction of a second. To determine an amplifier’s maximum RMS output capability the “burst” signal is applied until it reaches its mechanical or thermal limit (when there is too much heat being produced).

How is RMS measured?

The proper way to measure RMS is to apply a continuous sine wave at the amplifier’s rated impedance and measure its output voltage. This way, you are going to get the true RMS value of that signal which has a lot more credibility than taking the peak or burst reading.

Measuring at different impedances would lead us to quite interesting results: if it were at 4 ohms, the RMS power would be quite a bit lower than if it were at 2 ohms. This is because voltage doubles when the load impedance halves so you have to produce twice as much voltage in order to get the same output.

Although we are talking about doubling or halving of output power here (or four times or half as much power when the impedance quadruples), the resulting difference in volume is hardly noticeable. The reason is that our ears’ sensitivity to loudness doubles or halves with every 3dB increase and decrease of volume respectively (I have explained this simply here). This means, an amplifier with a maximum output of 100 watts per channel at 4 ohms should be able to deliver a maximum of 200 watts per channel at 2 ohms, and so on with other impedances.

If you would like to read some more on power ratings I recommend All about Power.

What is dyno certification?

Dyno: an abbreviation for Dynamometer which is basically equipment that measures the amount of torque or horsepower being delivered by the engine to the driveshaft. It can also be used to determine the power requirements needed for an electric motor to achieve a certain speed and vice versa when used in conjunction with an alternator.

A dynamometer is basically a specially built drum that rolls instead of rotates due to its eccentric load which simulates real road conditions better than an engine dyno. An engine dyno, which is also called a “rolling road”, has the load on its drum either statically (by adding weights) or dynamically through a real gear and belt system plus dummy shafts and flywheel to match what a car would be running at its normal speed.

What is the difference between electric motor dynamometer and internal combustion engines?

The only difference between an electric motor dynamometer and one for internal combustion engines is that the former has an electric motor connected to its output instead of a mechanical load while the latter simulates a car’s drivetrain by matching belt and pulley ratio with that of the engine.

More often than not, you will find both types used together in order to get more accurate readings on specific components like the alternator, transmission, and battery.

A gauge is a device used to indicate the value of some characteristics like temperature (thermometer), pressure (barometer), speed (speedometer), and so on. There are also gauges for electrical systems that indicate voltage in volts and current in amps using needles or LEDs instead of lines or marks like regular analog gauges.

Just like output ratings, there are a lot of different means to measure voltages and currents in order for manufacturers to advertise their equipment’s capabilities but the only proper way is by using steady state sinusoidal AC waveforms at rated impedance as explained above. The voltage should be measured across the positive and negative terminals of the AC power source and the current is then measured in between those same terminals.

This way you get RMS values which are far more accurate than reading it off an ordinary voltmeter or millimetre, especially when measuring high voltage AC lines or heavy-duty audio amplifiers where the presence of harmonics (which don’t count for much) would be very minimalized at best.

A load is any device that consumes current (or power) from an external source, in our case, an electric motor or a battery-operated consumer electronic device like the radio. When you use batteries with your car’s audio system it acts as a resistor and such resistance is what we call “load” when talking about electrical systems.

How much power does an amp require?

A way to determine how much power is needed for a specific amp in order to run it at its full potential (which would be different from one amplifier to another due to design and implementation) is by measuring the current or voltage in the system while playing music through it. The more current/voltage you measure, the more power is being drawn from the source.

Here’s a quick explanation of how to do it:

1) Connect your voltmeter across the positive and negative terminals of your battery (or power supply). This will measure the voltage across the whole system which includes wiring, amplifiers, speakers, etc.

2) Play music through your amp with an input level meter (or a voltmeter set to its highest scale) and take note of the voltage across the system with the characteristic frequency response (bass, midrange, and treble).

3) Divide the lowest voltage by your maximum current measured in step 2.

4) Multiply this fractional number with the rated RMS voltage of your battery or power supply.

Example: If your lowest voltage across the whole system measured was 11.5 volts at 100 Hz with a maximum current of 2 amps, then you will need a total power capacity of 32 watts. Since this is a fractional number that cannot be used directly to calculate the current draw, we multiply it with 12 volts (RMS) which gives us an answer of a 38 amp current capacity.

5) Always be sure to measure voltages and currents with the system running at full power. This means that you should play your music at a high level from beginning to end without stopping for any reason (to avoid momentary voltage drops).

6) Use a resistor matching the amplifier’s impedance in order to simulate a load when measuring voltage (ex: for 2 ohms use a 1-ohm resistor).

7) Never disconnect or remove anything from the system while it is on. Doing this will damage your equipment if not done properly and could also be fatal, especially on car audio systems.

8) We don’t recommend the use of cheap multimeters for this application. Good quality ones like digital oscilloscopes with well-shielded probes should be used in order to not alter the voltage being measured by acting as a current path.

9) Don’t measure the voltage when the engine is running unless you know what you’re doing. It’s also good practice to disconnect the negative terminal of the battery when working with high voltage coils (ex: the one on your spark plug).

Related: 7 Signs of a bad car amplifier-Guide

The resistance of a speaker coil in an audio amplifier can be anywhere from 0.5 ohms to 8 or 16 ohms depending on many factors but mostly on impedance and power handling. A wiring diagram is included below as an example of how to hook up an amplifier. Always be sure that your amp can handle the total load (which includes wiring, speakers, and a resistor if used for simulating a load) by checking RMS ratings in its specs sheet.

On the other hand, an oscilloscope is required when measuring current on car audio systems because of several reasons: one being that it’s much easier to control voltage than current (you can always directly measure it with a voltmeter but not the other way around) and the fact that we need an accurate voltage reference in order to calculate how much power is being drawn from the source.

In this case, simply connect an oscilloscope probe across the + and – terminals of your battery. You should read a Sine wave with some sort of DC offset (the amount depends on your current draw). The average voltage of this sine wave is the RMS voltage, and multiplying this number by 1.4 will give you the peak-to-peak value which you can then use to calculate total power in watts with Ohm’s Law using the formula P=VI.

This method is not perfect since it only gives you an accurate power reading at a certain frequency but this will work just fine in our case because bass frequencies are the ones more affected by impedance changes on your system.

One final note: It’s possible to damage your speakers if you use an amplifier that has too much power for them. This is easily avoidable by making sure your amp does not exceed 1% of its RMS power into 4 ohms (ex: a 450W RMS amp into 4 ohms will never draw more than about 1.35 amps). Also, it’s a good idea to get speakers that handle double the power of what your amp can produce (ex: for an 800W RMS amplifier get speakers rated at 1600W or higher) because this will give you more headroom.

FAQs:

What is RMS output?

RMS (Root Mean Square) is the preferred method of obtaining power measurements for audio signals. The idea behind it is to give you an idea of how powerful your sound system will be perceived by the audience/listener.

This means that the human ear perceives lower sound levels than what they are actually exposed to. For example, a 1 kHz sine tone at 0dB (RMS) is about 94dB. If you play this tone through your sound system, it will be perceived as loud as the actual 94dB level.

What is a good RMS for speakers?

Answer: Four ohms.

A speaker’s RMS is the electrical resistance of the speaker, which reveals how efficiently it can push air to create sound. A 4-ohm speaker will play louder than a 2-ohm one of the same power. The most common speakers are 8-, 6-, and 4-ohm models, but audiophiles may want to look for lower numbers – some quality speakers are 2 ohms or even 1 ohm!

Does a higher RMS mean louder?

Answer: Not always.

The sound’s volume is a function of the square of the RMS amplitude. So if you double the power of a device, it doesn’t necessarily mean that you will hear everything twice as loud. In some instances, you may only get an increase in output by 6dB which would be below the normal threshold of hearing sensitivity and unable to diagnose hearing loss.

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