Calculate the power requirement and find out why the 100-volt technology is so practical

Find the perfect ratio of amplifier, speaker and watts when planning new PA projects

How do low-impedance systems and 100-volt technology differ in the amplifier-loudspeaker combination? Imagine we are planning a sound system in gastronomy. To do this, it must be clear how amplifiers, speakers and power are combined. This is good basic knowledge for newcomers, beginners and hobbyists. We clarify a few terms, clear up misunderstandings and break a lance for 100 volt technology. Caution: Help yourself to a hot beverage. Sit back. It's going to get technical.

The basics: Impedance and Sensitivity

Impedance is a measure of the electrical resistance of components, given in ohms. We use impedance among other things to determine compatibility between amplifier and speaker boxes. Speakers are often rated between 4 and 8 ohms. Many amplifiers work best in the 6 to 12 ohm range. Let's make it short: It's okay to connect speakers with a higher impedance to an amplifier that operates at a lower impedance. Where you have to be careful: You should probably not connect speakers with a lower impedance (4 ohms) to an amplifier with a higher minimum impedance (10 ohms).

Much more in our articles about impedance, speakers and amplifiers

This property is better known as sound pressure. It indicates how loud a speaker is in decibels when operated at a distance of one metre with an output of 1 watt. There is a direct connection between volume and watt supply, i.e. the amplifier. If the distance to the speaker and the power used are the same, a speaker with a lower sensitivity will sound quieter than a speaker with higher sound pressure. That doesn't mean higher sensitivity is better. It just means that a higher-sensitivity speaker will produce a higher volume and potentially save you from investing in a more powerful amplifier. However, this value says nothing about the sound quality, keyword: Frequency response.

Find out more in our article on sound pressure - a technically important indicator explained simply.

A common misconception: For amplifiers and speakers no power (in watts) is measured. For speakers, the load capacity is determined within a certain range, up to which a speaker, for example, still only just does not distort or possibly even incur damage. So a speaker never has any power because it does not produce any energy. When talking about active speakers, that's different: In that case, it is ultimately the integrated power amplifier that delivers power.

This also often leads to the misconception that more watts means higher volume. This is not (always) the case. The wattage of speakers and amplifiers is about

  1. how much power a speaker can handle,
  2. how much power an amplifier puts out.

Beginners often combine an amplifier with low power with high power speakers. Also because only the peak or maximum power is considered for the amplifier. However, this is not the way to achieve the optimal combination for a sound system in gastronomy. In the following, we will explain why amplifier data sheets often state a dynamic or maximum (or peak) power and an RMS power.

Caution: Doubling the power of the amplifier does not double the volume.

The relationship between amplifier power and volume is often misunderstood. The correct way would be: The amplifier power corresponds to the acoustic power. Doubling the amplifier power increases the sound power by 3 dB – provided there is sufficient capacity. However, doubling the (sound) power does not lead to a doubling of the sound pressure. So basically: The acoustic power generated by the amplifier and speaker causes sound pressure waves to travel through air – this is audible sound pressure. Sound pressure is also what a sound pressure level meter (SPL) measures.

  • Doubling the sound pressure requires an increase in amplifier power of 6 dB (x4).
  • A tenfold increase in sound pressure requires a 20 dB (x100) increase in amplifier power.

That means:

  • an increase in amplifier power by 3 dB doubles the sound power, but only increases the sound pressure by a factor of 1.4,

  • an increase of the amplifier power by 6 dB doubles the sound pressure (and the power is increased by a factor of 4),

  • an increase in amplifier power by 20 dB results in 10 times the sound pressure and 100 times the power.


Pay attention to the terminology: "Volume" is subjective – and should always be proportionate to the location

Volume is perceived differently by each person. It also depends on the duration of the sound, type, frequency and other subjective factors. Most studies indicate that our hearing needs an increase of about 10 dB to perceive twice the volume. Some studies assume as little as 6 dB. Psychoacousticians make the following assumptions:

  • Doubling the power (+3 dB) results in an increase in perceived volume of about 25%.

  • Quadrupling the power (+6 dB) results in an increase in perceived volume of about 50%.

  • Increasing the power 10 times (+10 dB) results in an increase of the perceived volume of about 100%.

How multiple speakers share the "load" – and what to consider when adding sound sources to your coverage

Often users simply want to connect more speakers to their amplifier to increase the power (meaning: output). But that tends to reduce the performance. The misunderstanding: "Power rating" is misunderstood. You cannot connect another 100-watt speaker to an amplifier connected to a 100-watt speaker and expect 200 watts of power. The 200 watts are then only the maximum capacity that could be filled. The power rating of the speaker is the power that it can safely output during operation – not the power that is physically possible at the load limit. It depends on the amp. The maximum power output of an amplifier, in turn, depends on the construction of the amplifier and the total impedance of the speakers connected to it. Speakers share the power: When an amplifier has a certain output power, it divides this power between the connected speakers. With eight speakers, the power is shared between all eight speakers. The main reason for adding speakers to an existing system shouldn't be for performance – it should be for coverage with sound sources. How the speakers share the power of the amplifier depends on the cabling. Namely, whether the impedance of each speaker is the same or not – and whether the speakers are connected in series, in parallel, or in a combination of series and parallel:

  • If all speakers connected to the amplifier have the same impedance, the power is shared equally. Whether connected in series or parallel.

  • If the speakers connected in parallel each have a different impedance the lower impedance speakers draw more power than the higher-impedance speakers.

  • If the speakers connected in series have a different impedance, the speakers with the higher impedance will draw more current than the speakers with the lower impedance.

A common misconception: Amplifier power is not measured, it is calculated

Let's recall physics lessons for a moment:

  • A voltmeter measures voltage in volts.

  • An ammeter measures current in amperes.

  • An ohmmeter measures resistance in ohms.

Use these measurements to calculate the amplifier power (in watts): Power is voltage squared divided by resistance. An example: Let's say you have an amplifier connected to an 8 ohm load. For a constant sine wave, measure 20 volts at the speaker output of the amplifier. Knowing the resistance (8 ohms) and voltage (20 volts), you can calculate the power:


Power = (20 times 20) divided by 8 = 50 watts.

The biggest complication is that the output does not actually have a constant level. Because the input (the current) does not have one either. Let's assume that an RMS signal is present at the amplifier input. That's why it's also a sine curve that comes out of it: Generators in power stations are the origin of the classic AC voltage.

The biggest complication is that the output does not actually have a constant level. Because the input (the current) does not have one either. Let's assume that an RMS signal is present at the amplifier input. That's why it's also a sine curve that comes out of it: Generators in power stations are the origin of the classic AC voltage.

A rotor in the generator rotates 360 degrees. The resulting voltage has an alternating polarity, i.e. a sinusoidal curve. The level is constantly going up and down, positive and negative. However, if you measure it with a meter, you will get a constant current with constant voltage. That's because a meter reads what's called RMS power.

RMS stands for Root Mean Square

"RMS power" is a mathematical term for effective output. It is 70.7% of the peak voltage. In our example, we measured 20 volts RMS at the output of the amplifier. The output therefore oscillates between +28.29 and -28.29 volts. 70.7% of 28.29 volts is 20 volts. Remember: Power equals voltage squared divided by resistance. This is true at any point along the sine wave. So if we take the voltage value and multiply it by itself and then divide by the constant resistance (8 ohms) we get the output power 50 watts. At the peaks of the sine curve, the power will be up to 100 watts. The effective work output is always half of the peak output.

Average continuous power or power rating

Average power is the level of power that the amplifier can continuously produce. Therefore, it is called the average continuous power, the average of the sine curve. In specifications, therefore, the average continuous power should be used to indicate amplifier power when designing speakers. Because that refers to the power that an amplifier can produce continuously with the specified load. This is referred to as RMS power in many amplifier power data sheets. For most specifications, you can consider RMS power as average continuous power or power rating.

The most meaningful specification for the load capacity of a speaker is the power rating (RMS), for amplifiers the power rating (RMS).

The power rating indicates how powerful an amplifier is in normal operation

Simply put, the power rating delivers a fixed wattage of power into a fixed ohm value, for example 50 watts per channel to 4 and 8 ohms. This is the power that a device can easily handle over a long period of time.

Pay attention to the power rating and wattage of your amplifier. Compare this to the recommended load for your speaker.

A speaker's peak power is the maximum wattage that its moving coil can handle in very short, occasional bursts. It's the power required to reach the speaker's maximum output for a millisecond or two. This constant peak power would quickly melt the wires in the speaker's moving coil. While that peak power may be a large, impressive number, it's not important for sustained operation. That's like saying: "I can fly a metre through the air." That's true, but only very briefly – in one jump. A speaker only works for a short time under this high load. We call this value: music performance. Because it is not entirely unimportant either: It indicates up to when peaks in the sound can still be tolerated by the speaker for a short time.

For low-impedance systems: How much amplifier power do I need?

Using watts and dB as a guide to choosing the right amplifier power is problematic because the scales are not linear. First define your goal. Do you want to power your speakers in such a way that they release as much power as possible – i.e. are as loud as possible? Then first check how much power your speakers can handle without being damaged. To do this, first take a look at the data sheet of the speaker. Pay attention to the specification of the nominal impedance. Usually that's 2, 4, 8 or 16 ohms, at least when it comes to low-impedance speakers. Next, look for the speaker's specification labelled "Continuous Power Rating." This leaves a margin of 3 to 6 dB for signal peaks.


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If you use a limiter to prevent the power amplifier from being overwhelmed, you should use a power amplifier that delivers 2 to 4 times the continuous power rating of the speakers per channel.

Speakers are designed to handle short-duration peaks

If you cannot prevent the power amplifier from being overwhelmed, the amplifier power should match the speaker power rating. This is the maximum power that the speaker may reach continuously without being damaged. This way, the loudspeaker will not be damaged if the amplifier is overloading by an overload of the input. In this case, there is no headroom for peaks, so you will need to drive the speaker at less than its full power rating if you want to avoid distortion. General rule: Keep the amplifier power at 1.6 times the power rating per channel.


An example for low-impedance applications

The impedance of your speaker is 4 ohms. Its power rating is 100 watts. To stay in the safe zone, the 4 ohm power of the amplifier should be 1.6 x 100W or 160W power rating per channel. Note that when two speakers are connected in parallel, their total impedance is halved. For example, two 8 ohm speakers connected in parallel have an impedance of 4 ohms. In this case, each speaker would receive half the 4 ohm power of the amplifier.

Why 100 volt technology is so practical: The simple calculation of amplifier power and speakers

With 100-volt technology the issue of the number of speakers, the level of load capacity and the strength of the PA amplifier is very simple. Let's take a PA amplifier that delivers 200 watts. You can divide this 200-watt "power pool" among different speakers as you like. The requirement of a given speaker with100-volt technology is specified as the power rating for a given SPL output. Let's say we chose two sizes of ceiling speakers: One with a power of 15 watts and one with 5 watts. Keep in mind that this value is not the speaker's power rating, but the power it draws from the PA amplifier. The load capacity of the speaker itself is not relevant here. To find out how many speakers the PA amplifier can drive, all you have to do is add up the number of 15 watt speakers and the number of 5 watt speakers and make sure that total doesn't exceed 200 watts. The total load capacity of the connected speakers must not exceed the power rating of the amplifier.


Pair of 2-way PA speaker systems, black

Modern 100 volt speakers offer high sound quality and speech intelligibility.

When planning a 100 volt system, it is important that the combined power rating does not exceed the power rating of your amplifier. It is advisable to leave some headroom so as not to overwhelm the system.

Caution: Using a lot more power can damage the speakers

The reason is mostly that the speaker chassis reaches its limits. On the other hand: If you use much less power, that also presents problems. If you constantly overwhelm the PA amplifier with a loudspeaker that is too large, it can also overheat.

The best performance with 100 volt systems

100 volt technology is designed for music applications in the background and for voice transmission. Highest audio fidelity is usually not a primary requirement. However, good 100-volt systems certainly deliver high audio quality. For this please note: Since a 100-volt line system uses transformers, care must be taken not to saturate the cores of these transformers with excessive energy. This way, the system works well and the amplifier remains undamaged. A saturated transformer core becomes apparent as a very low impedance at the output terminals of the amplifier. That's close to a short circuit. This in turn causes a

  1. premature overheating of the amplifier,

  2. protective circuits that mute the sound unnecessarily

  3. a poor performance of the device. In terms of audio, this is expressed in a distorted, squawking noise, similar to a wrongly aligned moving coil.

Is it really that easy to calculate 100-volt systems? There is one more thing...

There are two factors that make it a bit more complicated. On the one hand, losses in the cables themselves and losses in the audio transformers. It's a small dilemma: Getting information about the losses in the transformers is difficult, for that you would have to set up the system first. But you can only do that when we know the required power of the PA amplifier. But we only know that after measuring the losses. Fortunately, there is a reliable rule of thumb: Amplifier power should be about 50% greater than what your speakers are getting. So if the total capacity of your speakers is 100 watts per channel, you should use one PA amplifier with an output of about 150 watts per channel. This ensures that you have the power and therefore the SPL you need.


Would you like to learn more about PA technology and other audio technology? Browse through the magazine by MONACOR.

Headergraphik: Adobe stock - raweenuttapong; Graphik, Adobe Stock - Zizo

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