Power Archive

POWER – What’s a watt?

Posted By Andy Kos

Over the years in the audio industry, I have made numerous attempts to explain some of the concepts used with regard to speaker/amplifier power. Most are summarised below, with links to some of the articles covering each topic in more detail. If you’re serious about sound, and curious about power, these are well worth a read, and will help you make more sense of power.

What is Power (Watts)?

Power is a measure of how fast energy is being used or delivered. One watt is defined as one joule per second, which in audio terms is the rate at which energy is transferred from an amplifier to a loudspeaker. High power for a short burst and lower power delivered continuously can result in the same total energy, which is why power must be considered over time.

For example, a 4 W burst for 0.25 seconds followed by 0.75 seconds of silence delivers the same energy as a 2 W burst for 0.5 seconds followed by 0.5 seconds of silence, or 1 W delivered continuously for 1 second.

This simplified example is an analogy for understanding peak, program, and continuous power. Peak power represents short, high-energy bursts, program power represents longer bursts with more time at a high level, and continuous power represents energy delivered without breaks. Although real music does not follow fixed duty cycles, all three cases above average to the same energy rate: 4 W × 0.25 = 1, 2 W × 0.5 = 1, and 1 W × 1 = 1.

This is why loudspeaker power ratings typically follow the same pattern: program power is usually twice the continuous rating, and peak power is typically four times the continuous rating. The numbers relate to the same underlying energy, but describe how that power is delivered over time.

RMS Power

RMS is a mathematical method that works extremely well for steady sine waves, such as AC mains power, where voltage and current are continuous and predictable. Music is not like this, so “RMS power” is not ideal for describing real audio behaviour. Some amplifier manufacturers still use the term, but it often includes a hidden crest factor or burst condition, meaning the figure is not a true continuous power level but a calculated equivalent.
Read more…

AES / Continuous Power

AES power defines how much power a loudspeaker can handle on average over time using a standardised broadband noise signal. It represents the long-term thermal limit of the voice coil and is the most reliable figure for continuous operation. Unlike RMS-style ratings, AES power is designed specifically for real audio signals rather than steady test tones.

Program (Music) Power

Program power allows for higher short-term peaks while keeping the long-term average power the same as the AES rating. It reflects the dynamic nature of music, where loud transients are followed by quieter moments. Program power is headroom, not extra continuous power, and should never be treated as a sustained operating level.
Read More on AES / Program Power

How much Power do you need?

What’s up with the Watts?
Power ratings in audio can be confusing because music is dynamic, not constant. Its hard to know what you want, what’s best and how to use power figures sensibly when choosing speakers and amplifiers.
Read More…

Pe – Power Handling Capacity

Often seen in manufacturers technical data, Pe is the long term power handling capacity, usually measured using the AES standard (but not always) and some manufacturers have their own test criteria and will often name this ‘nominal power handling’ This is not necessarily comparable between all speaker brands – also a little explanation as to why MORE POWER does not necessarily mean MORE VOLUME
Read More..

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RMS Power

Posted By Andy Kos

What does RMS actually mean?

RMS stands for Root Mean Square. It is a mathematical method, not a type of power. It is normally applied to voltage or current, but for many years it has been used in the audio industry to describe amplifier and loudspeaker power.

Why? Simply because it was the best available method at the time, and no better, widely agreed standard existed.

I am often asked “What’s the RMS power?” My usual answer is that RMS is not particularly suitable for audio. If you want to understand why, read on. Otherwise, just accept that AES power is the standard you should be using for loudspeakers.

Why do we have RMS at all?

RMS comes from electrical engineering, where it works extremely well for AC power systems. It allows an AC signal to be converted into an equivalent DC value that produces the same heating effect.

In the UK, mains electricity is described as 240 V AC. That figure is already an RMS value. In reality, the waveform swings to about 339 V peak, or 679 V peak-to-peak.

The RMS figure is very useful. If an electric heater draws 10 A from a 240 V supply, we call it a 2400 W heater. The voltage and current are constant, the waveform is a steady 50 Hz sine wave, and the power delivery is continuous. This is a perfect use case for RMS.

[Image: AC sine wave showing peak, peak-to-peak, and RMS level]

Why RMS doesn’t map cleanly to audio

Audio amplifiers and loudspeakers do not operate with constant sine waves. Music is dynamic, the amplitude changes constantly, and power delivery is anything but steady.

To work around this, various test standards were created using controlled noise signals instead of tones. For loudspeakers, common examples included EIA RS-426A and IEC 268-5.

With a known test signal, it is possible to calculate an equivalent RMS value using averaging and squaring maths. This is where the idea of “RMS power” for speakers came from. However, it was never especially accurate, and often resulted in unrealistically low power ratings.

The amplifier vs speaker mismatch

Over time, it became normal to match amplifier and speaker ratings directly. For example, using a 400 W RMS amplifier with a 400 W RMS speaker.

The problem is that the two numbers were not measuring the same thing.

Amplifiers were often tested at 1 kHz using a continuous sine wave into a resistive load. This frequently overstated real-world power, because at lower frequencies (around 40–100 Hz) the power supply could not always sustain the same output. In practice, usable power at 100 Hz could be 10% lower than at 1 kHz.

Meanwhile, loudspeakers could often tolerate short-term peaks above their RMS rating. This is why users traditionally chose a slightly larger amplifier, to provide headroom.

Conclusion

RMS was not useless, but it was never a complete or accurate way to relate amplifier power to loudspeaker power. There was always an element of estimation and experience involved.

This mismatch is exactly why modern standards moved on, and why RMS power is no longer the best reference point for real-world audio systems.

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Making sense of power

Posted By Andy Kos

AES Power, Program Power, and Amplifier Power Explained

Power ratings in audio are confusing because they try to describe something that is constantly changing. Music is not a steady signal, yet power ratings are often presented as if everything operates at a fixed level. To make sense of AES power, program power, and amplifier power ratings, it helps to think in terms of power over time, rather than a single number.

Summary

AES power describes how much power a loudspeaker can handle on average over time. Program (music) power allows for higher short-term peaks, not higher continuous power. Real music delivers power in bursts rather than as a constant load. Modern amplifiers, especially Class D designs, are very good at producing high peak power briefly, while long-term power is limited by heat, power supplies, and mains capacity. The aim of this article is to show how average power, burst power, and time are related, and why a headline figure such as a 2000 W peak can be entirely real while still not representing the long-term power demand of a system. By looking at how music behaves over time, and using simple visual examples, it becomes much easier to understand how loudspeaker ratings, amplifier ratings, and even 13 A mains plugs all make sense in practice.

AES Power vs Program (Music) Power

Modern loudspeaker drivers are usually specified with two related power figures: continuous power (often defined using the AES standard) and program or music power.

AES power represents the long-term average thermal capability of the loudspeaker. It indicates how much power the voice coil can safely dissipate as heat over time using a defined broadband test signal. In simple terms, AES power is a safe long-term operating limit.

Program (music) power is typically quoted as twice the AES power, which corresponds to a +3 dB increase. Importantly, this does not mean the loudspeaker can handle twice the average power. The long-term average power remains the same as the AES rating.

The difference between AES and program power is not extra heat capacity, but crest factor. Program power allows for higher short-term peaks while keeping the long-term average unchanged. The signal is allowed to get taller for brief moments, but not heavier overall.

To understand why this distinction matters, it helps to look at how power is delivered over time.

Power over time: short, high peaks

In the first diagram, the vertical axis represents instantaneous power, and the horizontal axis represents time. The shaded red areas show when power is being delivered.

The diagrams are illustrative rather than literal. Their purpose is to explain concepts, not to define exact test conditions or limits.

Figure 1: Short-duration, high-peak power delivered in brief bursts over time.

Each rectangle represents a short burst of power:

  • Peak power: 2000 W
  • Duration: 0.5 seconds

Power multiplied by time gives energy. A 2000 W burst lasting 0.5 seconds delivers the same energy as 1000 W delivered for a full second:

2000 W × 0.5 s = 1000 W × 1 s

Although the instantaneous power is high, it is only present briefly. When averaged over a longer time window, the effective power is much lower. This is the key idea behind program power: higher peaks are allowed, but they do not increase the long-term average.

This type of power delivery closely resembles real music. Bass hits, kick drums, and transients are short, intense bursts separated by quieter moments.

To make the diagrams easier to understand, I have intentionally used simple numbers, 2000W, 1000W, 0.5 seconds – it makes the maths much easier. You can see each red rectangle is divided up into 8 smaller rectangles, which is easy to visualise.

Same energy, delivered differently

In the Figure 2, the same total energy is delivered in a different way. Instead of short peaks, power is delivered continuously. This is similar to electrical systems such as heaters, power is delivered continuously to a static load, the power level does not go up or down, it remains constant. Music is not like this, amplifier and music power is dynamic, and constantly changing. The power an amplifier delivers to the speaker, and draws from the mains supply varies with time.

Figure 2: The same total energy delivered as lower, continuous power over the same time period.

  • Power level: 1000 W
  • Duration: 1 second

The shaded area is the same size as in the Figure 1, which means the total energy is identical. The average power is also the same. You can see this visually: the area still covers exactly eight grid squares, just arranged differently.

In this example, the continuous 1000 W case does not represent a significant challenge for the amplifier. An amplifier capable of delivering 2000 W peaks will typically have no difficulty sustaining 1000 W continuously, as the average power and thermal load remain well within its design limits.

The real limitation appears when high power is sustained for longer periods. While short bursts of 2000 W are easily achievable, maintaining that level for several seconds places extreme demands on the power supply and output stage. Voltage rails sag, current limiting engages, and thermal protection may begin to operate.

This is where many Class D amplifiers reach their limits. They are designed to deliver very high short-term power with ease, but they are not intended to sustain maximum output continuously, particularly at low frequencies.

What this means for loudspeakers

From the loudspeaker’s point of view, heating depends on average power over time, not peak power. The voice coil does not care whether energy arrives in short bursts or steadily; what matters is how much heat builds up overall.

AES power therefore describes a realistic long-term thermal limit. It represents the average power a loudspeaker can dissipate safely over time without overheating. In the simplified examples shown here, this is illustrated by the second diagram, where the average power level remains constant.

Program or music power acknowledges that real music is dynamic and contains peaks and lulls. This is illustrated in the Figure 3, where the total shaded area remains the same, but the instantaneous power rises to higher peaks. The average power is unchanged, the program material just has a higher crest factor with more pronounced peaks and lulls.

Figure 3: Illustrating crest factor for music/program power.

This simplified example shows how a loudspeaker can safely handle higher short-term peaks, provided the long-term average power remains within the AES rating. Program power just shows the speaker can handle higher short term peaks, as long as the long-term average power remains within the AES limit.

Problems arise when program power is treated as a continuous operating level. If the programme material has little dynamic range, or if heavy compression and limiting are applied, the crest factor is reduced and the average power rises toward the peak level. In this situation the loudspeaker is no longer operating within its intended thermal limits and the voice coil can overheat.

Program power is therefore best understood as a headroom allowance for dynamic signals, not as a sustained power rating. It best represents live music, particularly percussive sounds. Electronic, synthesised music is often compressed, and has long extended bass notes with low dynamics.

What this means for amplifiers

Modern amplifiers, particularly Class D designs, behave much like the first diagram rather than the second.

They are extremely good at delivering short bursts of high power thanks to high-voltage rails and efficient output stages. This is why many modern amplifiers are rated using standards such as EIAJ, which better reflect burst capability and musical crest factor.

What these amplifiers cannot do is sustain very high power indefinitely, especially at low frequencies. Long, continuous bass notes place heavy demands on the power supply, causing voltage sag, current limiting, or thermal protection to intervene.

This is why amplifier power ratings often look impressive on paper but drop significantly under continuous sine-wave testing, particularly into low impedances.

Matching amplifier power to speaker power

Program power is useful when choosing an amplifier because it indicates how much headroom is available for musical peaks. A common and sensible approach is to choose an amplifier capable of delivering somewhere between the AES power and the program power of the loudspeaker.

This provides enough headroom for dynamics without pushing the driver beyond its long-term thermal limits. However, once amplifier power approaches program ratings, proper use of limiters and compressors becomes essential to prevent excessive average power.

How can this make sense on a 13A plug?

The same power-over-time logic also explains why large amplifiers can operate from ordinary mains supplies. To take this one step further, it is useful to look at a more realistic musical signal rather than a simple rectangle, which represents power being fully on or fully off.

Figure 4 shows a simplified ADSR-style envelope, loosely resembling a typical percussive sound such as a drum hit. The instantaneous power still rises briefly to around 2000 W, but the time spent at high power is much shorter than in the rectangular examples.

Figure 4: A simplified percussive envelope showing brief high-power peak typical of a real musical signal.

As a result, the total shaded area is smaller, meaning less total energy is delivered overall. Despite the high peak, the average power remains relatively low. This is exactly the type of signal that modern Class D amplifiers handle extremely well: short, high-power bursts delivered cleanly without clipping and distortion. To clarify, this is not intended to suggest that a Class D amplifier cannot sustain peaks for longer than shown – indeed most can. The diagram is simply a representative example of real-world music, intended to show how musical signals translate into long-term average power, and why the ability to handle short bursts of high power is important for preserving dynamics.

This behaviour explains why large amplifiers can produce impressive peak power figures while still operating safely from standard mains connections. The peaks are brief, the average power is modest, and the electrical system only needs to support the long-term average rather than the instantaneous maximum.

For reference, the percussive example above has been approximated into a final diagram (Fig. 5) showing the same energy spread out as continuous power over time. Although the instantaneous peak reaches around 2000 W very briefly, the equivalent long-term average power is much lower, in the region of 600W.

Figure 5: The same energy from Figure 4 redistributed as continuous power, showing the equivalent long-term average.

This illustrates an important point: a short, high-power percussive event may look extreme when viewed instantaneously, but when averaged over time it represents a far more modest power demand. Even when additional sounds are present, the medium-term average power may only rise to around 800-900 W.

Applied across a four-channel amplifier, this suggests that even when all channels are working hard, the combined long-term average power is often closer to 3000W rather than the headline peak figures. While this approaches the practical limits of a 13 A mains supply, real music contains loud passages, quieter sections, and natural breaks. These variations reduce the long-term average further, keeping operation within safe limits.

This is why high-power amplifiers can operate from standard mains connections. Peak power figures describe short-term capability, not continuous demand. In the case of amplifiers such as the JAM Systems Q10, which is rated at up to 2500 W EIAJ per channel into 2 ohms, the apparent mismatch between output power and a 13 A plug disappears once power is considered over time rather than at its instantaneous maximum. Realistically this amp is at the limits of a 13A supply, which is why it comes with a heavy duty mains cable with 2.5mm cable and a heavy duty plug.

After being asked countless times how the JAM Systems Q10 can operate from a 13A plug, this article was written to explain exactly that. This article now serves as the standard explanation.

The key takeaway

Power ratings make far more sense when you consider how power is delivered over time. Peak power, program power, and amplifier ratings all describe different aspects of the same thing: short-term capability versus long-term limits.

Many people dismiss peak power figures because of how terms such as PMPO were misused in consumer hi-fi, often wildly overstating real capability. However, genuine high burst power serves a real purpose. It allows the dynamics of the original programme material to be preserved, delivering very large transients when required, but only for short periods of time.

AES power defines what is safe on average. Program power defines how much headroom is available for musical peaks. Understanding the difference makes amplifier choice, system setup, and real-world behaviour far easier to predict.

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What Power Driver Do You Need?

Posted By Andy Kos

What’s up with the Watts?business path choice

Choosing the right loudspeaker driver can feel like a minefield, especially if you’re new to PA sound. One of the most confusing areas is power ratings, usually quoted in watts.

To make matters worse, advances in materials and testing standards have seen many drivers increase their quoted power ratings by 25% or more, sometimes with no physical changes to the driver at all. Add in terms like RMS, Continuous, Program, and Peak power, and it’s no surprise there’s confusion.
This article mains to explain what those power ratings actually mean, clears up some common myths, and helps you choose sensible amplifier and speaker combinations.

Q: My amp is rated at 400W per channel. Will a 600W driver damage it by drawing too much power?

A: No. An amplifier’s power rating describes the maximum power it can deliver to a speaker before it reaches the limits of its power supply and begins to clip or distort. A loudspeaker’s power rating describes the maximum power it can safely absorb before overheating or failing.

Speakers do not “pull” power from an amplifier. Provided the impedance load is correct, a speaker cannot draw more power than the amplifier is capable of supplying.

Learn more about impedance and why it matters

Q: If I replace my 400W speakers with 450W speakers will they go louder?
A: Not necessarily. The limiting factor is usually the amplifier. If your amp is rated at 400W, you will not get more than 400W of clean output without distortion and potential amplifier damage. If your amplifier can deliver 450W, higher power handling may allow slightly higher output, but it may make no difference at all, and in some cases the speaker may even be quieter.
The key factor is efficiency. Some speakers convert electrical power into sound more effectively than others. If two speakers are operating at the same power level, the more efficient one will be louder. This is normally indicated by the sensitivity rating, measured in dB @ 1W / 1m.
Efficiency and Sensitivity

Q: Which power rating should I look at?

If you’re new to this, the most useful figure is the continuous power rating, usually specified using the AES standard. This gives a sensible indication of how much power a driver can handle of ‘continuous sound’ under realistic conditions and is the figure most manufacturers now quote.

You may also see a program or music power rating, which is typically around twice the AES rating. Peak power ratings are often quoted as four times the continuous rating and are of little practical use. If you see a peak figure, dividing it by four will usually give a reasonable idea of the true continuous power capability.

Q: What do the power ratings mean?

Continuous / “RMS” Power. Historically, loudspeaker power ratings were often quoted using continuous sine-wave tests, sometimes at a single frequency such as 1 kHz. These tests were easy to define and repeat, but they were not representative of real music and placed unusually high thermal stress on the voice coil.

The term “RMS power” is technically incorrect, as power itself does not have an RMS value; RMS applies to voltage or current. The RMS voltage is used in the power calculation, which is where the term originated. While RMS is useful for steady, resistive loads such as heaters or cable thermal calculations, it is not an ideal way to describe how loudspeakers behave with dynamic audio signals.

As a result, RMS power has largely been replaced by standardised noise-based tests that better represent music and broadband programme material, most notably the AES standard.

Over the years, manufacturers have used several recognised standards (a few still reference older ones):

  • IEC 268-5 (1978) – International Electrotechnical Commission
  • EIA RS-426-A (1980) – Electronic Industries Association
  • AES2-1984 – Audio Engineering Society
  • AES2-2012 – now the most widely adopted standard

When many manufacturers moved from the EIA standard to AES testing, some drivers saw power ratings increase by 25% or more without any physical design changes. One example we are aware of is a high-power 18″ driver that was re-rated from 600W to 800W purely as a result of the change in test method.

How is this possible? The AES standard defines a broadband pink noise signal with a specified crest factor for power testing, which differs from older methods. Many manufacturers implement the AES test using controlled noise over a defined period to stress the voice coil thermally, and this often results in higher quoted power figures compared to older standards. While the exact test duration and setup can vary by manufacturer, the AES rating provides a more consistent benchmark for comparing loudspeaker power handling.

Music / Program Power.

Often quoted as Program or Music power, this figure is typically defined as twice the continuous (AES or equivalent) power rating, representing a +3 dB increase. This does not mean the loudspeaker can handle twice the average power. Instead, program power allows for higher short-term peaks while the long-term average power remains the same as the continuous rating. In practical terms, this corresponds to a signal with a higher crest factor than the standard continuous test signal.

Real music contains peaks and valleys rather than a constant energy level. Program power reflects this by permitting greater instantaneous power during musical transients, provided the average power over time does not exceed the continuous rating. For system design, program power is best viewed as a headroom figure rather than a usable continuous operating level. Treating program power as a sustained power rating will almost certainly result in loudspeaker damage, however program power is useful for calculating amplifier power to get sufficient headroom. Opinions vary but most people suggest getting an amplifier slightly larger than AES power is a good start. If you want decent headroom, maybe aim halfway between AES Power and Program power – but at this point you have to start exercising caution with compressors and limiters to ensure the long term power rating does not get too high.

Peak Power:

This is the maximum very short-term power a driver can survive, and is typically quoted as four times the continuous (AES) power rating, representing a +6 dB increase. It exists almost entirely as a theoretical limit and has little relevance to real-world system design.

Peak power should not be used for amplifier matching, system sizing, or safe operating levels. Its primary practical use is for marketing, or for impressing someone who doesn’t know anything about sound.

Should I buy the most powerful speakers I can afford?

Probably not. It’s usually better to choose speakers that are appropriate for your amplifier power and intended use.

High power drivers are typically designed to survive large amounts of electrical and mechanical stress. This often involves design trade-offs such as heavier moving parts, longer voice coils, and suspensions optimised for high excursion. While these features increase power handling, they do not automatically increase efficiency.

As a result, a very high power driver is not necessarily louder at low or moderate power levels than a lower power driver with higher sensitivity. If you compare two extreme examples, such as a 100W driver and a 1000W driver, both driven from a 100W amplifier, the lower power driver may actually produce more output simply because it converts the available power into sound more efficiently.

The higher power driver only begins to show its advantage when sufficient power is available to drive it closer to its intended operating range. With a larger amplifier, it will ultimately produce far more output than the smaller driver ever could. However, when amplifier power is limited, choosing a driver with power handling far in excess of what the amplifier can deliver offers little benefit, and could be detrimental. Typically a 1000W woofer can be heavy and inefficient compared to a 200W woofer. On a smaller amp of 200W, the 200W woofer could actually play louder than the 1000W woofer which is inefficient.

In short, more watts on the specification sheet do not guarantee more sound. Sensitivity and appropriate system matching matter far more than headline power ratings.

So what if I exceed the power ratings?

You run the risk of overheating the voice coil and causing thermal failure. However, staying within the recommended power rating is not a guarantee of reliability.

Loudspeakers can also be damaged mechanically through excessive cone movement. This is described by excursion limits such as Xmax and Xlim. It is entirely possible to destroy a driver through over-excursion without ever exceeding its rated power, particularly at low frequencies or in poorly controlled enclosures.

There is also an important interaction between excursion, bandwidth, and cooling. In some situations a driver can reach its thermal limits at power levels well below its rated AES power.

For example, running a loudspeaker over a very narrow pass band (such as 30–40 Hz) in a cabinet tuned close to that frequency can result in extremely low cone excursion. While this may reduce mechanical stress, it also reduces air movement around the voice coil. Since many drivers rely partly on cone motion to aid cooling, limited excursion can significantly reduce heat dissipation.

In these conditions, particularly in small enclosures with restricted airflow, the usable thermal power handling may be substantially lower than the published AES rating. In extreme cases it can be closer to 50% of the rated value, despite excursion remaining well within safe limits.

What about Power Compression?

Power compression is the hidden problem that can upset even the best-planned systems and make published specifications feel misleading. Many manufacturers choose not to quote power compression figures at all, and some avoid mentioning it entirely.

Loudspeaker sensitivity is specified at 1 W measured at 1 m. At this very low power level, the voice coil remains cool and the driver is highly efficient at converting electrical energy into sound.

In real use, voice coils heat up. Most are wound with copper, which has a positive temperature coefficient of approximately 0.39% per degree Celsius. It is entirely possible for the voice coil of a high-power driver to reach temperatures approaching 200°C, resulting in a resistance increase of 50% or more.

As the voice coil resistance rises, the effective impedance of the driver increases. An 8 Ω loudspeaker may behave more like a 13–14 Ω load at high power. The amplifier delivers less current, acoustic output drops, and a significant proportion of the input power is lost as heat rather than sound.

The practical result is reduced output at high drive levels. A well-designed driver with good thermal management and low power compression can be 3–4 dB louder at full power than an otherwise similar driver that suffers heavily from compression. For this reason, modern high-quality designs place increasing emphasis on cooling and heat dissipation to minimise power compression.

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Power Compression

Posted By Andy Kos

When selecting speakers, it’s common for people to just look at maximum power handling, and many manufacturers make a point of specifying seemingly unbelievable power handling capacity of 1000W or more. Its quite rare for manufacturers to specify power compression though, and it seems to be often overlooked by system designers.

It seems that loudspeakers to handle what appear to be insanely high levels of power compared to 10 or 15 years ago. Has there been some amazing technological breakthrough? Do we need to re-write the physics text books? No, it’s still just basic physics – so what are the changes?

Firstly, modern materials used in the construction of voice coils are able to withstand significantly higher temperatures before failing.  Why is this important? Well Cone loudspeakers are in fact very inefficient, with even the best transducers only converting around 5% of the electrical energy supplied into sound, the majority of the remainder is converted into heat. So a 1000W bass speaker running at full power may well be converting only 50W into acoustic power, and 950W of heat. Thats like having a 1kw bar heater in your bassbin! That’s a lot of heat, which can cause big problems.

Aside from improving construction materials, manufacturers are also refining designs to maximise heat transfer away from the voice oil, this also contributes to the increases in power handling capacity we are experiencing.

What’s all this got to do with power compression?

Enabling speakers to handle much higher temperatures might seem a good thing, as it increases maximum power handling, but it also has a detrimental effect. Most voice coils are made from copper or aluminium wire, both of which have a positive temperature co-efficient of around 0.4% per °C. What’s the significance of that? You will have heard of superconductors, which operate at extremely low temperatures in order to try to reduce and minimise resistance.  Loudspeaker voice coils  unfortunately work in the opposite way: as the temperature increases, the resistance also increases.

A modern state of the art voice coil is designed to withstand extremely high temperatures, often operating at up to 3000C or more when driven at full power. 0.4% may sound insignificant, but remember this is per °C – at only 2300C the voice coil DC resistance has almost doubled which causes the voice coil impedance to increase accordingly. Some simple maths and you can quickly see that the increase in temperature  can make your 8 ohm speaker start behaving more like a 16 ohm speaker.

So after setting your sound system carefully at the start of the night, an hour in, and it doesn’t sound as loud – you might wonder whats going on. Two things: firstly, your ears have a self defence mechanism: there are 2 tiny muscles in the middle ear that will contract when the ear is exposed to loud sounds. This contraction will reduce the loudness of the sounds reaching the inner ear, thereby protecting the inner ear against exposure to loud noises. This isn’t power compression, but it’s something to be aware of, as you may well be tempted to turn up the volume, I know from experience that a typical DJ will certainly try this, and end up running his mixer into overdrive in the attempt to get more volume.

The second factor is power compression, a typical loudspeaker can lose 3-6 dB of volume once power compression kicks in.

You could think of power compression a bit like the aerodynamics of driving a car. When you start moving, a certain level of power from your engine sets you hurtling forwards at high speed, but as you go faster, wind resistance increases, so you stop accelerating. You need to apply more power to increase speed, but wind resistance keeps increasing too, so you have to apply even more power.

If your amplifiers have headroom, your instincts will make you want to turn them up, to restore the original volume level. To some extent this will work, if you’re familiar with the maths, you’ll see whats going on. Your 8 ohm speaker at room temperature happily accepts 1000W from your amplifier, and gradually reaches an operating temperature of say 250°C. Your resistance has doubled, and your ‘new’ 16 ohm speaker will probably only be receiving around 500W from your amplifier. In a way, as the speaker reaches temperature, it ‘protects itself’ by reducing the power it is operating at, stopping it getting any hotter. If it were to cool a little, the power would increase again, causing it to heat up.

Lets suppose you turn the gain up on your amplifiers, determined to try to push 1000W through your speakers. As you apply more power, you will generate more heat,  perhaps reaching 350°C or more, with your speakers resistance continuing to increase to perhaps 20 or more ohms. Essentially you are fighting a losing battle, as you turn the gain up, the speaker fights back with a higher resistance. You will eventually reach a limit, either your amp will run out of headroom and you cant turn it any louder, or the other possibility, which happens all too often, is your speaker will overheat, and burn out causing catastrophic failure.

Now you know about power compression and the fact that speaker resistance increases with heat, you’ll probably realise that you actually have to push a speaker very hard in order to cause it fail – so if your speaker suddenly fails and you smell burning, the only person to blame is YOU, as you now know better than to try to fight power compression by applying more power.

Now consider what effect power compression will have. 3-6dB loss at full operating power is almost like switching off half your PA system. To achieve the same consistent volume you will need twice as many speakers!

What’s the solution? Either buy speakers with headroom, e.g. if you want to operate at around 500-600W, you might want to consider purchasing speakers rated at 800W or more. At 75% of rated power, the effects of power compression should be much less significant. Also, try to select speakers with improved cooling technology, that suffer less from power compression. Avoiding power compression could make your speakers twice as loud, meaning you could take half as many to the gig!

There are other side effects from the increased levels of heat in a speaker, T/S parameters can vary, bass can sound boomy and mid frequencies can sound muffled. For the best sound quality, its best to try to  minimise power compression effects,

 

 

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Pe – Power Handling Capacity

Posted By Andy Kos

Pe – Power Handling Capacity

Pe represents the thermal power handling capacity of a speaker driver, measured in watts (W). It indicates how much continuous power the voice coil can handle without overheating or suffering permanent damage. The test is done in a controlled environment with specific cabinet volume and controlled room temperature. The test environment may not be the same as your speaker design, for instance some manufacturers conduct their power tests for 18″ woofers in a very large cabinet (900 litres) which could be 6-8 times the size of your cabinet. This has a different volume of air, which can affect heat dissipation. Very small chambers in cabinets can adversely affect the power handling and make it much lower in real life than the manufacturers specifications

Power handling is not the same as loudness—a higher Pe rating doesn’t necessarily mean a louder speaker, as efficiency (η₀) and sensitivity (SPL @ 1W/1m) also play key roles. Many manufacturers rate Pe using AES, RMS, or program power standards, which define how power limits are tested. Manufacturers sometimes use slightly different parameters for their power calculations, such as whether they use minimum impedance, average impedance or nominal impedance to determine the power, which can distort results. Its worth checking this out in critical applications

Power Handling vs. Loudness – Why More Watts Doesn’t Always Mean More SPL

A higher power handling (Pe) doesn’t automatically mean a louder speaker—it only tells you how much power the driver can withstand before thermal failure. The actual loudness (SPL) depends on both efficiency (η₀) and sensitivity (SPL @ 1W/1m).

For example, consider two 18″ woofers:

  • Woofer A: η₀ = 3%, 500W Pe
  • Woofer B: η₀ = 1.5%, 1000W Pe

Even though Woofer B can handle twice the power, it has half the efficiency, meaning it produces the same SPL (or less) at full power as Woofer A does at half the power.

This is why efficient PA speakers can often achieve the same or greater loudness with less amplifier power, reducing thermal stress and power compression. If a speaker is inefficient, throwing more watts at it only results in more heat, not necessarily more sound.

The graph below illustrates the difference between high and low efficiency woofers, comparing the worst case (0.5% efficiency) you would need 2000W to reach to the SPL of a very efficient woofer (4% efficiency) operating at 250W. That’s a lot of extra power and heat to deal with.

For more info on power ratings, including AES vs. RMS vs. Peak Power, check out this article:
What’s Up With the Watts?

Filed in Loudspeaker Driver Parameters, Power, TS Parameters | Tagged: , ,