Is More Watts Better for Speakers?

Speaker power is one of the most confusing concepts in the professional audio world. It is generally believed that the higher the power of the speaker, the better the quality, and it is more worth looking forward to and owning. Moreover, power is often the decisive indicator that drives customers to purchase.

 

But if you study carefully, you will find that power is far less important to the overall performance of the speaker than other performance indicators.

 

The term "speaker power" needs further explanation to eliminate misunderstandings. It is the practice of many people to consider the speaker power and the output sound pressure level of the sensor, or even the size of the amplifier. But usually the speaker power has nothing to do with these.

 

First, let's discuss this term first to make it more meaningful. Can "Maximum Input Power Dissipation" be used? The concept of "input power" is appropriate because the speaker is a load of the power amplifier.

 

Assuming that the line impedance is small and negligible (if the correct standard wire is used, this assumption holds), the output power of the amplifier becomes the input power of the speaker. Because it is generally believed that the higher the power of the amplifier, the better (for example, a sports utility vehicle VS an economic car), so it is logical to think that the higher the power speaker, the better the product performance.

 

Amplifiers directly connected to speakers are called power amplifiers because their output voltage is higher than their input voltage. (Figure 1) The power of a power amplifier is measured according to its power generation capability. Usually the larger the value, the better, because it means that the amplifier has greater potential and can do more work.

 

 

The power of a speaker is measured according to its power dissipation capability. The power value refers to the continuous amount of power that the speaker can consume in the form of heat without damaging the speaker. Although at first glance, it seems that the greater the power dissipation, the better, but the premise is that the method to achieve greater power dissipation does not damage the performance of the speaker, this statement is only valid.

 

Modern power amplifiers act as constant voltage sources for speakers. This means that the output voltage of the amplifier and the load provided by the connected speakers are essentially independent of each other. If you use an amplifier to drive the signal, and measure the output voltage of the amplifier without any load connected to the output. Then connect a speaker to the output terminal, measure the output voltage of the amplifier again, and the reading on the voltmeter will not change significantly.

 

The difference between load and no load is: when load is applied, current will come out of the amplifier and flow through the speaker. The smaller the load impedance (the more speakers connected in parallel), the more current the load draws from the amplifier, and the greater the total power delivery between the voltage source and the load

 

This is why the total output power of the amplifier usually increases when driving more speakers. Note that the output power of the amplifier is increased, but this increased total power will be distributed to all connected speakers.

 

 Therefore, if two speakers are connected in parallel, the total power output of the amplifier increases, but the power allocated to each speaker does not necessarily increase. In fact, the power allocated to a single speaker will be slightly reduced. Therefore, it is best to keep the power amplifier load above 4 ohms to minimize the influence of the wire and avoid the amplifier's demand for excessive current.

 

 

1. One goes down

 

The power absorbed by the speaker from the amplifier is the product of voltage and current. According to the law of conservation of energy, all power from the amplifier must have its place. Part of the total power produces the mechanical vibration of the speaker, and the remaining power is converted into heat. The mechanical vibration of the cone makes the speaker sound.

 

Thermal energy is a useless by-product, so like any useless waste, thermal energy must be disposed of. Unfortunately, the conversion of electrical power to sound power is an inefficient process (usually less than 10%), so most amplifier power is converted into useless heat, which must be dissipated.

 

The power of a speaker describes the ability of the speaker to process heat, which is caused by the inefficiency of the energy conversion process. So it's back to the extended definition "maximum input power dissipation" we talked about earlier.

 

Therefore, it is wrong to associate speaker power with its sound performance. The high dissipation power value only means that the heat dissipation capacity of the speaker is stronger. But the power itself does not explain the effectiveness of the sound power generated by the speaker, and the effectiveness of the sound power generated by the speaker is the most important factor in the performance of the speaker.

 

The power dissipation of the speaker can be increased by reducing the performance of the speaker, which only needs to add some resistance components inside the speaker. However, the result is a large speaker power value but very low sound, which is not what we want.

 

The sound pressure level (SPL) generated by the speaker is more closely related to the applied voltage than to the applied power. Figure 3 can clearly show this.

 

 

The power of the sensor load varies with frequency. Although the SPL value often uses the input power value as a reference, in fact, it is more accurate to use the input voltage as a reference. In fact, speakers prefer a flat voltage response, because in this case, an equal drive voltage at each frequency will produce a flat amplitude response in the axial direction.

 

The ideal speaker can use the minimum power to produce the required sound pressure level. High-performance speakers should also generate less heat. Therefore, the ability of speakers to withstand high-power drives is not worth wondering. Because in essence, this ability cannot produce any benefits.

 

The ability to generate a lot of sound power with less input power is worthy of admiration. Think about the fuel consumption per kilometer of a car, and you will understand the issue of performance better. Speaker performance is about the concept of efficiency, not the concept of consumption. Horn load and interface placement are both methods used to increase speaker performance. Both methods are designed to generate more sound energy per watt of electrical power.

 

2. Reasonable perspective

 

People's misunderstanding of speaker power extends to everyday behaviors, such as choosing a light bulb. It is generally believed that the wattage of a bulb is closely related to the light output, and that the higher the wattage, the greater the brightness.

 

The light bulb also has a parameter called luminosity, which is used to describe the light output of the bulb, but few customers will refer to this parameter. Therefore, if a brighter bulb is needed, people tend to buy a larger bulb (higher wattage). It is a natural idea to extend this assumption to speakers. Next time, under the premise of a given power input, you can get the most value by buying the bulb with the highest lumen output.

 

The high power of the speaker does not mean that the sound produced by the speaker is large. Compared to saying, "Wow, this speaker can handle 5000 watts of power!" In fact, this is meaningless. If you ask yourself the following question, it will make more sense: "Why should I use a 5000 watt speaker to bring the audience Come with a maximum sound pressure level of 100 dB, without using another 100 watt speaker that can also provide the audience with a maximum sound pressure level of 100 dB?"

 

Among the speaker performance indicators, the more meaningful parameter is the maximum output sound pressure level. This parameter is calculated from the sensitivity of the speaker and the maximum input power. Speakers with lower power and higher sensitivity have more advantages than speakers with higher power and lower sensitivity.

 

Unfortunately, people's misunderstanding of power has caused the phenomenon of speaker manufacturers competing to produce high-power speakers. Large power value can help sales, but higher efficiency is the real factor that improves speaker performance.

 

 

3. Power test

 

 

There are many ways to determine the maximum input power of a speaker. These methods have their own advantages, but also share some common attributes. A meaningful power test must include:

 

--Broadband noise with bandwidth limitation for the input of the device under test

--Measurement method of power delivery between amplifier and device under test

--A metric used to describe the duration of speaker power dissipation

--Measure the SPL value of the speaker (ideally)

 

The noise input usually uses pink noise (equal energy per 1/n octave). Some measurement methods use flat pink noise, and other methods use signals that are weighted to simulate the content of the music spectrum. The latter method can produce higher rated power because more electrical energy is transferred to a lower frequency band. In the low frequency range, because the sensor structure is heavier, it usually consumes more heat energy.

 

In order to determine the amount of power delivered, the voltage and current applied to the device under test must be monitored. To calculate the power transfer, only the RMS (root mean square) voltage and the nominal impedance of the load are not enough. When the thermal energy of the device under test gradually increases, the load impedance will gradually increase, thereby reducing the power absorbed by the load (power compression).

 

When the speaker is operating near the extreme value of the power dissipation value, the usual practice of increasing the power output of the power amplifier to increase the power input of the load will not increase the sound pressure level, but may reduce the power transmission.

 

It is best to use decibels (that is, to measure the ratio) to measure the power. Using wattage will mislead people to believe that it is related to equipment performance.

 

Let's take the actual situation as an example. The sound level of a 500-watt continuous rated power speaker is only a little higher (+3 dB) than a 250-watt continuous rated power speaker. It is assumed that the performance of the two speakers is the same. This means that the substantial difference between the two speakers is very small, even though they differ greatly in power.

 

Most power tests will make some changes to the pink noise used to get a smaller crest factor-the peak value in the program sound source is reduced by a clipping circuit. The actual reason for clipping the waveform is that the amplifier can deliver more power to its load device.

 

The maximum output power of unclipped pink noise is approximately one-tenth of the amplifier's sine wave rated power. The pink noise after clipping is approximately one-half of the amplifier's sine wave rated power, which allows the use of reasonably sized amplifiers for power testing. Artificial clipping will not change the heat generation of the speaker too much, but the lower crest factor it provides can deliver more power (higher RMS voltage) to the load device of the amplifier.

 

The continuous power test will supply the speaker with 6 dB crest factor pink noise within a specified time period (such as 2 hours). This is a very demanding test for speakers, because the sound source is not stopped and cannot be cooled.

 

By reducing the duty cycle of the waveform, the rated power of the program attempts to simulate music or voice. If the sound signal is of the pulse type, some cooling can be obtained between pulses, and more short-term power can be applied to the measured device before damage to the device is avoided. Many manufacturers will estimate the double value of the continuous power value as the program power (+3 dB or 2 times is a reasonable assumption). The actual recommended amplifier power value is larger than these two values.

 

A reasonable estimate is to add +6 dB (4 times) to the continuous power. For example, starting from these definitions, a complete and meaningful power description of a speaker should be:

 

Maximum input power -200W/400W/800W (continuous, program, recommended amplifier size)

 

 

4. Similar comparison

 

You can now see the problems when comparing the power of different speakers. To ensure the correct comparison between similar parameters requires a lot of research, and many parameter tables do not give us enough information for us to compare in this way.

 

There is no danger in delivering power lower than its rated power to the speaker. In fact, the input power is smaller than the rated power value, and the speaker has a longer service life. In stable and reliable operation, I recommend limiting the input power to less than one-half of the continuous power (-3 dB). In the previous example, this meant using an 800-watt amplifier to deliver a typical program source (10 dB to 14 dB crest factor) that could be driven to the edge of clipping at the maximum.

 

In this case, the amplifier will deliver 80 watts or less of power to the speakers, which is a safe value lower than the continuous power. Because the potential output of the amplifier is very large, when using low crest factor program sound sources, you must be very careful not to turn the volume too high to cause damage to the speakers.

 

Finally, when increasing the volume of a sound system, it is also important to know when the critical point of the system is reached. For every 40% increase in the voltage applied to the speaker, the input power doubles and the sound level increases a little (+3 dB).

 

Remember that proportional odds are important in audio. The system volume is increased in 3 dB steps, and finally reaches the extreme point of heat dissipation. Continue to increase by 3 dB, and it will become the last straw to crush the camel. When the speaker is working at half the rated power, its sound level may be very close to the maximum. Therefore, there is no need to increase the power, which brings the risk of permanent damage to the speakers.

 

5. High power is easy to sell, but high efficiency is a better goal

 

 

The development of automobile technology reduces energy consumption and can produce vehicles with higher efficiency and lower operating costs. The audio industry should have similar goals and strive to achieve the required sound pressure level with less amplifier power.

 

As efficiency increases, speakers should gradually reduce the amount of energy that needs to be dissipated in the form of heat. Likewise, our fascination with higher power ratings should disappear.