How much power is needed to drive a specific speaker? There is no definite answer to this question. In fact, three different factors need to be considered when selecting the power amplifier power for the speakers.
1. Understand speaker power
For example, the power value on the EAW parameter table indicates that the speaker has passed the EAW standard power test. In this test, the speaker was "operated" to be damaged or malfunctioning. The rated power value obtained by the test will be used as a comparison point to compare with the rated power of other speakers. This value does not necessarily need to correspond to the better rated power of the power amplifier, nor is it used to measure the "safe" power amplifier power that should be used under real operating conditions.
The main purpose of EAW power test is to understand the limits of speaker thermal power handling. In the case of continuous signal input (measured by RMS voltage), the critical point of long-term damage or failure of the speaker due to heat is the thermal power handling limit of the speaker. In this test, the speaker was also input with a peak signal level that was 6 dB higher than the RMS level of the input signal. To some extent, these peak levels test the peak power handling capabilities of the loudspeaker. The pink noise signal used to test the full-range speaker is shaped into a standard EIA (Electronic Industries Association of America) frequency response shape, which simulates the average frequency response shape of a typical music program.
However, this shaped pink noise signal cannot represent all real audio signals. Naturally, the speaker's response to it is not equivalent to the speaker's response to the real audio signal. Generally speaking, in terms of thermal limit, the speaker will bear more load when reproducing this kind of pink noise signal than reproducing the typical music or voice signal. However, some audio signals-such as rock and dance music, and even some classical music-can put more load on the speakers than the shaped pink noise signal.
Since there is no universal standard, most professional speaker manufacturers use different test methods to obtain power parameters. Surprisingly, despite the different test methods, sometimes the results obtained are very close. These values are quite different, including thermal power, continuous power, RMS power, AES power, and EIA power. The difference in these power values is mainly due to the difference in test methods or test equipment, and there are actual differences in the power handling capabilities of non-speakers. Therefore, speakers with a power factor of around ±1.5 can be considered to have the same processing power. A factor of ±1.5 is approximately equivalent to an output tolerance of ±1.5dB. For example, a speaker with a rated power of 600 watts and a speaker with a rated power of 900 watts are likely to have the same capacity when processing the power of a real audio signal.
Please note that "music", "program", "peak" or similar power values are usually twice or more than the thermal power value (or RMS and continuous power, etc.). However, these values are rarely measured by facts. Generally, these power values only indicate that the loudspeaker can handle peak input above the larger rated thermal power limit.
2. Choose a power amplifier with appropriate rated power
A power amplifier with a suitable rated power should be selected for the speaker according to the required sound level and the type of audio signal. If you don’t know how to determine these metrics, please consult a qualified professional or contact EAW’s application support team.
Do not confuse the stated power ratings with the louder sound levels that can be achieved. The larger output is a function of amplifier power and speaker sensitivity. Therefore, a speaker with a sensitivity of 97dB (1W@1M) and a 100-watt power amplifier and a speaker with a sensitivity of 94dB and a power amplifier of 200 watts have the same larger output.
Loudspeaker drivers, especially compression drivers, are generally better able to withstand the instantaneous peak power than the drivers in the EAW power test. Dynamic audio signals such as percussion have a high instantaneous peak level; while audio signals such as speech, the level is constantly changing. In order to make full use of the peak processing function of the speaker and avoid clipping of the power amplifier, a power amplifier with a rated power greater than the power of the speaker should be selected to reproduce the peak level of the audio signal.
For low dynamic audio signals, such as heavy metal rock and high compression music, a power amplifier with a rated power lower than the speaker power may be required to avoid putting too much load on the thermal power processing of the speaker.
In addition, sometimes 500W continuous power (or RMS power) speakers may be used to reproduce low-level background music. At this time, only 25 watts of power amplifier can achieve the required sound level.
Therefore, the rated power of the power amplifier required for a particular application may be much higher or much lower than the power indicated on the speaker.
As a rule of thumb, it is assumed that under the condition of correct operation (see Part 3), in order to allow the speaker to give full play to its performance and achieve a suitable sound output level, EAW recommends the use of a power amplifier with a power rating of twice the speaker power. This allows the power amplifier to reproduce a peak signal that is 6dB higher than the indicated power. This is consistent with the output performance of the power amplifier used in the test signal and EAW power test. However, the method we recommend does not guarantee that the operation will always be foolproof, which involves the issues we talk about in the next section.
3. Prevent speaker damage
Preventing speaker damage or malfunction is not a function of amplifier power and speaker rated power. To prevent damage to the speakers, the audio system must be operated correctly to prevent the load on the speakers from exceeding the limit. If the audio system is improperly operated, even if you use an amplifier whose rated power is much lower than the speaker's power, it may cause the speaker to be damaged or malfunction. On the contrary, if you operate the audio system correctly, even if you use a power amplifier whose rated power exceeds the speaker's continuous power (or RMS power, average power, etc.), you can avoid speaker damage or malfunction.
Correct operation of the audio system includes: noting the type of audio signal, controlling the corresponding output level, and operating all electronic devices to ensure that no electronic clipping occurs in the signal chain.
Examples of improper operations include:
(1) Continuous microphone feedback;
(2) Perform equalization enhancement outside the operating frequency range of the loudspeaker;
(3) Excessive equalization enhancement within the operating frequency range of the loudspeaker;
(4) Let electronic clipping exist in the electronic chain, which includes a mixer, signal processing equipment or power amplifier;
(5) Excessive processing makes the speaker obvious distortion;
(6) Let the full power output of the power amplifier reproduce continuous tones, such as synthetic tones.
Regardless of the rated power of the speaker and the power of the power amplifier used, the above operations will easily cause the speaker to be damaged or malfunction. The operator of the sound system is responsible for ensuring that all equipment in the system is operated within the performance allowable range. Only in this way can it be ensured that the speakers will not be damaged and malfunction due to excessive load.
Appendix 1: About speaker "power"
The power test done by EAW and most professional speaker manufacturers actually measures not power, but voltage. They measure the RMS voltage value or average voltage value of the input signal. Then use this value to calculate the power through the traditional formula:
Power = square of voltage / nominal impedance
However, the value calculated by the formula has little basis in real applications, and the reasons are as follows:
(1) The nominal impedance of the speaker is not consistent with the actual impedance. In fact, the impedance of a typical loudspeaker often varies greatly with the frequency range.
(2) Speakers are generally reactive loads. This means that it can be used as an inductor or a capacitor, depending on the frequency. In reactive loads, voltage and current are not synchronized, so if the phase angle between voltage and current is not known, the actual power cannot be calculated. Therefore, the power calculation equation must include the phase angle:
Power = (voltage square x cosine phase angle)/impedance
Unless this equation is used to calculate the power of each frequency within the operating range, if it is used to calculate the total power, the correct result will not be obtained. Usually, only one of the four quantities in the above equation is measured, that is, voltage. If you only know the voltage value, you still can't solve the above equation.
Essentially, for a specific power parameter under a specific "nominal" impedance, the voltage is the same whether you are looking at the parameters of a speaker or a power amplifier. For example: 200 watts under 8 ohm load, whether it is a power amplifier or a speaker, the test voltage is 40 volts RMS.
So in fact, the power value we use in the audio parameters is just a substitute value for the test voltage. However, power is a parameter commonly known by convention, which can facilitate comparison between different power amplifiers and different speakers. Just remember that academically they do not represent the factual power of speakers.