How much power amplifier is needed to drive home theater speakers

How much power amplifier is needed to drive home theater speakers? There is no definite answer to this question. In fact, when choosing a power amplifier for home theater speakers, three different factors need to be considered.

1. Understand speaker power

For example, the power values on the EAW parameter table indicate that the speaker has passed EAW's standard power test. In this test, the speaker was "operated" to the point of damage or malfunction. The rated power value obtained from 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 optimal rated power of the amplifier, nor is it used to measure the "safe" amplifier power that should be used under real operating conditions.

The main purpose of EAW power testing is to understand the limits of speaker thermal power treatment. The critical point of permanent damage or failure of the speaker caused by heat under continuous signal input (measured by RMS voltage) is the thermal power processing limit of the speaker. In this test, the speaker was also input with a peak signal level, which is 6 dB higher than the RMS level of the input signal. To some extent, these peak levels test the peak power processing capability of the speaker.

The pink noise signal used to test full frequency speakers is shaped into a standard EIA (Electronic Industry Association of America) frequency response shape, which simulates the average frequency response shape of typical music programs.

However, this sculpted pink noise signal cannot represent all real audio signals. Naturally, the response of the speaker to it cannot be equated with the response of the speaker to the real audio signal. Generally speaking, in terms of thermal limit, speakers bear more load when reproducing this pink noise signal than when reproducing typical music or voice signals. However, some audio signals - such as rock and dance music, and even some classical music - can put more load on the speaker than the sculpted pink noise signal.

Due to the lack of universal standards, most professional speaker manufacturers use different testing methods to obtain power parameters. Surprisingly, despite different testing methods, sometimes the results obtained are very close. These values are very different, including thermal power, sustained power, RMS power, AES power, and EIA power. The differences in these power values are mainly due to different testing methods or equipment, rather than actual differences in the power processing ability of the speakers. Therefore, speakers with a power factor of around ± 1.5 can be considered to have the same processing capability. A factor of around ± 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 may have the same capacity when processing real audio signals.

Please note that "music," "program," "peak," or similar power values are usually twice or more times the thermal power value (or RMS and sustained power, etc.). However, these values are rarely measured based on facts. Usually, these power values only indicate that the speaker can handle peak inputs above the maximum rated thermal power limit.

2. Choose the appropriate rated power amplifier

The appropriate rated power amplifier should be selected for the speaker based on the required sound level and type of audio signal. If you are unsure how to determine these measurement indicators, please consult qualified professionals or contact EAW's application support team.

Discussion:

Do not confuse the indicated rated power with the maximum achievable sound level. The maximum output is a function of amplifier power and speaker sensitivity. Therefore, a sensitivity of 97dB（ 1w@1m ）A speaker using a 100 watt amplifier and a speaker with a sensitivity of 94dB and an amplifier power of 200 watts have the same maximum output.

Speaker drivers, especially compression drivers, are usually better able to withstand instantaneous peak power than drivers in EAW power testing. Dynamic audio signals such as percussion have high instantaneous peak levels; And for audio signals like language, the level is constantly changing. In order to fully utilize the peak processing function of the speaker and avoid power amplifier clipping, power amplifiers with a rated power greater than the speaker power 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, amplifiers with a rated power lower than the speaker power may be required to avoid placing too much load on the speaker's thermal power processing.

Additionally, sometimes a speaker with a continuous power of 500W (or RMS power) may be used to reproduce low-level background music. At this point, only a 25 watt amplifier is needed to achieve the desired sound level.

Therefore, the rated power of the power amplifier required for specific applications may be much higher or much lower than the power indicated by the speaker.

As an approximation method, assuming correct operation (see Part 3), in order to fully utilize the performance of the speaker and achieve an appropriate sound output level, EAW recommends using a power amplifier with a rated power of twice the speaker's power. This can allow the amplifier to reproduce a peak signal that is 6dB higher than the indicated power. This is consistent with the output performance of the amplifier used in the test signal and EAW power testing. However, the method we recommend does not guarantee that the operation will always be foolproof, which involves the issues we will discuss in the next section.

3. Prevent speaker damage

Preventing damage or malfunction of speakers is not the function of amplifier power and speaker rated power. To prevent damage to the speakers, it is necessary to operate the audio system correctly to prevent the speaker's load from exceeding its limit. If the audio system is not operated properly, even using amplifiers with a rated power much lower than the speaker power may cause damage or malfunction to the speaker. On the contrary, if the audio system is operated correctly, even using amplifiers with a rated power exceeding the speaker's continuous power (or RMS power, average power, etc.) can avoid speaker damage or malfunction.

Discussion:

Proper operation of the audio system includes paying attention to the type of audio signal, controlling the corresponding output level, and operating all electronic devices to ensure that electronic clipping does not occur within the signal chain.

Examples of improper operations include:

(1) Excessive processing leads to significant distortion of the speaker;

(2) Balanced enhancement outside the frequency range of speaker operation;

(3) Excessive equalization enhancement within the frequency range of speaker operation.

Regardless of the rated power of the speaker and the power of the amplifier used, the above operations can easily cause damage or malfunction to the speaker. The audio system operator is responsible for ensuring that all equipment in the system is operated within the allowable performance range. Only in this way can we ensure that the speaker will not be damaged or malfunction due to excessive load.

Appendix 1: About Speaker Power

The power tests conducted by EAW and most professional speaker manufacturers actually measure 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 using the traditional formula:

Power=square of voltage/nominal impedance

However, the values calculated through formulas have little basis in practical applications, for the following reasons:

(1) The nominal impedance of the speaker is not consistent with the actual impedance. In fact, the impedance of a typical speaker often varies greatly with the frequency range.

(2) Speakers are generally reactive loads. This means that it can serve as both an inductor and a capacitor, mainly 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 at each frequency within the operating range, it will not yield the correct result if used to calculate the total power. Usually, only one of the four quantities in the above equation, namely voltage, is measured. If only the voltage value is known, it is still impossible to solve the above equation.

Essentially, for specific power parameters under a specific "nominal" impedance, regardless of whether you are looking at the parameters of the speaker or amplifier, the voltage is the same. For example, under an 8-ohm load of 200 watts, whether it is an amplifier or a speaker, the test voltage is 40 volts RMS.

So in reality, the power value we use in audio parameters is just a substitute value for the test voltage. However, power is a commonly known parameter that facilitates comparison between different amplifiers and speakers. Just remember, academically they do not represent the actual power of the speaker.