The Secret of Speaker Power Parameters

    The main function of a power amplifier in a speaker is to amplify signals and provide sufficient power to the load (speaker). The impact of power amplifiers on sound quality mainly depends on whether the input signal can be amplified and transmitted without distortion, providing sufficient power to the load. The signal amplified and transmitted by a power amplifier is different from a simple harmonic signal and is a complex signal with instantaneous changes.

    If we look at this signal from its waveform, the original signal has many spikes, their energy is not large, but the peaks are very sharp and high. These peaks have a small contribution to loudness, but a significant impact on sound quality. If clipping occurs, the amplified sound sounds dry and hard. This is related to the details of subjective listening that we usually refer to. If during power amplification, we only pay attention to the transmission of energy (corresponding to loudness) and do not pay attention to the changes in the waveform during the transmission process (causing distortion), then we may hear a loud but unpleasant sound.

    For an active speaker, the power amplifier is located inside the speaker, and its job is also to drive the speaker and bring sufficient output power to the speaker. However, the nominal notation for speaker power we see is not very standard. Generally, speaker manufacturers label the power of the "speaker" as the "output power (RMS)" of the power amplifier (the power amplification circuit part of the active speaker), while RMS (root mean square) refers to the root mean square. Currently, in multimedia speaker labeling, it is mostly the root mean square power.

    The root mean square power is different from the average power and rated power. The specific algorithm is to take the mean square of the power values at each point in the sample and then square it. We will not delve into the calculation of the root mean square for now. What we need to discuss next is the relationship between the "root mean square" power and rated power, as well as speaker power.

    As mentioned earlier, the signal amplified by a power amplifier is a complex signal. According to the survey results of various instruments and program signals in acoustic engineering, the ratio of the maximum root mean square power (i.e. the peak peak power of the program signal on the load) to the average root mean square power (i.e. the average power of the program signal on the load) of most program signals is 3-10, with a maximum of 12.7.

    If the rated power of the power amplifier corresponds to the average root mean square power of the program signal, then the maximum output power of the power amplifier should be 3-10 times that to ensure that the output signal does not experience clipping. This is why we choose a power amplifier with a much higher power than the average root mean square power of the amplified program signal, which is also commonly referred to as power reserve.

    From the current low-end products, the maximum output power of power amplifiers should not have a power reserve of 10 times the root mean square power of the signal, and the power reserve during design is definitely different. This is one of the reasons why we encounter distortion issues at different or higher volume levels during regular testing. On the other hand, multimedia speakers rarely indicate the rated power, maximum output power, output RMS power, or even speaker power when labeling the power, which is a very confusing parameter indicator.

    In addition, if we pay attention to the nameplates on some speakers, there is also a power related value on them. What is the relationship between this value and the output of the power amplifier? In the Software design description, we can see the following statements: "In order to ensure the safety of the loudspeaker system matched with the power amplifier, the rated output power of the power amplifier is required to be equivalent to the nominal power of the matched loudspeaker system", "In order to ensure sufficient power reserve, the power amplifier with 1.2~2 times of the loudspeaker power is usually selected", etc. This formulation is actually incorrect, as the power of a power amplifier is not the same concept as the power of a speaker.

    The output power of a power amplifier generally refers to the sinusoidal output power under certain distortion limitations. We usually see that manufacturers indicate that the specified Total harmonic distortion is 0.1% after the power. When the output signal of the power amplifier on the rated load reaches this distortion, the output voltage is called the maximum output voltage. Using this voltage to calculate the output power of the power amplifier is the nominal output power of the power amplifier, which can also be understood as the maximum output power of the power amplifier.

    The nominal power of the speaker, which is often provided by manufacturers, is the powder noise power, which refers to the power that is fed to the specified analog program signal within the rated frequency range of the speaker and operates continuously for 100 hours without generating thermal or mechanical damage. Obviously, these two powers were specified and tested from completely different perspectives, and the two are not comparable. If the manufacturer can provide the sinusoidal power of the speaker (referring to the power fed back when using a sinusoidal signal as the test signal), then the two are comparable.

    However, manufacturers generally do not provide this data. So, is there a certain correspondence between the powder noise power and sinusoidal power of the speaker? The answer is - no! The powder noise power and sinusoidal power of speakers are completely different for different structures, materials, and specifications of speakers, and the latter is also related to frequency. Therefore, it is not advisable to compare the power of the power amplifier with the nominal power of the speaker in the design of speakers and amplifiers to characterize their power reserve.

    Obviously, comparing the number of speaker power with the power of the amplifier is meaningless. From the previous text, you can also understand that the topics we are currently discussing, such as whether the power is sufficient and whether the power reserve is sufficient, can only be based on subjective listening experience. It is meaningless to look at the labels on the speaker because everyone‘s labeling methods are not standardized and the standards are different, so naturally there is no comparability.