Multimedia speakers usually come with a manual, which indicates various parameters of the speakers, but for most users, these parameters may be the same as the heavenly book. In fact, there are many things that have been neglected intentionally or unintentionally in advertising or soft publicity. Let's explain them one by one below.
1 Speaker indicators
The power parameter is actually a basic parameter to measure the performance of a multimedia speaker, but because of the manufacturer's intentional avoidance, power has become a meaningless parameter in the description of many products.
The marked power of multimedia speakers are mainly as follows:
1. Rated output power (RMS): RMS power can be said to be the only truly meaningful among all power labeling methods. It refers to the maximum power that the power amplifier circuit can continuously output within the rated distortion range. Also called "effective power". When we discussed the power amplifier circuit earlier, the power referred to generally refers to the rated output power.
2. Music output power (MPO): refers to the instantaneous maximum output power of the power amplifier circuit when the distortion does not exceed the specified range.
3. Peak music output power (PMPO): refers to the instantaneous maximum output power of the power amplifier without considering the distortion.
The latter two powers are actually meaningless, because their so-called "moments" are often a few milliseconds that are not audible at all. However, many manufacturers are in the hope of increasing the power of their products, and are often willing to use these two labels, especially PMPO power. Most of the speakers with hundreds of watts in the market are like this, and some speakers even label their own power as 2000 watts!
This is a joke! A real 2000-watt amplifier and speakers are enough to make everyone in the community you live in can hear the music in your home. Even a real 300-watt speaker is enough to noisy the whole building. Is it a small desktop speaker? Can it be done? No wonder PMPO power is dubbed "JS power" by enthusiasts.
According to general practice, the ratio between PMPO power and RMS power is generally 5-8:1. That is to say, a speaker with a nominal output of 300W is actually just an ordinary speaker with an output power of about 30W!
The real famous brands will not use PMPO power. If the product is really good, why use this method of obscuring people's eyes? Therefore, seeing the PMPO logo at least shows that manufacturers are not confident in their products.
In addition to the power amplifier part, the power parameters in multimedia speakers also include the maximum withstand power of the speaker and the maximum output power of the power supply. The smallest of these three parameters is the maximum output power of the speaker. And there is a certain matching relationship between these three parameters. For example, the RMS power must be less than the maximum power of the speaker, otherwise the speaker will be burned out. The maximum output power of the power supply must be at least 150% of the RMS power, and the extra 50% is the so-called "power reserve", otherwise, the sound will be distorted at high volume or high dynamics (a large number of speakers on the market are This problem exists).
2. Frequency range and frequency response
These are two basic parameters that identify the sound restoration ability of a speaker. The former refers to the range between the lowest effective playback frequency and the highest effective playback frequency of the speaker, in hertz (Hz); the latter refers to an audio signal output at a constant voltage When connected to the speaker system, the sound pressure generated by the speaker increases or decays with the change of frequency, and the phase changes with the frequency. This relationship between sound pressure and phase and frequency is called frequency response. , The unit is decibel (dB).
Generally speaking, there are more frequency ranges marked on multimedia speakers, and the larger the range, the better the effect of course. But the problem is that many products are not labeled "frequency range of speakers", but "frequency range of power amplifier circuit". This leads to numerical values covering the range of human hearing, such as 20Hz-20KHz.
Of course, this is purely intentional to confuse the audience! The lowest playback frequency of the speaker can be calculated. According to the relevant empirical formula and the usual inverted design of multimedia speakers, even if the 8” speaker is used, the bass that can be played back is only 62.6Hz, using 6” or 4” It is as high as 80Hz or even above 100Hz. Below this frequency, its power will drop sharply, although the speaker is still moving, but no sound will be heard by people, that is, "only the bass is moving, but the bass is not heard. Come” phenomenon. Any sound that can be heard at this time is actually the noise produced by resonance!
In fact, the price of a speaker that can really emit 20Hz sound is probably enough to open a speaker manufacturer by ourselves. Therefore, when we see a manufacturer labeled "20Hz-20KHz", we can send it a sentence of "Go to XXX"...
Frequency response parameters are rarely provided by manufacturers. This may be because it is difficult to replace this parameter with other "similar parameters". However, some major manufacturers in the HI-FI industry, such as Hivi, still provide this chart. The frequency response chart is similar to the sound card frequency response chart of the previous issue, and the smoother the frequency response chart, the better the effect. But it should be noted that the speaker is not a sound card, it is impossible to have a straight horizontal line like a sound card, no matter how good a speaker, its frequency response is also a curve with a large curvature. But it should be as smooth as possible, there should not be any special peaks or troughs in the middle (this means that there is a special strengthening or weakening in a certain frequency band). And it should be as good as possible in the midrange. Shouldn't just consider the bass dive.
Distortion is the difference between a signal that has not been amplified by the amplifier and the signal after it has been amplified by the amplifier. The difference between the ratio of the amplified signal and the original signal is called distortion. The unit is percentage. That is, the degree of "sound staining" of the speaker to the signal. For multimedia speakers, a certain amount of distortion is not a bad thing, but it should be within a reasonable range. Generally speaking, the distortion of multimedia speakers should not be greater than 1%, and the subwoofer is more special, reaching 5%.
Fourth, the signal-to-noise ratio
The author thinks that there is nothing to explain. Generally speaking, the signal-to-noise ratio of multimedia speakers should be greater than 80DB, and the subwoofer should be greater than 70DB. Only speakers with a signal-to-noise ratio greater than 90DB are qualified to call themselves "quasi-HI-FI speakers".
Sensitivity refers to the input signal that can produce full power output. The lower the input signal, the higher the sensitivity, and the unit is also decibels (DB). For every 3dB difference in the sensitivity of the speaker, the output sound pressure will be doubled. Generally speaking, multimedia speakers mostly refer to input signals that can produce full power output. The lower the input signal, the higher the sensitivity. For every 3dB difference in the sensitivity of the speakers, the output sound pressure will double. Multimedia speakers are mostly high-sensitivity speakers above 90DB, because the power of the input sound source is very small. However, the increase in sensitivity comes at the expense of sound quality. The higher the sensitivity, the more distortion and noise can be heard. Therefore, some high-end multimedia speakers use low-sensitivity designs, but they have virtually increased the requirements for sound source equipment.
This concept is more complicated. To put it simply, the vector sum of the resistance, inductance, and capacitance (resistance, inductance, and capacitive reactance) in a circuit is the impedance. The unit is the same as the resistance value, which is also an ohm. The impedance mark in the speaker generally refers to its line input impedance. Generally, the input impedance of multimedia speakers is between 4 ohms and 16 ohms, but there are also larger ones. For multimedia speakers, the higher the impedance, the better the sound quality of the speakers, but the harder it is to drive them.