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Technical parameters of active speakers

2021-04-15 47
There are many technical parameter items of active speakers, and the most meaningful for readers to choose and use are the following:

1: Power

Power can be said to be the most meaningful and most meaningless parameter. It is the most meaningful because it directly determines the maximum effective output sound pressure level (commonly understood as the maximum volume) and low-frequency quality of the speaker. And it is the most meaningless, because there are more than a dozen power parameters, and many manufacturers on the market have extremely abused the concept of "peak power", making the originally very reusable parameters meaningless. .

The power parameters related to active speakers mainly include the following:
(1) Power amplifier: The output power of the power amplifier is the one with the most changes (or tricky) among the various parameters. The output power measured by the same power amplifier is different due to different test methods. The common ones are the following.
●Rated output power: refers to the maximum power that the power amplifier can continuously output within the rated total harmonic distortion range. It can also be called effective value power or root mean square (RMS) power.
●Peak power (P max): Because the maximum value of the sine wave AC voltage is 1.414 times the effective value. Therefore, the peak power (P max) is twice the root mean square power (P rms).
●Music output power (MPO): refers to the instantaneous maximum output power of the power amplifier to the music signal under the condition that the output distortion does not exceed the specified value, referred to as MPO.
●Peak music output power (PMPO): refers to the instantaneous maximum power that a power amplifier can output without considering distortion. The peak music output power is generally 5-8 times the root mean square (RMS) power.

For users, the only real significance of the above output power is the rated output power. Only at this power, the power amplifier can output music signals continuously without (low) distortion. This is a real power. Generally not big. Because the output power is directly related to the cost, if many low- and medium-priced speakers are calculated by (RMS), their output power is really pitiful, and it lacks the temptation to unintelligible customers. Therefore, many manufacturers are evasive to the rated output power. Among these types of power, the most boring is the peak music output (PMPO) power. Its test conditions are relaxation of distortion restrictions and extremely short moments (usually measured in milliseconds). But in fact, who can stand the sound regardless of distortion, and what kind of music lasts only a few milliseconds? Therefore, for practical use, this power is meaningless, but it is madly abused by profiteers. No wonder some people call it JS (profiteer) power.

At present, most active speakers use power amplifier integrated circuits. Therefore, if you want to know the maximum output power of active speakers (refers to the power amplifier part, excluding the power supply), you only need to find out the model of the power amplifier integrated circuit used. The parameters of some commonly used power amplifier integrated circuits are listed below for reference:
Model Power (w) / Distortion / Impedance (Ω) Power / Distortion / Impedance Manufacturer's recommendation (5 stars)
TDA1521/2616 12 x 2 / 1% / 8 15 x 2 / 10% / 8 Philips ★★★
TDA2030A 12 / 0.5% / 8 18 / 0.5% / 4 ST ★★
TDA7269 10 x 2 / 10% / 8   ST ★★★
TDA7370 6.5 x 4 / 10% / 4   ST ★
TDA7294 70 / 0.5% / 8 100 / 10% / 8   ★★★★
LM1875 20 / 0.015% / 8 25 / 1% / 8 NS ★★★★
LM1876 20 x 2 / 0.1% / 8   NS ★★★
LM3886 50 / 0.1% / 8 68 / 0.1% / 4 NS   ★★★★
    Note: ST's original TDA2030A is a pretty good power amplifier IC, but most manufacturers use its compatible models, and the sound quality and reliability are not as good as the original products, so only two stars are given in the recommendation.

(2): The rated power of the speaker: No matter how high the power amplifier is, it is useless if the speaker can't bear it. This is also an important factor that restricts the actual output power of active speakers.
(3): The effective output power of the power supply: usually refers to the rated output power of the power transformer, which is a very important parameter. Because most power amplifier integrated circuits work in Class A and B status, the output power of the power amplifier generally does not exceed 70% of the output power of the power supply.

For an active speaker system, its output power is determined by the smallest one of the above powers (a typical bottleneck effect). If you can't find more information, you can also estimate the effective output power of the speaker based on the price of the speaker. According to experience, the effective output power of low- and mid-range (under 500 yuan) active speakers generally does not exceed one-tenth of their selling price (units are watts, not counted as slaughtered), and high-end (over 500 yuan) active speakers The effective output power generally does not exceed one-fifteenth to one-twentieth of its selling price. This empirical value is more accurate in most cases, because the trader who loses money will not do it. For general multimedia applications, speakers with 5-10 watts of power per channel are basically sufficient. If you have higher requirements for sound quality, it is recommended to purchase active speakers with more than 20 watts per channel.


Technical parameters of active speakers


2: Signal-to-noise ratio:
The signal-to-noise ratio refers to the ratio of the maximum undistorted output voltage of the power amplifier to the residual noise voltage. Its unit is decibels. It is a parameter reflecting the noise level of the active speaker, and it is also an important indicator of the design and manufacturing level of the active speaker manufacturer. Low-noise speakers may not necessarily sound good, but loud speakers must not sound good. The signal-to-noise ratio must be at least 75 decibels to have a good playback effect. You can unplug the signal cable and turn the volume to the maximum when purchasing. If there is basically no noise from 20 cm away, you can pass it.

3: Frequency range:
The frequency range of the sound that the human ear can directly hear is about 20-20000Hz. With today's speaker technology, there is no problem with high frequency reaching 20000Hz, but it is very difficult to extend the low frequency end to 20Hz without distortion. Most The frequency range of low- and mid-range active speakers is about 100-16000 Hz, and the frequency range of higher-end active speakers can reach 50-20000 Hz. Generally, active speakers with a frequency range of 80-16000Hz can be used for ordinary multimedia applications. If you have higher requirements for sound quality or used for movie appreciation, it is recommended to purchase the lower limit of the low frequency to extend to 40-50Hz, and the high frequency can extend straightly Active speakers up to 20000Hz. The frequency range parameters can be found in the product promotional materials, but the indicators of some manufacturers are seriously untrue. Some speakers with only one or two hundred yuan dare to mark the frequency range to 20-20000 Hz, but in fact they can be flat and unreliable. There are few pairs of speakers in the world that reproduce this frequency range with distortion, so don't take it seriously. Readers can bring some records that are rich in high and low frequencies and are familiar to them for audition judgment when purchasing, or they can use test CDs with standard frequency signals or test software such as "Davids Audio Sweep Generator" or "Audio100 Audio" of the short song line. Tester" audio tester software for testing.
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