The following items are commonly used to measure the technical indicators of amplifiers: output power, frequency response range, signal-to-noise ratio and distortion. Their specific meanings are as follows:

1, output power

The physical definition of power is the product of the voltage applied to the load resistance and the current it flows through. After mathematical transformation, the square value of the voltage applied to the load resistance divided by the load resistance is the power applied to the load resistance. The unit of measurement of output power is Watt (W), abbreviated as Watt. The output power of an amplifier is its ability to apply voltage to a load. The greater the output power, the greater the voltage applied by the amplifier on the fixed load resistance. In the multimedia speaker, the speaker is the load resistance, that is, the greater the power, the greater the volume. In electrotechnics, the commonly used power index is the maximum undistorted continuous power (RNS) or average power, which is also common in the instruction manual of multimedia speakers.

The meaning of RNS power is the product of the effective values of voltage and current measured at both ends of the load under a given distortion condition. The distortion values vary according to different grades of products, such as 1%, 3%, 5% and 10%. Generally, it is 10% in multimedia speakers and 1% in high-fidelity power amplifiers. There is also a common power rating in multimedia speakers-music power. Music power was originally used to measure the maximum dynamic power of an amplifier to a music signal, but its algorithm has not been defined in a standard, so it has become a commercial nominal and has no practical significance. Now really qualified products will not use this nominal. By the way, the higher the power of an ordinary amplifier, the higher the manufacturing cost. The RVS power of the media speaker amplifier in general area is about 5W, and the higher requirement is about 20W. Note: Subwoofer power amplifier is not included.

2. Frequency response range

We know that the audio signal that the human ear can hear is a transient signal with different frequencies, waveforms and amplitudes from 18HZ-20KHZ, so the amplifier must have a wide enough working band to amplify the audio signal well. Generally, the frequency band of the amplifier needs to cover the bandwidth of the audio signal. But the bandwidth of the amplifier is always limited. We usually call the frequency response range of the amplifier when the high-end and low-end gains of the frequency decrease by 0.707 times (-3dB) respectively under the specified power conditions. The frequency response range of an excellent amplifier should be 18HZ-20KHZ. Generally speaking, the frequency response index of the amplifier is relatively easy to achieve.

3, signal-to-noise ratio

The ratio of the output signal voltage of the amplifier to the noise voltage simultaneously output. That is, the signal-to-noise ratio of the amplifier. Usually expressed in English characters S/N, the unit of measurement is decibel (dB). The greater the signal-to-noise ratio, the smaller the noise mixed in the signal and the higher the sound quality. On the contrary, the playback quality will be worse. Signal-to-noise ratio is an important index of multimedia speakers. Only high signal noise and sound playback can be clear, clean and hierarchical. In multimedia speakers, the signal-to-noise ratio of the amplifier is required to be at least greater than 70Db, preferably greater than 80dB. Generally, the signal-to-noise ratio of high fidelity amplifier is required to be greater than or equal to 90dB.

Step 4 deform

Distortion is the comparison between the signal before amplification and the signal after amplification by the amplifier. The difference obtained after comparison is called distortion, and its unit is percentage. There are many kinds of distortion: harmonic distortion, intermodulation distortion, phase distortion and so on. What we usually call distortion is harmonic distortion. Harmonic distortion is caused by the nonlinearity of the amplifier. The result of distortion is that the output of the amplifier produces harmonic components that are not in the original signal, which makes the sound lose its original timbre. In severe cases, the sound will be broken and harsh. The distortion degree of harmonic distortion of multimedia speakers at nominal rated power is 10%, and the higher requirements should generally be below 1%. Harmonic distortion can be divided into odd and even times. Through experiments and analysis, it is found that odd harmonic distortion can make people fidgety, while a small amount of even harmonic can make the timbre better.

Measure the technical index of the loudspeaker.

The following items are commonly used to measure the technical indicators of speakers: carrying power, frequency response range, sensitivity, distortion and so on. Their specific meanings are as follows:

1, carrying capacity

The withstand power of the loudspeaker mainly refers to the average power of the signal allowed to be applied to the input end of the loudspeaker under the condition that the loudspeaker is allowed to have a certain degree of distortion.

2. Frequency response range

The frequency response range of the sound box refers to the frequency response width of the sound box that can play back the audio signal within the specified amplitude change range under the rated power state. Theoretically, the frequency response range of the speaker should be as wide as possible, at least in the range of 18HZ-20KHZ.

But in fact, this is problematic. First, limited by the listening environment. Because the low frequency signal to be played back is limited by the room volume. Secondly, it is limited by the size and volume of the speaker. The wider the frequency response range of three speakers, the higher the requirements for power amplifier, otherwise the shortcomings of power amplifier will be exposed by speakers. For example, if the high-pitched sound of the speaker is good and there is noise in the high-frequency part of the power amplifier, then we will hear the high-frequency noise we don't want to hear. Fourthly, a rule is obtained through empirical analysis. That is, when the product of the upper and lower limits of the high and low frequency response of the speaker is about 500 thousand, the sound will be better. For example, when the lower limit of one speaker is 25HZ, the upper limit of the high-end should be 20 Hz, and when the lower limit of another speaker is 40HZ, the upper limit of the high-end should be about 12KHZ. Of course, this article is only empirical and can only be used as a reference. The frequency range of multimedia speakers is generally 70Hz- 10KHZ(-3dB). The higher requirement can be around 50- 16KHZ(-3dB). Note: This frequency response range already includes ultra-low speakers.

3. Sensitivity

The sensitivity of a loudspeaker refers to the sound pressure level measured one meter in front of the longitudinal axis of the loudspeaker plane when the signal of 1W 1KHZ is input through the loudspeaker input terminal. The unit of sensitivity is decibel (dB). The higher the sensitivity of the speaker, the smaller the power requirement of the amplifier. The sensitivity of ordinary speakers is in the range of 85-90dB. The sensitivity of multimedia audio phase is slightly lower.

Step 4 deform

The distortion definition of loudspeaker and amplifier are basically the same. The difference is that the amplifier inputs electrical signals and outputs electrical signals, while the speaker inputs electrical signals and outputs sound signals. Therefore, the distortion of loudspeaker refers to the distortion of electrical signal conversion. The allowable range of acoustic wave distortion is within 10%, and the average human ear is basically insensitive to distortion within 5%.

The basis of sound quality evaluation

The ultimate goal of buying a set of multimedia speakers is to have good sound quality, so what is sound quality? How to evaluate the sound quality? Let's take a look at this knowledge.

1, the physical properties of sound

Sound is the feeling that the vibration of an object drives the air to vibrate, and then it is perceived by the human ear. Sound consists of the following elements: volume, pitch, timbre and tone.

Volume: Volume is the loudness of sound, which is the subjective evaluation scale of sound strength by human ears, and its objective evaluation scale is the amplitude of sound.

Pitch: Pitch is the tone, which is the subjective evaluation scale of the human ear, and its objective evaluation scale is the frequency of the sound.

Tone: Tone is the spectrum of sound. The human ear can not only distinguish the loudness and pitch of sound, but also accurately judge the tone of sound. For example, when violin and piano play notes with the same pitch, people can distinguish which is violin and which is piano sound according to timbre and tone.

Tone: Tone is the waveform envelope of sound. The harmonic composition of sound and the envelope of waveform, including the transients at the beginning and end of sound, determine the characteristics of sound. In people's habits, timbre is usually called timbre.

2. The auditory characteristics of human ears

The auditory characteristics of human ears refer to people's psychological response to sound signals. The auditory characteristics of human ears reflect the sensitivity of people to different frequency sound intensities. When the signal is small, the human ear is not sensitive to high-end (above 600HZ) and low-end (below 500HZ) frequencies, but is most sensitive to frequencies from 3000 Hz to 4000 Hz. And the lower the volume, the more obvious this feature is. People describe this characteristic as an equal loudness curve of sound, and there is often an equal loudness switch in audio equipment, whose function is to appropriately improve or compensate high and low sounds when the volume is small.

3. Dynamic range of sound

The dynamic range of sound is the range from the weakest sound to the strongest sound. The dynamic range of sound is also related to frequency. The maximum frequency range of dynamic range is 1000-6000HZ, and the measurement unit of dynamic range is decibel (dB). In nature, the pronunciation of every object or musical instrument has its dynamic range, so the dynamic range of audio equipment must be large enough to reproduce these sounds with high fidelity. Generally, the dynamic range of multimedia speakers is better than 60dB, while high-fidelity speakers require more than 90Db.