The basic requirements of speaker box equipment

- Apr 10, 2018 -

In order to make a high fidelity voice in sound equipment such as pickup, sound amplifying, broadcasting and recording, we must put forward certain requirements for the performance of the audio equipment. Different audio devices have different functions, and their performance requirements are also different. Generally speaking, the performance of these audio devices should be weighed in terms of frequency range, dynamic range, distortion and SNR.

(I) frequency range

From the discussion of the last section, we know that different sounds have different spectral characteristics. Apart from the fundamental frequency, it contains a lot of homophonic sounds, so each sound has a certain frequency range, which we call the band width.

To propagate or record a sound signal perfectly, the audio equipment used must have a certain band width so that it can be transmitted or recorded in the frequency range of the sound.

Of course, when the signal is passed through the sound device, there must be a loss of some frequency components; especially the very high frequency harmonics, because they are beyond the frequency range allowed by the sound equipment, and when replayed, the sound is different from the original sound, that is, the distortion. If the distortion is very large, the voice we hear is obviously different from the original one, but if the distortion is not large, people will not be aware of it. Therefore, we usually put forward some specific requirements for the frequency range of the audio equipment in order to ensure the quality of listening. At the same time, according to the specific object and scope of use, we sometimes reduce some technical indicators to reduce the cost of audio equipment.

According to the characteristics of voice and musical frequency in frequency range, the corresponding frequency range of audio equipment is also different. For the voice transmission equipment, we need to improve the articulation of speech, so that the listeners can understand the speaker's speech. At this point, the high frequency section should be required to be wide enough. This is because the high frequency components in the voice are very weak, but they are the main components of some consonants. If the high frequency part is too narrow, it is not only harmful to the sharpness of the speech, but also the ambiguity of some words such as "three", "mountain", "four" and "ten". For example, the frequency range of a telephone is 300Hz-3400Hz, which concentrates most of the best in the voice. As far as the articulation of the voice is concerned, this frequency band is sufficient, but because its high frequency is not wide enough, it is difficult to distinguish some of the words. The bandwidth of the commonly used audio equipment should be larger than the bandwidth of the telephone system, such as the requirement to perfectly reflect the voice, and its frequency range should be no less than 8OHz-10000Hz.

In the transmission of musical sounds, the frequency range of various instruments is different, but to reflect the sound of various instruments, the sound equipment used must have a wide bandwidth. Usually, the bandwidth of this kind of audio equipment should not be less than 4OHz-15000Hz..

(two) dynamic range

The sound power of natural sound sources, such as voice and sound, is limited, but the sound power from different sound sources is different, its dynamic range is very large, and sometimes the sound power is very small, but sometimes it is very large. For example, in a symphony, for example, it is sometimes played only by a violin. It produces a very small sound power; sometimes a band plays together, and the sound power produced by them is very high. When the sound signals are converted from the microphone to the electrical signal and are further processed by other sound devices, this happens when the signal is very small, the signal may be confused with the inherent noise of the device, when the small signal is inaudible due to the noise disturbance; when the signal is large, the signal is likely to be caused by the loss of the signal. When the device cannot tolerate such a large signal, it produces truncated distortion and distorted voice.  These two situations are all we don't want to see. Therefore, a sound device should have a larger signal dynamic range. At the same time, in order to prevent small signal from being disturbed by noise, the minimum input signal amplitude should usually be determined.

In practice, a set of audio system is made up of several audio devices. At the same time, we should also pay attention to matching each other's input and output signals. If the output signal of the front stage equipment is too small, it is easy to mix with the noise to add to the input port of the post stage equipment, which reduces the signal to noise ratio of the signal. However, the output signal of the front stage equipment should not be too large, so as not to make the latter equipment fail to cause truncation distortion. Only if the input signal of each device is controlled within its dynamic range, can the output signal of the whole set of audio equipment be undistorted.

(three) distortion degree

In addition to having enough band width and dynamic range, the sound equipment should have the performance of small distortion, and the relative relationship between the frequency components of the signal should remain unchanged. That is to say, we must limit the linear and nonlinear distortion of the audio equipment.

The linear distortion index includes the amplitude of the audio device, the frequency response and the phase frequency response.

(four) signal-to-noise ratio

In addition to all kinds of distortion, noise is also a noticeable problem. We usually use signal-to-noise ratio to describe it.

Noise includes noise caused by power supply, 50Hz and its harmonics, and various components. The AC noise due to its low frequency of people's subjective feelings especially powerful.

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