一 The term
Speakers, commonly known as speakers; the "Electronic Sound Dictionary" published in 1993 pointed out that a speaker is an electroacoustic transducer that can convert electrical signals into acoustic signals and radiate into the air.
According to relevant information, the earliest invention of the speaker In 1877, the German Siemens (D.W.Scimens) pointed out the patent for the prototype of the loudspeaker. He first proposed an electric structure consisting of a circular coil placed in the meridional magnetic field.
In 1924, American C.W.Rice and E.W.Kollogg invented electric speakers.
二 The speaker principle
An electromagnet is applied to the speaker to convert the current into sound. It turns out that current has a close relationship with magnetic force. Try winding the copper wire around the iron plate, then connect the small battery, you will find that the iron plate can suck the 4D clip. When a current passes through the coil, a magnetic field is generated, and the direction of the magnetic field is determined by the right-hand rule.
The speaker uses both an electromagnet and a permanent magnet. Suppose now that you want to play C (frequency 256Hz, ie 256 vibrations per second), the player will output 256Hz AC. In other words, the direction of the current will be within one second. Change, 256 times. Each time the current changes direction, the direction of the magnetic field generated by the coil on the electromagnet also changes. We all know that the magnetic force is rejected by the same level, and the poles of the coil are attracted. The magnetic pole of the coil is constantly changing. It is attracted to the permanent magnet for a while, and repulsively, generating 256 vibrations per second. The coil is connected to a film that pushes the surrounding air as it vibrates with the coil. The vibrating air is not the sound? This is the principle of motion of the speaker.
Third, the annual output of loudspeakers in the world is hundreds of millions. It has a wide range of uses in communication, broadcasting, education, daily life, etc. It has become something that people can't leave without being clothed, clothed, smashed, and milled. For the technicians who are engaged in the design and manufacture of loudspeakers, it is necessary to deepen the theory, practice and process of the loudspeakers and to have a comprehensive understanding of the system. Some people say that the speaker is very simple, but it is a small insect-killing technique. Anyone can produce a speaker. This can't be said to be totally unreasonable. Acoustics is a small subject, and the speaker is a small device. However, the threshold of production is not high, from a dozen to dozens of parts. The other side of the single problem is that the speaker is not easy to do.
The speaker is an electroacoustic device and is one of the contents of electroacoustic research. Electroacoustics is an interdisciplinary subject including electronics, acoustics, electromagnetism, magnetism, and the like. Although there are only a few dozen parts in the speaker, the complexity and complexity are far more than our imagination, because of the following:
(1) The speaker has more energy conversion levels and more feedback. The energy conversion of a device that is usually encountered is only one type. For example, an electric motor converts electrical energy into mechanical energy. The engine converts mechanical energy into electrical energy. Electric lights convert electrical energy into light energy. A battery converts chemical energy into electrical energy. What happens here is only the conversion of one energy to another. The speaker is different. He converts electrical energy into mechanical energy and then converts mechanical energy into electrical energy, which is not common in various converters. Its many levels and feedback naturally bring complexity and diversity to the system. Electrical part, acoustic part, energy and mechanical part (mechanical vibration part) exist in one speaker system
(2) The working state of the speaker is not only static but also vibration, and the vibration is in three dimensions. This three-dimensional vibration system has multiple boundary conditions, so its vibration analysis is extremely complicated, and general mathematical tools are not enough. The Dutch scholar Frankort et al. derived a cone differential equation with a simultaneous first-order differential equation of 14 variables, and the vibration of the loudspeaker is also related to frequency and time, in fact it is in a multidimensional space.
(3) The speaker vibration system is only a centralized parameter system in the low frequency region. The vibration system is no longer a rigid body when the frequency is increased. When analyzing the speaker, the equivalent electrical method is often used, and the speaker is regarded as an equivalent circuit composed of concentrated parameters. So we are familiar with circuit theory, so using circuit theory to analyze the speaker will be handy. When analyzing the vibration of the speaker, it is assumed that the speaker is a rigid body, so that it is relatively convenient to wash. However, the above assumption is only suitable for the ground audio segment. When the frequency is increased, the speaker is no longer a concentrated parameter component, and the speaker diaphragm will have split vibration. Therefore, in the high frequency band, the analysis derived from the rigid body vibration assumption is invalid, and the formula derived from the equivalent circuit fails.
The distributed parameter system is also characterized in that these discrete elements are not independent of one another. Specifically, each point on the diaphragm vibrates differently, and each point has a different amplitude and phase, and each point affects each other.
It can also be compared with the electronic technology we are familiar with, so there are electrical components (resistors, inductors, capacitors, transistors, integrated circuits...) that are familiar with the logistics performance, as well as familiar circuit principles. According to the circuit diagram, an amplifier can be assembled. The difference between these components, whether it is an experienced engineer or a fledgling middle school student, is limited. But for speakers and speakers, it's not that simple. Assembling speakers in the same unit, if the experience is different, there may be a considerable gap.
(4) The evaluation of the speaker depends not only on a large number of objective test indicators, but also the objective test indicators cannot fully summarize the quality of the speaker.
The objective test indicators of the speakers are as many as 10, and there is an increasing trend. Most measurements are required in the anechoic chamber. Although there are now computer-aided measurements, the measurement of the anechoic chamber is still not replaced.
The subjective evaluation of the speaker is indispensable, and the subjective evaluation is highly discrete. It often varies from person to person, from time to time, from place to place, from song to song, and consciously or unconsciously. The impact of a kind of psychological suggestion. The results of the evaluation depend not only on the cultivation, quality, and mental state of the listener, but the sound itself is fleeting. It is more difficult than other items that require subjective evaluation, such as tea evaluation, which involves psychoacoustics and physiological acoustics. , environmental acoustics, musical acoustics, mathematical statistics, etc.
(5) The speaker manufacturing process involves many fields of papermaking, chemicals, adhesives, metal processing, magnet manufacturing, etc., and its comprehensiveness and diversity are mentioned. Among them, the change of the speaker diaphragm material is particularly important. Only changing the material of the diaphragm under the condition of constant geometry, not only the objective test index will change, but also the subjective sound quality will change.
