According to the working principle of the speaker, we know that the energy of the speaker radiates sound waves outward through the front and back vibration of the paper cone: when the paper cone moves forward, the air in front of it is compressed and the air behind it becomes sparse; when the paper cone moves backward, The situation is just the opposite. In this way, the sound waves before and after the direct injection will propagate around with a phase difference of 180°. At this time, when the sound wave behind the low basin is diffracted to the front of the direct spray, it will cancel each other out with the sound wave in front, and the energy of the radiated sound wave will be weakened. This situation is called "sound interference" phenomenon. The phenomenon of "sound interference" will worsen the frequency characteristics of the speaker. At low frequencies, the sound interference is more serious. Therefore, the cone speaker generally cannot be used directly exposed to the air, but is always installed in the speaker box.
The speaker box is also called a sound box, which is an acoustic device that assists the speaker to radiate sound, especially to better radiate low frequency sound. It is composed of a cabinet, one or several speaker units, sound-absorbing materials, frequency dividing circuits and other components. So we sometimes call it "speaker system". If we compare the speaker to a "good horse", then the speaker box is a "good saddle". Only a good horse with a good saddle can truly bring out the advantages of the speaker's high-fidelity sound reproduction.
In order to prevent sound interference, we can use open speakers to work. Open speakers, also known as baffles, are the simplest type of speakers. Its working principle is: a hard flat plate is extended from the periphery of the speaker cone to increase the blocking area, which is called a baffle, to isolate the inverted sound waves before and after the cone. The baffle makes the distance of the sound wave from the back of the paper cone to the front of the paper cone longer, and the attenuation is increased, thereby reducing interference and improving low-frequency characteristics. Therefore, the baffle of the speaker can reduce the sound distortion caused by the edge reflection of the speaker, so as to obtain a flat frequency response.
Cases and cabinets of early-produced radios, tape recorders, televisions, etc. can all be regarded as such speakers. In these machines, their speakers are often fixed directly on the cabinet to improve the sound quality.
This type of open sound box has the characteristics of simple structure, convenient use, and low price, but it also has disadvantages such as low work efficiency, bulky and unsightly shape. But because its low-frequency response is not ideal, it is rarely used in high-fidelity audio systems that require high sound quality.
The enclosed sound box is made by adding a back cover on the basis of the above-mentioned open sound box. Except for the mouth of the speaker cone, the speakers manufactured in this way are all sealed in the box. Sound-absorbing materials are required in the box to weaken the reflected sound waves. In this way, the sound waves radiated from the back of the speaker cone will not spread to the outside of the speaker, thereby reducing the interference with the sound waves in front of the cone and improving the bass sound quality.
Enclosed speakers are currently widely used speakers. It has the advantages of small size, convenient and flexible use, but its work efficiency is low. Many small audio systems currently use this speaker structure.