Bass reflector, also known as acoustic inverter, was invented by Thuras in 1930. In its load, there is a sound outlet on a panel of the box, and there are many positions and shapes of the opening, but most of them are also equipped with sound pipes. According to Helmholtz's vibration principle, the relationship between the internal volume of the box and the sound guide hole produces a certain frequency of * * * vibration, which is called the anti-* * vibration frequency. The backward radiation sound wave of the loudspeaker is reversed by the conduit and radiated to the front from the sound outlet, and is superimposed with the forward radiation sound wave of the loudspeaker in phase. It can provide wider bandwidth, higher sensitivity and less distortion than closed speakers. In an ideal state, the lower limit of the low-frequency playback frequency can be as much as 20% lower than the vibration frequency of the speaker. This kind of speaker can reproduce rich bass with a small box, and it is the most widely used type at present.
The acoustic resistance loudspeaker box is essentially a variant of the inverted loudspeaker box. The sound-absorbing material or structure is filled in the outlet channel as a semi-closed box to control the inverted loudspeaker, so that it can be buffered, thereby reducing the anti-vibration frequency and broadening the bass playing frequency band.
The transmission line shell is named after the transmission line of classical electrical theory. There is a sound pipe made of sound absorption wall behind the speaker, and its length is one quarter or one eighth of the wavelength of low-frequency sound to be raised. Theoretically, it attenuates the sound waves from the back of the cone basin, preventing the sound waves from reflecting to the open end and affecting the sound radiation of the woofer. In fact, however, the transmission line loudspeaker has a slight damping and tuning function, which increases the sound output of the loudspeaker near or below the vibration frequency of * *, and reduces the stroke while enhancing the bass output. Usually, the sound tube of this speaker is folded in a maze, so it is also called a labyrinth or maze.
Drone cone speaker is a branch of bass reflex speaker, also called empty paper cone speaker. Published by Olson and Preston in 1954. Its opening and sound outlet are replaced by an empty paper basin (passive basin) without magnetic circuit and voice coil. The radiated sound generated by the vibration of the passive cone is in phase with the forward radiated sound of the loudspeaker. The air in the box and the passive cone support element * * * form a composite acoustic compliance and the passive cone mass to form resonance, which enhances the bass. The main advantages of this kind of loudspeaker are that it avoids the unstable sound generated by the reflection sound hole, and can obtain good sound radiation effect even if it is very small, so it has high sensitivity, can effectively narrow the working range of the loudspeaker, has little standing wave influence, and has clear and transparent sound.
Coupled-cavity loudspeaker is a box structure between closed type and bass reflex type, published by Henry Langyu 1953. Its output is output by a sound hole driven by one side of the cone basin, and the other side of the cone basin is coupled with a closed box. The advantage of this kind of speaker is that the amount of air pushed by the speaker is greatly increased at low frequencies. Because the coupling cavity is a tuning system, when the motion of the cone is limited, the output of the sound outlet does not exceed the sound output of a single cone, which broadens the low-frequency playing range, so the distortion is reduced and the power is increased. The A A S W (Acoustic Subwoofer) speaker published by Chuan Dao Kohiko of Lo-D in 1969 is a coupled cavity speaker, which is suitable for reproducing bass without distortion with a small-caliber long-stroke speaker.
Horn-shaped housings are mostly in the form of folding horns for home use. Its horn mouth is coupled with a large air load, and the diameter of the driving end is very small. The back of this speaker is completely sealed, and the pressure in the box cavity is as high as the back of the speaker cone. In order to keep the pressure balance before and after the cone basin, an inverted horn is installed in front of the horn. Folding horn speaker is a derivative of inverted speaker, and its acoustic effect is better than closed speaker and general bass reflex speaker.
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I hope my answer can help you.