2. Bass reflex speakers are also called inverted speakers. In its load, there is a sound outlet on the panel of the box. There are many positions and shapes of openings, but most of them are also equipped with sound pipes. According to the principle of * * * vibration, 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 sound wave radiated backward from the loudspeaker is reversed by the conduit, radiated forward from the sound outlet, and superimposed in phase with the sound wave radiated forward from the loudspeaker, which can provide a wider bandwidth, higher sensitivity and less distortion than the closed type. Ideally, the lower limit of the low-frequency playback frequency can be 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.
3. The acoustic resistance speaker is essentially a variant of the inverted speaker. The sound-absorbing material or structure is filled in the sound outlet pipe as a semi-closed box, which is controlled to reverse and buffer, so as to reduce the anti-vibration frequency and broaden the bass playing frequency band.
4. The transmission line speaker is named after the transmission line of classical electrical theory. There is a sound tube made of sound-absorbing wall behind the speaker, and its length is 1/4 or 1/8 of the low-frequency sound wavelength to be improved. Theoretically, it attenuates the sound wave from the back of the cone and prevents it from reflecting to the open end, thus 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 mostly labyrinth, so it is also called labyrinth or labyrinth.
5. Passive radiation speaker is a branch of bass reflex speaker, also known as empty paper basin speaker. Its opening and sound outlet are replaced by an empty paper cone (passive cone) without magnetic circuit and voice coil. The radiation generated by the passive cone vibration is in phase with the forward radiation sound of the loudspeaker. The composite acoustic compliance composed of the air in the box and the passive cone support assembly resonates with the passive cone mass to enhance the bass. The main advantage of this speaker is that it avoids the unstable sound generated by the reflection sound hole, and can obtain good sound radiation effect even if it is small, so it has high sensitivity, can effectively reduce the working radiation of the speaker, has little standing wave influence, and has clear and transparent sound.
6. Coupled cavity loudspeaker is a box structure between closed and bass reflex. 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. Speaker is a kind of coupled cavity speaker, which is suitable for reproducing bass without distortion with small caliber and long stroke speaker.
7. Horn speakers are usually in the form of folding horns. The horn mouth of the horn adds a great air load to the mouth, and the diameter of the driving end is very small. The back of this speaker is completely sealed, and most of the pressure in the box cavity is on 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 loudspeaker is a derivative of inverted loudspeaker, and its sound effect is better than that of general bass reflex loudspeaker of closed loudspeaker.