About Labyrinth Speaker

The labyrinth speaker actually reflects the sound waves on the reverse side of the speaker unit through a long pipe, and the length of the sound emission pipe is the design focus of the labyrinth speaker. A well-designed labyrinth speaker, when the horn unit is working, the radiated sound wave is opposite to the sound wave phase in front of the horn unit, and the playback pipe in the labyrinth should play a suppressing role. When the radiated sound wave is in phase with the sound wave in front of the speaker unit, the playback channel of the labyrinth speaker should play a lifting role. This is the main starting point of the labyrinth speaker. If the length of the sound tube is set to 1/1 At 2 wavelengths, the phase will move, which is equal to 180 degrees. At this time, the sound wave released at the end opening of the sound pipe of the labyrinth speaker will be in the same phase as the sound emitted in front of the speaker unit. The length is 1/4 wavelength, the above formula is also true, and can shorten the length of the sound tube, generally take the even value, is the correct way to design the labyrinth box. If you take the 3/4 wavelength of the resonance frequency fo, or the 3/4 wavelength of its frequency multiplication, the output radiation will be reduced, because the radiation wave at the outlet of the sound tube is in antiphase with the sound wave behind the horn unit Relationship. Therefore, the sound output of the resonance frequency fo will be suppressed. The result of odd 1, 3, 5 values.

If the basic resonance peak of the speaker unit of the designed labyrinth speaker is the same as the anti-resonance point of the sound tube, the low-frequency dive ability will be reduced to 1.33 times. The design of the labyrinth speaker is usually to first measure the resonance frequency fo of the horn unit itself, and use the following formula to find the length of the sound pipe: sound tube length = n × 344/4 × fo …… (1), Where n is 1, 3, 5, 7, and 344 of the odd value, and 344 is the speed of the sound wave. Substitute different odd values ​​of n into the formula to see which value is close to the lower limit of the designed low frequency, which is the best value of n. The lower limit of the replay frequency of the labyrinth speaker can be obtained by the following formula: f put = 2 × fo / n …… (2) For example, there is a pair of JDL-8 speaker units at hand. If you want to design a labyrinth speaker, JDL-8 It is an 8-inch unit fo = 35Hz. Use formula (1) to find the length of the playback channel:
1. When n = 1, the length of the sound tube (m) = 1 × 344/4 × 35 = 344/140 = 2.45m
2. When n = 3, the length of sound tube (m) = 3 × 344/4 × 35 = 1032/140 = 7.37m
3. When n = 5, the length of sound tube (m) = 5 × 344/4 × 35 = 1720/140 = 12.28m
Then use the formula to calculate the lower frequency limit f to be increased:
1. When n = 1, f put = 2 × 35 / n = 70/1 = 70Hz
2. When n = 3, f put = 2 × 35/3 = 70/3 = 23.3Hz
3. When n = 5, f put = 2 × 35/5 = 70/5 = 14Hz

From the calculation results, if the value of n is 1, the length of the playback pipe only needs to be 2.45 meters. The structure of the cabinet is relatively simple, but the dive at low frequencies can only reach 70 Hz, which is not ideal. When n is 5, the low-frequency dive can reach 14Hz, but the length of the pipeline must go to 12.28 meters, which is very difficult in structure and production, and it needs a large cabinet to meet, in addition to the general 8-inch horn The unit itself is also difficult to release frequencies below 20Hz, and you can't help if you want to use a long pipeline to upgrade. Therefore, when selecting the lower limit frequency of the labyrinth speaker, you must also consider the low-frequency dive ability of the speaker itself. Only in the effective range of the speaker unit can the maze pipeline have the ability to improve, beyond the unit's own dive range, the maze The pipeline can not replace the horn unit to emit low-frequency sound waves. Therefore, the length of the labyrinth sound tube is usually taken to be equivalent to 1/4 wavelength of the resonant frequency of the horn. At this time, the acoustic impedance of the labyrinth sound tube is very large, and the range of the voice coil movement and nonlinear distortion of the horn unit itself are reduce.

Although the effect of the labyrinth speaker is very good, the structure is relatively complicated, which limits its large-scale development. The design of this speaker should pay attention to reduce the adverse effects of the high-frequency harmonic oscillation frequency in the playback sound tube on the frequency response characteristics generated by the maze system. Therefore, sound-absorbing materials should be applied to the sound tube. And strive to make the structure of each part of the speaker sound and reliable, to avoid the occurrence of air leakage in the internal pipeline, and also require the cross-sectional area of ​​each part of the sound-emitting pipeline to be no less than the effective area of ​​the diaphragm of the speaker unit used.

The labyrinth speakers that can be seen on the market today include the British-made TDL series products, which were designed and developed by the factory's founder John Wright. John Wright believes that although the inverted speaker has increased the low-frequency radiation energy to a certain extent, it cannot dive deep into the low frequency. Transmission line (labyrinth) speakers can do this. We know that if you want to hear 20Hz low-frequency sound, the length of the room must be about 17 meters, even if the 1/2 wavelength is at least 8 meters, the average family is very Such a listening environment is rare, and such a length can be achieved by using a labyrinth speaker to produce such a length.

Labyrinth speakers also have shortcomings. The main reason is that the structure is bulky and complex, the structure is too small to achieve, and the poor design is prone to excessive low frequency and excessive fat, because the sound wave has to go through a long section in the playback pipe The distance, therefore, gives a feeling that the low frequency speed is too slow, just as if the low frequency dragged a tail.

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