Labyrinth speakers are also called tortuous speakers or transmission line speakers. The most common one is TDL speakers made in the UK. There are many products on the market. This kind of sound box is made of a rectangular cross-section folded reflection pipe behind the paper cone of the speaker unit, which is coupled with the surrounding medium. The cross-sectional area of the sound reproduction pipe is generally equal to the effective area of the diaphragm of the speaker unit. The design of this structural form of speakers is completely different from the traditional closed speakers and inverted speakers. There are two main points in the design of this type of speakers: First, the labyrinth speaker should be effectively controlled when working. The basic resonance frequency fo; The second is that the sound channel of the labyrinth system is required to increase the designed low-frequency lower limit frequency and energy.
The labyrinth speaker actually reflects the sound waves on the back of the speaker unit through a long pipe, and the length of the sound channel is the design focus of the labyrinth speaker. For a reasonably designed labyrinth speaker, when the horn unit is working, the radiated sound waves are in the opposite phase to the sound wave in front of the horn unit, and the sound channel in the labyrinth should be suppressed. When the radiated sound wave is in phase with the sound wave in front of the horn unit, the sound channel of the labyrinth speaker should play a role in improving. This is the main starting point of the labyrinth speaker. If the length of the sound tube is set to 1/of the radiated sound frequency 2 wavelengths, the phase will move, equal to 180 degrees. At this time, the sound wave released by the end opening of the labyrinth speaker sound channel will be in the same phase as the sound produced in front of the speaker unit. The same is true. If a sound tube is set The length of is 1/4 wavelength. The above formula is also valid, and can shorten the length of the sound tube. Generally, it is the correct way to design the labyrinth box. If you take 3/4 wavelength of the resonance frequency fo, or 3/4 wavelength of its double frequency, the output radiation will be reduced. This is because the radiation wave at the exit of the sound tube and the sound wave behind the horn unit are in opposite phase. Caused by the relationship. Therefore, the sound output at the resonance frequency fo is suppressed. The result of odd 1, 3, and 5 values.
If the basic resonance peak of the horn 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 a labyrinth speaker is generally to first measure the resonant frequency fo of the used speaker unit itself, and use the following formula to find the length of the sound pipe: sound tube length=n×344/4×fo……(1), In the formula, n is the odd value of 1, 3, 5, 7, and 344 is the speed of the sound wave. Substituting different odd values of n into the formula to see which value is close to the lower limit of the designed low frequency is the best value of n. The lower limit frequency of the labyrinth speaker can be obtained as follows: famp=2×fo/n…… (2) For example, there is a pair of JDL-8 speaker units at hand, and I 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 pipe:
1. When n=1, the sound tube length (m)=1×344/4×35=344/140=2.45m
2. When n=3, the sound tube length (m)=3×344/4×35=1032/140=7.37m
3. When n=5, the sound tube length (m)=5×344/4×35=1720/140=12.28m
Then use the formula to calculate the low-frequency lower limit frequency f amplifier you want to boost:
1. When n=1, famp=2×35/n=70/1=70Hz
2. When n=3, famp=2×35/3=70/3=23.3Hz
3. When n=5, famp=2×35/5=70/5=14Hz
From the calculation results, if n takes the value 1, the length of the sound channel is only 2.45 meters, and the structure of the cabinet is relatively simple, but the low-frequency dive can only reach 70Hz, which is not ideal. When n is set to 5, the low-frequency dive can reach 14Hz, but the length of the pipe has to be 12.28 meters, which is very difficult in structure and production, and it needs a large box to meet it, and the general 8-inch speaker The unit itself is also difficult to release frequencies below 20 Hz, and I cannot help if I want to use a long pipeline to increase it. Therefore, when selecting and designing the lower limit frequency of the labyrinth speaker, the low-frequency diving ability of the horn must also be considered. Only within the effective range of the horn unit, the labyrinth pipe has the lifting ability, which exceeds the diving range of the unit itself. The pipe cannot replace the speaker unit to emit low-frequency sound waves. Therefore, the length of the labyrinth sound tube is usually 1/4 wavelength equivalent to the resonant frequency of the horn. At this time, the acoustic impedance of the labyrinth sound tube is very large, and the voice coil movement range and nonlinear distortion of the horn unit itself are large. reduce.
Although the labyrinth speaker works well, its structure is relatively complicated, which limits its extensive development. When designing this kind of speakers, attention should be paid to reducing the adverse effects of the high-frequency harmonic oscillation frequency in the sound tube on the frequency response characteristics of the labyrinth system. Therefore, sound-absorbing materials should be applied to the sound tube. And strive to make the structure of each part of the speaker firm and reliable, and avoid the leakage of internal pipes. It is also required that the cross-sectional area of each part of the sound-emitting pipe should not be less than the effective area of the diaphragm of the speaker unit used.
Labyrinth speakers that can be seen on the market now include the British TDL series, designed and developed by the founder of the factory, John Wright. John Wright believes that although the inverted speaker can increase the low-frequency radiation energy to a certain extent, it cannot make the low-frequency dive deep. However, transmission line (maze) speakers can do this. We know that if you want to hear 20Hz low-frequency sound, the length of the room must reach about 17 meters, even if it is 1/2 wavelength, it must be at least 8 meters. There is rarely such a listening environment, and using labyrinth speakers to produce such a length can achieve such a feeling.
Labyrinth speakers also have shortcomings. The main thing is that the structure is cumbersome and complex, and the structure is too small to be realized. If the design is not good, it is easy to have too much low frequency and too fat. Because the sound wave has to travel a long section in the playback pipe The distance, therefore, gives a feeling that the low frequency speed is too slow, as if the low frequency drags a tail.