What is a transmission line subwoofer?

Like the transmission line type horn, it has a closed pipe with a large and small inside. The large one connects the back of the woofer and receives the back wave of the unit. The small one is the exit. The length of the pipe must be at least one quarter of the wavelength of the lowest cutoff frequency, and the inner wall of the pipe needs to be placed with appropriate sound absorbing material. The function of the pipeline is to use the back wave of the woofer to extend the low frequency cutoff frequency to achieve a lower frequency response. The advantage is that the low frequency can be extended downwards. The transmission subwoofer's cabinet manufacturing cost is the crown of all subwoofers, so it is even rarer on the market.