But just make the frequency band wider, okay? Various manufacturers and users who pursue the ultimate have higher requirements. Otherwise, just adding a subwoofer to a pair of bookshelf boxes can easily cover the frequency range of 30Hz to 20kHz, and the price is only tens of thousands of yuan, perhaps not yet. What they are considering is that the designed speaker should not only cover the audible frequency band of the human ear, but also achieve the perfect sound quality as much as possible. The word "perfect" is easy to write, but difficult to make, and how difficult it is depends on how perfect you want to achieve. Therefore, the design of the box, the selection of speaker units, the design and production of frequency dividers, and the selection of materials all need to be considered. Top speakers are even more cost-effective, so it is not surprising that the cost is not high.