《天工开物·中篇·锤锻》
声音分为高低两种，关键在于圆泡的厚薄及深浅的细微差别：一般而言，重打数锤的声调比较低，而轻打数锤的声调比较高。
声分雌与雄，则在分厘起伏之妙。重数锤者，其声为雄。
Sounds are divided into high and low, the key to the difference lies in the thickness and depth of the round bubble: Generally speaking, the sound created by hammering multiple times is lower, while the sound created by hammering a few times is higher.