The horn in ultrasonic welding is tuned by adjusting its length and cross-sectional area to match the resonance frequency of the transducer. The tuning process involves adjusting the length of the horn and the position of the nodal point, which is the point on the horn that experiences the least amount of motion during ultrasonic vibration.

The tuning is usually performed by trial and error, where the length of the horn is gradually shortened or lengthened until the best amplitude and power output are achieved. Once the optimal length is determined, the position of the nodal point is adjusted by adding or removing material from the horn until the amplitude and power output are maximized.

In addition to the length and cross-sectional area, other factors that can affect the tuning of the horn include the material properties, temperature, and humidity. Therefore, it is important to re-tune the horn periodically to maintain optimal performance.