25 kHz vs. 40 kHz: How to Choose the Right Ultrasonic Frequency?

Published: March 2025 | By LeelaSonic Technical Team

When buying an industrial ultrasonic cleaner, the most confusing specification for many engineers is the Frequency. You will often see machines listed as 25 kHz, 33 kHz, or 40 kHz. But does it really matter?

The short answer is: Yes. Choosing the wrong frequency can either damage your delicate parts or fail to clean your heavy parts effectively. In this guide, LeelaSonic explains the simple difference so you can buy the right machine.

Understanding the Basics: Bubble Size

Ultrasonic cleaning works by creating vacuum bubbles (cavitation). The frequency determines the size of these bubbles.

• Low Frequency (25 kHz) = Large, powerful bubbles.
• High Frequency (40 kHz) = Small, gentle bubbles.

Think of it like this: 25 kHz is a sledgehammer used for demolition, while 40 kHz is a scrub brush used for detailed cleaning.

When to Choose 25 kHz (The Heavy Lifter)

A frequency of 25 kHz creates high-energy shockwaves. It is aggressive and designed for heavy industrial contaminants.

Best Applications:

• Cast iron engine blocks.
• Heavy steel gears with thick grease.
• Removing rust, carbon deposits, and paint.
• Large injection molds.

Warning: Do not use 25 kHz on delicate items like electronics or aluminum with a mirror finish, as it may cause "pitting" (tiny holes) on the surface.

When to Choose 40 kHz (The Universal Standard)

This is the most common frequency used in 90% of industrial applications. It offers a perfect balance of power and penetration. The smaller bubbles can enter tiny blind holes and threads that larger bubbles cannot fit into.

Best Applications:

• PCB & Electronics: Removes flux without damaging soldering.
• Surgical Instruments: Cleans blood and tissue from box joints.
• Jewellery: Safe for gold, silver, and diamonds.
• Precision machined parts with complex geometries.

Quick Selection Guide

Can I Have Both?

Yes! For facilities that handle diverse parts, LeelaSonic manufactures Dual-Frequency Generators. These allow you to switch between frequencies depending on the load.