Audible noise from transformers and inductors is a common complaint in consumer electronics, industrial equipment and residential power systems. The 50/60 Hz hum from line transformers, or the higher-frequency whine from switching power supplies, can make products uncomfortable to live with.
This guide explains why magnetics make noise, and the most effective ways to reduce or eliminate it.
Shaanxi SiRui Technology Co., Ltd. engineers design low-noise magnetic components for consumer and industrial applications. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Why Transformers Make Noise
Magnetostriction: magnetic domains in the core expand and contract with each AC cycle. Primary cause of 50/60 Hz hum.
Loose laminations or windings: vibrating against each other amplifies noise.
Switching frequency whine: 20–100 kHz switching, with harmonics falling into the audible range.
2. Line Frequency (50/60 Hz) Noise Reduction
- Tighter core clamping: compress core with clamps, bands or potting
- Toroidal cores: inherently quieter (closed flux, no gaps)
- Potting / encapsulation: epoxy or silicone dampens vibration dramatically
- Isolation mounting: rubber or silicone grommets prevent chassis vibration transfer
3. Switching Frequency Noise Reduction
- Fundamental above 20 kHz: moves into ultrasound, eliminating whine
- Low-magnetostriction materials: ferrites, powder cores, nanocrystalline
- Tight winding tension: loose windings vibrate
- Metal shield / can: contains noise
4. Noise Sources and Fixes
| Source | Frequency | Fix |
|---|---|---|
| Magnetostriction | 50/60 Hz + harmonics | Potting, tighter clamp, better core |
| Loose laminations | 100/120 Hz | Tighten clamps, varnish impregnation |
| Switching frequency | 20–100 kHz | Raise above 20 kHz, litz winding |
| Windings vibrating | Various | Tight winding, potting |
5. Sirui-Tech Low-Noise Design
- Tightly clamped cores with proper bands
- Toroidal core options for inherently quieter operation
- Potting / encapsulation for noise-critical applications
- Low-magnetostriction materials (nanocrystalline, powder cores)
Conclusion
Audible noise from magnetics is almost always caused by magnetostriction amplified by mechanical looseness. The most effective fixes are tighter clamping, potting, and choosing inherently quiet core shapes (toroidal). For switching power supplies, ensuring fundamental frequency above 20 kHz eliminates the most annoying whine.
Need a low-noise magnetic component? Contact Sirui-Tech at sales@sirui-tech.com with your noise requirement.