Microphone capsules are typically connected to the input of an amplifier, making them part of a sensitive circuit that can be easily affected by environmental electromagnetic interference, resulting in noise.
The capsule itself is enclosed in a metal housing that provides shielding, making it difficult for external interference to enter. However, the primary source of interference often comes through the signal wires connected to the microphone capsule.
Many engineers overlook the importance of selecting appropriate signal wires. Using two basic wires without shielding can easily introduce noise and electromagnetic interference into the system.
To reduce noise and interference, it's essential to use shielded wires-such as twisted pair cables or shielded cables.
1. Twisted Pair Cables
A twisted pair consists of two wires of the same specification twisted together like a braid. In general electromagnetic environments, twisted pair cables offer good resistance to high-frequency interference.
Why do twisted pair cables reduce interference?
When electromagnetic interference reaches the cable, opposing magnetic fields are generated on the positive and negative lines. Because the wires are twisted, the interference cancels itself out, effectively reducing noise.
The tighter the twist, the better the interference cancellation effect.
2. Shielded Cables
In environments with strong and low-frequency interference, twisted pairs may not be effective. In such cases, shielded cables are a much better choice.
A shielded cable consists of a metal layer wrapped around the signal wire. This metal shield is typically grounded.
When low-frequency interference-such as 50Hz power-line electromagnetic fields-hits the cable, it is blocked or absorbed by the outer metal shield. Since the shield is grounded, the interference is safely directed to ground, removing it from the signal path.
Shielding Quality
Not all shielded cables are the same:
- Low-grade shielded cables have loosely wound copper strands.
- Mid-grade cables use denser copper shielding for better protection.
- High-end shielded cables feature tightly woven mesh shielding that fully wraps the inner wire, offering the best noise protection-though they are more expensive.
