Understanding shielded audio cables: Their importance and applications

Designing an audio-visual system is not just about selecting and assembling equipment; it is also crucial to ensure the entire system operates stably and delivers the expected performance of each individual component. However, when these systems are installed in real-world environments such as theaters, churches, recording studios, concert halls, television stations, or conference centers, they often fail to achieve the desired quality.

The main cause of this issue is unwanted interference affecting audio signal transmission, primarily due to radio frequency interference (RFI) or electromagnetic interference (EMI) along the cable. In general, longer cables are more susceptible to interference, which can result in humming, static noise, or unexpected sounds in the output.

The fundamental function of an audio signal cable is to transmit audio signals from one point to another. However, beyond this primary role, the cable must also prevent unwanted interference from distorting the original signal. When selecting the right cable for an application, shielding capability is a critical factor to consider. The most effective solution to combat RFI and EMI is to use shielded audio signal cables.

>>See more: A glance at audio cables

Shielding is a technique used to control electromagnetic interference (EMI) by preventing unwanted noise from reaching the receiving device. Shielding layers can be applied at the signal source, the receiving device, or anywhere along the signal transmission path. In the case of electric field interference, the effectiveness of shielding depends on factors such as thickness, electrical conductivity, and the continuity of the shielding material.

In shielded audio cables, the shielding layer protects the conductor - where the audio signal is transmitted - from external interference. This shielding is typically made from copper strands and also serves as a grounding path to minimize noise. Before choosing an audio cable, it is essential to understand the different types of shielding available to ensure the cable meets your specific application needs.

Shielding can be applied at various levels within an audio-visual system, from small circuit components to large-scale setups such as shielded rooms. Regardless of the size or application, the fundamental physics of shielding remains the same. Proper shielding techniques effectively reduce interference, ensuring that audio and video signals are transmitted with the highest possible quality.

3.1 Braided shield audio cables

A braided shield protects audio signal cables by surrounding them with interwoven copper strands. This shielding type offers several advantages:

• Flexible coverage: The shielding coverage can be adjusted by changing the braiding angle, strand count, and weave density. Coverage typically ranges from below 50% to nearly 97%.
• Uniform shielding: The consistent coverage effectively blocks radio frequency interference (RFI), which has very short wavelengths and can penetrate some other shielding types.

However, braided shielding also has some drawbacks:

• High production cost: The braiding process is complex, requiring specialized machinery operating at low speeds, increasing manufacturing expenses.
• Lower flexibility: The woven shield reduces cable flexibility, making it more prone to damage if twisted or bent sharply.

Due to its limited flexibility, braided shield audio cables are commonly used in fixed installations and recording studios, where cables are less frequently bent or twisted compared to live event applications.

3.3 Foil shielded audio cables

A foil shield provides maximum shielding coverage of up to 100%. This is achieved using a thin layer of aluminum foil backed with Mylar, combined with a copper drain wire for grounding.

Advantages:

• Complete coverage (100%): Offers maximum protection against electromagnetic interference (EMI) and radio frequency interference (RFI).
• Highly effective at high frequencies: Due to metal-to-metal contact, foil shielding is particularly effective at blocking high-frequency interference.
• Lightweight and cost-effective: The use of a thin aluminum layer makes foil shielding lighter and more affordable than braided or spiral shields.

Disadvantages:

• Limited flexibility: The copper drain wire makes the cable stiffer, reducing its ability to bend easily.
• Prone to damage from repeated bending: Continuous bending or twisting may cause the thin aluminum foil to tear or lose continuity, reducing its shielding effectiveness.