Why Shield the Cavities of Electric Guitars?

The sound produced by an electric musical instrument, such as a guitar, results from a chain of components and devices. This chain is susceptible to interference and noise. These interferences come from surrounding electronic devices or faulty electrical installations and can degrade the audio signal quality. For musicians, achieving an undistorted audio signal is crucial. This is where shielding becomes an essential solution, crucial for preserving audio quality. Why and how are electric guitar cavities shielded?

The Principle of Shielding

What is the Purpose of Shielding?

The goal of shielding is to preserve and transmit the guitar’s pure signal, without loss, alteration, or noise, from the instrument to the amplifier. It aims to minimize or eliminate external noise interference not inherent in the instrument’s audio output. This is achieved within the electric guitar’s cavity. The interior cavity is enveloped with conductive materials creating a protective barrier. This principle is analogous to Faraday’s Cage.

Shielding applies to all electric instruments. While this article focuses on electric guitars, electric cellos and electric violins also require this process.

What is Faraday’s Cage?

A Faraday cage blocks electromagnetic fields. It’s a completely enclosed and airtight barrier against interference. The principle relies on the redistribution of electric charges within the Faraday cage material. Therefore, interferences do not reach the components inside the cavity; they are neutralized upon encountering the conductive material. Faraday cages are used to protect equipment sensitive to interference. The name “Faraday” is a tribute to Michael Faraday, a British physicist extensively involved in 19th-century electromagnetic and electrochemical industries.

How to Shield a Guitar or Any Other Musical Instrument?

Identifying the Problem Source

This is a crucial step before shielding a musical instrument. If you experience no interference problems, shielding your guitar is unnecessary. If that is not the case, troubleshooting is required. Analyze all elements in the audio chain to identify sources of unwanted noise. Here are some troubleshooting steps:

• Connect the guitar directly to the amplifier, without any other components, and lower the guitar’s volume. Does the amplifier produce humming?
• Are the interference noises constant or only present in your studio or rehearsal room?
• Are the interference noises present even when the guitar’s jack cable is unplugged?
• Does the noise still occur if you listen through headphones connected to a pedal board or effects processor output?
• Does touching certain parts of the guitar cause the noise to disappear?
• Are the noises still present even with high-quality new cables?

Troubleshooting often involves eliminating components until the interference source is isolated. Multiple contributing factors are common. These problems can appear after years of guitar use; a weak solder connection or a loose wire can sometimes introduce parasitic noise.

How to Shield Your Guitar?

This article focuses on shielding the instrument. If other equipment is generating the noise, contact that manufacturer’s customer service.

What Needs to Be Shielded?

On electric guitars, electrical components are often clustered in a cavity. A Faraday cage around these components improves the signal-to-noise ratio, addressing guitar-produced noise. Conductive materials are inserted within the cavity to create a barrier, redirecting external interference away from these components.

Any cavity housing a component should be shielded. However, not all are. Pickups, potentiometers, and pickup selectors are cavities that often need shielding. Inadequate shielding can introduce buzzing. Completely perfect shielding is not always practical. For example, the pickup cavity is open and can’t be a perfect Faraday cage. However, shielding it to some degree can reduce interference.

Materials Used

Various conductive materials are suitable. Effective shielding depends on the material’s thickness and type. Magnetic paint, graphite, copper foil or tape, nickel, and aluminum are common choices. The critical factors here are shielding effectiveness, installation time, and cost-effectiveness.

Conductive paints are frequently used on entry-level models. They typically include copper, graphite, and silver, sometimes mixed with other materials. The luthier applies several layers to the interior of the cavity to create a Faraday cage. Copper tape or foil are also common applications; they’re placed inside the cavity and over the pickguard to achieve full coverage. Ensuring proper contact with the pickguard material is critical. Clean, well-planned internal wiring with consistent wire lengths follows.

Some luthiers use custom-cut aluminum sheets for enhanced shielding. Heavier materials, like iron, are less common due to added instrument weight, especially impacting instruments played on the shoulder (e.g., violins). Shielding shouldn’t significantly increase the instrument’s weight.

Checking the Shielding

Continuity testing with a multimeter verifies shielding effectiveness.

1. Turn on the multimeter and select the ohmmeter function.
2. Touch the probes to two different shielded areas; you should read 0.00 ohms.
3. Test various points on the shielding.

Remember to re-test after reassembling the guitar to ensure all metallic components are connected: the output jack to the shield, the pickguard to the shield and so forth.

Grounding

Effective shielding requires grounding. Without grounding, shielding is ineffective. This involves a metal washer and screw. Screw the washer through the shielded cavity wall, solder the screw wire to the guitar’s ground, and then check using a multimeter. If your chosen screw is painted, ensure you remove the paint from the screw’s metal head to ensure good contact with the wire.

Where Does Noise Come From?

This encompasses a broad range of potential sources. Interference can arise under various conditions. Every element in the audio chain can contribute to signal degradation.

The electrical system of an electric guitar is exposed to ambient electromagnetic radiation. The main elements generating a guitar’s signal (pickups, potentiometers, jack input, wiring, etc.) are sensitive to interference from nearby radio systems, mobile phones, transformers, dimmers, Wi-Fi networks, etc. This interference pollutes the signal, potentially degrading audio. One example is when a local radio station’s signal is picked up by the guitar’s amplifier.

Magnetic pickups, especially single-coil pickups, are particularly susceptible to magnetic interferences — this has fueled invention of humbucker pickups, designed precisely to minimize noise issues.

Shielding electric guitar cavities is more than a technical enhancement, but is essential for delivering clear, high-quality sound without interference and eliminating unwanted buzzing and noise. It’s a critical part of constructing and maintaining electric musical instruments and is relevant to any musician seeking to refine the signal quality. A luthier or any advanced musician can perform this maintenance.