Guitar Cavity Shielding — Project Smash

Mike Foster
Mar 30, 2019 · 5 min read

Guitar pickups, of course, are built to — wait for it — pick up noise. As a guitar player, I’m assuming you really just want your pickups to pick up intentional noises that you make with the strings of your guitar. Unfortunately, depending on the environment you’re playing in, there’s potentially lots of noise pollution that can cause interference and result in persistent humming. Shielding the cavities of your guitar may help to reduce this hum and improve the overall sound of your guitar.

Of course I say “may help” to cover my ass a little bit here. As with most things related to guitars and the sounds they make, there’s lots of debate on whether shielding actually makes a difference. I would love to take a scientific approach to answering this question in the future. However, my personal take on it is that I can’t see how shielding wouldn’t have an impact. There’s so many different types of signals around us all the time, from cellphones to the electrical noise from fluorescent lights. Some argue that shielding doesn’t help because you can’t make a Faraday cage due to the fact that the pickups must remain exposed. My professional experience as a software engineer that’s worked on mobile devices for 15 years tells me otherwise. One thing we often have to do is test what happens when the phone loses its signal. The way we would do this is by wrapping the phones in tin foil. I know, really high tech stuff we’re talking about here. It’s true that if we didn’t fully wrap the phone, the signal would not be lost. Even the smallest opening would allow the phone to maintain its signal. However, the signal does weaken drastically in those cases, often going from four bars down to one bar. So, even though you won’t be able to remove all interference, I do think you can drastically reduce it. And, I think that’s all anyone is claiming when it comes to shielding guitars. With that said, here’s some learnings from my own experience…

Things you need

Here’s the list of things I used in shielding Smash.

  1. Copper Foil Tape
  2. Scissors
  3. An X-Acto Knife
  4. A pencil
  5. A Multimeter

There’s a few different options for shielding. As I mentioned above, tin foil can work. I’m not sure how well it would work. You would need to provided your own adhesive. And, it might not look that great from an aesthetics stand point. But, it could work, if you had no other options. There’s a conductive shielding paint that you can buy. I’ve never tried this myself, as it’s a pretty expensive option, especially relative to my preferred option, copper foil tape. Copper foil tape works great. It’s pretty easy to work with, and it’s cheap. It comes with its own adhesive that doesn’t impact conductivity. And, it looks pretty cool. I bought my tape from The Art of Tone, which had the cheapest price I could find.

Note, for Smash I ended up using about six feet of shielding tape. I haven’t done enough guitars to know if this is the norm or if my approach was wasteful.

It should be obvious why the scissors and X-Acto knife were necessary. The pencil might not be so obvious. I actually used the eraser of the pencil for applying the tape in tight spots and corners. It works much better than my fat fingers.

Finally, the multimeter allows you to check for continuity. How this works is that the multimeter sends a current through its probes. You then touch the probes to different points of the shielding. This should close the circuit, meaning the current can flow from one probe to the other. When the circuit is closed, the multimeter will register this. On my multimeter, there’s an audio mode. When the circuit closes, the multimeter beeps. If you come across a spot where the circuit doesn’t close, this mean you have a hole in your continuity. You’ll need to go back and patch your shielding.

It’s important to maintain continuity across the entire shielding, to ensure no interference is leaking through. So, make sure to check for continuity early and often.

WARNING: Copper shielding tape is sharp

As you can see in the video I posted, I actually cut myself while shielding. This occurred when trying to smooth the tape near the edge. The eraser of the pencil probably would’ve helped to avoid this.

Over Hang the Cavity’s Edge

Not only are you shielding the cavity, you need to shield the cavity cover too. Having an aluminum pickguard, I was able to skip this step, I think. The anodizing might actually be non-conductive. I need to research this a bit more, maybe perform a few experiments. Regardless, we want to maintain continuity between the cavity shielding and cavity cover shielding. That’s why it’s important to slightly over hang the edge of the cavity. Just make sure your over hang is still hidden under the cavity cover.

Strip Size is Key

There’s lots of different angles to guitar cavities. The characteristics of the angle you’re working on should determine the shape and size of the piece of tape you’re placing. Trying to force a wide strip into a tight corner is going to be tough and probably not look great. Cutting a couple of narrower strips might have better results.

Peel Slooowly

This seems like a dumb thing to point out, but what I noticed when peeling the copper foil tape from its backing is that if I peeled it too fast it actually springs back, resulting in a rolled up piece of tape. You might’ve guessed that it’s a huge pain to unroll the tape in this situation. The video I posted shows my immediate struggles because of this. Just be aware.

The overall process took me about an hour and 45 minutes. It’s a pretty tedious process, though I actually like it. It scratches the obsessive, detail oriented part of my brain. As I mentioned, I created a video of my process, that I’ve embedded below. Feel free to check it out.


Guitar making and other misadventures.

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