Mysterious Acoustic Guitar Buzz
A few weeks ago, I discussed a problem over email with someone. It was something I’d seen a number of times over the years so I thought it’d be worth getting into here too.
Some background first:
On an acoustic guitar, the bridge is typically glued to the guitar soundboard. Sometimes the string tension can begin to separate these parts. This often manifests as a lifting bridge — a gap develops at the rear of the bridge as the strings try to pull it from the body. If it's not dealt with, this glue joint can fail completely and the bridge can be pulled off the body completely. Never fun.
Pinless bridges (where the strings are not anchored through the bridge and soundboard and wedged in with bridge pins) tend to exacerbate this issue. Anchoring the string ball-ends at the rear of the bridge — above the guitar top — brings introduces a whole other kettle of physics.
So, guitar makers sometimes add some reinforcement to the glue joint. This is more common with pinless bridges but you'll find it on regular bridges too.
One or more small-diameter bolts/machine screws are installed through the bridge and guitar top. These are generally positioned near the rear of the bridge, where the lifting force is greatest. Outside, the bolt head is typically hidden in a counter-bored section and covered with an inlay disc — sometimes pearl(oid), to make a feature of it, or a darker plastic disc to disguise it.
Inside the guitar, a washer and nut are treaded on the bolt and tightened up.
And that brings me to the problem I opened with.
A guitar soundboard vibrates a lot. Over time, those vibrations can work the nuts loose. I’ve seen guitars with no nuts left (I like to imagine owners fishing small nuts out of the guitar and scratching their heads wondering how it got there).
I’ve also seen guitars with mysterious buzzes and rattles that worked hard to avoid being tracked down. Yep, you guessed it… rattling nuts and washers inside the guitar. When the nut is loose, but hasn't fallen off, that and the washer can make quite a buzzing as you play.
If you’ve a bridge like this and a weird buzz, it’s definitely worth checking to make sure all your bridge-bolt nuts are good and tight. Actually, if you’ve a bridge with reinforcing bolts, it’s worth doing this from time to time anyway. Those little bolts are doing an important job and you don’t want them becoming loose. If they become loose, your bridge might also become loose. Consider this regular, preventative maintenance.
An inspection mirror can make this a little easier but you can do this by feel. Look for those inlay dots at the back of your bridge and you’ll get an idea of how many bolts are present and where they’re located. Their ends will protrude from the guitar top/bridge plate inside. You should be able to feel if the nuts are nice and snug.
A word of caution. On guitars fitted with an under-saddle pickup, the pickup hook-up cable will also protrude from under the bridge. This can be delicate so be aware of it. Don’t go barging in with big ham-fists. 😉
If you do find a loose nut, getting it tight again can be a bit tricky. You may not have a nut driver or socket small enough. A small adjustable spanner/wrench can work but, while I wouldn’t normally recommend using a pliers for tightening nuts, I do find myself reaching for a small pair of pliers for this job.
The trick is that you’re just going to hold the nut securely with the pliers. The tightening will be done from the other end.
The inlays can generally be popped out relatively easily. If the nut is loose, you can use a small wooden block to butt against the end of the bolt inside the guitar. Then you can (carefully) push it up and this will often be enough to pop out the inlay. Use your other hand to apply some counter-pressure against the bridge area of the guitar top itself — this avoids stressing the top.
Alternatively (and a little safer if you’re unsure of the last method), you can use a sharp-pointed scribe or tiny screwdriver to work at the bridge around the disc so you can gain some purchase at the side of the inlay. Then you can lever it out.
Underneath, you’ll find the top of the bolt has a slot or Philips head. Gripping the nut inside and using a screwdriver from outside will get things good and snug. The inlay can generally just be pressed back into place.
As I write this, I’ve no idea why manufacturers don’t use some sort of Nyloc-type locking nut here. These things are subject to a lot of vibration and can use any help they can get to stay put. Next time I get one, I’ll try remember to check sizes and see if there are locking nuts available.
This article written by Gerry Hayes and first published at hazeguitars.com
