Acoustic Guitar Tone and String Break Angle

String Break Angle at the Bridge #3: Acoustic

The top or soundboard of an acoustic guitar vibrates as you play. This moves the air inside the body and that moving air shoots out the sound-hole. I like to think of the top as being like an amplifier and the body as being like a speaker, moving the air out.

Of course that’s simplistic, but it’s a nice analogy to impress how important a role is played by that vibrating guitar top. The strings’ vibrations are transferred to the top which moves the air inside and gives the guitar its tone.

And that’s why it’s vital to ensure the strings’ energy is transferred as efficiently as possible.

Energy Transfer

There are a number of things that you can do to help get that guitar top moving. If you’ve got a cheaper, plastic saddle, a well-cut saddle from a material like bone can really be an upgrade for instance and you’ll get most bang for your buck from that. Many swear by different bridge pin materials but you might not hear as much ‘night-and-day’ difference.

Different string gauges (or types) can make a big difference. In my youth, I assumed that heavier strings would mean more tone (MORE TONE!!!) but that’s not always the case. Some tops react better to a lighter gauge of string and some will love heavier. Experiment — you might be surprised.

For now, though, we’re just going to consider the string angle.

Saddle Break Angle

If you’ve been following along with our discussions of string break angle over nuts and saddles, you’ll remember that it can be a really big deal.

The steeper the angle that the string ‘breaks’ over the saddle or nut, the more downward pressure it applies to that saddle or nut. Too steep can cause problems.

Aaaaannnd… Too little can cause problems.

Especially on acoustic instruments.

This saddle is far too low. See how some string barely contact it as they pass over.

You can see from the image above that some of the strings are barely touching the saddle, even tuned up to pitch.

This is a bit further gone than some, but there are many guitars out there with low saddles not far off this.

Such a shallow angle means the string won’t play cleanly and, importantly, can’t transfer its vibrations to the guitar top.

Bad news for tone.

Under-Saddle Transducer Output

The piezo pickups that sit under the saddles of many electro acoustic guitars depend on pressure to generate an electrical current. Without a solid, downward pressure from the strings onto the saddle, the UST pickups will not perform at their best and you’ll get a weak, noisy, or imbalanced output.

Piezo under saddle pickups need a healthy string angle over the saddle.

Acoustic Saddle Height and Action

Of course the issue is action. Usually the reason that the saddle is so low is to allow for a lower string height along the fretboard. Just raising the saddle will also raise the action.

Yep. And here, we’re in a similar situation to the same problem on an electric guitar. What we do to address the problem on an electric guitar is to remove the neck and shim it to change the angle it attaches to the body.

While that’s a relatively straightforward job on a bolt-on neck electric instrument, it’s a lot move involved on an acoustic. Neck resets are usually possible but tend to be more expensive. Other options exist, like shaving the bridge lower, but they’re not always possible or recommended.

Unfortunately, if an acoustic instrument is at or near the point in the photo above, you’ve got some tough decisions: live with it, raise the action, or reset the neck.

Ramping String Slots

It’s possible to alter the string slots (where the string exits the pin hole). Doing so moves the strings' exit a bit closer to the saddle, increasing its angle.

Cutting/increasing a ramp where the strings exit the pin-holes can improve string break angle

I generally use a Dremel tool with a couple of small bits for this but you can do it with a small saw or needle file too. Just be careful — it’s really easy to damage your guitar top if you get too fast and free, and accidentally pull the file out of the hole, stabbing the top with your next down stroke.

A Note on Bridge Design

Image ©Gibson Brands, Inc. Used for purposes of commentary. 

Image ©Gibson Brands, Inc. Used for purposes of commentary. 

Some bridges can really make this saddle break angle issue worse than it needs to be. Gibson’s moustache bridge, for instance frequently has the bridge pins located quite a distance back from the saddle. This distance makes for a shallower break angle over the saddle. Annoyingly, they then inlay two blocks of pearl between pins and saddle so you can’t even do the ramping trick.

There's less leeway to lower a saddle on instruments like this. I’ve seem more than a couple of Gibson Jumbos where that ‘live with it/raise action/reset neck’ decision was required much earlier than it should have been.