What defines the loudness of an acoustic guitar?

Question

I would like a loud sound without any amplification (purely acoustic sound). Which guitar traits affect it? Do you recommend any particular styles or brands of guitar?

I assume that guitars with heavier strings and bigger body are usually louder. Are there any other criteria, like the wood, its thickness, or the bridge? Which guitar bodies are designed specifically for louder sound?

I know, that the loudness doesn't really matter, other things like intonation and tone are surely much more important, but I'm currently interested in it.

What are your experiences?

Answer 1

M. Werner is close, I think, but not quite there. More important than the volume of air per se, is the pressure differential between the compressions and rarefaction of the air and the surface area over which the kinetic transfer takes place. It's all about the top: the "drumhead" of the guitar. A larger top will hit more air as it rises and pull more air as it falls. A softer wood will beat the air harder by offering less resistance to the source vibration.

The trade-off happens because if the wood is too soft won't endure the stress of the vibration. It shakes itself to pieces. But if the wood is too hard it won't vibrate with sufficient amplitude. Various coatings including chitin from crusteceans permit a softer wood without losing structural integrity.

So for maximum volume you want large dimensions (particularly the top), and as soft a wood as will endure the tension.

Also, strings with greater mass will transfer more energy to the top. There's a brand called D&R (perhaps, others too) that has a "compressed" string. The make .030 gauge wrapped string by taking a .032 (or higher) and then squeezing it down to .030. It bends like a .030 'cause it's at normal tension, but the increased mass means more signal.

But beyond that are flatwound strings, which lose a lot of the upper harmonics. You do get more of the fundamental, but those upper harmonics carry most of the "volume" because higher pitches achieve greater sonic intensity (in the act of hearing) at the same physical intensity. If you have a Bass singer and a Soprano yelling at the same volume, you can hear the Soprano from farther away. That's just the way human hearing works, it's not in the physics.

The same mass argument would tend to suggest that strings with larger atomic mass would transfer more energy. But then elasticity comes in and I don't understand that part.

Answer 2

The more air you move, the more volume produced. So generally, bigger guitars, the dreadnaughts and jumbos, tend to have the most volume. However, that's not always the case; and there are many other factors that can contribute to the instrument's overall tone. Construction, wood types, bracing styles... The loudest guitar I ever heard was a pre-war Martin D28 at a fiddle contest. Everyone was playing unamplified, and that guitar cut through the rest of the combo with amazing power.

Sheer volume isn't much prized by most acoustic players, however. It's the quality of the tone and the overall balance. Many of those big guitars tend to be bass-heavy and "thumpy".

Many years ago, before electronic amplification was available, the way street performers went for more volume was the resonator-type guitars. That's why they were originally invented.

Answer 3

Cutaway guitars are quieter than guitars with standard bodies. If loudness is your priority, then forget about the cutaway feature.

Answer 4

And...

And string "action" - higher action is louder. And the angle at which the string attaches to the body (as in Millenial style guitars) - a greater angle is louder. And the place at which you pluck the strings - this varies (by guitar and by individual string) but the string is usually louder near the double-octave harmonic next to the sound hole. And your plucking technique - several nuances can render louder results. And the shape and smoothness of your nails/pick. And the placement of the guitar against your body (which muffles the vibrations) - the guitar is usually louder if there is less surface area contacting the body, and these contact points primarily a corner joints. And the mass on the soundboard - usually the vibration is better/louder if there is less (or no) metal used on the bridge. And your playing style or position on the neck - open strings tend to be louder than fretted strings. And the distribution of the mass across the neck (as in the use of a headstock weight to rebalance the mass) - sometimes fretted notes can be made louder by placing a certain weight on the headstock. And the rigidity of the bridge and nut - bone tends to be louder than plastic. Etc.

Answer 5

I’m NOT a luthier! Don’t rely on my advise on this. But, I have read that the higher the strings are from the guitar’s top, the louder it will sound. This seems to me to mean:lousy action = more volume.

There are those who maintain that a sound post will not only make the guitar louder to the player (which I KNOW is true) but also increase the overall volume “out front.”

The Santa Cruz website describes a technique of (once you have installed new strings) loosening one or more of the wrapped strings, taking the ball end out of the saddle, and twisting it 2 or 3 times to tighten the wrap. (Roll the ball end toward you and re-install.) This is said to add brightness and is useful for making quieter strings stand out more.