Sustain
 

What is it in the build process that contributes to an acoustic guitar having a good sustain?

It usually starts with wood selection.

I like Ervin Somogyi's concept of "type 1" and "type 2" sustain.

Type 1 is like a solid body guitar, where the soundboard is too heavy/stiff to move much, so the guitar is quiet but sustains for a long time as the energy remains largely confined to the string.

Type 2 uses the back as a flywheel to absorb some energy from the soundboard and feed it back over time. Without this, a highly efficient soundboard converts the whole string energy to sound in a short time (loud, but short sustain). Low damping back wood has a big advantage here.

And a third thing is to minimize losses, for example by making the neck and sides heavy so they won't move, keeping all vibration confined to the soundboard and/or back. Surface hardness of the back/sides may have an effect as well.

There seem to be 3 main schools of high-end building.
1. Light everything. Low to medium type 1 sustain depending on soundboard stiffness, medium to high type 2 sustain depending on back wood, medium to high losses depending on woods.
2. Light soundboard, heavy everything else. Low to medium type 1 sustain depending on soundboard stiffness, low type 2 sustain, low losses.
3. Light and loose soundboard and back, heavy sides/neck. Low type 1 sustain, high type 2 sustain, low losses (provided low damping back wood is used).

what is good sustain for an acoustic and how do you measure it? I play an open chord (usually C) and count until I can't hear it - but this is not very repeatable or scientific...

brian

Notes that stick around long enough to get their say in and then vamoose.