Sustain on an acoustic guitar?

Dean wrote:   A compressor like the Boss CS-3 will not make the note last any longer than it already does - what it does is hold the volume level of the note constant for that time (ie it will not slowly decay naturally)... internally the CS-3 has a voltage controlled amplifer that gradually increase the gain (volume) as the note decays. You can mimic this on an electric guitar or mic'd up acousting by turning the volume control manually as the note is played.

While this is strictly true, the practical result is that you get an apparent longer-lasting note i.e. the note remains audible for longer.

This video of another sustainer pedal (on electric) is more clear than the Boss CS-3's for understanding what the pedal does to the note sound (especially in its first part with clean sound to understand what it could do when plugged to an acoustic). It explains it exactly as you described but it also shows that the practical result is a longer-sounding note. As long as you can maintain some vibration in the string, the note will keep on sounding at audible level for longer. But if you mute the string vibration the sound will stop immediately.

Heavier strings on a weak guitar could break it, it is also possible that you'll never keep it in tune because the tension of the string could bend the guitar. If your guitar goes out of tune when you pull on the neck then I wouldn't recommend putting heavier strings on.

 

A compressor like the Boss CS-3 will not make the note last any longer than it already does - what it does is hold the volume level of the note constant for that time (ie it will not slowly decay naturally)... internally the CS-3 has a voltage controlled amplifer that gradually increase the gain (volume) as the note decays. You can mimic this on an electric guitar or mic'd up acousting by turning the volume control manually as the note is played.

 

Guitars sustain because the energy stays in the string and isn't lost through guitar body. This energy enters the guitar through the nut and the bridge and the dissipates into the guitar body by causing the body to vibrate at the string frequency. Obviously in an acoustic this vibration is a desirable thing because it amplifies the note so the audience can hear it, but it also means that the strings don't sustain very well. Heavier strings mean that you have to put more energy into the system to begin with, which gives you more energy to lose and so the note rings out for longer. The obvious ways of improving sustain is to make the body stiffer and more dense so that it doesn't absorb the string-energy, and making the machine heads (tuners), the nut and bridge hold the strings more rigidly so the string can "store" that energy efficiently. As Jacob has said in the second post of this thread - fingering also has an effect here - poor fretting or woolly fingering will dampen the note quicker. Of course making the guitar body stiffer requires some serious woodwork modifications.