Jim Pitman wrote:Stephen perhaps my statement is too generalized. There comes a point when too much acoustic volume can generate feedback via the sound from the amp. Sure, then the feed back is constructive or destructive - quite unpredictable. But most if not all solid body instruments rarely reach that threshold at normal amp/guitar distances.
Actually, coming from a rawk background... that's where I lived. When you do it right, the thing comes alive... lighter-bodied guitars act this way, which is why swamp-ash was favored for guitars over baseball-bat ash (like my '70s Strat, very heavy, lots of sustain, not much hook-up or character to the sound).
I've had two very solid/heavey PSG guitars with thick tops that you would think would have a lot of sustain - in fact they didn't and the overtones on those guitars was relatively subdued as well. - sounded too pure and uninteresting. I tried many pickups in each to no avail.
As I've related, we may be discussing two different effects... and a heavy sponge would be expected to sustain less than a light titanium. Resonance, mass, coupling, isolation... complex stuff!
The sustain theory I put forth is the longevity of vibration for a string can be increased by sound waves from the body adding to its' amplitude. - acoustic resonance to a degree, but merely increasing the vibrating surface area ore letting the surface vibrate, ie thinner top contributes.
The pickup merely needs to sensitive enough to pick it up.
Obviously the pickup saps energy from the string... it's a dynamo system, after all. My point here is that *anything* taken from the string decreases sustain... if you add some back (via acoustic coupling) you have still decreased sustain from a 'perfect' system. One thing the acoustic resonance does is modify harmonics... perhaps in a pleasing way. This acoustic resonance would also tend to be sensitive to the same frequencies coming from the amp/speaker... in effect reinforcing the sustain. I think we can both see that the guitar can't be considered a 'closed system' when there's an amp around.
This part of my post is a "theory" really. However it is based on the experiences with the PSGs I've owned. I imagine one has to get the vibrations from the surface of the guitar to be in phase with the string movement, otherwise it will kill the sustain. Phase relation will change with frequency so this is frequency dependent.
From my pickup making experience generally we like it when the upper mid-range is reinforced.
Yes, the 'knock'... the pickup's peak and Q, along with the guitar's resonances, determine the final product there. I guess my final point, pretty pedantic I must agree, is that max pure sustain happens in a vacuum, with a perfectly elastic string strung between perfectly immobile supports... in a closed system. Thanks for your thoughts on this, BTW.
Too much junk to list... always getting more.
