Ed and Bobbe are now talking about something I am puzzled about - the effect of body resonance on a solid-body electric guitar or steel guitar. We also discussed this a couple of years ago. With an acoustic instrument, of course the resonance properties of the body top are very critical to the sound. The strings themselves have long sustain, rich overtones, and very little volume. They don't move much air. It is the vibrations imparted from the stings to the top that move air and create most of the sound we hear. In general, the the lighter and more flexible the the top, the more volume we hear, and the less sustain. That's a banjo. It creates a very loud pluck, with almost no sustain. Somewhere in between are resonator guitars. The thin metal resonator gives a lot of volume, with some sustain. A standard wood top acoustic guitar has less volume, and more sustain. In this continuum, you generally swap off between volume and sustain. By draining off vibrational energy from the string to the top, you create volume at the expense of sustain. In order to capture the tone of the resonator or top, acoustic pickups are attached to the top or saddle.
Now a magnetic pickup is a completely different animal. These pickups can be microphonic and pick up some body vibrations. Most people consider that a bad thing, but in previous discussions some people actually liked the tone they get with a certain amount of microphonics. But aside from that, a magnetic pickup captures only the vibrations of the string, not the body, top or resonator. In this situation, the body subtracts vibrational energy from the strings. For this spectrum, at one end we have a big box archtop jazz guitar, which has a very mellow sound without a lot of sustain. The sound is mellow because the high overtones are the fastest to die out and the quickest to drain off into the body. This leaves the mid and low overtones and the fundamental in the string vibrations to be captured by the pickup. At the other extreme is a solid plank of a body, like on a lap steel. The thick hard body absorbs very little string energy, and so the strings are mostly left with their natural high overtones and long sustain to be captured by the pickup. Any loss in volume is not very relevant, because we just crank up the amplifier - that's sort of the whole point of a magnetic pickup. So the volume/sustain swap off we are familiar with in acoustic instruments, for all practical purposes doesn't really apply with magnetic pickups. We can use a hollow body, and subtract off the high overtones, or a solid body, and keep the high overtones, and can use amplification to keep the volume constant.
In modern electric steel guitars, we are only talking about solid bodies. So let's think about that. Do we want any resonance at all in the body? Imagine if we had a body so hard and rigid it subtracted off essentially no vibrational energy - say a block of diamond with carved bridge and nut. Then the pickup would capture all the overtones, and the sound would be very bright, with long sustain. At the other end of the spectrum would be a mushy body that absorbed most of the vibrational energy of the string very quickly - say a body made of something soft, like wet clay. Loose attachment of the bridge and nut would also work like that. Somewhere in between those extremes is the typical 3/4" piece of tone wood, typically rock maple. I think a lot of people mistakenly carry over the above thinking about acoustic top resonance, and expect the steel guitar body resonance to somehow "create" or at least translate the string energy into volume, sustain, and tone. But that kind of resonance in a solid-body moves very little air, and only creates the sound you hear with the guitar unplugged. Yes, in a quiet room, you can put your ear to an unplugged tele, strat or steel guitar, and hear a little acoustic sound from the body. But that is totally swamped out when the guitar is plugged in and amplified. What you hear is not the air movement of an acoustic instrument, but instead you hear what cannot really be heard on an acoustic instrument - the actual vibrations of the strings alone, captured and amplified by the magnetic pickup and amp.
So I think we all agree that on electric guitars, body resonance mostly affects tone by what it subtracts from string vibrations heard by the pickup. So body resonance has a very different role than in acoustic instruments. But maybe it is not that simple. Bobbe and some others claim that the body resonance can "feedback" into the strings and accentuate certain overtones. If that occurs, would it be good or bad? By analogy, in a bass speaker cabinet, the resonance of the cabinet must be controlled very precisely to smoothly boost the shoulder where the bass frequencies begin to fall off, without creating unwanted narrow resonance around a particular frequency that causes particular notes to "boom." Can the resonance of a solid-body electric guitar be controlled like that to benefit tone? I'm not sure.
Obviously instrument makers manipulate solid-body shape and material to get different tones in solid-body guitars. They use mahogany, maple, swamp ash, grain patterns, solid wood, laminated wood, etc. Are they only working with subtractive manipulations, or are they also manipulating active supportive resonance of certain frequencies? Maybe it doesn't matter, because it is only the end results that we care about, and we don't care how they get the results. But to me this is an intregueing question, and I'd like to hear any thoughts. Maybe right now we only have thought experiments, but it sure would be nice to hear about any real experimental evidence. Ed? Bobbe? Anyone?
Edited: Dave M. posted while I was writing. We have the same questions, but it seems like we have both stated the question without any answers.
bob
... thanks for your very intelligent replies and posts... I always learn something from your writings!!! bob
I just tried play'in my Dekley without any strings, it did'nt have any tone at all !! I believe strings are very important
