If the pickups are just electromagnets detecting vibrations in metal strings, what effect does the guitar (size, shape, type of wood, solid body, hollow body) have on the pickups?
Most argue that the pickups are similar to microphones. However, direct contact with the pickup by material other than metal does not produce any significant sound from an amplifier.
How can wood vibrations from the body effectively transfer to the electromagnetic pickup to affect tone in a significant way?
I think the best way to think about this is to not only think about the wire (moving guitar string) cutting through the magnetic field of the pick-ups (stationary) but also to think about the pick-ups themselves moving with the resonance of the wood that they are fixated to.
Now you must consider the frequency response of the instrument as a whole and this would definitely be affected by the choice of wood. How much it affects the sound is another question. I personally believe the subtle differences end up being audible due to the degree of amplification. But in the grand scheme of things, this is just a part of the entire signal chain that can effect your sound.
Of course it does not affect the "sound of the pickups", but the pickups don't have any sound to themselves anyway: they only pick up the sound that's coming from the guitar strings and modify it.
The sound of the strings, on the other hand, is affected quite a lot by the mechanical resonances of the guitar, in particular by the neck but also by the body. Because on a frequency the guitar can easily resonate to, the strings are able to release much more energy into the environment than for a frequency where the body does not move along at all. And which frequencies these are depends on a lot of parameters, which are different for every guitar type and even for guitars built in exactly the same way but from different types of wood.
So if you equip, for instance, a Les Paul and a tele with exactly the same pickups an circuitry, you will still get very notably different sounds. The difference is even more obvious when you also consider hollow-body guitars: quite a lot of these actually do have the same pickups and circuitry on them as Les Pauls, but still sound completely different.
On the other hand, if you use a massive block of granite, which is so heavy and hard that it will resonate but very little, you get a very long sustain (most damping is then due to string stiffness and perhaps even air friction) and a literally very hard sound, because none of the overtones are filtered particularly strong.
One of the major ways the vibrations can affect the sound of the guitar is by allowing greater feedback influence (most especially with hollow-body electric guitars). Example, Trey Anastasio has several extremely resonant guitars, and that controlled feedback is a signature of his sound.
As for actual EM influence in this case, there isn't any; but that doesn't mean the body of the guitar can't have a tremendous effect on the guitar's sound and playability.
Solid body electric guitars resonance or acoustic vibrations response is very important in relation to strings vibrations frequencies which are transduced by the electromagnetic pickups.
Individual acoustic characteristics in a wood guitar body will determine how the strings vibrate and the colour of tone or timbre of the particular instrument (before any analog or digital influences).
The wood instrument and strings are a dynamic mechanical system under tension. When an electric guitar is played by a musician, the acoustic vibrations of the strings are reflected back by the instrument wood determining how the strings vibrate, which vibrations are then picked up by the electromagnetic pickups.
Various electric guitar instruments using similar tuning, scale lenght and strings type will sound different depending on the type or species of wood used, the mass and shape of wood elements or the type of assembly of different wood elements e.g. "bolt-on neck" or "set neck" guitars.
The differences are generating the variations in the frequencies spectrum (fundamental tones and overtones volumes and time characteristics - e.g. sustain) which electromagnetic pickups are collecting and transmitting to the electric signal amplification chain through to speakers and audience ears.
I agree with you 100%. magnetic pickups only pick up the string vibration not the vibration of the material the guitar is made of. Weither the guitar is made out of 4" granite slab or a broom stick the pickup is not going to pickup the vibration of the stick or granite, it is only going to pick up the vibration of the string. But that's not the 'END OF STORY', it's only half the story.
What to consider is not how the material the string is mounted to affects the pickups ability to pickup the vibrations of the string, but how the material the string is mounted to affects the vibration of the string itself.
So if you have a 4" granite guitar and a broomstick guitar, yes you're right the pickup is only picking up the string not the material, but the broomstick is going to act more like a shock absorber then the granite is. How ridged the material is ancored to will affect how the string vibrates.
So sicne the string anchored to the granite does not vibrate in the same exact way as the string anchored to the broomstick, and as you say, the pickup only picksup the string vibrations the output is not going to be exactly the same.
I agree that the bridge and the nut do make a difference but the material that connects the bridge to the nut also makes a difference. if the nut and bridge are mounted to something very dence and ridgid, when you pluck the string, more of that energy will stay in the string. If your nut and bridge are mounted to something less dense and ridgid, when you pluck the string more of that energy will be absorbed by the material.
So it's not a matter of how different materials affect the pickups ability to pick up the string, but how different materials affect the strings ability to vibrate.
The energy of the string being struck creates an oscillation. An oscillation is a back and forth movement. When the strings are first struck the pickups only "hear" the string. This is the attack of the note. The energy of the string going out to the body and the pickups. As the oscillation comes back, the energy from the attack is now reversed. Going from guitar body to the strings. Every time the oscillation swings back, the material of the body plays a larger part of what is heard.
The question is "does the body of the guitar affect the tone?". The tone is composed of many frequencies which are present on the vibrating string. I believe there are two things that need to be answered to know if it does. 1. What is the amplitude of the reflection coefficients at the two boundaries (the nut and the bridge) from 0 to 20 kHz on two identical guitars except for one parameter ( i.e. their bodies made from different wood)? If this is known, then it would let us know how much of a particular frequency makes it through the boundaries and how much is reflected. 2. When the guitar is strummed, the body vibrates and therefore the pickup vibrates. This will affect the magnetic field around the pickup. The physics is the same (Faraday's law) regardless of which is moving relative to each other( i.e. the pickup can move relative to the string or the string can move relative to the pickup to cause a change in the magnetic field and thereby a change in the voltage). How will the vibration of the pickup change the output voltage of the pickup, and is it different on the two guitars? That is my two cents.
It's likely that if the body of a guitar has any effect on the string timbre it's likely so small as to be inaudible given the coloration a signal chain of pickup- electronics-cable-pedals-amp-speaker-room imparts on guitar tone.
The purpose of a solid body electric is to reduce and deaden resonance as much as possible so that maximum volume before feedback can be achieved. Most pickups are wax potted to prevent the internal coils from vibrating and picking up noise microphonically. The pickup does not pickup sound- it merely senses vibrating metal that disturbs it's magnetic field. This is why electric guitars never sound like acoustic guitars- it's sensing an isolating string vibration.
The major factors influencing timbre are the type of pickups (and placement) the nut, the bridge and how or where the string is struck. Whatever the string is directly touching influences how it vibrates. The body is the furthest from the string. Vibrational energy has to pass through the nut and the bridge, then into the neck and the body. The string vibration is already very weak- these vibrations get weaker as they pass through these mediums- where some energy gets reflected and some passes through. Feel the body vibrate with your hands after you strike the string and listen to the string acoustically- hear any difference in timbre? I don't.
I can hear the difference between single coils and humbuckers, can tell if it's a neck, middle or bridge pickup etc, but I've never heard if anyone being able to identify wood species based on amplified tone given the numerous factors in between.
Listen to amplified acoustic guitars. They pretty much all sound electric, negating much of the coloration of the wood box. A pickups job in life is to isolate the string sound from the body of the guitar- if it isn't then you're feeding back uncontrollablly.
The last example is that of Shovelman- he plays a -you guessed it- a shovel, with pickups and a nut and bridge to hold the strings. No body wood to speak of- it sounds pretty much exactly like an electric guitar.
The only thing your body wood is for is to be a frame for everything to stay held together and maybe to look pretty. It could have an influence on sustain if you have a good contact between the string bridge and wood, but not timbre. You'll control timbre through your amp, pickups and how you strike the string.
Wood Is Not Magnetic. The only thing that matters is what the string comes in contact with, the bridge, the nut, the tuners, a guitar pick, and the player playing, as long as the hardware and electronics are exactly the same, the wood will have no bearing on the sound as perceived by an electro magnetic guitar pickup, they are not microphones and wood is not magnetic, END OF STORY !!!!
