Wood/pickup resonation

[Knightmeir]

I don't know where the hell to put this, and I can't find anything on it in the forum, so hopefully it'll fit here.

A couple days ago, one of my coworkers and I were discussing guitar stuff. I had brought in a JS and my VWH to work... I had mentioned the many different Jem models out there, and mentioned I had owned a DBK previously. He asked what the differences were, and of course I made mention of different pickups, woods, etc... Then he said something that struck me as odd. He said that he didn't understand how the wood the body is made of can have an effect on the way the guitar sounds, mainly because the way pickups pick up the vibrations from the strings. He said something about pickups only being able to "hear" from one direction, and that's straight from the strings.

The best way IMO to hear how the string vibration truly resonates is by placing your ear on the guitar without plugging into an amp or anything. Just the clean sound straight through the wood. I do understand how harder woods can vary from softer woods, etc... but I guess I am a bit intrigued by how pickups actually pick the sound up. This includes the difference between direct mounted or pickguard mounted pickups as well.

Does anyone have a better explanation as to how this all works, other than, "I just know that's why it works?" I'm stuck in the category of knowing why, just not really how.

[Drew]

Here's my gut feeling -

The strings resonate when you pick them. As they're attached to the body, this causes corresponding sympathetic resonances in the body which, as the body is also connected to the strings, also causes sympathetic resonances back in the strings, at various harmonic frequencies. These interact with, augment and/or cancel, the original vibrations in the strings, "coloring" the tone.

Direct-mounted and pickguard mounted is pretty tricky, but I think unplugged a guitar with a plastic pickguard sounds quite a bit different from an all wood one - effectively, it's somewhat akin to semi-hollow, abiet one with a plastic top and VERY thick sides.

Now, how about feedback from someone who actually knows what tey're talking about?

[damo7v]

i can accept that different body woods will make an appreciable difference to almost any ear.

i think part of the difference btw direct-mounted and pickguard-mounted type guitars will be more to do with the amount of wood routed out for a pg-mounted type guitar, rather than the surface the pick-up is mounted to.

i think we're discussing the nth degree here. i suspect it's somewhat akin to those people who taste wines and remark on the "subtle hint of licorice overtones" (wtf???). the rest of us just want to get drunk, you know?

[sepsis311]

I think Drew is pretty much on track. I took the following text from
http://www.jetguitars.com/treatise.html
Don't worry, i read it first to be sure it was relevant.

WOODS. The wood in a guitar receives the vibration from the string by means of coupling, vibrates in response, and transmits the vibration back to the strings. The pattern of vibration of the wood in the instrument is the resonance, and how it feeds back and forth to the strings determines how the harmonic pattern changes during the envelope. Generally, Thicker slabs of wood and denser wood both resonate at higher frequencies, because they have more mass. You can hear this by tapping heavier, lighter, thinner, and thicker boards and comparing the tones. Length is also a factor (look at a xylophone) but most guitars are very close to the same length. (The difference in scale length is physically very slight regarding resonance, and at any rate is greatly overshadowed by the effects of the difference in string tension.) The note that you hear when you tap a board is the resonant frequency of the board, in other words, the fundamental. An electric guitar likewise has a resonant frequency peak that is the resultant of the entire construction of the instrument. The overall mass of a guitar also has another major effect, and that is on the attack and sustain portions of the envelope. They both are increased. So, in designing an electric guitar, there is a balance between optimizing the attack/sustain, and keeping the resonant peak from getting high enough to impart a detectable shrillness in the sound.
The guitar is made up of 4 main parts that are different densities. These are the neck, fingerboard, body, and top. I believe this order represents their relative importance also. So, while some parts may be of high density, other parts are lower density. The way they add up and interact will determine the resonance of the guitar. Remember that resonance affects the envelope (responsiveness) of the guitar as well as the harmonic character.
Here is how I rate guitar woods in density, from high to low:
1. Ebony, wenge, cocobolo
2. Rosewoods, purpleheart, bocote, paduak
3. Hard Maple (can be flamed, birdseye)
4. Soft (quilted) maple, ash
5. Alder, mahogany
6. Korina, mahogany (mahogany is variable)
7. Swamp ash, cedar, redwood
8. Basswood
This is a good place to point out also, that some metal parts like truss rods and neck joint screws that are integral to the guitar, also add to the density equation. And metal is much denser than the densest wood.

[nightfiend14]

great post sepsis, lots of good information in there.

[lyconxero]

Hmm....I didn't know that basswood was less dense than Alder. Since it's tone was described between that of Alder and Mahogany I just figured its density was also in between. Guess you really do learn or re-learn something new every day.

[Knightmeir]

Damn good stuff!

Thanks!

[artificial infection]

Wow interesting, but what difference does it make if the pickups are DIRECT mounted compared to standard mouting on lets say, H-S-H guitars? How does effect the resonance or sound?

[frankfalbo]

The direct mount/mounting ring/pickguard debate is a big waste of time IMO. Pickups sense string vibrations. The only way they sense more than that is if they are slightly microphonic. All pickups are somewhat microphonic, just to varying degrees. So if they receive vibrations through the mounting method, technically it can have an effect on the sound produced, negligible at best. Like the "subtle hint of licorice overtones" mentioned above. The debate boils down to do you think your pickups will respond at all to acoustic vibrations? If you do, then what percentage of the sound will be made up of acoustic resonations vs. the actual magnetic disturbance? 1%? Maybe even less?

[eviltwin]

Interesting quote sepsis, but your man, Jeffrey Earle T., misses a couple of big points. Different materials have different material properties, in particular stiffness. Resonance of any structure is determined by geometry, mass (density) and stiffness. Indeed Basswood (Tilia) has a relatively low density but the stiffness is also different from Alder and Mahogany, to name two. Simply ranking wood according to density is rubbish.

He is also wrong when he says that higher density woods have higher resonance frequencies. In fact higher mass (density) equates to lower frequencies. But in most woods density and stiffness are correlated, denser woods are in general also stiffer. Simply tapping woods leads to this explainable mistake.

Finally acoustic resonance is very different from structural resonance as it is the shape and size of the sound chamber that determines resonance. An acoustic/hollow body's sound comes from the interaction between sound chamber resonance and top (+sides/back) resonance. Again Jeffrey Earle T. is wrong when he describes chambering, incorrectly correlating lower mass with lower frequencies.

You may also want to have a look at this thread:
http://www.jemsite.com/forums/showthread.php?t=10990

Taking metal (trussrods) into the equation the mistake becomes even clearer. Woods (Basswood all the way up to Ebony) have stiffnesses (the technical term is Modulus of Elasticity) ranging from 10 GPa to 20 GPa along the grain. In some directions even lower.

Aluminium at around 3 times the density of Mahogany is approx 7-3.5 times stiffer (Aluminium is 70 GPa)
Steel at around 10 times the density of Mahogany is 20-10 times stiffer (Steel is 210 GPa)