I probably have 50 long posts about it here on Talk Bass, going back over a decade. I should probably edit them all together into a single dissertation and post it in the Wiki section. The title would be some thing like: Principles For Adjusting The Sound Of An Electric Bass Through Structural Stiffness Of The Wooden Frame. Maybe with a picture of me wearing a lab coat, in front of a whiteboard covered with scribbling. Or not.
Here are a couple, to get you started. These are just quickly slapped in here without editing. The conversation is somewhat disjointed and may not be complete.
Here's a quick summary of how the wood frame affects the sound of an electric bass:
When you pluck the string, it goes into a cyclic vibration. It wiggles back and forth in a complex form. If you measure and plot out a spectrum analysis curve, it's a series of spikes at the fundamental and octaves. Those spikes are all determined by the string's mechanical characteristics: vibrating length, tension, diameter, wrap structure, metallurgy etc. That's the inherent "sound" of the string, a profile of frequency spikes.
That cyclic vibration of the string causes the whole frame of the bass to vibrate. The string's vibration makes the frame vibrate by pulling (in cyclic frequencies) on the two string anchor points, the tuner post and the tailpiece. It also pushes, in cyclic frequencies, on the two fulcrum points, the nut and the bridge saddle. That's how the string applies energy to the bass's frame, through those four points.
The mechanical stiffness of the bass's frame determines how much it vibrates. The stiffer the frame, the less the string is able to flex it and make it vibrate. If the frame is a block of granite, it isn't going to move at all, regardless of how the string pushes and pulls on it. The string rings on with its own inherent frequency profile.
If the frame is softer (less stiff), then the string is able to push it around. It pushes and pulls on the frame, making it wiggle back and forth, in a complex pattern of vibration. The string is putting energy into the frame, making it vibrate. This draws energy out of the string. The string's vibration gets lower and lower in amplitude, until it runs out of energy and stops moving. The string's energy has all been transferred into the frame, making the frame vibrate.
The stiffer the frame, the longer it takes to drain the energy out of the string. The string rings along on its own, decreasing in amplitude at a slow rate. Sustain. With a softer frame, the string gets quieter at a faster rate. Low sustain. If the frame is really soft and flexible, the energy is drained out of the string in just a cycle or two. Thump and it's dead.
Here's where things get more complicated: When the softer frame gets driven into vibration by the string, it reacts to the frequency spikes that the string is vibrating at. The frame tries to do the same dance. But it can't. It has its own mechanical stiffness and damping properties that are different from the string. So, when the frame vibrates, its frequency spike curve is somewhat different from what the string is doing. Some spikes are higher, or lower. Or barely at all. And, as the note goes on, the frame's vibration gets out of phase with the string's vibration.
When the frame's vibration gets out of sync with the string's vibration, it starts pulling down some frequencies more than others, making some spikes on the string louder or softer. The frame's crazy bouncing can even add some frequency spikes onto the string that weren't there when it was first plucked. That's what background harmonics are; new spikes in the string's vibration that were added by the frame bouncing back, at frequencies between what was originally on the string. All this is happening as the string is slowly going down in energy.
And that's how the frame of the bass can change the sound on the string:
The plucked string has a frequency profile
If the frame is soft enough, the string tries to make the frame vibrate along with it.
Because of its own structure, the frame can't match that same vibration. It does its own dance.
The conflict between the string's vibration and the frame's vibration causes the string's vibration profile to change as it draws down. They are fighting each other.
The pickup reads this change on the string's vibration, and sends it on down the line to the amp.
That's the process of how the wood and metal structure of the bass can change the sound that you hear out through the amp. How much the structure affects the sound is determined by the overall stiffness of the structure. How the structure affects the sound is a complicated mix of the mechanical properties of the parts of the structure; the dimensional size of the parts, stiffness and damping properties of the wood, mechanical reinforcements, all kinds of things. But all related to how the frame flexes under load.
Two other important points that often cause confusion:
The vibration of the frame that we're talking about above is not the same thing as Natural Frequency Resonance. That thing that causes Dead Spots. Natural Frequency Resonance is its own physical phenomena, which is determined by the frame's geometry, stiffness and mass. If the vibration of the frame (caused by the string's vibration) happens to be the same frequency as the Natural Frequency of the frame, then the Natural Frequency Resonance gets going. The frame starts shaking on its own, killing the vibration on the strings, and eventually exploding in flames. Probably not. But these are two different things. That's why I call the vibration of the frame vibration, not resonance.
There's a lot of discussion about how an electric bass sounds unplugged, and how it relates to all this. When we're messing around with the frame of the bass to change the sound, we're talking about the sound on the string that gets read by the pickup and sent along to the amp. That's the point of all this, to change the amplified sound. But playing an electric bass unplugged is a useful diagnostic. You can feel how much the frame is vibrating in your hands. A stiff frame bass won't vibrate much. A soft frame bass will vibrate a lot. And, in that vibration, you can get an idea if some frequency ranges are vibrating especially hard or soft. If the frame is vibrating a lot, it will also create some soft acoustic sound around it. It's shaking the air that it's hanging in. That unplugged acoustic sound isn't a full representation of what the bass will sound like through the amp, but it will give you some idea of whether the frame is participating in shaping the sound. It's useful information, but don't get hung up on how a bass sounds unplugged.
Another:
Hollow Body vs Solid Body Sound TB 10/2015
The body shape can change the overall tone of the bass, but only if it significantly changes the stiffness of the body. If the body is made stiff, by being thick, using a hard wood, no chambering, etc., then you can change the shape and it won't make any difference in the sound. But, if you cut away enough wood that it becomes significantly weaker structurally, then it will affect the tone. Both the low end and the high end become weaker and mushier, and the sustain is less. That's what happened with Geddy's bass. He cut away so much that the body became structurally weaker.
In the case of comparing the P-bass to the 2x4, they are both real stiff. So they sound the same.
That's the element that's missing from all of these long arguments about whether wood matters, or whether the bass's frame affects the tone: The net stiffness of the frame is what affects the tone.
If you build the frame of a bass really stiff, then it will have almost no effect at all on the tone. The sound going to the amp will be all strings and pickups. Most mass produced basses are built that way. Slabs of wood with pickups and strings. And most customers are happy with that.
But, if you start trimming away at the structure to make it weaker, then it will start affecting the tone. This can be done by making the body thinner, cutting internal chamber, cutting away at the external shape, or using softer woods. The weaker you make the structure, the more it will affect the sound on the strings. Which gets additionally shaped by the pickup and sent on to the amp. And the weaker it is, the more you are able to hear the differences between different woods. That's what builders like myself do. We deliberately make the structure weaker, down into that zone where the wood does matter, and play around with different woods and different shapes of the parts to finely shape the tone.
Another example:
Suppose you build three P-Basses which have thick unchambered bodies, and are identical, except the bodies are made from three different woods. Those three basses will probably sound just about identical. They are all stiff structures, so it doesn't matter what wood the bodies are made from. Their sound is strings and pickups.
Now, suppose you take those same three basses and thin the bodies down to, say, 1 1/4" thick. Everything else is the same. The three basses will sound different from before; softer, mushier high and low end, richer background coloration. You will also now hear some difference between them. The different woods have different stiffnesses. Once you've reduced the overall stiffness of the bodies down to the point where they are affecting the tone, then you will be able to hear the tone differences that the different woods make.
So there's your answer: Wood doesn't make a difference, except when the bass is built so that it does make a difference. And the shape probably won't affect the tone.....unless you take it too far. Then it might.
It's that simple!
More:
Here's another of my old posts that may help with the basics: It was about the tone differences between Bolt-on, neck-thrus, and set necks.
You're not imagining things! The frame of your new neck-thru bass is clearly stiffer overall than the Jazz or the Washburn. That is, it takes more pounds of force to flex it. That's why the strings feel tighter. It's not that the tension in the strings is higher; that's fixed by the scale length and the note that they are tuned to. But when you pull the string to the side with your fingertip, you are yanking on the tuner and the bridge, causing the bass's frame to bend a little bit. The stiffer the frame is built, the more pounds you'll feel on your fingertip as you pluck. So, the sensation is that the strings are tighter, and they snap more when you release. That's one of the things you get with a stiff-frame bass.
Neck-thru construction basses are generally stiffer than bolt-ons, but not always. You can build a neck-thru from soft woods with a thin profile, and it can be soft and springy. And, you can certainly build a bolt-on to be very stiff. It all depends on how the bass is built. The stiffness of the frame is one of the factors we luthiers play around with to get the feel and tone where we want it.
More:
A bass is like an archery bow; a wooden frame with a string stretched tightly between the two ends. Obviously, the archery bow is an exaggerated example, but when you pull the string off to the side, the wooden frame bends to take up the shorter length. The string isn't made of rubber; it's a very stiff material lengthwise, stiffer than the wood. When you pull the string off to the side the two anchor points at each end get pulled towards each other, with a lot of force. The result is that the two wooden arms of the bow bend from the load. The stiffness of those two wooden arms determines the power of the bow, and how many pounds of force it takes to pull the string off to the side some fixed amount. The thicker the bow arms, the harder you have to pull sideways on the string.
When you release the bow string, it snaps back towards straight, overshoots past straight, then swings back the other way. It oscillates back and forth for a while, decreasing the amplitude with each swing, until it finally comes to a stop in a straight line, under the nominal tension. Every time the string oscillates off to the side of center, the bow frame's wooden arms are again being flexed, for the same geometric reason as described above. As the string oscillates and slows down, the wooden arms go through a cycle of increasing and decreasing load. If you watch the tips of the wooden arms, they are flexing in and out with every cycle of the string. The "out" is every time the string crosses the centerline and is straight for an instant. The "in" is when the string is deflected off to the side. The frame is moving as long as the string is moving.
The same thing happens on a bass, but on a smaller scale. Hopefully you're not pulling the string that far off to the side! The bass is a wooden frame with a steel string stretched tightly between the tuner post and the bridge. The steel is a lot stiffer than the wood. I'm sure you've watched the neck and body flex as you bring the strings up from loose to full tension. You can see the strings lifting up off the fingerboard, to end up at some height above the fingerboard. That's the bass's wooden frame bending into a curve, just like the arms on the archery bow.
When you pull the string off to the side (when plucking), you are forcing the bass's frame to bend just a little bit more. The stiffer the frame is, the more pounds it takes to pull the string the same distance to the side, just like the archery bow. When you release it, the string snaps back and goes into the back-and-forth oscillations. The wooden frame is also flexing back and forth with every cycle of the string. The movement is visually small, but it's definitely happening. It has to. Something has to move.
That cyclic flexing of the wood frame is at the heart of the final tone that an electric bass makes. The flexing of the wood frame changes the sound on the string, because with every cycle that it flexes, it removes some energy from the string. On a soft wooden frame that flexes easily, the string dies out quickly. Less high end and less sustain. On a very stiff wooden frame, the frame doesn't flex as much, and the string rings longer and with a wider frequency range. Stretch a string across a block of granite, and the frame doesn't move at all. The string will keep ringing all day. In that case, when you pluck the string, all of the flexing is being done by the steel in the string. On a granite guitar, you're hearing the pure sound of the string itself.
And yes, I'm talking about the plugged in sound of the bass. The tone curve that rings on the string is detected by the pickup and sent off to the amp.
Here's the important thing to understand:
The stiffer the bass's structure is, the more you are hearing the tone that the string itself is making. The structure flexes less, so therefore it has less effect on the tone on the string.
The softer (more flexible) the bass's structure is, the more the structure is able to modify the tone on the string. The flexing itself changes the tone, but ONLY if the structure is able to flex.
That difference is the reason why we so often get into heated arguments around here on whether the wood frame affects the tone of an electric bass. The answer is yes or no, depending on the bass.
On basses that are built with very stiff frames, the amplified tone does indeed come primarily from the character of the strings and the curve shaping of the pickup. The wood has very little to do with it.
However;
When you build a bass structure to be more flexible, then it will have a significant effect on the tone out through the amp, and the feel on the strings. The more it's able to flex, the greater the effect, and the less the bass sounds like pure steel strings. That's why we luthiers fuss with all the different woods and shapes of the structures. We're trying to make our basses sound less like metal and more like a violin.
?
That's it exactly. An excellent example of what's going on. Now, is the new body very much different dimensionally from the old one? The lower stiffness of the body may be partly due to your weakening it in the design, and partly due to switching to the softer mahogany. Whichever, you got there. You softened the overall structure enough that you got the frame to start bringing in background coloration. Those are the off-harmonics in the background that make the warm sound.
You can push it further if you like, to bring out even more of the warmth. Keep trimming away at the body, mostly in the area right between the neck pocket and the bridge. Trim it thinner front-to back, rout some slots, whatever you like. But go slowly. You're in the "zone" now. It doesn't take much once you've got the body working. But, if you go too far, you can always add some reinforcements to stiffen it back up.
Here's where it all gets so confusing to most people. If I were working with you, I could show you how to build a replica of your mahogany body, still out of mahogany, but with enough reinforcements and dimensional changes that it would end up with the same stiffness as the original maple body. Hell, we could make similar looking bodies from 10 different woods, but adjusting them each to the same stiffness. All stiff bodies, but made of different woods.
The test results would be dramatic: They would all sound the same! And the crowds in the streets with the WOOD DOESN'T MATTER banners would be cheering! Definitive proof that you can build a bass body out of any kind of wood, and there won't be any difference in sound! That's what it proves, right? Right?
No, not really. What it proves is that if you have a batch of bodies that are all built to the same stiffness, then the wood choice doesn't matter. That's it.
Here's the other side of the experiment:
I could build you a maple body that would resemble your mahogany body, but I could trim it away enough to bring its structural stiffness down pretty close to the mahogany body. It wouldn't sound exactly the same, but it would be close. The warm background coloration, with the reduced range and sustain. This maple body would sound like what you'd expect of a mahogany body. Yes, you can build a bass with a carbon fiber neck and a maple body, and have it end up with a nice warm tone. Nothing to do with the pickups. It's all about the stiffness of the structure.
You can see why the arguments get so confusing.
Conclusions:
1.) You can't say that a particular wood will cause a bass to sound a particular way. Likewise, you can't say that a particular sound from a bass is caused by the presence of a particular wood. Maybe, but it's probably more complicated than that. You can get to a particular tone from different directions, using different choices of wood.
2.) You also can't say that wood doesn't matter...at all. In many cases, the wood choice may not make any tone difference to the player. But with your Steinberger, you've shown that it does.
It's all about the structural stiffness, and the choice of wood is just one of the variables.
I've got to get back to the shop. Those are some of the basics. I'll pull up some more later, if you are still interested.
PLEASE DO!
Interested would be an understatement. At this point I have an entire directory structure full
of Bruce Johnson posts as well as Turnaround posts. The careful in depth analysis of both are
fantastic. There is a lot of variation in the quality of setup advice out there. I have settled on
these two as the most believable. The copies of these posts are starting to take up lots of
disk space, so I have resorted to a text file with the subject headers and URL of the posts.
That might be a good idea. Instead of a edited single dissertation, just collect titles and URLs.
Then they could at least be found. So far I collect only what I happen to find by accident/search.
