Sustain ?

[yankees1]

On a F5 mandolin build what can a builder do to increase the sustain produced by the mandolin ? Choice of top wood ? ( Engelman) Arrangement of tone bars ? graduation of the top ?

[Marty Jacobson]

All of those are potential things that are part of the recipe for a particular instrument. Also scale length, string gauge, bridge mass, break angle, action height, etc. There are a lot of factors. When I'm going for lots of sustain, I often carve the back thinner than I would with a bluegrass instrument, and leave the top pretty rigid. The size of the soundports seems to make a difference, but that's probably more to do with the relationship of the air modes to the particular plates than something specific about sustain.

[CWRoyds]

I have no luthier knowledge, but I do know that my Northfield 5-bar Engelmann top Artist model has unbelievable sustain.
I have never played an F5 with anywhere near the sustain of this instrument.

I understood that the sustain in this mandolin is due to the number and position of the tone bars and the Engelmann being a softer tone wood, but I could have misunderstood.

Sometimes it is almost too much sustain, mainly when playing fast bluegrass.
I may have to get another F5 for straight bluegrass, but I would never get rid of this 5-Bar Artist model.
It is unbelievable.

[fscotte]

Funny that Marty would mention a stiffer top and loose back. The most sustainful mando I built had just that, a stiffer top and very, very loose back. It sounded like a small guitar with its sustain.

[sunburst]

In general, heavier = more sustain. Lighter = louder.
To make sound, the energy from the plucked strings sets the mandolin in motion, and the more efficient that mandolin is at converting that movement (vibration) to audible sound, the louder it is. The mandolin makes audible sound from string energy, and uses that string energy up in the process, so a loud, responsive mandolin will have less sustain than a quieter, less responsive mandolin. There is a trade off between loudness and sustain because the energy from a plucked string is finite and limited, and once it is used up it is used up. Louder generally means that string energy is being used up quickly.
A heavier top will yield more sustain, a stiffer top will yield more sustain, and a heavier mandolin in general will yield more sustain.
There is also coupling to consider. When a top and back work well together, when they couple well, they sort of help one another steal string energy to produce more (louder) sound. To couple well, a top and back must be near, but not the same, in resonant frequencies. That could explain why, in Marty's and fscotte's examples the stiff top and loose back yielded more sustain.
Then there is the air resonance to consider, and on and on...
I've left a lot of stuff out here. Even if I wrote all I know about it, this would be many pages, and that does not scratch the surface of what there is to know about it. Suffice it to say that it is more complicated than spruce species, tone bar placement and such.

[yankees1]

In general, heavier = more sustain. Lighter = louder.
To make sound, the energy from the plucked strings sets the mandolin in motion, and the more efficient that mandolin is at converting that movement (vibration) to audible sound, the louder it is. The mandolin makes audible sound from string energy, and uses that string energy up in the process, so a loud, responsive mandolin will have less sustain than a quieter, less responsive mandolin. There is a trade off between loudness and sustain because the energy from a plucked string is finite and limited, and once it is used up it is used up. Louder generally means that string energy is being used up quickly.
A heavier top will yield more sustain, a stiffer top will yield more sustain, and a heavier mandolin in general will yield more sustain.
There is also coupling to consider. When a top and back work well together, when they couple well, they sort of help one another steal string energy to produce more (louder) sound. To couple well, a top and back must be near, but not the same, in resonant frequencies. That could explain why, in Marty's and fscotte's examples the stiff top and loose back yielded more sustain.
Then there is the air resonance to consider, and on and on...
I've left a lot of stuff out here. Even if I wrote all I know about it, this would be many pages, and that does not scratch the surface of what there is to know about it. Suffice it to say that it is more complicated than spruce species, tone bar placement and ch.

You state that a heavier and stiffer top will produce more sustain but I thought a top wood such as Engelman would produce more sustain over a heavier and stiffer red spruce ?

[sunburst]

You state that a heavier and stiffer top will produce more sustain but I thought a top wood such as Engelman would produce more sustain over a heavier and stiffer red spruce ?

What makes you think that?

[yankees1]

What makes you think that?

I have read this in many places on the internet and the cafe.

[sunburst]

This is the kind of generalization that players, marketers, and even some builders perpetuate, mostly from lack of actual knowledge of how instruments work. It is the kind of thing we need to learn to ignore and learn for ourselves how things work.
An individual builder may be able to make broad generalizations about what to expect from various wood species when he/she uses them the way he/she knows how, but it is a stretch to assume that any given spruce species gives universally similar results from builder to builder, especially considering the infinite variation in wood within a species.
The stiffer, heavier top will give the builder more opportunity for more sustain whether that top is red spruce, engelmann, European, sitka or whatever.

[yankees1]

Only know what I read, but-----------most articles/comments I read state that a red spruce top sound decays much faster and an Engelman top decays much less or slower. So, from your comments it is the builder who built the instrument to produce this ?

[fscotte]

Red spruce is generally heavier for a given stiffness than engelmann. I've never really noticed much difference in sustain between the two. You can make engelmann just as stiff and heavy as red spruce. It all comes down to how you carve the plates. If you want lighter and stiffer, make the arch more bulbous. That tends to be the bluegrass sound, staccato, punchy, etc..

If you want more sustain, try a lower arch, which will tend to be a bit heavier, and keep it just as stiff or stiffer. That tends to be more of the flat top (I call it guitarish) tone we find in oval holes and flat tops.

[fatt-dad]

Things like modulus and compressive strength vary from one species to another. So, if the strength and modulus of one wood was different than another wood and they were both carved to the same gradations, I'd think the material properties would yield distinction between sustain.

I'm no builder.

f-d

[yankees1]

Thanks for all your wisdom ! I won't "sustain" this thread any longer !!

[amowry]

Something that complicates it is that (as John mentioned above) louder mandolins have less sustain because more string energy is converted to sound, but because they're louder you can hear each note longer as it decays. A string stretched in a perfectly rigid frame would have the most sustain because no energy would be "lost" to producing sound, but you wouldn't hear the note at all. That tends to reduce the perceptible difference in sustain between instruments. Rather than talking just about sustain, it might be more useful to describe the overall ADSR (attack/decay/sustain/release) curve for a given instrument, e.g. it is tall and skinny, or short and wide I guess what I'm trying to say is that sustain is just one aspect of the overall character that makes an instrument distinctive. When choosing an instrument I'd suggest asking whether the overall character appeals to you, rather than focusing too much on one element. Not sure where that leaves the discussion...

[fatt-dad]

it also varies from string to string. Here's just a simple experiment I made using a decibel meter. Not scientific, but interesting. I think this was on my A3?



f-d

[DavidKOS]

Better tremolo = more sustain!

That's what the tremolo was invented for.

[sblock]

suburst and amowry have it absolutely right. There is only so much energy in a string, imparted from the pick. Now, energy is conserved, so you can't get something from nothing! Any initial vibratory string energy will emerge, eventually, either as sound from the instrument, or it will go into damping (heat production). If your mandolin is loud, that means that it converts string energy quickly and efficiently into sound, with comparatively little damping. If you seek an instrument with greater sustain, then you're basically asking for the string energy to be metered out comparatively slowly (but that means in smaller doses). Of course, the inevitable sources of damping kill off both loudness and sustain, but it is much harder to maintain sustain in the presence of much damping. The three relevant variables are: mass, stiffness, and damping. It is not, in general, possible to tweak these three things very independently, because they arise from related material properties of the wood and air chamber.

A more massive mandolin (e.g., from heavier, thicker wood) will generally tend to be quieter. However, those same characteristics will tend to give it sustain, as others have already pointed out. But with the greater mass often comes more damping -- which can kill off the sustain, all else being equal. Stiffer surfaces often have less damping, so you can also try for additional sustain by trading off some of the mass for greater stiffness. And as sunburst pointed out, a top whose resonance couples poorly to the back of the instrument will share energy with it more slowly, and therefore radiate sound more slowly, i.e., deliver more sustain. Unless that sustain is killed off by damping, that is. Which is where stiffness comes into play, imparted, in some cases, by bracing, as well as by wood selection, graduations, and air chamber/shape properties -- as you see, it's complicated!

I agree completely with amowry when he points out the the sound might be better described in term of some temporal (sonic) sequence, like attack/decay/sustain/release.

[O. Apitius]

With my "seat-of-the-pants" approach to building, I'm not quite buying the idea that you can't have both above average volume and above average sustain in the same mandolin. One thing I have not heard mentioned in this complex subject is the role of the re-curve area of the plate acting as a sprung suspension system. In my mind, and perhaps only there, I see the re-curve area along with the total shape of the arch as a sort of 3-dimensional leaf spring. I feel that the shape of the arch and re-curve area is very important to a very well functioning and efficient plate. Of course this has to work in conjunction with the mentioned factors of density, strength to weight ratio, mass and last, but by no means least, modulus of elasticity.

I see the top as being spring loaded with the downward force of the combined string tension. About 30 to 40lbs depending on string gauge and bridge height according to an old Frets magazine article where Roger Siminoff set up a jig to measure this and other aspects of string tension.
Therefore, as I see it, if the re-curve and arch are carved properly and the other factors such as stiffness and so on are properly dialed in, the top will store energy like a compressed spring. Now when I pluck a string with say 2 lbs. of force, the top will move downward until its stiffness overcomes the extra 2 lbs and then it will release some of its stored energy and start traveling in the opposite direction thus adding a small fraction of energy back to the string. Of course this is not 100% efficient and some of the inputted energy will be lost to heat. My explanation of this phenomenon may be scientifically wrong but if so, I still do not buy the theory that volume and sustain are basically mutually exclusive, becuase I have witnessed otherwise. FWIW, I quit school 3 months after my 16th birthday. 'dumbest thing I ever did. I wasted 3 months!At least today I can still form the occasional independent thought.

BTW, I've had this picture of how the re-curve works in my mind for many years and a few years ago it was reinforced for me when I was rebuilding my 4 cylinder motorcycle engine. I had never done this before and I was quite surprised at how strong those valve springs are. At first I thought, those valve assemblies must be taking an awful lot of horse power to turn over. I mentioned this to a mechanic friend and he said that they actually take very little. Then he explained to me that as one cam is pushing down and compressing one of those strong springs, another cam is being pushed the opposite way by the stored energy in its spring so the effect, overall is fairly neutral. I confirmed this by cranking over the valve assembly (8valves) by hand and noticing that it didn't require much strength at all.

[O. Apitius]

it also varies from string to string. Here's just a simple experiment I made using a decibel meter. Not scientific, but interesting. I think this was on my A3?



f-d

I wonder if the significant increase in sustain of the "D" string has anything to do with the strong possibility that the Helmholtz frequency is also in that neighborhood.

[sunburst]

In order for loudness and sustain to both be increased, the efficiency of the system must be increased. That is, more string energy is converted to sound and less is lost to damping/friction. I don't remember what the numbers are, but I do know that the vast majority of string energy is lost to damping/friction, so we are only dealing with a small portion of the available energy from the strings when we tweak things to increase loudness or sustain, and even in a hypothetical system where we have improved efficiency as much as we reasonably can, there will still be a trade-off between loudness and sustain, but we can have more of both compared to a less efficient system.

[fatt-dad]

I wonder if the significant increase in sustain of the "D" string has anything to do with the strong possibility that the Helmholtz frequency is also in that neighborhood.

I too wonder more than I know! I've heard about Helmholtz. I really notice the decay seems related to some harmonics and a lot of other stuff. Maybe when Mandolin's are described by strong mids or highs, its related to these seperate sustain matters?

I'm no builder. Just a curious engineer. We'll, and plucker!

f-d

I'm

[sblock]

Oliver,

The only way, even in principle, to increase BOTH the loudness and sustain, without violating the laws of physics, that is, would be to somehow convert the available vibrational string energy into acoustic radiation much more efficiently than the average mandolin does. Basically, that translates into finding a way to reduce the instrument's damping, which is where the available string energy is lost, if it doesn't go into sound production.

There are some other tricks that can improve loudness at the level of the audience, like radiating more of the sound forward, and less of it towards the player, but I will leave these aside for the moment. Besides, these things don't count for a lot. Yes, oval holes project forward less, and f holes project forward more, but the difference is not really all that great.

Reducing the damping is easier said than done! The damping is closely related to the "Q factor", which is the ratio of the energy stored to the energy lost per cycle of vibration. For a mechanical oscillator (like a vibrating piece of wood), we have:

Q = (1/D)*SQRT(M*k),

where D is the damping coefficient, M is the mass, and k is the stiffness, and SQRT( ) means to take the square root.

This leads to a conundrum. If you increase the stiffness too much, to raise the Q value for a given amount of damping, you can wind up with an instrument that will strongly favor the frequencies near resonance -- but not others. You wind up with an uneven instrument voice. The extreme of this case is a pure Helmholtz resonator (air cavity resonance), which only picks out a single frequency (sort of like blowing into an empty beer or coke bottle)!

But how do you reduce the damping on its own, without at the same time reducing the mass and stiffness? Therein lies the rub! You do have a choice of woods with different intrinsic properties, and these offer some options, but not a lot. You can use something other than wood (like carbon fiber-reinforced composites), and these have a wider range of intrinsic properties. But they tend to sound rather different from wood, and we don't want to change the "mandolin voice" too much! There's just not much wiggle room, here.

Anyway, yes, there is some merit to your concept about the thinner recurve region near the top rim acting as a compliant "spring," and the top as a more massive "piston" that rides up and down on this spring (driven by strings), with the air in the instrument alternately being compressed and rarified. However, this physical simplification only describes the LOWEST-ORDER (a.k.a. "trampoline") mode of the overall instrument vibration. But most of the acoustic energy that we hear from a mandolin comes from the higher-order modes, where the situation is very much more complex than that, and we can no longer conceive of the vibrations in this simple way. That is not to say that the recurve isn't an important element -- only that adjustments to the recurve don't always work the way you might think they might, based on simple models.

Yes, you can try to increase both loudness and sustain, but realize that (1) these two things tend to work directly against one another, for the most part, and (2) you have to somehow find a way to reduce the damping without sacrificing tone, which sure ain't easy!

But if it were easy, everyone would do it...

[Larry Simonson]

Is a banjo an example of high loudness low sustain? What about a dobro?

[Bertram Henze]

Is a banjo an example of high loudness low sustain?

Yes, and a Fender strat is the opposite (without an amp, of course)

What about a dobro?

Resonator instruments are like speakers; they spatially focus more than other string instruments, i.e. most of the power is radiated forward (as opposed to a normal instrument which roughly radiates in every direction). Therefore, in front of the resonator you hear more, behind you hear less.

[rcc56]

Practical mandolin statement: Well made oval hole mandolins tend to sustain better than well made f-hole mandolins.
Try a good F-4 sometime.