Sustain--How to build in?

[pelone]

Is sustain a quality related to:
1. Volume of chamber
2. Top thickness that is thin
3. Top that is thick
4. bracing
5. Strings that are robust or thin

How do I build in more sustain?

[peter.coombe]

How long is a piece of string?

[Jim Hilburn]

Make an oval.

[Jim Rowland]

A note that pops and decays quickly is a characteristic and sometimes the intent of an arched mandolin or guitar. If you want more sustain,go flatter on the back and top. In fact,if you need just loads of sustain, go with a flattop. Some arched instruments do have more sustain than others,but aside from the above,I couldn't tell you definitely why.
Jim

[Rick Turner]

Stiffen the neck (see carbon fiber thread, and don't despair, we all get quite civil at the end...), add mass to the peghead, make the top thicker, put on a brass bridge top. Your interior chamber size will have little to do with anything. Make a solid body. Make it out of rosewood. It will sustain for days.

[billkilpatrick]

sounds like luthery owes more to alchemy than carpentry ...

[Dave Cohen]

"Sustain" in acoustic plucked stinged instruments is complicated beyond anything that you might have imagined. For one thing, it is highly dependent on frequency, and in a very complicated way. With mandolins, it also depends on the type of mandolin. Regarding your five factors:

1. Volume of chamber: not in any simple way that you would predict.
2. and 3. are really the same thing: Leaving a given top thicker will leave its modal frequencies higher in general. That will effect the frequency dependence of "sustain", but not any overall characteristic of the instrument.
4. bracing: Not much, if at all.
5. strings: Well, yes, but there are other more dominant factors.

"Sustain" depends on the string motion decaying slowly. For slow decay, you need low losses. But losses are what acoustic plucked stringed instruments are all about. Strings lose energy to their own internal structure (most prominent in nylon & gut strings), to the friction due to moving through air (called "viscous damping") and to the body and neck motions of the instrument itself. Without those motions, you wouldn't have an acoustic instrument, so to some extent, decaying notes are a characteristic of acoustic plucked stringed instruments.

http://www.Cohenmando.com

[man dough nollij]

Isn't it true that in general, you would want it to be on the heavy side, and as rigid as possible? Vintage ovals have good sustain, and also happen to have stubby, rigid necks.

A banjo is very flexible, and would be light without the tone ring. I'm the construction is not that rigid (long, thin neck, hardware attachments).

Banjos have the least sustain, so I would think that to get the most sustain, you would want to build an "Antibanjo". Eh?

[Rick Turner]

It's called a Gibson Les Paul.

[man dough nollij]

It's called a Gibson Les Paul.

Actually, that's just what I was thinking. In general, more sustain is better in electric guitars, right?

[DerTiefster]

Just like basic artillery theory, the principles are simple (falling bodies) but the real practice involves lots of complications like air resistance, tumbling projectile, etc. I came close to giving a first principles description (all I know about the subject, really) as post #2 in this thread, but wasn't certain what kind of question the poster was asking. It seems he was interested in basics, so I'll try my hand at it.

Sustain is a measure how long the string keeps vibrating with about the same amplitude (same stored energy in the spring motion). There are damping influences, like your sleeve inadvertently placed on the strings at the bridge. Oh. It's not vibrating any more. Ah. now it is.

The energy the pick stores in the string results in a vibration of the string and mandolin body/soundboard. If the mandolin were as light as the string, it would vibrate as much and your body against the mando body would sop up the energy like a pillow stops a tuning fork. So a rigid back can help improve sustain by not vibrating against your clothes so much. Similarly, making the headstock and tailpiece more massive tends to keep the vibration in the string. I read of someone finding one mandolin didn't change much with a ToneGard and another did. That would mean to me that the first mando had not much back vibration/flexure and the second had more. Doesn't say what you need, just says it can be a parameter to use.

but the energy HAS to get turned into sound, and that's the job of the soundboard and its holes. Those holes act as antennae do for a radio transmitter. The soundboard (top of mando) vibrates and sets up oscillations in the air of the sound chamber. And yes, in front of it, too. These pressure waves couple out the sound hole(s) to project sound energy into the air. If you have wet, green wood in the mandolin, it will not be as springy. The sponginess would tend to absorb the sound, not letting the wood spring back when the sound wave slightly distorts its shape. An internal wet blanket. So the wood compression characteristics matter.

All of the energy absorbing mechanisms defeat the production of sound. The making of sound transfers energy from the mandolin to the air, which is a desirable thing. But if you project too efficiently, you get a rapid decay of the energy in the string. Less sustain. Solid body guitars don't vibrate much and they are massive. The string just sits and vibrates. Sustain all day long. The pickups don't sap much energy from the string, so it keeps vibrating. The amplifier boosts the sound so you can hear it. But if your f-hole mandolin really projects, it pulls energy too fast from the mandolin and you get big sound at first, then lots less.

As Dave has pointed out in other posts, the string can be vibrating parallel to the top (less vibration pressure against the top, so it moves less and couples less to the air and sound), or perpendicular to the top (pressing against it and moving it and tthe air behind it). Bridge design and fretboard flex can affect how rapidly these two "polarizations" interchange. If the mandolin keeps the two separate, you might have an early "bark" strongly coupling the perpendicular mode out and quickly dying away to the underlying long-sustain parallel mode which could have different tonal characteristics. Just my thought on that.

The devil is in the details: what wood, how much neck flexure, bridge dynamics, sound hole and sound box design for "proper" coupling to the air, and all that. So, I tried to sketch how these things interact from first principles, not how you get them to do what you want to do. I hope it's kind of what you wanted. You can build a mandolin to have little sustain. If done in certain ways, like packing it full of feathers or installing a rubber bridge, it could be undone. Others (wood choice) can't so readily be undone.

I sure hope this is the kind of answer you wanted. I'm more familiar with metal cans full of radio waves, but the general principles are the same for wooden boxes full of sound waves.

[pelone]

Great response to my question. The mando I just completed has a sweet woice, not much punch or sustain. I used Port Orford Cedar for the carved top. A nice blonde color with little evidence of striations of growth rings/grain.

I am pulling it off and I am presently in the process of crafting a shallower top from salvaged Douglas Fir that has been aging since 1950 in the form of spectator seats in a university gymnasium. The growth rings are straight and tight and have a nice golden quality to it. The boards were true 2 by 12's and the wood gives me plenty to work with. Thanks for the great feedback.

[pelone]

" a sweet voice " not woice. Sorry for my lack of editing on the previous post.

[DerTiefster]

You seem to be discounting the chances of the bridge or tailpiece affecting the qualities you seek. I don't know whether that's wise or not. In experimentation, we usually choose the order of controlled measurements to keep the budget in check. Changing out the top as a first response seems a bit hasty.

[Michael Lewis]

How long has the instrument been together? Has it been dedamped? Good bridge? Stiff neck? Good set up?

[Michael Lewis]

Use hard and springy materials, your Douglas fir should be a good choice.

[Rod_Neep]

A fun trick to play on your buddies.....

Play THEIR instrument pressed against your belly, and play YOUR instrument held away from your belly.

Bear in mind that they never hear their own instrument from the front when they play it, and therefore the trick deceives their ears. They will instantly compare their own instrument with yours.

The volume and sustain of yours will be much greater! The smaller the instrument, the greater the effect. (e.g. mandolin or ukulele).

Magic pill for more volume and sustain = no belly touching the back of the instrument.

Rod

[BlueMountain]

I play primarily jazz, and I want a sort of thickness to the sound, and responsiveness, but not much sustain. A tone cannon, but with very fast decay. My favorite mandolin for this sound is a Collings MT2V that sounds perfect to me: that is, it sounds like Don Stiernberg's Nugget.

I picked up another mandolin at a great price that showed a lot of promise in that direction, and I thought I could make it more Collings-like by adding an Allen tailpiece, such as the Collings has. So I installed that yesterday. Same tuners, same tailpiece, same JazzMando flat-wound strings. I should have known better. I'm now getting immense sustain from that tailpiece. It won't work at all. I'm going to have to go back to a standard tailpiece.

Strange that the Allen tailpiece doesn't cause endless sustain on the Collings.

What would happen with an ebony tailpiece?

[DerTiefster]

....Strange that the Allen tailpiece doesn't cause endless sustain on the Collings...The energy is going somewhere. Maybe the Collings is just a better projector and the strings can't keep up.
...What would happen with an ebony tailpiece?I know of only one way to find out, but then again, I'm an experimental physicist. Tell us when you find out.

[Rick Turner]

That's what I love about you experimental physicists...you actually want to try things and experiment before you give judgement! The lutherie world is full of young luthiers who want to theorize things to death and know absolutely what the results will be before they pick up a chisel.

Not talking present company...just a general observation.

[first string]

To echo/underline two points that have already been made, but which may have been drowned out by some of the (very interesting) technical/theoretical points, make the back with rosewood, and use CF reinforcement for the neck. I was looking for a mandolin with a lot of sustain, and opted for that combo, and it worked wonders for my Clark. It has more sustain than any f holed mando I've ever heard. That said, I do sort of wish I had gone with an oval hole, which was what I ordered originally (but which I changed to f holes because of the demise of my only f hole mando). As you probably know, ovals provide a lot more sustain.

Here's a question for you builders: Do archtops really have inherently less sustain than flattops? That seems to be the conventional or received wisdom, but I wonder if that is merely a result of some of the design conventions that are typical of the respective styles. That is, pin bridges for flattops and floating for archtops. And almost invariably (especially in guitars), round holes for flattops, and f holes for archtops. Could an archtop with a rosewood back, a pin bridge, and an oval or circular sound hole have as much sustain as a flattop? Thoughts?

[Martyweir]

"Do archtops really have inherently less sustain than flattops?"

Well, A flat top is sort of like a box with at least two (semi) parallel surfaces, so I would think the Axial Room Mode theory would come into play some what. Basically the sound waves caught between two parallel surfaces create a or boost in sustain and volume, etc - usually wave length dependent with a frequency or standing wave, but I'm sure it affects sustain at all wave lengths. We've all experienced it to some degree. Singing in the shower for example, you hit that note that just resonates forever? No, just my shower? Wierd, very relavent when recording, room shape & size is ALWAYS a factor. Archtop / back insturments (non parallel surfaces) should eliminate this effect altogether and reduce sustain.

Rick, is this an issue you have to deal with when building guitars?

[Tavy]

Jumping in where fools fear to tread....

1) What about string tension and bridge break angle? I was under the impression that higher tension and greater break angle == more punch and less sustain, while lower tension and/or low break angle == more sustain, less punch. I note most bowl backs (and folk style oval holes) tend to have low profile bridges with a lower break angle than arch tops with their more angled necks. Just a random observation.

2) Does hole shape really make that much difference? I was under the impression that what mattered was surface area of the hole, and much less it's position and shape? I thinking here of ovation-style multiple small holes as well as the oval vs f debate.

Thinking out loud yours, John.

[DerTiefster]

On the area vs. diameter issue, have you heard of phased array radar? The idea is to synthesize a large-diameter (long wavelength == low frequency) transmitter from an array of smaller ones. Small changes in relative phase of the array change the direction in which the emitted signal goes, so you get the benefit of a swiveling antenna without the mechanical pain, so it's not just the long wavelength that's the gain.

But an instrument like the ovation -may- be designed to get a larger effective size of the "transmitter" and better bass projection without suffering the penalty of having a large emitting area. There are lots of details in which devils can hide. Your mention of string tension and break angle is another. Same tension in strings with bigger break angle means more pressure on the top, which means more pressure changes from string vibrations, which means more motion of the top, and more sound energy inside the soundbox. More losses (passive as well as projected sound) means less sustain. In general, not in every example because of possible compensating effects.

As Dave Cohen said, it's marvelously complex and lots of stuff happens and lots of stuff you'd not even think of actually matters. And I'm only an armchair kind of guy, not well practiced as a player and I've never even repaired an instrument, let alone designed or made one.

[first string]

For the sake of keeping this discussion going (and because I think it's genuinely interesting), check out this Sobel Archtop 12 String:

http://www.dreamguitars.com/sold/Sobell_12%20string_88107.htm

There's a link on the page to hear Al Petteway playing it. Pretty good sustain for an archtop I think. Just imagine if you hybridized the design a little more.

[Rick Turner]

The pressure on the top thing is interesting...you can have too much. The idea is to mechanically "bias" the top so it responds up and down properly. Overload it with pressure, and you'll damp it mechanically and you'll get less output, though you may increase sustain. The top is like a spring...load it just right and it can move with equal ease up and down. Load it too much, and it bottoms out.

[Dave Cohen]

I spent some time doing some theory, but more doing experiments. I consider myself an experimentalist.

Regarding breakover angle: I built some mandolins early on with 7-8 degree neck angles, as opposed to the traditional 4.6 degree angle. Those mandolins were no louder, nor did they sustain any longer, than the ones built subsequently with 4.6 degree neck angles. The one thing about the high neck angle mandolins that stood out is that they were awkward to play.

Regarding cast tailpieces: A typical stamped tailpiece has a mass of about 30 grams. Cast tailpieces typically have masses over twice that, say about 70-90 grams, depending on the tailpiece. A pretty light mandolin body will have a mass of around 300 grams. So switching from a stamped to a cast tailpiece will increase the total mass by, say, about 30-50 grams. That is a little more than 10% - enough to potentially make some difference, but nowhere near enough to make an "incredible" difference. A tailpiece is a point of rigid attachment. Except for an incremental difference in sustain, Adding mass to the body of the instrument is not a good idea. It is extra mass that you have to set in motion by plucking the (much lighter) string, and will, imo, steal from the responsiveness of the instrument.

It is interesting to read the claims of "incredible sustain" in threads like this one. Wanting to believe that the instrument you bought and/or tricked out is up to all's expectations is a well-known phenomenon. Trouble is, no one making those claims ever actually measures anything related to sustain. What you have to measure in order to avoid artifacts is the decay time or characteristic time. In the physics biz, we usually define the characteristic time as the amount of time it takes for a note to decay in amplitude to 37% (= 1/e) of its' highest value. We use that because it is independent of things like of how hard you pluck the string, atmospheric conditions, etc.

I have made characteristic time measurements on a few mandolins, in particular a Calace Neapolitan and an f-hole type mandolin. There are a couple of things that stood out in those measurements:

1. Dacay times for mandolins are short - much shorter than guitars, but not as short as banjos.

2. The single thing that dominates differences in characteristic times from note to note and from mandolin to mandolin is body motion. String amplitude decays because the string loses energy in three ways: (a) to friction from moving through air, (b) from internal losses in the string itself, and (c) to motions of other coupled vibrating systems, in this case, to the mandolin body.

2.(c) turns out to be the dominant factor in mandolins, if not in all plucked stringed instruments. When the frequency of a plucked note is near the peak frequency of a particular body motion, the string loses energy to that body motion and the string's amplitude decays. In Neapolitans (i.e., bowlbacks), nothing happens in the body until about 450 Hz, i.e., around the open A 2nd string. WHat I found was the the Neapolitan sustained very well up to about 450 Hz, then, as the body got active, the characteristic times dropped by a factor of 10 or more and stayed low. Same thing was true for the f-hole type mandolin. The "main" body modes occur from about 270-450 Hz. So what I observed was that the decay times for the first few notes (e.g., G, 196 Hz,...) were relatively long. At around 250 Hz, the decay times started dropping, and remained low until about 500 Hz. Then they dropped again at around 650 Hz, which is the frequency at which the next motion, the sideways rocking motion, occurs. This repeated itself up to above 1.5 kHz or so, at which point I stopped doing measurements. So the first and most important thing to understand when talking about sustain is "sustain of what note(s)?" The second most important thing is that you can't really do much to overcome the limitations that the instrument body itself imposes on sustain. If you actually do succeed in building an instrument with "incredible" sustain, I'll bet dollars to doughnuts that it won't be a particularly good instrument, and you won't like it.

http://www.Cohenmando.com

[yoshka]

I can't really add anything to the discussion but I have learned quite a bit about sound dynamics and sustain and the factors involved. Just wanted to say thanks to the folks that have the knowledge and take the time to write.
Yossi