Any function to recurve

[red7flag]

The Hester I have has a really pretty recurve on the outside of the top and back. Was wondering if the beautiful look has any function. Thanks?

[Pete Jenner]

There have been a few threads on this but I always look forward to what people have to say.

[bart mcneil]

Yes it has a very important function. The top and to some the degree the back are designed to flex slightly. You can't see it but the strings vibrate against the bridge and the bridge carries the vibrations down to the top and the top vibrates amplifying the sound of the the plucked string. The top then becomes literally an air pump. Violins work the same way and the mando kind of follows the violin and how it works in amplifying sound. The top is thinnest on its sides near its edge allowing greater flexibility to carry the vibration. You could undoubtedly design it a different way and still allow the vibration to take place but this is a case of form following its function as an air pump. I guress you could compare the thinness near the edges as a hinge on a bellows. It is designed to allow flexing.

[Marty Jacobson]

The recurve provides an essential sexiness function. The sexiness increases according to the square of the smoothness of the recurve divided by the lumpiness of the scroll.

[Russ Donahue]

The recurve provides an essential sexiness function. The sexiness increases according to the square of the smoothness of the recurve divided by the lumpiness of the scroll.

Aaah. Of course. Clearly that is in part what drives MAS as well, correct?

[Willie Poole]

I compare it to a church bell, a bell with a recurve sounds different then one without it...

Willie

[bart mcneil]

If I recall correctly Chinese bells do not traditionally have re-curves. Perhaps that is why if you listen really hard you still can't hear them. Where as the church bell right down the street has a re-curve and rings out really well.

[Ken]

Bart is correct in saying that the recurve allows the top to move better, but you can get similar results by simply thinning the edge of the top and back to where you want to be. I've built both ways and would be hard pressed to tell you I can hear a difference. My guess is that the recurve started as a production method where the 3/16ths thick edge of the mandolin top or back allows the bottom of the binding to be at the same level as the top of sides which then allows you to easily align it with the cross piece at the 15th fret. Plus if the mandolin is unbound, then a 3/16 thickness gives you more beef on the edges in case of bumps and dings.

[StuartGold]

Seems to me that a recurve moves the thinnest part of the top inward toward the bridge creating a slightly higher pitched resonating surface. Does that make any sense?

[fscotte]

The recurve is an essential part of the power of a bow. You can have bows without recurve, but they are less powerful given all other variables are the same. If you look at a cross-section of the plates, you see a bow. The strings act very similar to how a bow works. You strike the string, it pulls the ends of the mandolin, causing it to act like a bow. So perhaps the recurve provides the plates more power.

[Graham McDonald]

What Marty says. I have just finished a mandolin with virtually no recurve, but the appropriate graduations and it works perfectly well. Remember with a violin the purfling is cut into the recurve and that has to have some effect on the plates resonate.

Dave Cohen? Any more scientific explanations of what is going on?

[sunburst]

Yes it has a very important function. The top and to some the degree the back are designed to flex slightly. You can't see it but the strings vibrate against the bridge and the bridge carries the vibrations down to the top and the top vibrates amplifying the sound of the the plucked string. The top then becomes literally an air pump. Violins work the same way and the mando kind of follows the violin and how it works in amplifying sound. The top is thinnest on its sides near its edge allowing greater flexibility to carry the vibration. You could undoubtedly design it a different way and still allow the vibration to take place but this is a case of form following its function as an air pump. I guress you could compare the thinness near the edges as a hinge on a bellows. It is designed to allow flexing.

I hate to do this, but here goes...
There is just too much misinformation in that post to not bring it to the attention of those wanting to learn about this stuff.
The top and back are flexible, that part is correct. The strings apply pulses of force to the bridge, not vibrations per se. The bridge and top mostly move as a unit setting the normal modes of motion of the top in motion (and from there, the whole of the mandolin). No other movement happens in the top other than the normal modes of motion, according to the laws of physics. The top, working together with the back and the rest of the instrument is part of an "air pump", but only in the lower frequency modes of motion. Higher frequency sounds are produced by the mandolin in other ways, mostly radiating from the surface of the instrument, and are not the result of the body pumping air. The modes of motion in the top and back plates are "global". That means that the whole plate is involved right to where it is glued to the rim. The recurve area makes no apparent difference in the shape or positions of the modes of motion. it does not act as hinge. Violins and mandolins work differently, though somewhat similarly. The sound post in the violin modifies the shapes, positions and frequencies of the plate modes, and acting as a physical connection between the top and back so that the bow acting upon the tall bridge enhances the air pumping aspect of the lower frequencies in the violin. Once again, higher frequency sounds from the violin are not dependent on the body pumping air.
Whatever the recurve may have been designed for, it's true function appears to be almost exclusively aesthetic, or it's as Marty says.
I'm with Graham here in hoping that Dave will come along and shed some light on this, correct anything I got wrong, and once again teach us all something!

As others have said, I've heard mandolins that sounded just fine and had no recurve area at all.

[bernabe]

There's no known or proven function to re-curve as we see it visually. It just so happens to be where plates are the thinnest most of the time which does matter in the overall scheme of things. I guess a lot of folks believe, in order to be the "proper" thickness near the edge, it must visually curve back up. Its been successfully done with and without and everywhere in between. You're not going to get a unanimous opinion on this but, I think most builders would probably lean toward the re-curve as visual appeal and/or a market preference more than anything. Notice I used the words "no known or proven function". If its out there please share....I like re-curve.

[bernabe]

Dang, one more minute and I wouldn't have had to 'two finger" type all that.

[fscotte]

Perhaps it assumes the roll of adding sustain to the top. Since the plates are essentially springs. Put most of the mass in the center of the spring and the least amount of mass in the recurve. Whatever the purpose, we will at least invent one...

[Dave Cohen]

John Sunburst covered it pretty well. So many made-up conjectures. I don't understand why so many people seem to think they should make up something in response to a question like the one in this thread. I mean, "allows the top to move better"?,..."a slightly higher-pitched resonating surface"?,..."the recurve acts like a bow"??,..." "provides the plates more power"???,..."assumes the role of adding sustain to the top"????. For even more laughs, try the current thread on the function of the f-scroll. To those who feel compelled to make up stuff in response to questions like this, I have a couple of suggestions. The first is to read Bob Benedetto's book, "Making an Archtop Guitar". In his last chapter, he admonishes aspiring luthiers, when asked a question by a customer about how something works, to not make something up if you don't really know the answer. Instead, tell the truth and say that you don't know the answer. The customer will appreciate your candor. If, on the other hand, you make something up and the customer later finds out that it is bogus, you will reap what you sow and lose respect. The second suggestion has to do with what to do when you think about some question like this one and come up with a conjecture about the asnwer. How about checking your conjecture against a physics text, or, dare I say, the musical acoustics literature? You might learn something, and you also might prevent yourself from looking foolish.

A couple of pertinent facts about recurves: One is that the lining on a mandolin is about 3/16" - 7/32" wide, and the ribs are another 1/16" - 0.090" wide (depending on the builder). The interior of the lining is effectively the location at which the edge of the plate is "clamped". That is approximately 0.3" in from the outer edge of the mandolin body, and it is also pretty close to the area of minimum thickness in the recurve. For bowed string instruments, the numbers are different, but the area of minimum thickness in those is also just inside the recurve. Iirc, the original intent of the recurve in bowed string instruments was to provide greater thickness in the plate over the glue joint with the ribs and lining, for the purpose of structural stability. It is something that is not really needed in archtop mandolins and archtop guitars, but managed to get established anyway as a carryover tradition. Orville Gibson thought he was improving the mandolin by making it's morphology more violin-like, and in that he gained a following. In mandolins, the recurve does look interesting, and also looks to be a nice transition to the binding.

http://www.Cohenmando.com/

[Pete Jenner]

In recent threads it has also been shown that the commonly held belief that plates need to be graduated from thicker in the middle to thinner near the edges is also a furphy. I think we've established that plates need to be mandolin shaped, light and stiff. Hopefully all this nonsense about springs, hinges, bows and bells will now cease. Recurves appeal to the eye and the touch. That is all.

[bassthumper]

I had asked the "recurve" question in 2008 after wondering to what degree the very noticable differences in my Weber SE & Collings MF had in the undeniable diffences in volume, tone, etc. in two mandolins that look nearly identical next to each other across the room.

a freind with zero experience in psaltries but 50 years in fine woodwork was examining them and admiring the craftsmanship of both... he was mesmerized... he kept asking if that recurve made the difference... I explained what little I knew about mandolin construction variences then asked on a few threads in the builders section.

Big Joe and several others explained it well...one gentleman posted pix of a serously radical recurve on a high $$ custom
A by a big name lutier... I beleive the recurve is one of several techniques luthiers use in shaping potential voicing in the instrument.

[Pete Jenner]

Anyone interested in reading some of Dave and Thomas D. Rossing's work, can download the entire CAS journal (and many more dating back to the sixties) here for free.

[Ivan Kelsall]

It may very well be a throw back to the design of the Violin, & included in Orville Gibson's new mandolin design purely for aesthetic reasons. It's doubtful that OG performed many acoustic experiments before launching the new design,so i suspect that the new mandolin design,having an arched top & back similar to a Violin,also sported the re-curve of that instrument. If you look at the Guitar in the photo.,it has a flat top,but also has the re-curved edge. So,i wonder if OG did indeed think that there was a 'sound' reason for it ?,
Ivan

[fscotte]

Threads like this remind me of something John Monteleone said. When describing the function of tonebars, he said that tonebars help transmit sound evenly across the top, acts like a filter...

The way I look at it, if it helps Monteleone build or imagine how to build a better instrument by seeing the tonebars this way, then that's exactly their purpose for Monteleone. No reason to laugh or scoff at a builder, despite who he is, whether great or small, if he's enjoying the build process and making a decent mandolin.

Replace tonebars with recurve in the above scenario. If that helps one build a better mandolin by seeing it act as a hinge, then that's exactly it's purpose.

[Rob Grant]

Not to throw a spanner in the works, but as an old diesel fitter, I still find it rather oddly coincidental that the most efficient mechanical pump diaphragms have a very similar shape as the re-curved, graduated tops and backs of some of our favorite mandolin styles. Isn't this also true with speaker cones? Convergent evolution or a useless bit of wood working bling?

An example of a solenoid driven pump diaphragm. Note re-curve and "graduated" centre section...

[sunburst]

Peter, you can't honestly believe that there is any chance that "all this nonsense about springs, hinges, bows and bells will now cease". Finding out how things really work is no fun for a lot of people. Even when learning what is actually known about how they work is as easy a following a link and reading about it for free, It's just more fun for many people to make things up.
High level luthiers are not immune to making things up. Sometimes the techniques they settle upon make good sense in terms of how the instrument works, but their explanations can be completely off the mark.
I find that sometimes customers don't like to hear the truth. When asked about tone bars and what they do, I've said "I don't know", only to see a sort of blank, surprised expression on the customer's face. If I start off telling them what I do know about tone bars, I don't get much past lateral and longitudinal stiffness and barely into plate mode frequencies before their eyes glaze over and they're ready to move on to the next lesson. What they really wanted to hear was some hocus pocus about vibrations being distributed or traveling down the bars from the bridge to the edges of the top, or about how tuning them to D# and E on a moonless night while listening to Gregorian chants gives the mandolin it's special, unequaled sound.

[red7flag]

A study was done about banjos and presented on a popular banjo forum that showed that the neck determined more of the quality of the sound than the pot. This result went counter to most threads and knowledge that were commonly expressed on that foum. I can remember the consternation in the banjo community trying to assimilate the findings of this study to the collective knowledge of the website. I was going along reading and I thought learning from the earlier posts on this thread. I was enjoying the bow analogy. Then John and Dave came along and blew my acquired misconceptions right out of the water. This has been fun. Thanks guys.

[bart mcneil]

So you really believe that you can prove that "... tuning them to D# and E on a moonless night while listening to Gregorian chants gives the mandolin it's special, unequaled sound." doesn't really work????

Some of us pray for excellence in our playing, performing and our instruments.... Can you really prove that doesn't work either????

So maybe the re-curve does have mystical powers you science guys aren't aware of.

I rest my case...