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What does the back do?


Don Noon

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I have done enough experiments and regraduations focusing on the top of the violin, so I kindof have a feel for what's going on with the top.

 

The back is more of a mystery to me, and I haven't done any regraduations where I left the top alone and only messed with the back.

 

There's theory and measurements... yes, the back moves more and produces more sound in the low and mid frequencies, so that's where I would expect the most influence to be.  However, the top and back are quite tightly coupled, so there could easily be more going on in the way of cross influences.  Certainly in the low frequencies the stiffness of the back should make a difference in the feel and playability of the instrument, perhaps even more than  in the sound.

 

But I don't have enough experience at this to know anything for a fact.  I welcome any facts opinions on the subject.

 

Right now I'm wasting effort rehabilitating a recently aquired cheap old student-quality fiddle, as most of my other experimental cheapos have been experimented into oblivion.  The top is thinned and will go back on today, with the very thick back intact (5.5 mm center, only very small areas down to 3).  After I see what I have, I intend to thin the back and see what changes.

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I have done enough experiments and regraduations focusing on the top of the violin, so I kindof have a feel for what's going on with the top.

 

The back is more of a mystery to me, and I haven't done any regraduations where I left the top alone and only messed with the back.

 

What are your findings regarding the top?

 

I remember reading something that says the back is for power (whatever that means).  And the quality of the wood doesn't matter too much.   But something has to matter.  Otherwise, why would we all make the centre so much thicker?  I would love to hear what other people say about the back.

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I'm going to stick my neck out to just give my gut feeling on this. No experimentation or data to support it. My feeling is that the back also acts as a resonator, along with the front. Thinner edges allow flex, just like the front.The soundpost couples the two, and transmits vibration directly from the front to the back. I'm going to guess that too much mass in the back would really damp a violin. What would happen if you used a piece of 1/4" cement board as a back?

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I'm only a player!

 

That said, I can dramatically change the sound color of my cellos, especially my realively thin-backed baroque cello, by placing my hand on certain areas of the back. When doing the same on the front, there isn't that much change in the sound color/character. So I'd say the back has a huge influence on the character of the sound.

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I think it would be interesting to set up a violin with no back at all, to see just what a top sounds like on its own.

 

Would it be worth an experiment:  Instead of putting a whole back on, if necessary, just put a strip of wood or a dowel with a spot wide enough to support a post and running the length to help the top counter the pull of the strings.  In other words, as little back as possible.   I've always assumed—not having any science behind my assumption—that the back controls the top, mellows things out, focuses the tone, but probably also augments the volume.   I have a feeling the sound would be quite bright, uncontrolled, and small without the back.  Even if I was right, that would partially answer "what it does" but not HOW.

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I'm sort of with Peter K-G, regarding this subject; as a whole.

Violins are acoustic instruments, and the entire corpus (of corpus!) acts as a whole.

When considering the back as a separate part of the violin, well, that's an interesting way to look at things, since the front and back and ribs  (and the neck) all move or vibrate accordingly together at the same time -  to make the distinct sound that is the violin. 

Yes, looking at the back as a separate animal, of sorts, seems a rather almost *medical* way to go about it.

Which is OK. But there are different approaches to medicine. 

I'm thinking that Peter may be suggesting a more "holistic" approach - of which, I believe I would agree with.

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I don't know much about violins.  But for violas the backs are always quite a bit heavier than the tops so they float top side upwards.  Then the f holes don't let water in.

 

I don't see what the point is of that, although I do see the reasoning for throwing a viola in the lake.  I would tend to fill it with concrete first, though.

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I think it would be interesting to set up a violin with no back at all, to see just what a top sounds like on its own.

 

That brought up a recollection of my topless fiddle.

post-25192-0-06004400-1420480460_thumb.jpg

 

The problem with this kind of thing is that the interactive aspects (which are significant) go away.  No A0, no B1+, and just a remnant of what looks like a B1-.  Many of the higher modes are also interactive, I believe, so nothing is really clear.

 

However, this topless fiddle had the strongest response in the 700 - 1000 Hz range, so one might guess that would be the range most affected by back choices.

 

Someday I might try a similar thing but the other way around, with just a thin strip on the back.  But not in the near future.

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I'm going to stick my neck out to just give my gut feeling on this. No experimentation or data to support it. My feeling is that the back also acts as a resonator, along with the front. Thinner edges allow flex, just like the front.The soundpost couples the two, and transmits vibration directly from the front to the back. I'm going to guess that too much mass in the back would really damp a violin. What would happen if you used a piece of 1/4" cement board as a back?

Where’s the “LIKE” button?   B)

 

The back acts exactly like the top, except:

 

•It’s made of maple, not spruce.

•The bridge does not drive it directly

•It does not have a bar

•it does not have sound holes

 

This may sound stupid, but I think there’s more to plates and sound than just these things.  For instance, what is the reciprocal effect of the sound post on the top?  Why does back graduation matter?  Why do minor thickness adjustments to parts of the back have significant effect on overall tone?

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I recently had 3 5string fiddles tried by 4 very good fiddle players with very surprising results.

fiddle #1 & #2 sitka tops .42SG, #3 engleman .37SG. arching and grads. very near identical. #'s 1&2 GDG 1734 pattern, #3 GDG Cannon pattern.

Each one has a progressively thicker back. #1 4mm. center, #2 $ 4.75mm.center, #3 5.5mm. center

weights from 105gr. to 116gr.

#1 sounds like an old dry fiddle, growly on the G&C, very easy to play

#2 (1piece quartersawn back) much smoother on the bottom end but not as easy to play.

#3 my favorite by far, very smooth bottom end and the sweetest top end I have ever played and very easy to play

#2 has since had the back thinned, and plays more like #1

I will leave to you to guess which one all the players prefered

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I'll look to see if I have this:

 

Influence of top and back plate stiffness on low frequency modes of the violin (in cooperation with C and B Hansen, B Niewczyk, and L. Frydén) 31st Interntional Acoustical Conference. Tatras, Slovakien 1997, invited paper)

 

I think I recall it may have been this paper where they made 3 top plates of different weights and stiffness and 3 different back plates of different weights and stiffness and then assembled them in different combinations (9?) to see what sounded best. 

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Personally I feel that the back works hand in glove with the top. The structural make up of the plates, based on their interaction with each other are crucial in creating the "air pump" that drives amplitude as well as core tone. To me the critical interaction, that I have no data for, nothing but speculation, is that the speed and or rate of travel of vibrational frequency and thus its "output" are highly dependent on a "delay" related to the bow hitting the string, then the vibration traveling to the bridge, then the top plate,then the post and finally to the back. This of course is happening in a fraction of a moment and once this cyclical "round" "relay" "circle" of vibration occurs. it is the thickness of the back and where that determines the "hand off" speed in the relay. 

 

Or there is a fractional amount of time that passes when first vibrated, as instantaneous as it all seems, there is an order {string,bridge,plate,post,back} and I think in simple terms a too stiff, too thick back "hands off" the vibration too early, or quickly, and a back that is too thin and flabby, will "hand off" the relay in a delayed or too late way. This gets in to "beneficial" vs counterproductive vibration cycles working against each other and in essence killing or throwing off the timing of the vibration circle, resulting in poor tone and lack of projection.

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I recently had 3 5string fiddles tried by 4 very good fiddle players with very surprising results.

fiddle #1 & #2 sitka tops .42SG, #3 engleman .37SG. arching and grads. very near identical. #'s 1&2 GDG 1734 pattern, #3 GDG Cannon pattern.

Each one has a progressively thicker back. #1 4mm. center, #2 $ 4.75mm.center, #3 5.5mm. center

weights from 105gr. to 116gr.

#1 sounds like an old dry fiddle, growly on the G&C, very easy to play

#2 (1piece quartersawn back) much smoother on the bottom end but not as easy to play.

#3 my favorite by far, very smooth bottom end and the sweetest top end I have ever played and very easy to play

#2 has since had the back thinned, and plays more like #1

I will leave to you to guess which one all the players prefered

 

You didn't mention anything about power. :D

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the one they liked best was quietest to the player but loudest from a distance of 6/8 feet. which do you think would do that?

Somehow I think the dynamics of understanding how one can "throw" their voice by saying something, but making it sound like the voice is coming from "over there" has something to do with what you are saying.

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I think it would be interesting to set up a violin with no back at all, to see just what a top sounds like on its own.

 

Would it be worth an experiment:  Instead of putting a whole back on, if necessary, just put a strip of wood or a dowel with a spot wide enough to support a post and running the length to help the top counter the pull of the strings.  In other words, as little back as possible.   I've always assumed—not having any science behind my assumption—that the back controls the top, mellows things out, focuses the tone, but probably also augments the volume.   I have a feeling the sound would be quite bright, uncontrolled, and small without the back.  Even if I was right, that would partially answer "what it does" but not HOW.

I don't think this experiment would produce much in the way of meaningful information. Because the box is now completely open, the natural internal air resonance is gone. This will drastically change the timbre.

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I'm sort of with Peter K-G, regarding this subject; as a whole.

Violins are acoustic instruments, and the entire corpus (of corpus!) acts as a whole.

When considering the back as a separate part of the violin, well, that's an interesting way to look at things, since the front and back and ribs  (and the neck) all move or vibrate accordingly together at the same time -  to make the distinct sound that is the violin. 

Yes, looking at the back as a separate animal, of sorts, seems a rather almost *medical* way to go about it.

Which is OK. But there are different approaches to medicine. 

I'm thinking that Peter may be suggesting a more "holistic" approach - of which, I believe I would agree with.

 

Yes, I like them to play nice together like a married couple! If you want to know how they come along you need to take all setup of a violin and gently hang the violin under the scroll heel, without squeezing the neck. Put your ear near the middle of the back plate and tap with your nail in the middle of top plate, then you will now how the top likes the back. The vice versa for how the back is in love with the top. The top can not respond to the back without a sound post but the back can respond to the top without the sound post.

 

If you like to hear them from a little distance and how they echo together. Knock with your index finger about a centimeter under the sadle and you will hear them in chord. Knock two centimeter under the scroll on the neck side and you will hear the top playing solo. Stupid tuners use to call these modes B1- & B1+, but in fact they are lovers and need to be in tune  :rolleyes:

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Personally I feel that the back works hand in glove with the top. The structural make up of the plates, based on their interaction with each other are crucial in creating the "air pump" that drives amplitude as well as core tone.  

 

"the back work hand in glove with the top"...

 - couldn't have said it better myself.

I don't like to look at them apart, or think of them as all that seperate really, as if they were completely separate entities...

I'm thinking that the discussion needs to be about the top, as it is very often made first, and with specific design parameters in mind, and then the "top and the back"...

I'm thinking that perhaps the back design may depend a lot on how the top is (or was) made and perhaps this may really affect the backs design.

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