Arch height affect on sound

[Thomas Coleman]

Hello all, 

Does anyone care to share their thoughts on arch height and it's relation to the sound of the instrument?  I have heard that in a VERY general way that low arches contribute to more power and projection while high arches contribute to a "sweeter" tone.  I'm about to varnish my first viola, a loose interpretation of the Mantegazza at the National Music Museum.  The arch height on the original viola is pretty high.  I think like 19 or 20 mm.  I made mine 18.5 mm.  An experienced maker commented that he thought the arch was too high.  I'm assuming by the context of the conversation that he meant "too high" from an acoustic viewpoint as opposed to an aesthetic one.  If you read biographical blurbs of Mantegazza there always seems to be something along the lines of "known for his fine violas", so I assume his high arched violas are well thought of.  Anyone with more experience than me care to share their thoughts on arch height in relation to acoustics?  As always,  thanks so much for any time you care to give my query.

 

[Roger Frankland]

I believe it is true that a higher, stiffer belly will contribute to creating a sweeter fiddle tone and I think there are some good fundamental reasons why. Apparently Stainer learned this a long time ago. I say apparently because I have not personally heard one of Stainer's high arched violins. The fiddle on my bench will have a higher arch, but shaping a high arch is not easy and can create other problems, so I am not sure how high to go.

[Don Noon]

I believe I see a trend that higher arching results in less power in the middle frequencies (around 1 kHz), which would tend to sound more refined but less powerful.

However, looking at Anders Buen's data correlations, higher arching shows lower B1+ amplitude and generally less power in the lower frequencies, below 600 Hz..

[Wolfjk]

Hi,

Arching, the FF holes and the general geometry of the belly regulates the lenght of grain and reedin of the spruce belly. Ahigher arch means that the shorter reeds dominate so the resonance favours the higher notes. the lower arch creates more longer reeds, therefor more resonance and more power/volume in the lower notes.

Other considerations are the shape of the FFs, the distance between the upper eyes of the FFs, and the thickness of the belly. However the main problem is always; how much resonance the bowing can bring into play? Bridge, sound post, and countless other fittings aso have influences.

[David Burgess]

 

Arching, the FF holes and the general geometry of the belly regulates the lenght of grain and reedin of the spruce belly. Ahigher arch means that the shorter reeds dominate so the resonance favours the higher notes. the lower arch creates more longer reeds, therefor more resonance and more power/volume in the lower notes.

 

So according to "reed theory", bent (rather than carved) archings should produce instruments which are strong on the low end, and weak on the high end???

[uncle duke]

 the lower arch creates more longer reeds, therefor more resonance and more power/volume in the lower notes.

 Bridge, sound post, and countless other fittings aso have influences.

A lower arch enables more of a level surface on the soundpost ends and bridge feet  -  a more direct line for vibrations and tension to flow through evenly.

[actonern]

"...A lower arch enables more of a level surface on the soundpost ends and bridge feet  -  a more direct line for vibrations and tension to flow through evenly."

 

Is that good or bad?

[uncle duke]

"...A lower arch enables more of a level surface on the soundpost ends and bridge feet  -  a more direct line for vibrations and tension to flow through evenly."

 

Is that good or bad?

I'd think that would be a good thing- people will want your instuments. 

 

The minor problem I have is the Strad belly contours I have made for myself over the past few years were traced, copied, interpreted by a short, chubby person, then I copied them.

   If Stradivari was a short,chubby person back then I'll have to live with it.  I may have to go the Staineresque route with higher and pinched in arching, assuming I make another,  just so I can possibly make a masterpiece violin that looks like something I'd do.  Making one change per build until I reach a pinnacle is something I hope I remember to do.  A bunch of different changes on one build will confuse the issue, being lucky will be a rarity.    

[Alma]

I have the highest arched violin I've ever seen; it's a grandfather's attic "Stainer" model, and it is mellow, aka sweet!

[Johnmasters]

"...A lower arch enables more of a level surface on the soundpost ends and bridge feet  -  a more direct line for vibrations and tension to flow through evenly."

 

Is that good or bad?

vibrations do not "flow". 

[uncle duke]

vibrations do not "flow". 

How would you describe it other than flow. 

  The main point I was visioning was if there is a more pronounced curvature of the belly, outside more than the inside, though the inside could be just as sloped, that the bridge feet and post ends would have a more difficult time because of the angle they would have to be set at.  

[Johnmasters]

How would you describe it other than flow. 

  The main point I was visioning was if there is a more pronounced curvature of the belly, outside more than the inside, though the inside could be just as sloped, that the bridge feet and post ends would have a more difficult time because of the angle they would have to be set at.  

I have made myself a pest in the past by pointing out that the vibrations are standing waves.   An outgoing wave and its reflection add to a standing wave.  (Transients are chaotic and short in life.) 

 

I think that intuitions that say that vibrations "travel" or flow is really a big misconception and is misleading.  Most of the people here like Schelski's model of the vibration modes of a violin.  This is what one always gets by looking at [steady state] modes of a violin.  Or any combination of modes.  (and you can see that they are not flowing.)

 

The ends of the post create a boundary condition where post and the contact points constrain top and back to be connected.  The post is so stiff that it acts like a rigid body.  At least compared with the stiffness of other parts of the body.  I don't know what point you were trying to make.

[uncle duke]

I have made myself a pest in the past by pointing out that the vibrations are standing waves.   An outgoing wave and its reflection add to a standing wave.  (Transients are chaotic and short in life.) 

 

I think that intuitions that say that vibrations "travel" or flow is really a big misconception and is misleading.

How about the soundpost and bridge acting as filters.  The more they aren't in a direct line the harder time they will have when they have to work.

  Direct line meaning angled bridge feet and angled soungpost ends more extreme than normally done.  With tighter radius curves I see a tougher way of starting out after set- up as compared to flatter surfaces for the same set-up procedures

. 

 You're not a pest John.  You just get the best of everyone- they give up to early during battle.

[Michael_Molnar]

I just think that there is an optimum height for a given model or form shape.

[Johnmasters]

How about the soundpost and bridge acting as filters.  The more they aren't in a direct line the harder time they will have when they have to work.

  Direct line meaning angled bridge feet and angled soungpost ends more extreme than normally done.  With tighter radius curves I see a tougher way of starting out after set- up as compared to flatter surfaces for the same set-up procedures

. 

 You're not a pest John.  You just get the best of everyone- they give up to early during battle.

Straight line does not mean anything.   Consider:  what in your mind is "flowing: ?   You have a choice to consider various parts fitting together with conditions at each joint.   Or you can look at the entire assembly as a single unit.  This is possible because vibrations do NOT flow.  It is a steady-state vibration in amplitude.  The shapes of the normal modes are the shapes of the displacement.  This displacement is of a stationary form for each normal mode.  That is WHY one looks at normal modes.  The space part and the time part of the normal mode functions are SEPERABLE in distance and time..  In other words,  there are special  shapes that swell and shrink in time.  These shapes do not move parallel to the surface.  They are constant functions of the surface coordinates multiplied by a sinusoidal function (in time only).

 

You asked the perfect question.   Many times,  I see people making conclusions based on a mental picture of something flowing. I have often tried to change this view,  seldom getting answers.  I finally threw up my hands.  But I answer you because you are right at the place to change your view.  The wave equation has certain very SPECIAL solutions that are seperable in space and time.  These are called the normal modes and they are very useful.  An arbitrary motion can be expressed as a superposition of many normal modes (in principal,  all of them,  an infinite number.)  

 

The surface of a swimming pool has all kinds of undulations,  but these are also a sum of spacial functions,  each multiplied by a seperate frequency term.  Consider the normal modes of a string;  that is the simplest example.  The swimming pool surface is the 2-D analogue.

 

It is a lot like a fourier transform except that each time-dependent function has its own shape function.  There are four coordinates (x,y,z,t)  and the x,y,z shape is a function with the tiime-dependence separated out as a multiplying function. (for each mode.)

 

Now watch Carl Stross come along and say its all baloney.

[Don Noon]

I just think that there is an optimum height for a given model or form shape.

... and what wood you are using

... and what kind of sound you want to get

[Wolfjk]

 

So according to "reed theory", bent (rather than carved) archings should produce instruments which are strong on the low end, and weak on the high end???

More or less!!! However once you pass 50 you hardly notice!

Still there is the sound post that makes it shorter the bassbar that makes it longer and the FFs that section it!

[Wolfjk]

 

A lower arch enables more of a level surface on the soundpost ends and bridge feet  -  a more direct line for vibrations and tension to flow through evenly.

Hi uncle duke,

Agood fit is important for both the bridge feet and sond post ends. Perhaps you afford too much function for the sound post? I think the only job of the soundpost is to shorten the reeds or grain in the top to give more resonance to the high notes of the E and A.

[uncle duke]

 

Hi uncle duke,

Agood fit is important for both the bridge feet and sond post ends. Perhaps you afford too much function for the sound post? I think the only job of the soundpost is to shorten the reeds or grain in the top to give more resonance to the high notes of the E and A.

What John says makes sense.  I'll stand corrected about what I thought the soundpost was doing or does.  He has a point to remember right before soundpost setting time what to keep in mind.  That would be do not have the soundpost setting interfere with the good work and time spent figuring out how the mode shapes are going to come into play.  Doesn't matter the arch shape, I just have to be careful with soundpost setting so that I don't drive mode 2, for example, all the way across the plate to the other ff hole, or soundbar at the least.  That's all for now.

[wellerwilliams]

Straight line does not mean anything.   Consider:  what in your mind is "flowing: ?   You have a choice to consider various parts fitting together with conditions at each joint.   Or you can look at the entire assembly as a single unit.  This is possible because vibrations do NOT flow.  It is a steady-state vibration in amplitude.  The shapes of the normal modes are the shapes of the displacement.  This displacement is of a stationary form for each normal mode.  That is WHY one looks at normal modes.  The space part and the time part of the normal mode functions are SEPERABLE in distance and time..  In other words,  there are special  shapes that swell and shrink in time.  These shapes do not move parallel to the surface.  They are constant functions of the surface coordinates multiplied by a sinusoidal function (in time only).

 

You asked the perfect question.   Many times,  I see people making conclusions based on a mental picture of something flowing. I have often tried to change this view,  seldom getting answers.  I finally threw up my hands.  But I answer you because you are right at the place to change your view.  The wave equation has certain very SPECIAL solutions that are seperable in space and time.  These are called the normal modes and they are very useful.  An arbitrary motion can be expressed as a superposition of many normal modes (in principal,  all of them,  an infinite number.)  

 

The surface of a swimming pool has all kinds of undulations,  but these are also a sum of spacial functions,  each multiplied by a seperate frequency term.  Consider the normal modes of a string;  that is the simplest example.  The swimming pool surface is the 2-D analogue.

 

It is a lot like a fourier transform except that each time-dependent function has its own shape function.  There are four coordinates (x,y,z,t)  and the x,y,z shape is a function with the tiime-dependence separated out as a multiplying function. (for each mode.)

 

Now watch Carl Stross come along and say its all baloney.

Then could one say that the waves spread out as ripples do when a stone is dropped into a pool of water?

[Peter K-G]

Then could one say that the waves spread out as ripples do when a stone is dropped into a pool of water?

 

In a way, but only for the higher modes you can see such a pattern. Try think about what Johnmasters wrote, it's not easy though to change thinking if one is on the wrong path. The sound comes from what moves the air. 

[David Burgess]

So according to "reed theory", bent (rather than carved) archings should produce instruments which are strong on the low end, and weak on the high end???

 

 

 

More or less!!!

 

But it seems to do the opposite, in my limited experience with bent archings.

[Carl Stross]

Straight line does not mean anything.   Consider:  what in your mind is "flowing: ?   You have a choice to consider various parts fitting together with conditions at each joint.   Or you can look at the entire assembly as a single unit.  This is possible because vibrations do NOT flow.  It is a steady-state vibration in amplitude.  The shapes of the normal modes are the shapes of the displacement.  This displacement is of a stationary form for each normal mode.  That is WHY one looks at normal modes.  The space part and the time part of the normal mode functions are SEPERABLE in distance and time..  In other words,  there are special  shapes that swell and shrink in time.  These shapes do not move parallel to the surface.  They are constant functions of the surface coordinates multiplied by a sinusoidal function (in time only).

 

You asked the perfect question.   Many times,  I see people making conclusions based on a mental picture of something flowing. I have often tried to change this view,  seldom getting answers.  I finally threw up my hands.  But I answer you because you are right at the place to change your view.  The wave equation has certain very SPECIAL solutions that are seperable in space and time.  These are called the normal modes and they are very useful.  An arbitrary motion can be expressed as a superposition of many normal modes (in principal,  all of them,  an infinite number.)  

 

The surface of a swimming pool has all kinds of undulations,  but these are also a sum of spacial functions,  each multiplied by a seperate frequency term.  Consider the normal modes of a string;  that is the simplest example.  The swimming pool surface is the 2-D analogue.

 

It is a lot like a fourier transform except that each time-dependent function has its own shape function.  There are four coordinates (x,y,z,t)  and the x,y,z shape is a function with the tiime-dependence separated out as a multiplying function. (for each mode.)

 

Now watch Carl Stross come along and say its all baloney.

 

Nope. I'm not going to do that. The entertainment value of your posts far outweighs their scientific ineptitude. You won't hear any criticism from me anymore, ever.

[Roger Frankland]

I have the highest arched violin I've ever seen; it's a grandfather's attic "Stainer" model, and it is mellow, aka sweet!

could you share a picture of this violin showing the arch?

[Mike Spencer]

At the VSA convention this last weekend they had a Jacob Stainer and a Peitro Guarneri of Mantua at the rare instrument table (amongst many others). Both beautiful instruments and highly arched. Stainer is obviously known for his highly arched instruments but the Pietro Guarneri of Mantua had a huge arch even when compared to the Stainer, just eye balling it I would guess it was well over 25mm.