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bkwood

Tuning The Sound Box

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As I am nearing completion of a smallish viola I mentioned to a luthier friend, who doesn't build violins but does build mandolins, that it made a satisfying musical sound when I pat the top. He asked if I had tuned it with the ff holes. I hardly even pay attention to tuning the plates as I carve them. I don't know how much one would have to open up ff holes to change the pitch of the completed instrument box. Am I missing something or is this an important thing to do? For what it's worth it thumps a low A.

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That's fine.  Now finish it, set it up, and go play it before a herd of experts-in-their-own-minds shows up to pour mud in our pellucid waters, and berate us for our ignorance of the arcane secrets of our craft.  [Leaves by a transwarp conduit to a galaxy far, far away.]   :ph34r:  ^_^ 

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2 hours ago, Violadamore said:

That's fine.  Now finish it, set it up, and go play it before a herd of experts-in-their-own-minds shows up to pour mud in our pellucid waters, and berate us for our ignorance of the arcane secrets of our craft.  [Leaves by a transwarp conduit to a galaxy far, far away.]   :ph34r:  ^_^ 

I thought that transwarp conduits would only get you to a different quadrant...

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8 hours ago, Three13 said:

I thought that transwarp conduits would only get you to a different quadrant...

Not when using a combination of Ancient and Traveler technology.  It's all simply wormholes, anyway.

1 hour ago, JacksonMaberry said:

Oh lordy, a star wars and star trek reference in the same breath... Saints preserve us! :lol:

Just added some Stargate SG1, as well.  :P  :lol:

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17 hours ago, bkwood said:

As I am nearing completion of a smallish viola I mentioned to a luthier friend, who doesn't build violins but does build mandolins, that it made a satisfying musical sound when I pat the top. He asked if I had tuned it with the ff holes. I hardly even pay attention to tuning the plates as I carve them. I don't know how much one would have to open up ff holes to change the pitch of the completed instrument box. Am I missing something or is this an important thing to do? For what it's worth it thumps a low A.

Forget it. 

The A0 air mode Frequency is roughly proportional to the f hole area to the one fourth power: F ~A^0.25 so you have to change the area a real lot to get much effect.

For example if you start with a typical viola  A0 frequency of 220Hz and you would like to increase it to 250Hz you would have to increase the area by this ratio:

(250/220)^4 = (1.136)^4  = 1.67

The new f hole area has to be 1.67 times larger.  Since the area is equal to the f hole length times its width you can vary either one or both to get the larger area,  You can keep the f hole the same width and make it 1.67 times longer (really long !) Or if you want to keep the same shape you can increase both the length and width by the square root of 1.67 or 1.29 times longer and wider.

 

But most small violas have A0 frequencies which are too high to begin with so it is desirable to make the f hole area smaller to lower the A0 frequency.   If for example your starting A0 frequency is 250Hz is thought to be too high and you want to get it down to a more typical 220Hz then the above proportions are inverted:

(220/250)^4 = 0.88^4 = 0.6 

So the new smaller hole area has to be 0.6times smaller (its hard to put the wood back).   If you keep the same width it would have to be 0.6 times the length (really short!)

 

There's actually several issues here:  How big a frequency change is needed to be detectable by listeners?   How much do I want to change it and which direction should the change go?  How do I make this change?  Finding the answers to these questions isn't easy--but finding horcruxes isn't easy either.

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57 minutes ago, Marty Kasprzyk said:

...But most small violas have A0 frequencies which are too high to begin with so it is desirable to make the f hole area smaller to lower the A0 frequency.   ...

How do you determine what is "too high"?

On my small (40cm) viola that got a tone certificate at VSA2018, I intentionally made extra-large sound holes to get the A0 even higher, close to C, so that the first overtone of the open C string would get a little more power.  For larger violas, that alignment is not feasible.

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4 hours ago, Don Noon said:

How do you determine what is "too high"?

On my small (40cm) viola that got a tone certificate at VSA2018, I intentionally made extra-large sound holes to get the A0 even higher, close to C, so that the first overtone of the open C string would get a little more power.  For larger violas, that alignment is not feasible.

I've also heard it said (regarding mandolins) that it is good to tune the body somewhere between diatonic notes in order to prevent certain notes from dominating. I'm not going to change anything in my viola at this point–it's ready to varnish. I don't take it too seriously, but it's interesting to think about. Did you find your open C had more presence, and how did you know if it did? Would you expect higher C notes to also have more power?

Congratulations on the certificate.

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31 minutes ago, bkwood said:

I've also heard it said (regarding mandolins) that it is good to tune the body somewhere between diatonic notes in order to prevent certain notes from dominating. I'm not going to change anything in my viola at this point–it's ready to varnish

Varnishing can change many things. I long ago abandoned stringing up instruments "in the white", because I didn't find it useful. Not that it can't be fun and entertaining.

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On 10/4/2019 at 2:42 PM, Violadamore said:

...  [Leaves by a transwarp conduit to a galaxy far, far away.]   :ph34r:  ^_^ 

Is that the same as a Stargate? I'm looking up the dialing pattern...

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9 hours ago, Don Noon said:

How do you determine what is "too high"?

On my small (40cm) viola that got a tone certificate at VSA2018, I intentionally made extra-large sound holes to get the A0 even higher, close to C, so that the first overtone of the open C string would get a little more power.  For larger violas, that alignment is not feasible.

That's my point like you said "I intentionally made extra-large holes to get the A0 even higher"....it takes really big changes in f hole area to make any noticeable affect in the A0 frequency. I hope my comment doesn't Hz.

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There has to be far more involved in the A0 note.  That is the sound you get humming into the F hole, isn't it?  I haven't kept track of that.  The 385 mm long, fat (we'll call it big boned) 5 string viola that I'm making just happened to be upstairs, so I checked it, and it is 207 Hz.  The volume isn't huge.  The plates aren't flabby.  The f holes fairly long, and quite straight, like slashes.  Should I try to get it up to A?  Why?  Would it for sure be better?

I don't know why it is low.  But maybe it will work.  If it was high, it would be high.  Maybe that would work.  

It's just like tapping on the box.  I just tried that too.  314 or so tapping by the bridge,  half that at the lower block.  There's an overtone of about 350 coming though in the upper block.  That's just the way that it is.  Put them all together and it will be unique.  It will still sound like a viola/violin, but it will be unique.  

What's wrong with that?

Ken

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50 minutes ago, Ken_N said:

There has to be far more involved in the A0 note.  That is the sound you get humming into the F hole, isn't it?  I haven't kept track of that.  The 385 mm long, fat (we'll call it big boned) 5 string viola that I'm making just happened to be upstairs, so I checked it, and it is 207 Hz.

I would be shocked if the A0 of that size instrument was more than 10 Hz away from 250 Hz.  Definitely not 207 Hz.  Unless you made the body out of wood-grained neoprene.

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Don,

I use the Szynalski online tone generator.  I just checked it again.  250 is WAY too high.  It really bounces around at 204 or so.  I don't know why.   The 16.5" viola I lowered the bridge on the other day is 204 as well.  A del Gesu model I strung up yesterday, after re doing the varnish is about 264.  

Hah!  The high arched 16" viola is 204 as well.  I guess I'm an anomaly.

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Those that know me are probably not too surprised to see me chime in on this topic. ;-)

I have long  (perhaps too long) advocated for the idea of voicing instruments before varnishing, (but perhaps after sealing) with the instrument 'in the white'. I've been developing a methodical system for accomplishing this which is based on the reciprocal or bi-directional relationship of the surface of the instrument and the strings. Simply put, the strings drive the surface in the same way that the surface drives the strings.

In practice this means that when a string vibrates it creates various patterns of vibrations on the surface, if the surface is tapped, the strings will vibrate in response to the specific acoustic profile of that area that is being tapped. In this way acoustic 'targets' can be chosen and modified. Further, as an area is being modified other frequencies are also affected, this can also be observed.  Any surface of the instrument is open to modification (think ribs). Individual strings and frequencies can be isolated by damping all but one string and/or tuning it to the desired pitch. The instrument can be then played and an assessment of the changed be determined.  

The changes are normally not huge, on the order of a sound post adjustment, but they are cumulative. Occasionally a dramatic change  is heard, which I believe has to do with a psycho-acoustic phenomenon having to do with filling in missing harmonics. The lighter the instrument the more effective the adjustments. Because the scraping is done on the outside and, subtly and mostly imperceptibly alter the arching, some of the acoustic changes may survive  regraduation.

I usually combine the use of the reciprocating vibrating strings as well as a spectrum analyzer to make adjustments. 

This 'tuning' method is wholly compatible with the working methods of the Cremonese violin makers because they finished the instrument from the outside after it was assembled (see Roger Hargrave)

Will all the acoustic changes survive the varnishing process? Remain intact forever? Make the instrument sound worse? Everything is possible but one must compare it to the alternative, where one is more or less stabbing in the dark and if luck is with you the instrument sounds fine. Admittedly after having finished an instrument and playing it in the white I've opted not to risk making any changes. But this approach does open otherwise unavailable options for the violin maker.

Oded Kishony

 

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56 minutes ago, Oded Kishony said:

Those that know me are probably not too surprised to see me chime in on this topic. ;-)

I have long  (perhaps too long) advocated for the idea of voicing instruments before varnishing, (but perhaps after sealing) with the instrument 'in the white'. I've been developing a methodical system for accomplishing this which is based on the reciprocal or bi-directional relationship of the surface of the instrument and the strings. Simply put, the strings drive the surface in the same way that the surface drives the strings.

In practice this means that when a string vibrates it creates various patterns of vibrations on the surface, if the surface is tapped, the strings will vibrate in response to the specific acoustic profile of that area that is being tapped. In this way acoustic 'targets' can be chosen and modified. Further, as an area is being modified other frequencies are also affected, this can also be observed.  Any surface of the instrument is open to modification (think ribs). Individual strings and frequencies can be isolated by damping all but one string and/or tuning it to the desired pitch. The instrument can be then played and an assessment of the changed be determined.  

The changes are normally not huge, on the order of a sound post adjustment, but they are cumulative. Occasionally a dramatic change  is heard, which I believe has to do with a psycho-acoustic phenomenon having to do with filling in missing harmonics. The lighter the instrument the more effective the adjustments. Because the scraping is done on the outside and, subtly and mostly imperceptibly alter the arching, some of the acoustic changes may survive  regraduation.

I usually combine the use of the reciprocating vibrating strings as well as a spectrum analyzer to make adjustments. 

This 'tuning' method is wholly compatible with the working methods of the Cremonese violin makers because they finished the instrument from the outside after it was assembled (see Roger Hargrave)

Will all the acoustic changes survive the varnishing process? Remain intact forever? Make the instrument sound worse? Everything is possible but one must compare it to the alternative, where one is more or less stabbing in the dark and if luck is with you the instrument sounds fine. Admittedly after having finished an instrument and playing it in the white I've opted not to risk making any changes. But this approach does open otherwise unavailable options for the violin maker.

Oded Kishony

 

Nice to see you posting Oded, it's been a long time since I've seen you here.

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I'm with Oded in this. I make only F-5 mandolins (though I have set of wood prepared for dG violin for my oldest son on bench now) and I always string in the white and do some adjustments with strings on. First it was just experimenting but some changes are quite predictable especially as I work with one model only and do similar archings and graduation patterns to start with. This takes good ear and knowing what you want to hear - your taste should coincide with taste of your customers.

I believe it is possible to get consistent result without this if you have good ear, enough experience (e.g. many violins made), very consistent wood source and procedures for grading and selecting wood.

I never had consistent wood source (till now - I have enough maple for 50 or so instruments all from the same tree we cut and dozen or so spruce splits from same log) so I had to experiment to get consistent results. These days, with wood from same trees for last 4-5 instruments I can get pretty close before I string them up and do just very minor  (if any) modifications in the white. But when I will use that red maple one piece slab I will surely leave some margin for tweaking...

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3 minutes ago, HoGo said:

But when I will use that red maple one piece slab I will surely leave some margin for tweaking...

 What might apply to mandolins might not apply equally to violins. Because the thicknesses of the plates and ribs are less to begin with there is less to remove. Just how much wood should one leave to allow for tweaking on a violin?

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22 minutes ago, bkwood said:

 What might apply to mandolins might not apply equally to violins. Because the thicknesses of the plates and ribs are less to begin with there is less to remove. Just how much wood should one leave to allow for tweaking on a violin?

The thicknesses of best mandolis are really close to as thin as it can before the body collapses (especially tops as there is no soundpost to help) so in this they are quite similar. I generally graduate tops of mandolins from spruce of unknown properties to 3.5 mm at "recurve" to 4.7 mm center and depending on stiffness I end at ~3mm to ~4.2 mm sometimes the center is thinner and edges thicker, sometimes vice versa and the graduation transition can be slightly different and certain areas too (like moon-shaped area under fingerboard extension or leaving thicker strip (7-8cm wide) down along centerline towards tailpiece if the top needs more thinning and I don't want to risk losing structure over tone). Top below 4mm at center is result of extremely stif/hard piece of spruce.

I guess on violin 2-3 tenths of mm on top could be enough to change the tone very noticeably, but you should have good numbers that are close, but not too thin to start with.

I posted my notes 13 years ago on mandolin site: https://www.mandolincafe.com/forum/threads/25580-Outside-tuning? even the attached sound samples are still available . Notice how working just at the edges changes sound noticeably so If Strad worked the channeling after assembly he could hear some changes as well if he had strings on.

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3 hours ago, HoGo said:

The thicknesses of best mandolis are really close to as thin as it can before the body collapses (especially tops as there is no soundpost to help) so in this they are quite similar (to violins).

>

>

What happens when you put a sound post in?

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12 minutes ago, Marty Kasprzyk said:

What happens when you put a sound post in?

The other mandolin players look at you funny?

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10 hours ago, Oded Kishony said:

Those that know me are probably not too surprised to see me chime in on this topic. ;-)

I have long  (perhaps too long) advocated for the idea of voicing instruments before varnishing, (but perhaps after sealing) with the instrument 'in the white'. I've been developing a methodical system for accomplishing this which is based on the reciprocal or bi-directional relationship of the surface of the instrument and the strings. Simply put, the strings drive the surface in the same way that the surface drives the strings.

In practice this means that when a string vibrates it creates various patterns of vibrations on the surface, if the surface is tapped, the strings will vibrate in response to the specific acoustic profile of that area that is being tapped. In this way acoustic 'targets' can be chosen and modified. Further, as an area is being modified other frequencies are also affected, this can also be observed.  Any surface of the instrument is open to modification (think ribs). Individual strings and frequencies can be isolated by damping all but one string and/or tuning it to the desired pitch. The instrument can be then played and an assessment of the changed be determined.  

The changes are normally not huge, on the order of a sound post adjustment, but they are cumulative. Occasionally a dramatic change  is heard, which I believe has to do with a psycho-acoustic phenomenon having to do with filling in missing harmonics. The lighter the instrument the more effective the adjustments. Because the scraping is done on the outside and, subtly and mostly imperceptibly alter the arching, some of the acoustic changes may survive  regraduation.

I usually combine the use of the reciprocating vibrating strings as well as a spectrum analyzer to make adjustments. 

This 'tuning' method is wholly compatible with the working methods of the Cremonese violin makers because they finished the instrument from the outside after it was assembled (see Roger Hargrave)

Will all the acoustic changes survive the varnishing process? Remain intact forever? Make the instrument sound worse? Everything is possible but one must compare it to the alternative, where one is more or less stabbing in the dark and if luck is with you the instrument sounds fine. Admittedly after having finished an instrument and playing it in the white I've opted not to risk making any changes. But this approach does open otherwise unavailable options for the violin maker.

Oded Kishony

 

Welcome back, Oded.  Thanks for the illuminating post.  :)

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6 hours ago, Marty Kasprzyk said:

What happens when you put a sound post in?

First there are two "tonebars" on mandolin - one on each side but they are much thinner than typical violin bass bar, typically 6.5 and 7.5mmhigh 1/4" wide. I've played one or two mandolins where owners put in soundpost(s) to help sagging top and these mandolins sounded kinda like plucked violins with much less sustain and volume than normal mandolins. Perhaps they would sound better played with a bow...

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